src/Compilers/CSharp/Test/Symbol/Symbols/StaticAbstractMembersInInterfacesTests.cs - main - githubmirror/roslyn

src/Compilers/CSharp/Test/Symbol/Symbols/StaticAbstractMembersInInterfacesTests.cs
34 304 строки2 MB
Copilot
Report an error for dynamic evaluation of `&&`/`||` when left operand is statically typed as an interface (#80962)
08 ноя 2025, 02:21
08 ноя 2025, 02:212bf680e
// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

#nullable disable

using System;
using System.Collections.Immutable;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading;
using Microsoft.CodeAnalysis.CSharp.Symbols;
using Microsoft.CodeAnalysis.CSharp.Symbols.Metadata.PE;
using Microsoft.CodeAnalysis.CSharp.Symbols.Retargeting;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.CSharp.Test.Utilities;
using Microsoft.CodeAnalysis.Emit;
using Microsoft.CodeAnalysis.PooledObjects;
using Microsoft.CodeAnalysis.Test.Utilities;
using Roslyn.Test.Utilities;
using Xunit;

namespace Microsoft.CodeAnalysis.CSharp.UnitTests.Symbols
{
    public class StaticAbstractMembersInInterfacesTests : CSharpTestBase
    {
        internal const TargetFramework _supportingFramework = TargetFramework.Net60;

        [Fact]
        public void MethodModifiers_01()
        {
            var source1 =
@"
public interface I1
{
    abstract static void M01()
    ; 

    virtual static void M02()
    ; 

    sealed static void M03() 
    ; 

    override static void M04() 
    ; 

    abstract virtual static void M05()
    ; 

    abstract sealed static void M06()
    ; 

    abstract override static void M07()
    ; 

    virtual sealed static void M08() 
    ; 

    virtual override static void M09() 
    ; 

    sealed override static void M10() 
    ; 
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,26): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract static void M01()
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M01").WithArguments("abstract", "10.0", "11.0").WithLocation(4, 26),
                // (7,25): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual static void M02()
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M02").WithArguments("virtual", "10.0", "11.0").WithLocation(7, 25),
                // (7,25): error CS0501: 'I1.M02()' must declare a body because it is not marked abstract, extern, or partial
                //     virtual static void M02()
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "M02").WithArguments("I1.M02()").WithLocation(7, 25),
                // (10,24): error CS8703: The modifier 'sealed' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     sealed static void M03() 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M03").WithArguments("sealed", "10.0", "11.0").WithLocation(10, 24),
                // (10,24): error CS0501: 'I1.M03()' must declare a body because it is not marked abstract, extern, or partial
                //     sealed static void M03() 
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "M03").WithArguments("I1.M03()").WithLocation(10, 24),
                // (13,26): error CS0106: The modifier 'override' is not valid for this item
                //     override static void M04() 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M04").WithArguments("override").WithLocation(13, 26),
                // (13,26): error CS0501: 'I1.M04()' must declare a body because it is not marked abstract, extern, or partial
                //     override static void M04() 
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "M04").WithArguments("I1.M04()").WithLocation(13, 26),
                // (16,34): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract virtual static void M05()
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M05").WithArguments("abstract", "10.0", "11.0").WithLocation(16, 34),
                // (16,34): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract virtual static void M05()
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M05").WithArguments("virtual", "10.0", "11.0").WithLocation(16, 34),
                // (16,34): error CS0503: The abstract method 'I1.M05()' cannot be marked virtual
                //     abstract virtual static void M05()
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "M05").WithArguments("method", "I1.M05()").WithLocation(16, 34),
                // (19,33): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static void M06()
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M06").WithArguments("sealed").WithLocation(19, 33),
                // (19,33): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract sealed static void M06()
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M06").WithArguments("abstract", "10.0", "11.0").WithLocation(19, 33),
                // (22,35): error CS0106: The modifier 'override' is not valid for this item
                //     abstract override static void M07()
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M07").WithArguments("override").WithLocation(22, 35),
                // (22,35): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract override static void M07()
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M07").WithArguments("abstract", "10.0", "11.0").WithLocation(22, 35),
                // (25,32): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static void M08() 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M08").WithArguments("sealed").WithLocation(25, 32),
                // (25,32): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual sealed static void M08() 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M08").WithArguments("virtual", "10.0", "11.0").WithLocation(25, 32),
                // (25,32): error CS0501: 'I1.M08()' must declare a body because it is not marked abstract, extern, or partial
                //     virtual sealed static void M08() 
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "M08").WithArguments("I1.M08()").WithLocation(25, 32),
                // (28,34): error CS0106: The modifier 'override' is not valid for this item
                //     virtual override static void M09() 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M09").WithArguments("override").WithLocation(28, 34),
                // (28,34): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual override static void M09() 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M09").WithArguments("virtual", "10.0", "11.0").WithLocation(28, 34),
                // (28,34): error CS0501: 'I1.M09()' must declare a body because it is not marked abstract, extern, or partial
                //     virtual override static void M09() 
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "M09").WithArguments("I1.M09()").WithLocation(28, 34),
                // (31,33): error CS0106: The modifier 'override' is not valid for this item
                //     sealed override static void M10() 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M10").WithArguments("override").WithLocation(31, 33),
                // (31,33): error CS8703: The modifier 'sealed' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     sealed override static void M10() 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M10").WithArguments("sealed", "10.0", "11.0").WithLocation(31, 33),
                // (31,33): error CS0501: 'I1.M10()' must declare a body because it is not marked abstract, extern, or partial
                //     sealed override static void M10() 
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "M10").WithArguments("I1.M10()").WithLocation(31, 33)
                );

            ValidateMethodModifiers_01(compilation1);
        }

        private static void ValidateMethodModifiers_01(CSharpCompilation compilation1)
        {
            var i1 = compilation1.GetTypeByMetadataName("I1");
            var m01 = i1.GetMember<MethodSymbol>("M01");

            Assert.True(m01.IsAbstract);
            Assert.False(m01.IsVirtual);
            Assert.True(m01.IsMetadataVirtual());
            Assert.False(m01.IsSealed);
            Assert.True(m01.IsStatic);
            Assert.False(m01.IsExtern);
            Assert.False(m01.IsAsync);
            Assert.False(m01.IsOverride);
            Assert.Null(i1.FindImplementationForInterfaceMember(m01));

            var m02 = i1.GetMember<MethodSymbol>("M02");

            Assert.False(m02.IsAbstract);
            Assert.True(m02.IsVirtual);
            Assert.True(m02.IsMetadataVirtual());
            Assert.False(m02.IsSealed);
            Assert.True(m02.IsStatic);
            Assert.False(m02.IsExtern);
            Assert.False(m02.IsAsync);
            Assert.False(m02.IsOverride);
            Assert.Same(m02, i1.FindImplementationForInterfaceMember(m02));

            var m03 = i1.GetMember<MethodSymbol>("M03");

            Assert.False(m03.IsAbstract);
            Assert.False(m03.IsVirtual);
            Assert.False(m03.IsMetadataVirtual());
            Assert.False(m03.IsSealed);
            Assert.True(m03.IsStatic);
            Assert.False(m03.IsExtern);
            Assert.False(m03.IsAsync);
            Assert.False(m03.IsOverride);
            Assert.Null(i1.FindImplementationForInterfaceMember(m03));

            var m04 = i1.GetMember<MethodSymbol>("M04");

            Assert.False(m04.IsAbstract);
            Assert.False(m04.IsVirtual);
            Assert.False(m04.IsMetadataVirtual());
            Assert.False(m04.IsSealed);
            Assert.True(m04.IsStatic);
            Assert.False(m04.IsExtern);
            Assert.False(m04.IsAsync);
            Assert.False(m04.IsOverride);
            Assert.Null(i1.FindImplementationForInterfaceMember(m04));

            var m05 = i1.GetMember<MethodSymbol>("M05");

            Assert.True(m05.IsAbstract);
            Assert.True(m05.IsVirtual);
            Assert.True(m05.IsMetadataVirtual());
            Assert.False(m05.IsSealed);
            Assert.True(m05.IsStatic);
            Assert.False(m05.IsExtern);
            Assert.False(m05.IsAsync);
            Assert.False(m05.IsOverride);
            Assert.Null(i1.FindImplementationForInterfaceMember(m05));

            var m06 = i1.GetMember<MethodSymbol>("M06");

            Assert.True(m06.IsAbstract);
            Assert.False(m06.IsVirtual);
            Assert.True(m06.IsMetadataVirtual());
            Assert.False(m06.IsSealed);
            Assert.True(m06.IsStatic);
            Assert.False(m06.IsExtern);
            Assert.False(m06.IsAsync);
            Assert.False(m06.IsOverride);
            Assert.Null(i1.FindImplementationForInterfaceMember(m06));

            var m07 = i1.GetMember<MethodSymbol>("M07");

            Assert.True(m07.IsAbstract);
            Assert.False(m07.IsVirtual);
            Assert.True(m07.IsMetadataVirtual());
            Assert.False(m07.IsSealed);
            Assert.True(m07.IsStatic);
            Assert.False(m07.IsExtern);
            Assert.False(m07.IsAsync);
            Assert.False(m07.IsOverride);
            Assert.Null(i1.FindImplementationForInterfaceMember(m07));

            var m08 = i1.GetMember<MethodSymbol>("M08");

            Assert.False(m08.IsAbstract);
            Assert.True(m08.IsVirtual);
            Assert.True(m08.IsMetadataVirtual());
            Assert.False(m08.IsSealed);
            Assert.True(m08.IsStatic);
            Assert.False(m08.IsExtern);
            Assert.False(m08.IsAsync);
            Assert.False(m08.IsOverride);
            Assert.Same(m08, i1.FindImplementationForInterfaceMember(m08));

            var m09 = i1.GetMember<MethodSymbol>("M09");

            Assert.False(m09.IsAbstract);
            Assert.True(m09.IsVirtual);
            Assert.True(m09.IsMetadataVirtual());
            Assert.False(m09.IsSealed);
            Assert.True(m09.IsStatic);
            Assert.False(m09.IsExtern);
            Assert.False(m09.IsAsync);
            Assert.False(m09.IsOverride);
            Assert.Same(m09, i1.FindImplementationForInterfaceMember(m09));

            var m10 = i1.GetMember<MethodSymbol>("M10");

            Assert.False(m10.IsAbstract);
            Assert.False(m10.IsVirtual);
            Assert.False(m10.IsMetadataVirtual());
            Assert.False(m10.IsSealed);
            Assert.True(m10.IsStatic);
            Assert.False(m10.IsExtern);
            Assert.False(m10.IsAsync);
            Assert.False(m10.IsOverride);
            Assert.Null(i1.FindImplementationForInterfaceMember(m10));
        }

        [Fact]
        public void MethodModifiers_02()
        {
            var source1 =
@"
public interface I1
{
    abstract static void M01()
    {}

    virtual static void M02()
    {}

    sealed static void M03() 
    {}

    override static void M04() 
    {}

    abstract virtual static void M05()
    {}

    abstract sealed static void M06()
    {}

    abstract override static void M07()
    {}

    virtual sealed static void M08() 
    {}

    virtual override static void M09() 
    {}

    sealed override static void M10() 
    {}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,26): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract static void M01()
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M01").WithArguments("abstract", "10.0", "11.0").WithLocation(4, 26),
                // (4,26): error CS0500: 'I1.M01()' cannot declare a body because it is marked abstract
                //     abstract static void M01()
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "M01").WithArguments("I1.M01()").WithLocation(4, 26),
                // (7,25): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual static void M02()
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M02").WithArguments("virtual", "10.0", "11.0").WithLocation(7, 25),
                // (10,24): error CS8703: The modifier 'sealed' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     sealed static void M03() 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M03").WithArguments("sealed", "10.0", "11.0").WithLocation(10, 24),
                // (13,26): error CS0106: The modifier 'override' is not valid for this item
                //     override static void M04() 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M04").WithArguments("override").WithLocation(13, 26),
                // (16,34): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract virtual static void M05()
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M05").WithArguments("abstract", "10.0", "11.0").WithLocation(16, 34),
                // (16,34): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract virtual static void M05()
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M05").WithArguments("virtual", "10.0", "11.0").WithLocation(16, 34),
                // (16,34): error CS0500: 'I1.M05()' cannot declare a body because it is marked abstract
                //     abstract virtual static void M05()
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "M05").WithArguments("I1.M05()").WithLocation(16, 34),
                // (16,34): error CS0503: The abstract method 'I1.M05()' cannot be marked virtual
                //     abstract virtual static void M05()
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "M05").WithArguments("method", "I1.M05()").WithLocation(16, 34),
                // (19,33): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static void M06()
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M06").WithArguments("sealed").WithLocation(19, 33),
                // (19,33): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract sealed static void M06()
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M06").WithArguments("abstract", "10.0", "11.0").WithLocation(19, 33),
                // (19,33): error CS0500: 'I1.M06()' cannot declare a body because it is marked abstract
                //     abstract sealed static void M06()
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "M06").WithArguments("I1.M06()").WithLocation(19, 33),
                // (22,35): error CS0106: The modifier 'override' is not valid for this item
                //     abstract override static void M07()
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M07").WithArguments("override").WithLocation(22, 35),
                // (22,35): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract override static void M07()
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M07").WithArguments("abstract", "10.0", "11.0").WithLocation(22, 35),
                // (22,35): error CS0500: 'I1.M07()' cannot declare a body because it is marked abstract
                //     abstract override static void M07()
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "M07").WithArguments("I1.M07()").WithLocation(22, 35),
                // (25,32): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static void M08() 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M08").WithArguments("sealed").WithLocation(25, 32),
                // (25,32): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual sealed static void M08() 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M08").WithArguments("virtual", "10.0", "11.0").WithLocation(25, 32),
                // (28,34): error CS0106: The modifier 'override' is not valid for this item
                //     virtual override static void M09() 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M09").WithArguments("override").WithLocation(28, 34),
                // (28,34): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual override static void M09() 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M09").WithArguments("virtual", "10.0", "11.0").WithLocation(28, 34),
                // (31,33): error CS0106: The modifier 'override' is not valid for this item
                //     sealed override static void M10() 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M10").WithArguments("override").WithLocation(31, 33),
                // (31,33): error CS8703: The modifier 'sealed' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     sealed override static void M10() 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M10").WithArguments("sealed", "10.0", "11.0").WithLocation(31, 33)
                );

            ValidateMethodModifiers_01(compilation1);
        }

        [Fact]
        public void MethodModifiers_03()
        {
            var source1 =
@"
public interface I1
{
    abstract static void M01()
    ; 

    virtual static void M02()
    ; 

    sealed static void M03() 
    ; 

    override static void M04() 
    ; 

    abstract virtual static void M05()
    ; 

    abstract sealed static void M06()
    ; 

    abstract override static void M07()
    ; 

    virtual sealed static void M08() 
    ; 

    virtual override static void M09() 
    ; 

    sealed override static void M10() 
    ; 
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (7,25): error CS0501: 'I1.M02()' must declare a body because it is not marked abstract, extern, or partial
                //     virtual static void M02()
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "M02").WithArguments("I1.M02()").WithLocation(7, 25),
                // (10,24): error CS0501: 'I1.M03()' must declare a body because it is not marked abstract, extern, or partial
                //     sealed static void M03() 
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "M03").WithArguments("I1.M03()").WithLocation(10, 24),
                // (13,26): error CS0106: The modifier 'override' is not valid for this item
                //     override static void M04() 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M04").WithArguments("override").WithLocation(13, 26),
                // (13,26): error CS0501: 'I1.M04()' must declare a body because it is not marked abstract, extern, or partial
                //     override static void M04() 
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "M04").WithArguments("I1.M04()").WithLocation(13, 26),
                // (16,34): error CS0503: The abstract method 'I1.M05()' cannot be marked virtual
                //     abstract virtual static void M05()
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "M05").WithArguments("method", "I1.M05()").WithLocation(16, 34),
                // (19,33): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static void M06()
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M06").WithArguments("sealed").WithLocation(19, 33),
                // (22,35): error CS0106: The modifier 'override' is not valid for this item
                //     abstract override static void M07()
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M07").WithArguments("override").WithLocation(22, 35),
                // (25,32): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static void M08() 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M08").WithArguments("sealed").WithLocation(25, 32),
                // (25,32): error CS0501: 'I1.M08()' must declare a body because it is not marked abstract, extern, or partial
                //     virtual sealed static void M08() 
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "M08").WithArguments("I1.M08()").WithLocation(25, 32),
                // (28,34): error CS0106: The modifier 'override' is not valid for this item
                //     virtual override static void M09() 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M09").WithArguments("override").WithLocation(28, 34),
                // (28,34): error CS0501: 'I1.M09()' must declare a body because it is not marked abstract, extern, or partial
                //     virtual override static void M09() 
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "M09").WithArguments("I1.M09()").WithLocation(28, 34),
                // (31,33): error CS0106: The modifier 'override' is not valid for this item
                //     sealed override static void M10() 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M10").WithArguments("override").WithLocation(31, 33),
                // (31,33): error CS0501: 'I1.M10()' must declare a body because it is not marked abstract, extern, or partial
                //     sealed override static void M10() 
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "M10").WithArguments("I1.M10()").WithLocation(31, 33)
                );

            ValidateMethodModifiers_01(compilation1);
        }

        [Fact]
        public void MethodModifiers_04()
        {
            var source1 =
@"
public interface I1
{
    abstract static void M01()
    {}

    virtual static void M02()
    {}

    sealed static void M03() 
    {}

    override static void M04() 
    {}

    abstract virtual static void M05()
    {}

    abstract sealed static void M06()
    {}

    abstract override static void M07()
    {}

    virtual sealed static void M08() 
    {}

    virtual override static void M09() 
    {}

    sealed override static void M10() 
    {}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,26): error CS0500: 'I1.M01()' cannot declare a body because it is marked abstract
                //     abstract static void M01()
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "M01").WithArguments("I1.M01()").WithLocation(4, 26),
                // (13,26): error CS0106: The modifier 'override' is not valid for this item
                //     override static void M04() 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M04").WithArguments("override").WithLocation(13, 26),
                // (16,34): error CS0503: The abstract method 'I1.M05()' cannot be marked virtual
                //     abstract virtual static void M05()
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "M05").WithArguments("method", "I1.M05()").WithLocation(16, 34),
                // (16,34): error CS0500: 'I1.M05()' cannot declare a body because it is marked abstract
                //     abstract virtual static void M05()
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "M05").WithArguments("I1.M05()").WithLocation(16, 34),
                // (19,33): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static void M06()
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M06").WithArguments("sealed").WithLocation(19, 33),
                // (19,33): error CS0500: 'I1.M06()' cannot declare a body because it is marked abstract
                //     abstract sealed static void M06()
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "M06").WithArguments("I1.M06()").WithLocation(19, 33),
                // (22,35): error CS0106: The modifier 'override' is not valid for this item
                //     abstract override static void M07()
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M07").WithArguments("override").WithLocation(22, 35),
                // (22,35): error CS0500: 'I1.M07()' cannot declare a body because it is marked abstract
                //     abstract override static void M07()
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "M07").WithArguments("I1.M07()").WithLocation(22, 35),
                // (25,32): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static void M08() 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M08").WithArguments("sealed").WithLocation(25, 32),
                // (28,34): error CS0106: The modifier 'override' is not valid for this item
                //     virtual override static void M09() 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M09").WithArguments("override").WithLocation(28, 34),
                // (31,33): error CS0106: The modifier 'override' is not valid for this item
                //     sealed override static void M10() 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M10").WithArguments("override").WithLocation(31, 33)
                );

            ValidateMethodModifiers_01(compilation1);
        }

        [Fact]
        public void MethodModifiers_05()
        {
            var source1 =
@"
public interface I1
{
    abstract static void M01()
    ; 

    virtual static void M02()
    ; 

    sealed static void M03() 
    ; 

    override static void M04() 
    ; 

    abstract virtual static void M05()
    ; 

    abstract sealed static void M06()
    ; 

    abstract override static void M07()
    ; 

    virtual sealed static void M08() 
    ; 

    virtual override static void M09() 
    ; 

    sealed override static void M10() 
    ; 
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular7_3,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,26): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract static void M01()
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M01").WithArguments("abstract", "7.3", "11.0").WithLocation(4, 26),
                // (7,25): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual static void M02()
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M02").WithArguments("virtual", "7.3", "11.0").WithLocation(7, 25),
                // (7,25): error CS0501: 'I1.M02()' must declare a body because it is not marked abstract, extern, or partial
                //     virtual static void M02()
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "M02").WithArguments("I1.M02()").WithLocation(7, 25),
                // (10,24): error CS8703: The modifier 'sealed' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     sealed static void M03() 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M03").WithArguments("sealed", "7.3", "11.0").WithLocation(10, 24),
                // (10,24): error CS0501: 'I1.M03()' must declare a body because it is not marked abstract, extern, or partial
                //     sealed static void M03() 
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "M03").WithArguments("I1.M03()").WithLocation(10, 24),
                // (13,26): error CS0106: The modifier 'override' is not valid for this item
                //     override static void M04() 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M04").WithArguments("override").WithLocation(13, 26),
                // (13,26): error CS8703: The modifier 'static' is not valid for this item in C# 7.3. Please use language version '8.0' or greater.
                //     override static void M04() 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M04").WithArguments("static", "7.3", "8.0").WithLocation(13, 26),
                // (13,26): error CS0501: 'I1.M04()' must declare a body because it is not marked abstract, extern, or partial
                //     override static void M04() 
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "M04").WithArguments("I1.M04()").WithLocation(13, 26),
                // (16,34): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract virtual static void M05()
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M05").WithArguments("abstract", "7.3", "11.0").WithLocation(16, 34),
                // (16,34): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract virtual static void M05()
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M05").WithArguments("virtual", "7.3", "11.0").WithLocation(16, 34),
                // (16,34): error CS0503: The abstract method 'I1.M05()' cannot be marked virtual
                //     abstract virtual static void M05()
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "M05").WithArguments("method", "I1.M05()").WithLocation(16, 34),
                // (19,33): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static void M06()
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M06").WithArguments("sealed").WithLocation(19, 33),
                // (19,33): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract sealed static void M06()
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M06").WithArguments("abstract", "7.3", "11.0").WithLocation(19, 33),
                // (22,35): error CS0106: The modifier 'override' is not valid for this item
                //     abstract override static void M07()
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M07").WithArguments("override").WithLocation(22, 35),
                // (22,35): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract override static void M07()
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M07").WithArguments("abstract", "7.3", "11.0").WithLocation(22, 35),
                // (25,32): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static void M08() 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M08").WithArguments("sealed").WithLocation(25, 32),
                // (25,32): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual sealed static void M08() 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M08").WithArguments("virtual", "7.3", "11.0").WithLocation(25, 32),
                // (25,32): error CS0501: 'I1.M08()' must declare a body because it is not marked abstract, extern, or partial
                //     virtual sealed static void M08() 
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "M08").WithArguments("I1.M08()").WithLocation(25, 32),
                // (28,34): error CS0106: The modifier 'override' is not valid for this item
                //     virtual override static void M09() 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M09").WithArguments("override").WithLocation(28, 34),
                // (28,34): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual override static void M09() 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M09").WithArguments("virtual", "7.3", "11.0").WithLocation(28, 34),
                // (28,34): error CS0501: 'I1.M09()' must declare a body because it is not marked abstract, extern, or partial
                //     virtual override static void M09() 
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "M09").WithArguments("I1.M09()").WithLocation(28, 34),
                // (31,33): error CS0106: The modifier 'override' is not valid for this item
                //     sealed override static void M10() 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M10").WithArguments("override").WithLocation(31, 33),
                // (31,33): error CS8703: The modifier 'sealed' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     sealed override static void M10() 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M10").WithArguments("sealed", "7.3", "11.0").WithLocation(31, 33),
                // (31,33): error CS0501: 'I1.M10()' must declare a body because it is not marked abstract, extern, or partial
                //     sealed override static void M10() 
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "M10").WithArguments("I1.M10()").WithLocation(31, 33)
                );

            ValidateMethodModifiers_01(compilation1);
        }

        [Fact]
        public void MethodModifiers_06()
        {
            var source1 =
@"
public interface I1
{
    abstract static void M01()
    {}

    virtual static void M02()
    {}

    sealed static void M03() 
    {}

    override static void M04() 
    {}

    abstract virtual static void M05()
    {}

    abstract sealed static void M06()
    {}

    abstract override static void M07()
    {}

    virtual sealed static void M08() 
    {}

    virtual override static void M09() 
    {}

    sealed override static void M10() 
    {}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular7_3,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,26): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract static void M01()
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M01").WithArguments("abstract", "7.3", "11.0").WithLocation(4, 26),
                // (4,26): error CS0500: 'I1.M01()' cannot declare a body because it is marked abstract
                //     abstract static void M01()
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "M01").WithArguments("I1.M01()").WithLocation(4, 26),
                // (7,25): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual static void M02()
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M02").WithArguments("virtual", "7.3", "11.0").WithLocation(7, 25),
                // (10,24): error CS8703: The modifier 'sealed' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     sealed static void M03() 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M03").WithArguments("sealed", "7.3", "11.0").WithLocation(10, 24),
                // (13,26): error CS0106: The modifier 'override' is not valid for this item
                //     override static void M04() 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M04").WithArguments("override").WithLocation(13, 26),
                // (13,26): error CS8370: Feature 'default interface implementation' is not available in C# 7.3. Please use language version 8.0 or greater.
                //     override static void M04() 
                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion7_3, "M04").WithArguments("default interface implementation", "8.0").WithLocation(13, 26),
                // (16,34): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract virtual static void M05()
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M05").WithArguments("abstract", "7.3", "11.0").WithLocation(16, 34),
                // (16,34): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract virtual static void M05()
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M05").WithArguments("virtual", "7.3", "11.0").WithLocation(16, 34),
                // (16,34): error CS0500: 'I1.M05()' cannot declare a body because it is marked abstract
                //     abstract virtual static void M05()
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "M05").WithArguments("I1.M05()").WithLocation(16, 34),
                // (16,34): error CS0503: The abstract method 'I1.M05()' cannot be marked virtual
                //     abstract virtual static void M05()
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "M05").WithArguments("method", "I1.M05()").WithLocation(16, 34),
                // (19,33): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static void M06()
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M06").WithArguments("sealed").WithLocation(19, 33),
                // (19,33): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract sealed static void M06()
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M06").WithArguments("abstract", "7.3", "11.0").WithLocation(19, 33),
                // (19,33): error CS0500: 'I1.M06()' cannot declare a body because it is marked abstract
                //     abstract sealed static void M06()
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "M06").WithArguments("I1.M06()").WithLocation(19, 33),
                // (22,35): error CS0106: The modifier 'override' is not valid for this item
                //     abstract override static void M07()
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M07").WithArguments("override").WithLocation(22, 35),
                // (22,35): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract override static void M07()
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M07").WithArguments("abstract", "7.3", "11.0").WithLocation(22, 35),
                // (22,35): error CS0500: 'I1.M07()' cannot declare a body because it is marked abstract
                //     abstract override static void M07()
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "M07").WithArguments("I1.M07()").WithLocation(22, 35),
                // (25,32): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static void M08() 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M08").WithArguments("sealed").WithLocation(25, 32),
                // (25,32): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual sealed static void M08() 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M08").WithArguments("virtual", "7.3", "11.0").WithLocation(25, 32),
                // (28,34): error CS0106: The modifier 'override' is not valid for this item
                //     virtual override static void M09() 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M09").WithArguments("override").WithLocation(28, 34),
                // (28,34): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual override static void M09() 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M09").WithArguments("virtual", "7.3", "11.0").WithLocation(28, 34),
                // (31,33): error CS0106: The modifier 'override' is not valid for this item
                //     sealed override static void M10() 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M10").WithArguments("override").WithLocation(31, 33),
                // (31,33): error CS8703: The modifier 'sealed' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     sealed override static void M10() 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M10").WithArguments("sealed", "7.3", "11.0").WithLocation(31, 33)
                );

            ValidateMethodModifiers_01(compilation1);
        }

        [Fact]
        public void SealedStaticConstructor_01()
        {
            var source1 =
@"
interface I1
{
    sealed static I1() {}
}

partial interface I2
{
    partial sealed static I2();
}

partial interface I2
{
    partial static I2() {}
}

partial interface I3
{
    partial static I3();
}

partial interface I3
{
    partial sealed static I3() {}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,19): error CS0106: The modifier 'sealed' is not valid for this item
                //     sealed static I1() {}
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "I1").WithArguments("sealed").WithLocation(4, 19),
                // (9,5): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
                //     partial sealed static I2();
                Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(9, 5),
                // (9,5): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
                //     partial sealed static I2();
                Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(9, 5),
                // (9,27): error CS0106: The modifier 'sealed' is not valid for this item
                //     partial sealed static I2();
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "I2").WithArguments("sealed").WithLocation(9, 27),
                // (14,5): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
                //     partial static I2() {}
                Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(14, 5),
                // (14,5): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
                //     partial static I2() {}
                Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(14, 5),
                // (14,20): error CS0111: Type 'I2' already defines a member called 'I2' with the same parameter types
                //     partial static I2() {}
                Diagnostic(ErrorCode.ERR_MemberAlreadyExists, "I2").WithArguments("I2", "I2").WithLocation(14, 20),
                // (19,5): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
                //     partial static I3();
                Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(19, 5),
                // (19,5): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
                //     partial static I3();
                Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(19, 5),
                // (24,5): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
                //     partial sealed static I3() {}
                Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(24, 5),
                // (24,5): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
                //     partial sealed static I3() {}
                Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(24, 5),
                // (24,27): error CS0106: The modifier 'sealed' is not valid for this item
                //     partial sealed static I3() {}
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "I3").WithArguments("sealed").WithLocation(24, 27),
                // (24,27): error CS0111: Type 'I3' already defines a member called 'I3' with the same parameter types
                //     partial sealed static I3() {}
                Diagnostic(ErrorCode.ERR_MemberAlreadyExists, "I3").WithArguments("I3", "I3").WithLocation(24, 27)
                );

            var i1 = compilation1.GetTypeByMetadataName("I1");
            var m01 = i1.GetMember<MethodSymbol>(".cctor");

            Assert.False(m01.IsAbstract);
            Assert.False(m01.IsVirtual);
            Assert.False(m01.IsMetadataVirtual());
            Assert.False(m01.IsSealed);
            Assert.True(m01.IsStatic);
            Assert.False(m01.IsExtern);
            Assert.False(m01.IsAsync);
            Assert.False(m01.IsOverride);
            Assert.Null(i1.FindImplementationForInterfaceMember(m01));
        }

        [Fact]
        public void SealedStaticConstructor_02()
        {
            var source1 =
@"
partial interface I2
{
    sealed static partial I2();
}

partial interface I2
{
    static partial I2() {}
}

partial interface I3
{
    static partial I3();
}

partial interface I3
{
    sealed static partial I3() {}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,19): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
                //     sealed static partial I2();
                Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(4, 19),
                // (4,27): error CS0106: The modifier 'sealed' is not valid for this item
                //     sealed static partial I2();
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "I2").WithArguments("sealed").WithLocation(4, 27),
                // (9,12): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
                //     static partial I2() {}
                Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(9, 12),
                // (9,20): error CS0111: Type 'I2' already defines a member called 'I2' with the same parameter types
                //     static partial I2() {}
                Diagnostic(ErrorCode.ERR_MemberAlreadyExists, "I2").WithArguments("I2", "I2").WithLocation(9, 20),
                // (14,12): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
                //     static partial I3();
                Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(14, 12),
                // (19,19): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', 'event', an instance constructor name, or a method or property return type.
                //     sealed static partial I3() {}
                Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(19, 19),
                // (19,27): error CS0106: The modifier 'sealed' is not valid for this item
                //     sealed static partial I3() {}
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "I3").WithArguments("sealed").WithLocation(19, 27),
                // (19,27): error CS0111: Type 'I3' already defines a member called 'I3' with the same parameter types
                //     sealed static partial I3() {}
                Diagnostic(ErrorCode.ERR_MemberAlreadyExists, "I3").WithArguments("I3", "I3").WithLocation(19, 27)
                );
        }

        [Theory]
        [CombinatorialData]
        public void AbstractStaticConstructor_01(bool isVirtual)
        {
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"
interface I1
{
    " + modifier + @" static I1();
}

interface I2
{
    " + modifier + @" static I2() {}
}

interface I3
{
    static I3();
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,21): error CS0106: The modifier 'abstract' is not valid for this item
                //     abstract static I1();
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "I1").WithArguments(modifier.Trim()).WithLocation(4, 21),
                // (9,21): error CS0106: The modifier 'abstract' is not valid for this item
                //     abstract static I2() {}
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "I2").WithArguments(modifier.Trim()).WithLocation(9, 21),
                // (14,12): error CS0501: 'I3.I3()' must declare a body because it is not marked abstract, extern, or partial
                //     static I3();
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "I3").WithArguments("I3.I3()").WithLocation(14, 12)
                );

            var i1 = compilation1.GetTypeByMetadataName("I1");
            var m01 = i1.GetMember<MethodSymbol>(".cctor");

            Assert.False(m01.IsAbstract);
            Assert.False(m01.IsVirtual);
            Assert.False(m01.IsMetadataVirtual());
            Assert.False(m01.IsSealed);
            Assert.True(m01.IsStatic);
            Assert.False(m01.IsExtern);
            Assert.False(m01.IsAsync);
            Assert.False(m01.IsOverride);
            Assert.Null(i1.FindImplementationForInterfaceMember(m01));
        }

        [Fact]
        public void PartialSealedStatic_01()
        {
            var source1 =
@"
partial interface I1
{
    sealed static partial void M01();
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var i1 = compilation1.GetTypeByMetadataName("I1");
            var m01 = i1.GetMember<MethodSymbol>("M01");

            Assert.False(m01.IsAbstract);
            Assert.False(m01.IsVirtual);
            Assert.False(m01.IsMetadataVirtual());
            Assert.False(m01.IsSealed);
            Assert.True(m01.IsStatic);
            Assert.False(m01.IsExtern);
            Assert.False(m01.IsAsync);
            Assert.False(m01.IsOverride);
            Assert.Null(i1.FindImplementationForInterfaceMember(m01));

            Assert.True(m01.IsPartialDefinition());
            Assert.Null(m01.PartialImplementationPart);
        }

        [Fact]
        public void PartialSealedStatic_02()
        {
            var source1 =
@"
partial interface I1
{
    sealed static partial void M01();
}
partial interface I1
{
    sealed static partial void M01() {}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            ValidatePartialSealedStatic_02(compilation1);
        }

        private static void ValidatePartialSealedStatic_02(CSharpCompilation compilation1)
        {
            compilation1.VerifyDiagnostics();

            var i1 = compilation1.GetTypeByMetadataName("I1");
            var m01 = i1.GetMember<MethodSymbol>("M01");

            Assert.False(m01.IsAbstract);
            Assert.False(m01.IsVirtual);
            Assert.False(m01.IsMetadataVirtual());
            Assert.False(m01.IsSealed);
            Assert.True(m01.IsStatic);
            Assert.False(m01.IsExtern);
            Assert.False(m01.IsAsync);
            Assert.False(m01.IsOverride);
            Assert.Null(i1.FindImplementationForInterfaceMember(m01));

            Assert.True(m01.IsPartialDefinition());
            Assert.Same(m01, m01.PartialImplementationPart.PartialDefinitionPart);

            m01 = m01.PartialImplementationPart;

            Assert.False(m01.IsAbstract);
            Assert.False(m01.IsVirtual);
            Assert.False(m01.IsMetadataVirtual());
            Assert.False(m01.IsSealed);
            Assert.True(m01.IsStatic);
            Assert.False(m01.IsExtern);
            Assert.False(m01.IsAsync);
            Assert.False(m01.IsOverride);
            Assert.Null(i1.FindImplementationForInterfaceMember(m01));

            Assert.True(m01.IsPartialImplementation());
        }

        [Fact]
        public void PartialSealedStatic_03()
        {
            var source1 =
@"
partial interface I1
{
    static partial void M01();
}
partial interface I1
{
    sealed static partial void M01() {}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            ValidatePartialSealedStatic_02(compilation1);
        }

        [Fact]
        public void PartialSealedStatic_04()
        {
            var source1 =
@"
partial interface I1
{
    sealed static partial void M01();
}
partial interface I1
{
    static partial void M01() {}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            ValidatePartialSealedStatic_02(compilation1);
        }

        [Fact]
        public void PartialAbstractStatic_01()
        {
            var source1 =
@"
partial interface I1
{
    abstract static partial void M01();
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,34): error CS0750: A partial member cannot have the 'abstract' modifier
                //     abstract static partial void M01();
                Diagnostic(ErrorCode.ERR_PartialMemberCannotBeAbstract, "M01").WithLocation(4, 34)
                );

            var i1 = compilation1.GetTypeByMetadataName("I1");
            var m01 = i1.GetMember<MethodSymbol>("M01");

            Assert.True(m01.IsAbstract);
            Assert.False(m01.IsVirtual);
            Assert.True(m01.IsMetadataVirtual());
            Assert.False(m01.IsSealed);
            Assert.True(m01.IsStatic);
            Assert.False(m01.IsExtern);
            Assert.False(m01.IsAsync);
            Assert.False(m01.IsOverride);
            Assert.Null(i1.FindImplementationForInterfaceMember(m01));

            Assert.True(m01.IsPartialDefinition());
            Assert.Null(m01.PartialImplementationPart);
        }

        [Fact]
        public void PartialVirtualStatic_011()
        {
            var source1 =
@"
partial interface I1
{
    virtual static partial void M01();
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,33): error CS8798: Partial method 'I1.M01()' must have accessibility modifiers because it has a 'virtual', 'override', 'sealed', 'new', or 'extern' modifier.
                //     virtual static partial void M01();
                Diagnostic(ErrorCode.ERR_PartialMethodWithExtendedModMustHaveAccessMods, "M01").WithArguments("I1.M01()").WithLocation(4, 33)
                );

            var i1 = compilation1.GetTypeByMetadataName("I1");
            var m01 = i1.GetMember<MethodSymbol>("M01");

            Assert.False(m01.IsAbstract);
            Assert.True(m01.IsVirtual);
            Assert.True(m01.IsMetadataVirtual());
            Assert.False(m01.IsSealed);
            Assert.True(m01.IsStatic);
            Assert.False(m01.IsExtern);
            Assert.False(m01.IsAsync);
            Assert.False(m01.IsOverride);
            Assert.Same(m01, i1.FindImplementationForInterfaceMember(m01));

            Assert.True(m01.IsPartialDefinition());
            Assert.Null(m01.PartialImplementationPart);
        }

        [Fact]
        public void PartialVirtualStatic_012()
        {
            var source1 =
@"
partial interface I1
{
    public virtual static partial void M01();
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,40): error CS8795: Partial method 'I1.M01()' must have an implementation part because it has accessibility modifiers.
                //     public virtual static partial void M01();
                Diagnostic(ErrorCode.ERR_PartialMethodWithAccessibilityModsMustHaveImplementation, "M01").WithArguments("I1.M01()").WithLocation(4, 40)
                );

            var i1 = compilation1.GetTypeByMetadataName("I1");
            var m01 = i1.GetMember<MethodSymbol>("M01");

            Assert.False(m01.IsAbstract);
            Assert.True(m01.IsVirtual);
            Assert.True(m01.IsMetadataVirtual());
            Assert.False(m01.IsSealed);
            Assert.True(m01.IsStatic);
            Assert.False(m01.IsExtern);
            Assert.False(m01.IsAsync);
            Assert.False(m01.IsOverride);
            Assert.Same(m01, i1.FindImplementationForInterfaceMember(m01));

            Assert.True(m01.IsPartialDefinition());
            Assert.Null(m01.PartialImplementationPart);
        }

        [Fact]
        public void PartialAbstractStatic_02()
        {
            var source1 =
@"
partial interface I1
{
    abstract static partial void M01();
}
partial interface I1
{
    abstract static partial void M01() {}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,34): error CS0750: A partial member cannot have the 'abstract' modifier
                //     abstract static partial void M01();
                Diagnostic(ErrorCode.ERR_PartialMemberCannotBeAbstract, "M01").WithLocation(4, 34),
                // (8,34): error CS0500: 'I1.M01()' cannot declare a body because it is marked abstract
                //     abstract static partial void M01() {}
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "M01").WithArguments("I1.M01()").WithLocation(8, 34),
                // (8,34): error CS0750: A partial member cannot have the 'abstract' modifier
                //     abstract static partial void M01() {}
                Diagnostic(ErrorCode.ERR_PartialMemberCannotBeAbstract, "M01").WithLocation(8, 34)
                );

            var i1 = compilation1.GetTypeByMetadataName("I1");
            var m01 = i1.GetMember<MethodSymbol>("M01");

            Assert.True(m01.IsAbstract);
            Assert.False(m01.IsVirtual);
            Assert.True(m01.IsMetadataVirtual());
            Assert.False(m01.IsSealed);
            Assert.True(m01.IsStatic);
            Assert.False(m01.IsExtern);
            Assert.False(m01.IsAsync);
            Assert.False(m01.IsOverride);
            Assert.Null(i1.FindImplementationForInterfaceMember(m01));

            Assert.True(m01.IsPartialDefinition());
            Assert.Same(m01, m01.PartialImplementationPart.PartialDefinitionPart);

            m01 = m01.PartialImplementationPart;

            Assert.True(m01.IsAbstract);
            Assert.False(m01.IsVirtual);
            Assert.True(m01.IsMetadataVirtual());
            Assert.False(m01.IsSealed);
            Assert.True(m01.IsStatic);
            Assert.False(m01.IsExtern);
            Assert.False(m01.IsAsync);
            Assert.False(m01.IsOverride);
            Assert.Null(i1.FindImplementationForInterfaceMember(m01));

            Assert.True(m01.IsPartialImplementation());
        }

        [Fact]
        public void PartialVirtualStatic_021()
        {
            var source1 =
@"
partial interface I1
{
    public virtual static partial void M01();
}
partial interface I1
{
    public virtual static partial void M01() {}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var i1 = compilation1.GetTypeByMetadataName("I1");
            var m01 = i1.GetMember<MethodSymbol>("M01");

            Assert.False(m01.IsAbstract);
            Assert.True(m01.IsVirtual);
            Assert.True(m01.IsMetadataVirtual());
            Assert.False(m01.IsSealed);
            Assert.True(m01.IsStatic);
            Assert.False(m01.IsExtern);
            Assert.False(m01.IsAsync);
            Assert.False(m01.IsOverride);
            Assert.Same(m01, i1.FindImplementationForInterfaceMember(m01));

            Assert.True(m01.IsPartialDefinition());
            Assert.Same(m01, m01.PartialImplementationPart.PartialDefinitionPart);

            m01 = m01.PartialImplementationPart;

            Assert.False(m01.IsAbstract);
            Assert.True(m01.IsVirtual);
            Assert.True(m01.IsMetadataVirtual());
            Assert.False(m01.IsSealed);
            Assert.True(m01.IsStatic);
            Assert.False(m01.IsExtern);
            Assert.False(m01.IsAsync);
            Assert.False(m01.IsOverride);
            Assert.Same(m01, i1.FindImplementationForInterfaceMember(m01));

            Assert.True(m01.IsPartialImplementation());
        }

        [Fact]
        public void PartialAbstractStatic_03()
        {
            var source1 =
@"
partial interface I1
{
    abstract static partial void M01();
}
partial interface I1
{
    static partial void M01() {}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,34): error CS0750: A partial member cannot have the 'abstract' modifier
                //     abstract static partial void M01();
                Diagnostic(ErrorCode.ERR_PartialMemberCannotBeAbstract, "M01").WithLocation(4, 34)
                );

            var i1 = compilation1.GetTypeByMetadataName("I1");
            var m01 = i1.GetMember<MethodSymbol>("M01");

            Assert.True(m01.IsAbstract);
            Assert.False(m01.IsVirtual);
            Assert.True(m01.IsMetadataVirtual());
            Assert.False(m01.IsSealed);
            Assert.True(m01.IsStatic);
            Assert.False(m01.IsExtern);
            Assert.False(m01.IsAsync);
            Assert.False(m01.IsOverride);
            Assert.Null(i1.FindImplementationForInterfaceMember(m01));

            Assert.True(m01.IsPartialDefinition());
            Assert.Same(m01, m01.PartialImplementationPart.PartialDefinitionPart);

            m01 = m01.PartialImplementationPart;

            Assert.False(m01.IsAbstract);
            Assert.False(m01.IsVirtual);
            Assert.False(m01.IsMetadataVirtual());
            Assert.False(m01.IsSealed);
            Assert.True(m01.IsStatic);
            Assert.False(m01.IsExtern);
            Assert.False(m01.IsAsync);
            Assert.False(m01.IsOverride);
            Assert.Null(i1.FindImplementationForInterfaceMember(m01));

            Assert.True(m01.IsPartialImplementation());
        }

        [Fact]
        public void PartialVirtualStatic_031()
        {
            var source1 =
@"
partial interface I1
{
    public virtual static partial void M01();
}
partial interface I1
{
    static partial void M01() {}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (8,25): error CS8799: Both partial member declarations must have identical accessibility modifiers.
                //     static partial void M01() {}
                Diagnostic(ErrorCode.ERR_PartialMemberAccessibilityDifference, "M01").WithLocation(8, 25),
                // (8,25): error CS8800: Both partial member declarations must have identical combinations of 'virtual', 'override', 'sealed', and 'new' modifiers.
                //     static partial void M01() {}
                Diagnostic(ErrorCode.ERR_PartialMemberExtendedModDifference, "M01").WithLocation(8, 25)
                );

            var i1 = compilation1.GetTypeByMetadataName("I1");
            var m01 = i1.GetMember<MethodSymbol>("M01");

            Assert.False(m01.IsAbstract);
            Assert.True(m01.IsVirtual);
            Assert.True(m01.IsMetadataVirtual());
            Assert.False(m01.IsSealed);
            Assert.True(m01.IsStatic);
            Assert.False(m01.IsExtern);
            Assert.False(m01.IsAsync);
            Assert.False(m01.IsOverride);
            Assert.Same(m01, i1.FindImplementationForInterfaceMember(m01));

            Assert.True(m01.IsPartialDefinition());
            Assert.Same(m01, m01.PartialImplementationPart.PartialDefinitionPart);

            m01 = m01.PartialImplementationPart;

            Assert.False(m01.IsAbstract);
            Assert.False(m01.IsVirtual);
            Assert.False(m01.IsMetadataVirtual());
            Assert.False(m01.IsSealed);
            Assert.True(m01.IsStatic);
            Assert.False(m01.IsExtern);
            Assert.False(m01.IsAsync);
            Assert.False(m01.IsOverride);
            Assert.Null(i1.FindImplementationForInterfaceMember(m01));

            Assert.True(m01.IsPartialImplementation());
        }

        [Fact]
        public void PartialVirtualStatic_032()
        {
            var source1 =
@"
partial interface I1
{
    public virtual static partial void M01();
}
partial interface I1
{
    public static partial void M01() {}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (8,32): error CS8800: Both partial member declarations must have identical combinations of 'virtual', 'override', 'sealed', and 'new' modifiers.
                //     public static partial void M01() {}
                Diagnostic(ErrorCode.ERR_PartialMemberExtendedModDifference, "M01").WithLocation(8, 32)
                );

            var i1 = compilation1.GetTypeByMetadataName("I1");
            var m01 = i1.GetMember<MethodSymbol>("M01");

            Assert.False(m01.IsAbstract);
            Assert.True(m01.IsVirtual);
            Assert.True(m01.IsMetadataVirtual());
            Assert.False(m01.IsSealed);
            Assert.True(m01.IsStatic);
            Assert.False(m01.IsExtern);
            Assert.False(m01.IsAsync);
            Assert.False(m01.IsOverride);
            Assert.Same(m01, i1.FindImplementationForInterfaceMember(m01));

            Assert.True(m01.IsPartialDefinition());
            Assert.Same(m01, m01.PartialImplementationPart.PartialDefinitionPart);

            m01 = m01.PartialImplementationPart;

            Assert.False(m01.IsAbstract);
            Assert.False(m01.IsVirtual);
            Assert.False(m01.IsMetadataVirtual());
            Assert.False(m01.IsSealed);
            Assert.True(m01.IsStatic);
            Assert.False(m01.IsExtern);
            Assert.False(m01.IsAsync);
            Assert.False(m01.IsOverride);
            Assert.Null(i1.FindImplementationForInterfaceMember(m01));

            Assert.True(m01.IsPartialImplementation());
        }

        [Fact]
        public void PartialAbstractStatic_04()
        {
            var source1 =
@"
partial interface I1
{
    static partial void M01();
}
partial interface I1
{
    abstract static partial void M01() {}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (8,34): error CS0500: 'I1.M01()' cannot declare a body because it is marked abstract
                //     abstract static partial void M01() {}
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "M01").WithArguments("I1.M01()").WithLocation(8, 34),
                // (8,34): error CS0750: A partial member cannot have the 'abstract' modifier
                //     abstract static partial void M01() {}
                Diagnostic(ErrorCode.ERR_PartialMemberCannotBeAbstract, "M01").WithLocation(8, 34)
                );

            var i1 = compilation1.GetTypeByMetadataName("I1");
            var m01 = i1.GetMember<MethodSymbol>("M01");

            Assert.False(m01.IsAbstract);
            Assert.False(m01.IsVirtual);
            Assert.False(m01.IsMetadataVirtual());
            Assert.False(m01.IsSealed);
            Assert.True(m01.IsStatic);
            Assert.False(m01.IsExtern);
            Assert.False(m01.IsAsync);
            Assert.False(m01.IsOverride);
            Assert.Null(i1.FindImplementationForInterfaceMember(m01));

            Assert.True(m01.IsPartialDefinition());
            Assert.Same(m01, m01.PartialImplementationPart.PartialDefinitionPart);

            m01 = m01.PartialImplementationPart;

            Assert.True(m01.IsAbstract);
            Assert.False(m01.IsVirtual);
            Assert.True(m01.IsMetadataVirtual());
            Assert.False(m01.IsSealed);
            Assert.True(m01.IsStatic);
            Assert.False(m01.IsExtern);
            Assert.False(m01.IsAsync);
            Assert.False(m01.IsOverride);
            Assert.Null(i1.FindImplementationForInterfaceMember(m01));

            Assert.True(m01.IsPartialImplementation());
        }

        private (string modifier, string body) GetModifierAndBody(bool isVirtual)
        {
            if (isVirtual)
            {
                return ("virtual ", " => throw null;");
            }
            else
            {
                return ("abstract", ";");
            }
        }

        [Theory]
        [CombinatorialData]
        public void PrivateAbstractStatic_01(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"#pragma warning disable CS0067 // The event 'I1.E01' is never used
interface I1
{
    private " + modifier + @" static void M01()" + body + @"
    private " + modifier + @" static bool P01 { get; }
    private " + modifier + @" static event System.Action E01;
    private " + modifier + @" static I1 operator+ (I1 x)" + body + @"
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,34): error CS0621: 'I1.M01()': virtual or abstract members cannot be private
                //     private abstract static void M01();
                Diagnostic(ErrorCode.ERR_VirtualPrivate, "M01").WithArguments("I1.M01()").WithLocation(4, 34),
                // (5,34): error CS0621: 'I1.P01': virtual or abstract members cannot be private
                //     private abstract static bool P01 { get; }
                Diagnostic(ErrorCode.ERR_VirtualPrivate, "P01").WithArguments("I1.P01").WithLocation(5, 34),
                // (6,49): error CS0621: 'I1.E01': virtual or abstract members cannot be private
                //     private abstract static event System.Action E01;
                Diagnostic(ErrorCode.ERR_VirtualPrivate, "E01").WithArguments("I1.E01").WithLocation(6, 49),
                // (7,40): error CS0558: User-defined operator 'I1.operator +(I1)' must be declared static and public
                //     private abstract static I1 operator+ (I1 x);
                Diagnostic(ErrorCode.ERR_OperatorsMustBeStaticAndPublic, "+").WithArguments("I1.operator +(I1)").WithLocation(7, 40)
                );
        }

        [Fact]
        public void PropertyModifiers_01()
        {
            var source1 =
@"
public interface I1
{
    abstract static bool M01 { get
    ; } 

    virtual static bool M02 { get
    ; } 

    sealed static bool M03 { get
    ; } 

    override static bool M04 { get
    ; } 

    abstract virtual static bool M05 { get
    ; } 

    abstract sealed static bool M06 { get
    ; } 

    abstract override static bool M07 { get
    ; } 

    virtual sealed static bool M08 { get
    ; } 

    virtual override static bool M09 { get
    ; } 

    sealed override static bool M10 { get
    ; } 
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,26): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract static bool M01 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M01").WithArguments("abstract", "10.0", "11.0").WithLocation(4, 26),
                // (7,25): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual static bool M02 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M02").WithArguments("virtual", "10.0", "11.0").WithLocation(7, 25),
                // (10,24): error CS8703: The modifier 'sealed' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     sealed static bool M03 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M03").WithArguments("sealed", "10.0", "11.0").WithLocation(10, 24),
                // (13,26): error CS0106: The modifier 'override' is not valid for this item
                //     override static bool M04 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M04").WithArguments("override").WithLocation(13, 26),
                // (16,34): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract virtual static bool M05 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M05").WithArguments("abstract", "10.0", "11.0").WithLocation(16, 34),
                // (16,34): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract virtual static bool M05 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M05").WithArguments("virtual", "10.0", "11.0").WithLocation(16, 34),
                // (16,34): error CS0503: The abstract property 'I1.M05' cannot be marked virtual
                //     abstract virtual static bool M05 { get
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "M05").WithArguments("property", "I1.M05").WithLocation(16, 34),
                // (19,33): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static bool M06 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M06").WithArguments("sealed").WithLocation(19, 33),
                // (19,33): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract sealed static bool M06 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M06").WithArguments("abstract", "10.0", "11.0").WithLocation(19, 33),
                // (22,35): error CS0106: The modifier 'override' is not valid for this item
                //     abstract override static bool M07 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M07").WithArguments("override").WithLocation(22, 35),
                // (22,35): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract override static bool M07 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M07").WithArguments("abstract", "10.0", "11.0").WithLocation(22, 35),
                // (25,32): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static bool M08 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M08").WithArguments("sealed").WithLocation(25, 32),
                // (25,32): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual sealed static bool M08 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M08").WithArguments("virtual", "10.0", "11.0").WithLocation(25, 32),
                // (28,34): error CS0106: The modifier 'override' is not valid for this item
                //     virtual override static bool M09 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M09").WithArguments("override").WithLocation(28, 34),
                // (28,34): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual override static bool M09 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M09").WithArguments("virtual", "10.0", "11.0").WithLocation(28, 34),
                // (31,33): error CS0106: The modifier 'override' is not valid for this item
                //     sealed override static bool M10 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M10").WithArguments("override").WithLocation(31, 33),
                // (31,33): error CS8703: The modifier 'sealed' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     sealed override static bool M10 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M10").WithArguments("sealed", "10.0", "11.0").WithLocation(31, 33)
                );

            ValidatePropertyModifiers_01(compilation1);
        }

        private static void ValidatePropertyModifiers_01(CSharpCompilation compilation1)
        {
            var i1 = compilation1.GetTypeByMetadataName("I1");

            {
                var m01 = i1.GetMember<PropertySymbol>("M01");

                Assert.True(m01.IsAbstract);
                Assert.False(m01.IsVirtual);
                Assert.False(m01.IsSealed);
                Assert.True(m01.IsStatic);
                Assert.False(m01.IsExtern);
                Assert.False(m01.IsOverride);
                Assert.Null(i1.FindImplementationForInterfaceMember(m01));

                var m02 = i1.GetMember<PropertySymbol>("M02");

                Assert.False(m02.IsAbstract);
                Assert.True(m02.IsVirtual);
                Assert.False(m02.IsSealed);
                Assert.True(m02.IsStatic);
                Assert.False(m02.IsExtern);
                Assert.False(m02.IsOverride);
                Assert.Same(m02, i1.FindImplementationForInterfaceMember(m02));

                var m03 = i1.GetMember<PropertySymbol>("M03");

                Assert.False(m03.IsAbstract);
                Assert.False(m03.IsVirtual);
                Assert.False(m03.IsSealed);
                Assert.True(m03.IsStatic);
                Assert.False(m03.IsExtern);
                Assert.False(m03.IsOverride);
                Assert.Null(i1.FindImplementationForInterfaceMember(m03));

                var m04 = i1.GetMember<PropertySymbol>("M04");

                Assert.False(m04.IsAbstract);
                Assert.False(m04.IsVirtual);
                Assert.False(m04.IsSealed);
                Assert.True(m04.IsStatic);
                Assert.False(m04.IsExtern);
                Assert.False(m04.IsOverride);
                Assert.Null(i1.FindImplementationForInterfaceMember(m04));

                var m05 = i1.GetMember<PropertySymbol>("M05");

                Assert.True(m05.IsAbstract);
                Assert.True(m05.IsVirtual);
                Assert.False(m05.IsSealed);
                Assert.True(m05.IsStatic);
                Assert.False(m05.IsExtern);
                Assert.False(m05.IsOverride);
                Assert.Null(i1.FindImplementationForInterfaceMember(m05));

                var m06 = i1.GetMember<PropertySymbol>("M06");

                Assert.True(m06.IsAbstract);
                Assert.False(m06.IsVirtual);
                Assert.False(m06.IsSealed);
                Assert.True(m06.IsStatic);
                Assert.False(m06.IsExtern);
                Assert.False(m06.IsOverride);
                Assert.Null(i1.FindImplementationForInterfaceMember(m06));

                var m07 = i1.GetMember<PropertySymbol>("M07");

                Assert.True(m07.IsAbstract);
                Assert.False(m07.IsVirtual);
                Assert.False(m07.IsSealed);
                Assert.True(m07.IsStatic);
                Assert.False(m07.IsExtern);
                Assert.False(m07.IsOverride);
                Assert.Null(i1.FindImplementationForInterfaceMember(m07));

                var m08 = i1.GetMember<PropertySymbol>("M08");

                Assert.False(m08.IsAbstract);
                Assert.True(m08.IsVirtual);
                Assert.False(m08.IsSealed);
                Assert.True(m08.IsStatic);
                Assert.False(m08.IsExtern);
                Assert.False(m08.IsOverride);
                Assert.Same(m08, i1.FindImplementationForInterfaceMember(m08));

                var m09 = i1.GetMember<PropertySymbol>("M09");

                Assert.False(m09.IsAbstract);
                Assert.True(m09.IsVirtual);
                Assert.False(m09.IsSealed);
                Assert.True(m09.IsStatic);
                Assert.False(m09.IsExtern);
                Assert.False(m09.IsOverride);
                Assert.Same(m09, i1.FindImplementationForInterfaceMember(m09));

                var m10 = i1.GetMember<PropertySymbol>("M10");

                Assert.False(m10.IsAbstract);
                Assert.False(m10.IsVirtual);
                Assert.False(m10.IsSealed);
                Assert.True(m10.IsStatic);
                Assert.False(m10.IsExtern);
                Assert.False(m10.IsOverride);
                Assert.Null(i1.FindImplementationForInterfaceMember(m10));
            }
            {
                var m01 = i1.GetMember<PropertySymbol>("M01").GetMethod;

                Assert.True(m01.IsAbstract);
                Assert.False(m01.IsVirtual);
                Assert.True(m01.IsMetadataVirtual());
                Assert.False(m01.IsSealed);
                Assert.True(m01.IsStatic);
                Assert.False(m01.IsExtern);
                Assert.False(m01.IsAsync);
                Assert.False(m01.IsOverride);
                Assert.Null(i1.FindImplementationForInterfaceMember(m01));

                var m02 = i1.GetMember<PropertySymbol>("M02").GetMethod;

                Assert.False(m02.IsAbstract);
                Assert.True(m02.IsVirtual);
                Assert.True(m02.IsMetadataVirtual());
                Assert.False(m02.IsSealed);
                Assert.True(m02.IsStatic);
                Assert.False(m02.IsExtern);
                Assert.False(m02.IsAsync);
                Assert.False(m02.IsOverride);
                Assert.Same(m02, i1.FindImplementationForInterfaceMember(m02));

                var m03 = i1.GetMember<PropertySymbol>("M03").GetMethod;

                Assert.False(m03.IsAbstract);
                Assert.False(m03.IsVirtual);
                Assert.False(m03.IsMetadataVirtual());
                Assert.False(m03.IsSealed);
                Assert.True(m03.IsStatic);
                Assert.False(m03.IsExtern);
                Assert.False(m03.IsAsync);
                Assert.False(m03.IsOverride);
                Assert.Null(i1.FindImplementationForInterfaceMember(m03));

                var m04 = i1.GetMember<PropertySymbol>("M04").GetMethod;

                Assert.False(m04.IsAbstract);
                Assert.False(m04.IsVirtual);
                Assert.False(m04.IsMetadataVirtual());
                Assert.False(m04.IsSealed);
                Assert.True(m04.IsStatic);
                Assert.False(m04.IsExtern);
                Assert.False(m04.IsAsync);
                Assert.False(m04.IsOverride);
                Assert.Null(i1.FindImplementationForInterfaceMember(m04));

                var m05 = i1.GetMember<PropertySymbol>("M05").GetMethod;

                Assert.True(m05.IsAbstract);
                Assert.True(m05.IsVirtual);
                Assert.True(m05.IsMetadataVirtual());
                Assert.False(m05.IsSealed);
                Assert.True(m05.IsStatic);
                Assert.False(m05.IsExtern);
                Assert.False(m05.IsAsync);
                Assert.False(m05.IsOverride);
                Assert.Null(i1.FindImplementationForInterfaceMember(m05));

                var m06 = i1.GetMember<PropertySymbol>("M06").GetMethod;

                Assert.True(m06.IsAbstract);
                Assert.False(m06.IsVirtual);
                Assert.True(m06.IsMetadataVirtual());
                Assert.False(m06.IsSealed);
                Assert.True(m06.IsStatic);
                Assert.False(m06.IsExtern);
                Assert.False(m06.IsAsync);
                Assert.False(m06.IsOverride);
                Assert.Null(i1.FindImplementationForInterfaceMember(m06));

                var m07 = i1.GetMember<PropertySymbol>("M07").GetMethod;

                Assert.True(m07.IsAbstract);
                Assert.False(m07.IsVirtual);
                Assert.True(m07.IsMetadataVirtual());
                Assert.False(m07.IsSealed);
                Assert.True(m07.IsStatic);
                Assert.False(m07.IsExtern);
                Assert.False(m07.IsAsync);
                Assert.False(m07.IsOverride);
                Assert.Null(i1.FindImplementationForInterfaceMember(m07));

                var m08 = i1.GetMember<PropertySymbol>("M08").GetMethod;

                Assert.False(m08.IsAbstract);
                Assert.True(m08.IsVirtual);
                Assert.True(m08.IsMetadataVirtual());
                Assert.False(m08.IsSealed);
                Assert.True(m08.IsStatic);
                Assert.False(m08.IsExtern);
                Assert.False(m08.IsAsync);
                Assert.False(m08.IsOverride);
                Assert.Same(m08, i1.FindImplementationForInterfaceMember(m08));

                var m09 = i1.GetMember<PropertySymbol>("M09").GetMethod;

                Assert.False(m09.IsAbstract);
                Assert.True(m09.IsVirtual);
                Assert.True(m09.IsMetadataVirtual());
                Assert.False(m09.IsSealed);
                Assert.True(m09.IsStatic);
                Assert.False(m09.IsExtern);
                Assert.False(m09.IsAsync);
                Assert.False(m09.IsOverride);
                Assert.Same(m09, i1.FindImplementationForInterfaceMember(m09));

                var m10 = i1.GetMember<PropertySymbol>("M10").GetMethod;

                Assert.False(m10.IsAbstract);
                Assert.False(m10.IsVirtual);
                Assert.False(m10.IsMetadataVirtual());
                Assert.False(m10.IsSealed);
                Assert.True(m10.IsStatic);
                Assert.False(m10.IsExtern);
                Assert.False(m10.IsAsync);
                Assert.False(m10.IsOverride);
                Assert.Null(i1.FindImplementationForInterfaceMember(m10));
            }
        }

        [Fact]
        public void PropertyModifiers_02()
        {
            var source1 =
@"
public interface I1
{
    abstract static bool M01 { get
    => throw null; } 

    virtual static bool M02 { get
    => throw null; } 

    sealed static bool M03 { get
    => throw null; } 

    override static bool M04 { get
    => throw null; } 

    abstract virtual static bool M05 { get
    { throw null; } } 

    abstract sealed static bool M06 { get
    => throw null; } 

    abstract override static bool M07 { get
    => throw null; } 

    virtual sealed static bool M08 { get
    => throw null; } 

    virtual override static bool M09 { get
    => throw null; } 

    sealed override static bool M10 { get
    => throw null; } 
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,26): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract static bool M01 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M01").WithArguments("abstract", "10.0", "11.0").WithLocation(4, 26),
                // (4,32): error CS0500: 'I1.M01.get' cannot declare a body because it is marked abstract
                //     abstract static bool M01 { get
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "get").WithArguments("I1.M01.get").WithLocation(4, 32),
                // (7,25): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual static bool M02 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M02").WithArguments("virtual", "10.0", "11.0").WithLocation(7, 25),
                // (10,24): error CS8703: The modifier 'sealed' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     sealed static bool M03 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M03").WithArguments("sealed", "10.0", "11.0").WithLocation(10, 24),
                // (13,26): error CS0106: The modifier 'override' is not valid for this item
                //     override static bool M04 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M04").WithArguments("override").WithLocation(13, 26),
                // (16,34): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract virtual static bool M05 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M05").WithArguments("abstract", "10.0", "11.0").WithLocation(16, 34),
                // (16,34): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract virtual static bool M05 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M05").WithArguments("virtual", "10.0", "11.0").WithLocation(16, 34),
                // (16,34): error CS0503: The abstract property 'I1.M05' cannot be marked virtual
                //     abstract virtual static bool M05 { get
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "M05").WithArguments("property", "I1.M05").WithLocation(16, 34),
                // (16,40): error CS0500: 'I1.M05.get' cannot declare a body because it is marked abstract
                //     abstract virtual static bool M05 { get
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "get").WithArguments("I1.M05.get").WithLocation(16, 40),
                // (19,33): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static bool M06 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M06").WithArguments("sealed").WithLocation(19, 33),
                // (19,33): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract sealed static bool M06 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M06").WithArguments("abstract", "10.0", "11.0").WithLocation(19, 33),
                // (19,39): error CS0500: 'I1.M06.get' cannot declare a body because it is marked abstract
                //     abstract sealed static bool M06 { get
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "get").WithArguments("I1.M06.get").WithLocation(19, 39),
                // (22,35): error CS0106: The modifier 'override' is not valid for this item
                //     abstract override static bool M07 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M07").WithArguments("override").WithLocation(22, 35),
                // (22,35): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract override static bool M07 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M07").WithArguments("abstract", "10.0", "11.0").WithLocation(22, 35),
                // (22,41): error CS0500: 'I1.M07.get' cannot declare a body because it is marked abstract
                //     abstract override static bool M07 { get
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "get").WithArguments("I1.M07.get").WithLocation(22, 41),
                // (25,32): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static bool M08 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M08").WithArguments("sealed").WithLocation(25, 32),
                // (25,32): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual sealed static bool M08 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M08").WithArguments("virtual", "10.0", "11.0").WithLocation(25, 32),
                // (28,34): error CS0106: The modifier 'override' is not valid for this item
                //     virtual override static bool M09 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M09").WithArguments("override").WithLocation(28, 34),
                // (28,34): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual override static bool M09 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M09").WithArguments("virtual", "10.0", "11.0").WithLocation(28, 34),
                // (31,33): error CS0106: The modifier 'override' is not valid for this item
                //     sealed override static bool M10 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M10").WithArguments("override").WithLocation(31, 33),
                // (31,33): error CS8703: The modifier 'sealed' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     sealed override static bool M10 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M10").WithArguments("sealed", "10.0", "11.0").WithLocation(31, 33)
                );

            ValidatePropertyModifiers_01(compilation1);
        }

        [Fact]
        public void PropertyModifiers_03()
        {
            var source1 =
@"
public interface I1
{
    abstract static bool M01 { get
    ; } 

    virtual static bool M02 { get
    ; } 

    sealed static bool M03 { get
    ; } 

    override static bool M04 { get
    ; } 

    abstract virtual static bool M05 { get
    ; } 

    abstract sealed static bool M06 { get
    ; } 

    abstract override static bool M07 { get
    ; } 

    virtual sealed static bool M08 { get
    ; } 

    virtual override static bool M09 { get
    ; } 

    sealed override static bool M10 { get
    ; } 
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (13,26): error CS0106: The modifier 'override' is not valid for this item
                //     override static bool M04 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M04").WithArguments("override").WithLocation(13, 26),
                // (16,34): error CS0503: The abstract property 'I1.M05' cannot be marked virtual
                //     abstract virtual static bool M05 { get
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "M05").WithArguments("property", "I1.M05").WithLocation(16, 34),
                // (19,33): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static bool M06 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M06").WithArguments("sealed").WithLocation(19, 33),
                // (22,35): error CS0106: The modifier 'override' is not valid for this item
                //     abstract override static bool M07 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M07").WithArguments("override").WithLocation(22, 35),
                // (25,32): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static bool M08 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M08").WithArguments("sealed").WithLocation(25, 32),
                // (28,34): error CS0106: The modifier 'override' is not valid for this item
                //     virtual override static bool M09 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M09").WithArguments("override").WithLocation(28, 34),
                // (31,33): error CS0106: The modifier 'override' is not valid for this item
                //     sealed override static bool M10 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M10").WithArguments("override").WithLocation(31, 33)
                );

            ValidatePropertyModifiers_01(compilation1);
        }

        [Fact]
        public void PropertyModifiers_04()
        {
            var source1 =
@"
public interface I1
{
    abstract static bool M01 { get
    => throw null; } 

    virtual static bool M02 { get
    => throw null; } 

    sealed static bool M03 { get
    => throw null; } 

    override static bool M04 { get
    => throw null; } 

    abstract virtual static bool M05 { get
    { throw null; } } 

    abstract sealed static bool M06 { get
    => throw null; } 

    abstract override static bool M07 { get
    => throw null; } 

    virtual sealed static bool M08 { get
    => throw null; } 

    virtual override static bool M09 { get
    => throw null; } 

    sealed override static bool M10 { get
    => throw null; } 
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,32): error CS0500: 'I1.M01.get' cannot declare a body because it is marked abstract
                //     abstract static bool M01 { get
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "get").WithArguments("I1.M01.get").WithLocation(4, 32),
                // (13,26): error CS0106: The modifier 'override' is not valid for this item
                //     override static bool M04 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M04").WithArguments("override").WithLocation(13, 26),
                // (16,34): error CS0503: The abstract property 'I1.M05' cannot be marked virtual
                //     abstract virtual static bool M05 { get
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "M05").WithArguments("property", "I1.M05").WithLocation(16, 34),
                // (16,40): error CS0500: 'I1.M05.get' cannot declare a body because it is marked abstract
                //     abstract virtual static bool M05 { get
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "get").WithArguments("I1.M05.get").WithLocation(16, 40),
                // (19,33): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static bool M06 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M06").WithArguments("sealed").WithLocation(19, 33),
                // (19,39): error CS0500: 'I1.M06.get' cannot declare a body because it is marked abstract
                //     abstract sealed static bool M06 { get
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "get").WithArguments("I1.M06.get").WithLocation(19, 39),
                // (22,35): error CS0106: The modifier 'override' is not valid for this item
                //     abstract override static bool M07 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M07").WithArguments("override").WithLocation(22, 35),
                // (22,41): error CS0500: 'I1.M07.get' cannot declare a body because it is marked abstract
                //     abstract override static bool M07 { get
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "get").WithArguments("I1.M07.get").WithLocation(22, 41),
                // (25,32): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static bool M08 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M08").WithArguments("sealed").WithLocation(25, 32),
                // (28,34): error CS0106: The modifier 'override' is not valid for this item
                //     virtual override static bool M09 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M09").WithArguments("override").WithLocation(28, 34),
                // (31,33): error CS0106: The modifier 'override' is not valid for this item
                //     sealed override static bool M10 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M10").WithArguments("override").WithLocation(31, 33)
                );

            ValidatePropertyModifiers_01(compilation1);
        }

        [Fact]
        public void PropertyModifiers_05()
        {
            var source1 =
@"
public interface I1
{
    abstract static bool M01 { get
    ; } 

    virtual static bool M02 { get
    ; } 

    sealed static bool M03 { get
    ; } 

    override static bool M04 { get
    ; } 

    abstract virtual static bool M05 { get
    ; } 

    abstract sealed static bool M06 { get
    ; } 

    abstract override static bool M07 { get
    ; } 

    virtual sealed static bool M08 { get
    ; } 

    virtual override static bool M09 { get
    ; } 

    sealed override static bool M10 { get
    ; } 
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular7_3,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,26): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract static bool M01 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M01").WithArguments("abstract", "7.3", "11.0").WithLocation(4, 26),
                // (7,25): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual static bool M02 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M02").WithArguments("virtual", "7.3", "11.0").WithLocation(7, 25),
                // (10,24): error CS8703: The modifier 'sealed' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     sealed static bool M03 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M03").WithArguments("sealed", "7.3", "11.0").WithLocation(10, 24),
                // (13,26): error CS0106: The modifier 'override' is not valid for this item
                //     override static bool M04 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M04").WithArguments("override").WithLocation(13, 26),
                // (13,26): error CS8703: The modifier 'static' is not valid for this item in C# 7.3. Please use language version '8.0' or greater.
                //     override static bool M04 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M04").WithArguments("static", "7.3", "8.0").WithLocation(13, 26),
                // (16,34): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract virtual static bool M05 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M05").WithArguments("abstract", "7.3", "11.0").WithLocation(16, 34),
                // (16,34): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract virtual static bool M05 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M05").WithArguments("virtual", "7.3", "11.0").WithLocation(16, 34),
                // (16,34): error CS0503: The abstract property 'I1.M05' cannot be marked virtual
                //     abstract virtual static bool M05 { get
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "M05").WithArguments("property", "I1.M05").WithLocation(16, 34),
                // (19,33): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static bool M06 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M06").WithArguments("sealed").WithLocation(19, 33),
                // (19,33): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract sealed static bool M06 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M06").WithArguments("abstract", "7.3", "11.0").WithLocation(19, 33),
                // (22,35): error CS0106: The modifier 'override' is not valid for this item
                //     abstract override static bool M07 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M07").WithArguments("override").WithLocation(22, 35),
                // (22,35): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract override static bool M07 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M07").WithArguments("abstract", "7.3", "11.0").WithLocation(22, 35),
                // (25,32): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static bool M08 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M08").WithArguments("sealed").WithLocation(25, 32),
                // (25,32): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual sealed static bool M08 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M08").WithArguments("virtual", "7.3", "11.0").WithLocation(25, 32),
                // (28,34): error CS0106: The modifier 'override' is not valid for this item
                //     virtual override static bool M09 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M09").WithArguments("override").WithLocation(28, 34),
                // (28,34): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual override static bool M09 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M09").WithArguments("virtual", "7.3", "11.0").WithLocation(28, 34),
                // (31,33): error CS0106: The modifier 'override' is not valid for this item
                //     sealed override static bool M10 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M10").WithArguments("override").WithLocation(31, 33),
                // (31,33): error CS8703: The modifier 'sealed' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     sealed override static bool M10 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M10").WithArguments("sealed", "7.3", "11.0").WithLocation(31, 33)
                );

            ValidatePropertyModifiers_01(compilation1);
        }

        [Fact]
        public void PropertyModifiers_06()
        {
            var source1 =
@"
public interface I1
{
    abstract static bool M01 { get
    => throw null; } 

    virtual static bool M02 { get
    => throw null; } 

    sealed static bool M03 { get
    => throw null; } 

    override static bool M04 { get
    => throw null; } 

    abstract virtual static bool M05 { get
    { throw null; } } 

    abstract sealed static bool M06 { get
    => throw null; } 

    abstract override static bool M07 { get
    => throw null; } 

    virtual sealed static bool M08 { get
    => throw null; } 

    virtual override static bool M09 { get
    => throw null; } 

    sealed override static bool M10 { get
    => throw null; } 
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular7_3,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,26): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract static bool M01 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M01").WithArguments("abstract", "7.3", "11.0").WithLocation(4, 26),
                // (4,32): error CS0500: 'I1.M01.get' cannot declare a body because it is marked abstract
                //     abstract static bool M01 { get
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "get").WithArguments("I1.M01.get").WithLocation(4, 32),
                // (7,25): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual static bool M02 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M02").WithArguments("virtual", "7.3", "11.0").WithLocation(7, 25),
                // (10,24): error CS8703: The modifier 'sealed' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     sealed static bool M03 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M03").WithArguments("sealed", "7.3", "11.0").WithLocation(10, 24),
                // (13,26): error CS0106: The modifier 'override' is not valid for this item
                //     override static bool M04 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M04").WithArguments("override").WithLocation(13, 26),
                // (13,26): error CS8370: Feature 'default interface implementation' is not available in C# 7.3. Please use language version 8.0 or greater.
                //     override static bool M04 { get
                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion7_3, "M04").WithArguments("default interface implementation", "8.0").WithLocation(13, 26),
                // (16,34): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract virtual static bool M05 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M05").WithArguments("abstract", "7.3", "11.0").WithLocation(16, 34),
                // (16,34): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract virtual static bool M05 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M05").WithArguments("virtual", "7.3", "11.0").WithLocation(16, 34),
                // (16,34): error CS0503: The abstract property 'I1.M05' cannot be marked virtual
                //     abstract virtual static bool M05 { get
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "M05").WithArguments("property", "I1.M05").WithLocation(16, 34),
                // (16,40): error CS0500: 'I1.M05.get' cannot declare a body because it is marked abstract
                //     abstract virtual static bool M05 { get
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "get").WithArguments("I1.M05.get").WithLocation(16, 40),
                // (19,33): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static bool M06 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M06").WithArguments("sealed").WithLocation(19, 33),
                // (19,33): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract sealed static bool M06 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M06").WithArguments("abstract", "7.3", "11.0").WithLocation(19, 33),
                // (19,39): error CS0500: 'I1.M06.get' cannot declare a body because it is marked abstract
                //     abstract sealed static bool M06 { get
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "get").WithArguments("I1.M06.get").WithLocation(19, 39),
                // (22,35): error CS0106: The modifier 'override' is not valid for this item
                //     abstract override static bool M07 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M07").WithArguments("override").WithLocation(22, 35),
                // (22,35): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract override static bool M07 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M07").WithArguments("abstract", "7.3", "11.0").WithLocation(22, 35),
                // (22,41): error CS0500: 'I1.M07.get' cannot declare a body because it is marked abstract
                //     abstract override static bool M07 { get
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "get").WithArguments("I1.M07.get").WithLocation(22, 41),
                // (25,32): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static bool M08 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M08").WithArguments("sealed").WithLocation(25, 32),
                // (25,32): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual sealed static bool M08 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M08").WithArguments("virtual", "7.3", "11.0").WithLocation(25, 32),
                // (28,34): error CS0106: The modifier 'override' is not valid for this item
                //     virtual override static bool M09 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M09").WithArguments("override").WithLocation(28, 34),
                // (28,34): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual override static bool M09 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M09").WithArguments("virtual", "7.3", "11.0").WithLocation(28, 34),
                // (31,33): error CS0106: The modifier 'override' is not valid for this item
                //     sealed override static bool M10 { get
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M10").WithArguments("override").WithLocation(31, 33),
                // (31,33): error CS8703: The modifier 'sealed' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     sealed override static bool M10 { get
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M10").WithArguments("sealed", "7.3", "11.0").WithLocation(31, 33)
                );

            ValidatePropertyModifiers_01(compilation1);
        }

        [Fact]
        public void EventModifiers_01()
        {
            var source1 =
@"#pragma warning disable CS0067 // The event is never used
public interface I1
{
    abstract static event D M01
    ;

    virtual static event D M02
    ;

    sealed static event D M03
    ;

    override static event D M04
    ;

    abstract virtual static event D M05
    ;

    abstract sealed static event D M06
    ;

    abstract override static event D M07
    ;

    virtual sealed static event D M08
    ;

    virtual override static event D M09
    ;

    sealed override static event D M10
    ;
}

public delegate void D();
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,29): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract static event D M01
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M01").WithArguments("abstract", "10.0", "11.0").WithLocation(4, 29),
                // (7,28): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual static event D M02
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M02").WithArguments("virtual", "10.0", "11.0").WithLocation(7, 28),
                // (10,27): error CS8703: The modifier 'sealed' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     sealed static event D M03
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M03").WithArguments("sealed", "10.0", "11.0").WithLocation(10, 27),
                // (13,29): error CS0106: The modifier 'override' is not valid for this item
                //     override static event D M04
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M04").WithArguments("override").WithLocation(13, 29),
                // (16,37): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract virtual static event D M05
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M05").WithArguments("abstract", "10.0", "11.0").WithLocation(16, 37),
                // (16,37): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract virtual static event D M05
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M05").WithArguments("virtual", "10.0", "11.0").WithLocation(16, 37),
                // (16,37): error CS0503: The abstract event 'I1.M05' cannot be marked virtual
                //     abstract virtual static event D M05
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "M05").WithArguments("event", "I1.M05").WithLocation(16, 37),
                // (19,36): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static event D M06
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M06").WithArguments("sealed").WithLocation(19, 36),
                // (19,36): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract sealed static event D M06
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M06").WithArguments("abstract", "10.0", "11.0").WithLocation(19, 36),
                // (22,38): error CS0106: The modifier 'override' is not valid for this item
                //     abstract override static event D M07
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M07").WithArguments("override").WithLocation(22, 38),
                // (22,38): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract override static event D M07
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M07").WithArguments("abstract", "10.0", "11.0").WithLocation(22, 38),
                // (25,35): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static event D M08
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M08").WithArguments("sealed").WithLocation(25, 35),
                // (25,35): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual sealed static event D M08
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M08").WithArguments("virtual", "10.0", "11.0").WithLocation(25, 35),
                // (28,37): error CS0106: The modifier 'override' is not valid for this item
                //     virtual override static event D M09
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M09").WithArguments("override").WithLocation(28, 37),
                // (28,37): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual override static event D M09
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M09").WithArguments("virtual", "10.0", "11.0").WithLocation(28, 37),
                // (31,36): error CS0106: The modifier 'override' is not valid for this item
                //     sealed override static event D M10
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M10").WithArguments("override").WithLocation(31, 36),
                // (31,36): error CS8703: The modifier 'sealed' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     sealed override static event D M10
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M10").WithArguments("sealed", "10.0", "11.0").WithLocation(31, 36)
                );

            ValidateEventModifiers_01(compilation1);
        }

        private static void ValidateEventModifiers_01(CSharpCompilation compilation1)
        {
            var i1 = compilation1.GetTypeByMetadataName("I1");

            {
                var m01 = i1.GetMember<EventSymbol>("M01");

                Assert.True(m01.IsAbstract);
                Assert.False(m01.IsVirtual);
                Assert.False(m01.IsSealed);
                Assert.True(m01.IsStatic);
                Assert.False(m01.IsExtern);
                Assert.False(m01.IsOverride);
                Assert.Null(i1.FindImplementationForInterfaceMember(m01));

                var m02 = i1.GetMember<EventSymbol>("M02");

                Assert.False(m02.IsAbstract);
                Assert.True(m02.IsVirtual);
                Assert.False(m02.IsSealed);
                Assert.True(m02.IsStatic);
                Assert.False(m02.IsExtern);
                Assert.False(m02.IsOverride);
                Assert.Same(m02, i1.FindImplementationForInterfaceMember(m02));

                var m03 = i1.GetMember<EventSymbol>("M03");

                Assert.False(m03.IsAbstract);
                Assert.False(m03.IsVirtual);
                Assert.False(m03.IsSealed);
                Assert.True(m03.IsStatic);
                Assert.False(m03.IsExtern);
                Assert.False(m03.IsOverride);
                Assert.Null(i1.FindImplementationForInterfaceMember(m03));

                var m04 = i1.GetMember<EventSymbol>("M04");

                Assert.False(m04.IsAbstract);
                Assert.False(m04.IsVirtual);
                Assert.False(m04.IsSealed);
                Assert.True(m04.IsStatic);
                Assert.False(m04.IsExtern);
                Assert.False(m04.IsOverride);
                Assert.Null(i1.FindImplementationForInterfaceMember(m04));

                var m05 = i1.GetMember<EventSymbol>("M05");

                Assert.True(m05.IsAbstract);
                Assert.True(m05.IsVirtual);
                Assert.False(m05.IsSealed);
                Assert.True(m05.IsStatic);
                Assert.False(m05.IsExtern);
                Assert.False(m05.IsOverride);
                Assert.Null(i1.FindImplementationForInterfaceMember(m05));

                var m06 = i1.GetMember<EventSymbol>("M06");

                Assert.True(m06.IsAbstract);
                Assert.False(m06.IsVirtual);
                Assert.False(m06.IsSealed);
                Assert.True(m06.IsStatic);
                Assert.False(m06.IsExtern);
                Assert.False(m06.IsOverride);
                Assert.Null(i1.FindImplementationForInterfaceMember(m06));

                var m07 = i1.GetMember<EventSymbol>("M07");

                Assert.True(m07.IsAbstract);
                Assert.False(m07.IsVirtual);
                Assert.False(m07.IsSealed);
                Assert.True(m07.IsStatic);
                Assert.False(m07.IsExtern);
                Assert.False(m07.IsOverride);
                Assert.Null(i1.FindImplementationForInterfaceMember(m07));

                var m08 = i1.GetMember<EventSymbol>("M08");

                Assert.False(m08.IsAbstract);
                Assert.True(m08.IsVirtual);
                Assert.False(m08.IsSealed);
                Assert.True(m08.IsStatic);
                Assert.False(m08.IsExtern);
                Assert.False(m08.IsOverride);
                Assert.Same(m08, i1.FindImplementationForInterfaceMember(m08));

                var m09 = i1.GetMember<EventSymbol>("M09");

                Assert.False(m09.IsAbstract);
                Assert.True(m09.IsVirtual);
                Assert.False(m09.IsSealed);
                Assert.True(m09.IsStatic);
                Assert.False(m09.IsExtern);
                Assert.False(m09.IsOverride);
                Assert.Same(m09, i1.FindImplementationForInterfaceMember(m09));

                var m10 = i1.GetMember<EventSymbol>("M10");

                Assert.False(m10.IsAbstract);
                Assert.False(m10.IsVirtual);
                Assert.False(m10.IsSealed);
                Assert.True(m10.IsStatic);
                Assert.False(m10.IsExtern);
                Assert.False(m10.IsOverride);
                Assert.Null(i1.FindImplementationForInterfaceMember(m10));
            }

            foreach (var addAccessor in new[] { true, false })
            {
                var m01 = getAccessor(i1.GetMember<EventSymbol>("M01"), addAccessor);

                Assert.True(m01.IsAbstract);
                Assert.False(m01.IsVirtual);
                Assert.True(m01.IsMetadataVirtual());
                Assert.False(m01.IsSealed);
                Assert.True(m01.IsStatic);
                Assert.False(m01.IsExtern);
                Assert.False(m01.IsAsync);
                Assert.False(m01.IsOverride);
                Assert.Null(i1.FindImplementationForInterfaceMember(m01));

                var m02 = getAccessor(i1.GetMember<EventSymbol>("M02"), addAccessor);

                Assert.False(m02.IsAbstract);
                Assert.True(m02.IsVirtual);
                Assert.True(m02.IsMetadataVirtual());
                Assert.False(m02.IsSealed);
                Assert.True(m02.IsStatic);
                Assert.False(m02.IsExtern);
                Assert.False(m02.IsAsync);
                Assert.False(m02.IsOverride);
                Assert.Same(m02, i1.FindImplementationForInterfaceMember(m02));

                var m03 = getAccessor(i1.GetMember<EventSymbol>("M03"), addAccessor);

                Assert.False(m03.IsAbstract);
                Assert.False(m03.IsVirtual);
                Assert.False(m03.IsMetadataVirtual());
                Assert.False(m03.IsSealed);
                Assert.True(m03.IsStatic);
                Assert.False(m03.IsExtern);
                Assert.False(m03.IsAsync);
                Assert.False(m03.IsOverride);
                Assert.Null(i1.FindImplementationForInterfaceMember(m03));

                var m04 = getAccessor(i1.GetMember<EventSymbol>("M04"), addAccessor);

                Assert.False(m04.IsAbstract);
                Assert.False(m04.IsVirtual);
                Assert.False(m04.IsMetadataVirtual());
                Assert.False(m04.IsSealed);
                Assert.True(m04.IsStatic);
                Assert.False(m04.IsExtern);
                Assert.False(m04.IsAsync);
                Assert.False(m04.IsOverride);
                Assert.Null(i1.FindImplementationForInterfaceMember(m04));

                var m05 = getAccessor(i1.GetMember<EventSymbol>("M05"), addAccessor);

                Assert.True(m05.IsAbstract);
                Assert.True(m05.IsVirtual);
                Assert.True(m05.IsMetadataVirtual());
                Assert.False(m05.IsSealed);
                Assert.True(m05.IsStatic);
                Assert.False(m05.IsExtern);
                Assert.False(m05.IsAsync);
                Assert.False(m05.IsOverride);
                Assert.Null(i1.FindImplementationForInterfaceMember(m05));

                var m06 = getAccessor(i1.GetMember<EventSymbol>("M06"), addAccessor);

                Assert.True(m06.IsAbstract);
                Assert.False(m06.IsVirtual);
                Assert.True(m06.IsMetadataVirtual());
                Assert.False(m06.IsSealed);
                Assert.True(m06.IsStatic);
                Assert.False(m06.IsExtern);
                Assert.False(m06.IsAsync);
                Assert.False(m06.IsOverride);
                Assert.Null(i1.FindImplementationForInterfaceMember(m06));

                var m07 = getAccessor(i1.GetMember<EventSymbol>("M07"), addAccessor);

                Assert.True(m07.IsAbstract);
                Assert.False(m07.IsVirtual);
                Assert.True(m07.IsMetadataVirtual());
                Assert.False(m07.IsSealed);
                Assert.True(m07.IsStatic);
                Assert.False(m07.IsExtern);
                Assert.False(m07.IsAsync);
                Assert.False(m07.IsOverride);
                Assert.Null(i1.FindImplementationForInterfaceMember(m07));

                var m08 = getAccessor(i1.GetMember<EventSymbol>("M08"), addAccessor);

                Assert.False(m08.IsAbstract);
                Assert.True(m08.IsVirtual);
                Assert.True(m08.IsMetadataVirtual());
                Assert.False(m08.IsSealed);
                Assert.True(m08.IsStatic);
                Assert.False(m08.IsExtern);
                Assert.False(m08.IsAsync);
                Assert.False(m08.IsOverride);
                Assert.Same(m08, i1.FindImplementationForInterfaceMember(m08));

                var m09 = getAccessor(i1.GetMember<EventSymbol>("M09"), addAccessor);

                Assert.False(m09.IsAbstract);
                Assert.True(m09.IsVirtual);
                Assert.True(m09.IsMetadataVirtual());
                Assert.False(m09.IsSealed);
                Assert.True(m09.IsStatic);
                Assert.False(m09.IsExtern);
                Assert.False(m09.IsAsync);
                Assert.False(m09.IsOverride);
                Assert.Same(m09, i1.FindImplementationForInterfaceMember(m09));

                var m10 = getAccessor(i1.GetMember<EventSymbol>("M10"), addAccessor);

                Assert.False(m10.IsAbstract);
                Assert.False(m10.IsVirtual);
                Assert.False(m10.IsMetadataVirtual());
                Assert.False(m10.IsSealed);
                Assert.True(m10.IsStatic);
                Assert.False(m10.IsExtern);
                Assert.False(m10.IsAsync);
                Assert.False(m10.IsOverride);
                Assert.Null(i1.FindImplementationForInterfaceMember(m10));
            }

            static MethodSymbol getAccessor(EventSymbol e, bool addAccessor)
            {
                return addAccessor ? e.AddMethod : e.RemoveMethod;
            }
        }

        [Fact]
        public void EventModifiers_02()
        {
            var source1 =
@"#pragma warning disable CS0067 // The event is never used
public interface I1
{
    abstract static event D M01 { add {} remove {} }
    

    virtual static event D M02 { add {} remove {} }
    

    sealed static event D M03 { add {} remove {} }
    

    override static event D M04 { add {} remove {} }
    

    abstract virtual static event D M05 { add {} remove {} }
    

    abstract sealed static event D M06 { add {} remove {} }
    

    abstract override static event D M07 { add {} remove {} }
    

    virtual sealed static event D M08 { add {} remove {} }
    

    virtual override static event D M09 { add {} remove {} }
    

    sealed override static event D M10 { add {} remove {} }
}

public delegate void D();
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,29): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract static event D M01 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M01").WithArguments("abstract", "10.0", "11.0").WithLocation(4, 29),
                // (4,33): error CS8712: 'I1.M01': abstract event cannot use event accessor syntax
                //     abstract static event D M01 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_AbstractEventHasAccessors, "{").WithArguments("I1.M01").WithLocation(4, 33),
                // (7,28): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual static event D M02 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M02").WithArguments("virtual", "10.0", "11.0").WithLocation(7, 28),
                // (10,27): error CS8703: The modifier 'sealed' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     sealed static event D M03 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M03").WithArguments("sealed", "10.0", "11.0").WithLocation(10, 27),
                // (13,29): error CS0106: The modifier 'override' is not valid for this item
                //     override static event D M04 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M04").WithArguments("override").WithLocation(13, 29),
                // (16,37): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract virtual static event D M05 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M05").WithArguments("abstract", "10.0", "11.0").WithLocation(16, 37),
                // (16,37): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract virtual static event D M05 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M05").WithArguments("virtual", "10.0", "11.0").WithLocation(16, 37),
                // (16,37): error CS0503: The abstract event 'I1.M05' cannot be marked virtual
                //     abstract virtual static event D M05 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "M05").WithArguments("event", "I1.M05").WithLocation(16, 37),
                // (16,41): error CS8712: 'I1.M05': abstract event cannot use event accessor syntax
                //     abstract virtual static event D M05 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_AbstractEventHasAccessors, "{").WithArguments("I1.M05").WithLocation(16, 41),
                // (19,36): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static event D M06 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M06").WithArguments("sealed").WithLocation(19, 36),
                // (19,36): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract sealed static event D M06 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M06").WithArguments("abstract", "10.0", "11.0").WithLocation(19, 36),
                // (19,40): error CS8712: 'I1.M06': abstract event cannot use event accessor syntax
                //     abstract sealed static event D M06 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_AbstractEventHasAccessors, "{").WithArguments("I1.M06").WithLocation(19, 40),
                // (22,38): error CS0106: The modifier 'override' is not valid for this item
                //     abstract override static event D M07 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M07").WithArguments("override").WithLocation(22, 38),
                // (22,38): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract override static event D M07 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M07").WithArguments("abstract", "10.0", "11.0").WithLocation(22, 38),
                // (22,42): error CS8712: 'I1.M07': abstract event cannot use event accessor syntax
                //     abstract override static event D M07 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_AbstractEventHasAccessors, "{").WithArguments("I1.M07").WithLocation(22, 42),
                // (25,35): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static event D M08 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M08").WithArguments("sealed").WithLocation(25, 35),
                // (25,35): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual sealed static event D M08 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M08").WithArguments("virtual", "10.0", "11.0").WithLocation(25, 35),
                // (28,37): error CS0106: The modifier 'override' is not valid for this item
                //     virtual override static event D M09 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M09").WithArguments("override").WithLocation(28, 37),
                // (28,37): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual override static event D M09 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M09").WithArguments("virtual", "10.0", "11.0").WithLocation(28, 37),
                // (31,36): error CS0106: The modifier 'override' is not valid for this item
                //     sealed override static event D M10 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M10").WithArguments("override").WithLocation(31, 36),
                // (31,36): error CS8703: The modifier 'sealed' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     sealed override static event D M10 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M10").WithArguments("sealed", "10.0", "11.0").WithLocation(31, 36)
                );

            ValidateEventModifiers_01(compilation1);
        }

        [Fact]
        public void EventModifiers_03()
        {
            var source1 =
@"#pragma warning disable CS0067 // The event is never used
public interface I1
{
    abstract static event D M01
    ;

    virtual static event D M02
    ;

    sealed static event D M03
    ;

    override static event D M04
    ;

    abstract virtual static event D M05
    ;

    abstract sealed static event D M06
    ;

    abstract override static event D M07
    ;

    virtual sealed static event D M08
    ;

    virtual override static event D M09
    ;

    sealed override static event D M10
    ;
}

public delegate void D();
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (13,29): error CS0106: The modifier 'override' is not valid for this item
                //     override static event D M04
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M04").WithArguments("override").WithLocation(13, 29),
                // (16,37): error CS0503: The abstract event 'I1.M05' cannot be marked virtual
                //     abstract virtual static event D M05
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "M05").WithArguments("event", "I1.M05").WithLocation(16, 37),
                // (19,36): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static event D M06
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M06").WithArguments("sealed").WithLocation(19, 36),
                // (22,38): error CS0106: The modifier 'override' is not valid for this item
                //     abstract override static event D M07
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M07").WithArguments("override").WithLocation(22, 38),
                // (25,35): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static event D M08
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M08").WithArguments("sealed").WithLocation(25, 35),
                // (28,37): error CS0106: The modifier 'override' is not valid for this item
                //     virtual override static event D M09
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M09").WithArguments("override").WithLocation(28, 37),
                // (31,36): error CS0106: The modifier 'override' is not valid for this item
                //     sealed override static event D M10
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M10").WithArguments("override").WithLocation(31, 36)
                );

            ValidateEventModifiers_01(compilation1);
        }

        [Fact]
        public void EventModifiers_04()
        {
            var source1 =
@"#pragma warning disable CS0067 // The event is never used
public interface I1
{
    abstract static event D M01 { add {} remove {} }
    

    virtual static event D M02 { add {} remove {} }
    

    sealed static event D M03 { add {} remove {} }
    

    override static event D M04 { add {} remove {} }
    

    abstract virtual static event D M05 { add {} remove {} }
    

    abstract sealed static event D M06 { add {} remove {} }
    

    abstract override static event D M07 { add {} remove {} }
    

    virtual sealed static event D M08 { add {} remove {} }
    

    virtual override static event D M09 { add {} remove {} }
    

    sealed override static event D M10 { add {} remove {} }
}

public delegate void D();
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,33): error CS8712: 'I1.M01': abstract event cannot use event accessor syntax
                //     abstract static event D M01 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_AbstractEventHasAccessors, "{").WithArguments("I1.M01").WithLocation(4, 33),
                // (13,29): error CS0106: The modifier 'override' is not valid for this item
                //     override static event D M04 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M04").WithArguments("override").WithLocation(13, 29),
                // (16,37): error CS0503: The abstract event 'I1.M05' cannot be marked virtual
                //     abstract virtual static event D M05 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "M05").WithArguments("event", "I1.M05").WithLocation(16, 37),
                // (16,41): error CS8712: 'I1.M05': abstract event cannot use event accessor syntax
                //     abstract virtual static event D M05 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_AbstractEventHasAccessors, "{").WithArguments("I1.M05").WithLocation(16, 41),
                // (19,36): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static event D M06 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M06").WithArguments("sealed").WithLocation(19, 36),
                // (19,40): error CS8712: 'I1.M06': abstract event cannot use event accessor syntax
                //     abstract sealed static event D M06 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_AbstractEventHasAccessors, "{").WithArguments("I1.M06").WithLocation(19, 40),
                // (22,38): error CS0106: The modifier 'override' is not valid for this item
                //     abstract override static event D M07 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M07").WithArguments("override").WithLocation(22, 38),
                // (22,42): error CS8712: 'I1.M07': abstract event cannot use event accessor syntax
                //     abstract override static event D M07 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_AbstractEventHasAccessors, "{").WithArguments("I1.M07").WithLocation(22, 42),
                // (25,35): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static event D M08 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M08").WithArguments("sealed").WithLocation(25, 35),
                // (28,37): error CS0106: The modifier 'override' is not valid for this item
                //     virtual override static event D M09 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M09").WithArguments("override").WithLocation(28, 37),
                // (31,36): error CS0106: The modifier 'override' is not valid for this item
                //     sealed override static event D M10 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M10").WithArguments("override").WithLocation(31, 36)
                );

            ValidateEventModifiers_01(compilation1);
        }

        [Fact]
        public void EventModifiers_05()
        {
            var source1 =
@"#pragma warning disable CS0067 // The event is never used
public interface I1
{
    abstract static event D M01
    ;

    virtual static event D M02
    ;

    sealed static event D M03
    ;

    override static event D M04
    ;

    abstract virtual static event D M05
    ;

    abstract sealed static event D M06
    ;

    abstract override static event D M07
    ;

    virtual sealed static event D M08
    ;

    virtual override static event D M09
    ;

    sealed override static event D M10
    ;
}

public delegate void D();
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular7_3,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,29): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract static event D M01
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M01").WithArguments("abstract", "7.3", "11.0").WithLocation(4, 29),
                // (7,28): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual static event D M02
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M02").WithArguments("virtual", "7.3", "11.0").WithLocation(7, 28),
                // (10,27): error CS8703: The modifier 'sealed' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     sealed static event D M03
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M03").WithArguments("sealed", "7.3", "11.0").WithLocation(10, 27),
                // (13,29): error CS0106: The modifier 'override' is not valid for this item
                //     override static event D M04
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M04").WithArguments("override").WithLocation(13, 29),
                // (13,29): error CS8703: The modifier 'static' is not valid for this item in C# 7.3. Please use language version '8.0' or greater.
                //     override static event D M04
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M04").WithArguments("static", "7.3", "8.0").WithLocation(13, 29),
                // (16,37): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract virtual static event D M05
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M05").WithArguments("abstract", "7.3", "11.0").WithLocation(16, 37),
                // (16,37): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract virtual static event D M05
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M05").WithArguments("virtual", "7.3", "11.0").WithLocation(16, 37),
                // (16,37): error CS0503: The abstract event 'I1.M05' cannot be marked virtual
                //     abstract virtual static event D M05
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "M05").WithArguments("event", "I1.M05").WithLocation(16, 37),
                // (19,36): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static event D M06
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M06").WithArguments("sealed").WithLocation(19, 36),
                // (19,36): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract sealed static event D M06
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M06").WithArguments("abstract", "7.3", "11.0").WithLocation(19, 36),
                // (22,38): error CS0106: The modifier 'override' is not valid for this item
                //     abstract override static event D M07
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M07").WithArguments("override").WithLocation(22, 38),
                // (22,38): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract override static event D M07
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M07").WithArguments("abstract", "7.3", "11.0").WithLocation(22, 38),
                // (25,35): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static event D M08
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M08").WithArguments("sealed").WithLocation(25, 35),
                // (25,35): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual sealed static event D M08
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M08").WithArguments("virtual", "7.3", "11.0").WithLocation(25, 35),
                // (28,37): error CS0106: The modifier 'override' is not valid for this item
                //     virtual override static event D M09
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M09").WithArguments("override").WithLocation(28, 37),
                // (28,37): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual override static event D M09
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M09").WithArguments("virtual", "7.3", "11.0").WithLocation(28, 37),
                // (31,36): error CS0106: The modifier 'override' is not valid for this item
                //     sealed override static event D M10
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M10").WithArguments("override").WithLocation(31, 36),
                // (31,36): error CS8703: The modifier 'sealed' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     sealed override static event D M10
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M10").WithArguments("sealed", "7.3", "11.0").WithLocation(31, 36)
                );

            ValidateEventModifiers_01(compilation1);
        }

        [Fact]
        public void EventModifiers_06()
        {
            var source1 =
@"#pragma warning disable CS0067 // The event is never used
public interface I1
{
    abstract static event D M01 { add {} remove {} }
    

    virtual static event D M02 { add {} remove {} }
    

    sealed static event D M03 { add {} remove {} }
    

    override static event D M04 { add {} remove {} }
    

    abstract virtual static event D M05 { add {} remove {} }
    

    abstract sealed static event D M06 { add {} remove {} }
    

    abstract override static event D M07 { add {} remove {} }
    

    virtual sealed static event D M08 { add {} remove {} }
    

    virtual override static event D M09 { add {} remove {} }
    

    sealed override static event D M10 { add {} remove {} }
}

public delegate void D();
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular7_3,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,29): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract static event D M01 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M01").WithArguments("abstract", "7.3", "11.0").WithLocation(4, 29),
                // (4,33): error CS8712: 'I1.M01': abstract event cannot use event accessor syntax
                //     abstract static event D M01 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_AbstractEventHasAccessors, "{").WithArguments("I1.M01").WithLocation(4, 33),
                // (7,28): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual static event D M02 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M02").WithArguments("virtual", "7.3", "11.0").WithLocation(7, 28),
                // (10,27): error CS8703: The modifier 'sealed' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     sealed static event D M03 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M03").WithArguments("sealed", "7.3", "11.0").WithLocation(10, 27),
                // (13,29): error CS0106: The modifier 'override' is not valid for this item
                //     override static event D M04 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M04").WithArguments("override").WithLocation(13, 29),
                // (13,29): error CS8370: Feature 'default interface implementation' is not available in C# 7.3. Please use language version 8.0 or greater.
                //     override static event D M04 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion7_3, "M04").WithArguments("default interface implementation", "8.0").WithLocation(13, 29),
                // (16,37): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract virtual static event D M05 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M05").WithArguments("abstract", "7.3", "11.0").WithLocation(16, 37),
                // (16,37): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract virtual static event D M05 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M05").WithArguments("virtual", "7.3", "11.0").WithLocation(16, 37),
                // (16,37): error CS0503: The abstract event 'I1.M05' cannot be marked virtual
                //     abstract virtual static event D M05 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "M05").WithArguments("event", "I1.M05").WithLocation(16, 37),
                // (16,41): error CS8712: 'I1.M05': abstract event cannot use event accessor syntax
                //     abstract virtual static event D M05 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_AbstractEventHasAccessors, "{").WithArguments("I1.M05").WithLocation(16, 41),
                // (19,36): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static event D M06 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M06").WithArguments("sealed").WithLocation(19, 36),
                // (19,36): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract sealed static event D M06 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M06").WithArguments("abstract", "7.3", "11.0").WithLocation(19, 36),
                // (19,40): error CS8712: 'I1.M06': abstract event cannot use event accessor syntax
                //     abstract sealed static event D M06 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_AbstractEventHasAccessors, "{").WithArguments("I1.M06").WithLocation(19, 40),
                // (22,38): error CS0106: The modifier 'override' is not valid for this item
                //     abstract override static event D M07 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M07").WithArguments("override").WithLocation(22, 38),
                // (22,38): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract override static event D M07 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M07").WithArguments("abstract", "7.3", "11.0").WithLocation(22, 38),
                // (22,42): error CS8712: 'I1.M07': abstract event cannot use event accessor syntax
                //     abstract override static event D M07 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_AbstractEventHasAccessors, "{").WithArguments("I1.M07").WithLocation(22, 42),
                // (25,35): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static event D M08 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M08").WithArguments("sealed").WithLocation(25, 35),
                // (25,35): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual sealed static event D M08 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M08").WithArguments("virtual", "7.3", "11.0").WithLocation(25, 35),
                // (28,37): error CS0106: The modifier 'override' is not valid for this item
                //     virtual override static event D M09 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M09").WithArguments("override").WithLocation(28, 37),
                // (28,37): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual override static event D M09 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M09").WithArguments("virtual", "7.3", "11.0").WithLocation(28, 37),
                // (31,36): error CS0106: The modifier 'override' is not valid for this item
                //     sealed override static event D M10 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M10").WithArguments("override").WithLocation(31, 36),
                // (31,36): error CS8703: The modifier 'sealed' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     sealed override static event D M10 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M10").WithArguments("sealed", "7.3", "11.0").WithLocation(31, 36)
                );

            ValidateEventModifiers_01(compilation1);
        }

        [Fact]
        public void OperatorModifiers_01()
        {
            var source1 =
@"
public interface I1
{
    abstract static I1 operator+ (I1 x)
    ; 

    virtual static I1 operator- (I1 x)
    ; 

    sealed static I1 operator++ (I1 x)
    ; 

    override static I1 operator-- (I1 x)
    ; 

    abstract virtual static I1 operator! (I1 x)
    ; 

    abstract sealed static I1 operator~ (I1 x)
    ; 

    abstract override static I1 operator+ (I1 x, I1 y)
    ; 

    virtual sealed static I1 operator- (I1 x, I1 y)
    ; 

    virtual override static I1 operator* (I1 x, I1 y) 
    ; 

    sealed override static I1 operator/ (I1 x, I1 y)
    ; 
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,32): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract static I1 operator+ (I1 x)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "+").WithArguments("abstract", "10.0", "11.0").WithLocation(4, 32),
                // (7,31): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual static I1 operator- (I1 x)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "-").WithArguments("virtual", "10.0", "11.0").WithLocation(7, 31),
                // (7,31): error CS0501: 'I1.operator -(I1)' must declare a body because it is not marked abstract, extern, or partial
                //     virtual static I1 operator- (I1 x)
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "-").WithArguments("I1.operator -(I1)").WithLocation(7, 31),
                // (10,30): error CS8703: The modifier 'sealed' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     sealed static I1 operator++ (I1 x)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "++").WithArguments("sealed", "10.0", "11.0").WithLocation(10, 30),
                // (10,30): error CS0501: 'I1.operator ++(I1)' must declare a body because it is not marked abstract, extern, or partial
                //     sealed static I1 operator++ (I1 x)
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "++").WithArguments("I1.operator ++(I1)").WithLocation(10, 30),
                // (13,32): error CS0106: The modifier 'override' is not valid for this item
                //     override static I1 operator-- (I1 x)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "--").WithArguments("override").WithLocation(13, 32),
                // (13,32): error CS0501: 'I1.operator --(I1)' must declare a body because it is not marked abstract, extern, or partial
                //     override static I1 operator-- (I1 x)
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "--").WithArguments("I1.operator --(I1)").WithLocation(13, 32),
                // (16,40): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract virtual static I1 operator! (I1 x)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "!").WithArguments("abstract", "10.0", "11.0").WithLocation(16, 40),
                // (16,40): error CS0503: The abstract method 'I1.operator !(I1)' cannot be marked virtual
                //     abstract virtual static I1 operator! (I1 x)
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "!").WithArguments("method", "I1.operator !(I1)").WithLocation(16, 40),
                // (19,39): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static I1 operator~ (I1 x)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "~").WithArguments("sealed").WithLocation(19, 39),
                // (19,39): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract sealed static I1 operator~ (I1 x)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "~").WithArguments("abstract", "10.0", "11.0").WithLocation(19, 39),
                // (22,41): error CS0106: The modifier 'override' is not valid for this item
                //     abstract override static I1 operator+ (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "+").WithArguments("override").WithLocation(22, 41),
                // (22,41): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract override static I1 operator+ (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "+").WithArguments("abstract", "10.0", "11.0").WithLocation(22, 41),
                // (25,38): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static I1 operator- (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "-").WithArguments("sealed").WithLocation(25, 38),
                // (25,38): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual sealed static I1 operator- (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "-").WithArguments("virtual", "10.0", "11.0").WithLocation(25, 38),
                // (25,38): error CS0501: 'I1.operator -(I1, I1)' must declare a body because it is not marked abstract, extern, or partial
                //     virtual sealed static I1 operator- (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "-").WithArguments("I1.operator -(I1, I1)").WithLocation(25, 38),
                // (28,40): error CS0106: The modifier 'override' is not valid for this item
                //     virtual override static I1 operator* (I1 x, I1 y) 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "*").WithArguments("override").WithLocation(28, 40),
                // (28,40): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual override static I1 operator* (I1 x, I1 y) 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "*").WithArguments("virtual", "10.0", "11.0").WithLocation(28, 40),
                // (28,40): error CS0501: 'I1.operator *(I1, I1)' must declare a body because it is not marked abstract, extern, or partial
                //     virtual override static I1 operator* (I1 x, I1 y) 
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "*").WithArguments("I1.operator *(I1, I1)").WithLocation(28, 40),
                // (31,39): error CS0106: The modifier 'override' is not valid for this item
                //     sealed override static I1 operator/ (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "/").WithArguments("override").WithLocation(31, 39),
                // (31,39): error CS8703: The modifier 'sealed' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     sealed override static I1 operator/ (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "/").WithArguments("sealed", "10.0", "11.0").WithLocation(31, 39),
                // (31,39): error CS0501: 'I1.operator /(I1, I1)' must declare a body because it is not marked abstract, extern, or partial
                //     sealed override static I1 operator/ (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "/").WithArguments("I1.operator /(I1, I1)").WithLocation(31, 39)
                );

            ValidateOperatorModifiers_01(compilation1);
        }

        private static void ValidateOperatorModifiers_01(CSharpCompilation compilation1)
        {
            var i1 = compilation1.GetTypeByMetadataName("I1");
            var m01 = i1.GetMember<MethodSymbol>("op_UnaryPlus");

            Assert.True(m01.IsAbstract);
            Assert.False(m01.IsVirtual);
            Assert.True(m01.IsMetadataVirtual());
            Assert.False(m01.IsSealed);
            Assert.True(m01.IsStatic);
            Assert.False(m01.IsExtern);
            Assert.False(m01.IsAsync);
            Assert.False(m01.IsOverride);
            Assert.Null(i1.FindImplementationForInterfaceMember(m01));

            var m02 = i1.GetMember<MethodSymbol>("op_UnaryNegation");

            Assert.False(m02.IsAbstract);
            Assert.True(m02.IsVirtual);
            Assert.True(m02.IsMetadataVirtual());
            Assert.False(m02.IsSealed);
            Assert.True(m02.IsStatic);
            Assert.False(m02.IsExtern);
            Assert.False(m02.IsAsync);
            Assert.False(m02.IsOverride);
            Assert.Same(m02, i1.FindImplementationForInterfaceMember(m02));

            var m03 = i1.GetMember<MethodSymbol>("op_Increment");

            Assert.False(m03.IsAbstract);
            Assert.False(m03.IsVirtual);
            Assert.False(m03.IsMetadataVirtual());
            Assert.False(m03.IsSealed);
            Assert.True(m03.IsStatic);
            Assert.False(m03.IsExtern);
            Assert.False(m03.IsAsync);
            Assert.False(m03.IsOverride);
            Assert.Null(i1.FindImplementationForInterfaceMember(m03));

            var m04 = i1.GetMember<MethodSymbol>("op_Decrement");

            Assert.False(m04.IsAbstract);
            Assert.False(m04.IsVirtual);
            Assert.False(m04.IsMetadataVirtual());
            Assert.False(m04.IsSealed);
            Assert.True(m04.IsStatic);
            Assert.False(m04.IsExtern);
            Assert.False(m04.IsAsync);
            Assert.False(m04.IsOverride);
            Assert.Null(i1.FindImplementationForInterfaceMember(m04));

            var m05 = i1.GetMember<MethodSymbol>("op_LogicalNot");

            Assert.True(m05.IsAbstract);
            Assert.True(m05.IsVirtual);
            Assert.True(m05.IsMetadataVirtual());
            Assert.False(m05.IsSealed);
            Assert.True(m05.IsStatic);
            Assert.False(m05.IsExtern);
            Assert.False(m05.IsAsync);
            Assert.False(m05.IsOverride);
            Assert.Null(i1.FindImplementationForInterfaceMember(m05));

            var m06 = i1.GetMember<MethodSymbol>("op_OnesComplement");

            Assert.True(m06.IsAbstract);
            Assert.False(m06.IsVirtual);
            Assert.True(m06.IsMetadataVirtual());
            Assert.False(m06.IsSealed);
            Assert.True(m06.IsStatic);
            Assert.False(m06.IsExtern);
            Assert.False(m06.IsAsync);
            Assert.False(m06.IsOverride);
            Assert.Null(i1.FindImplementationForInterfaceMember(m06));

            var m07 = i1.GetMember<MethodSymbol>("op_Addition");

            Assert.True(m07.IsAbstract);
            Assert.False(m07.IsVirtual);
            Assert.True(m07.IsMetadataVirtual());
            Assert.False(m07.IsSealed);
            Assert.True(m07.IsStatic);
            Assert.False(m07.IsExtern);
            Assert.False(m07.IsAsync);
            Assert.False(m07.IsOverride);
            Assert.Null(i1.FindImplementationForInterfaceMember(m07));

            var m08 = i1.GetMember<MethodSymbol>("op_Subtraction");

            Assert.False(m08.IsAbstract);
            Assert.True(m08.IsVirtual);
            Assert.True(m08.IsMetadataVirtual());
            Assert.False(m08.IsSealed);
            Assert.True(m08.IsStatic);
            Assert.False(m08.IsExtern);
            Assert.False(m08.IsAsync);
            Assert.False(m08.IsOverride);
            Assert.Same(m08, i1.FindImplementationForInterfaceMember(m08));

            var m09 = i1.GetMember<MethodSymbol>("op_Multiply");

            Assert.False(m09.IsAbstract);
            Assert.True(m09.IsVirtual);
            Assert.True(m09.IsMetadataVirtual());
            Assert.False(m09.IsSealed);
            Assert.True(m09.IsStatic);
            Assert.False(m09.IsExtern);
            Assert.False(m09.IsAsync);
            Assert.False(m09.IsOverride);
            Assert.Same(m09, i1.FindImplementationForInterfaceMember(m09));

            var m10 = i1.GetMember<MethodSymbol>("op_Division");

            Assert.False(m10.IsAbstract);
            Assert.False(m10.IsVirtual);
            Assert.False(m10.IsMetadataVirtual());
            Assert.False(m10.IsSealed);
            Assert.True(m10.IsStatic);
            Assert.False(m10.IsExtern);
            Assert.False(m10.IsAsync);
            Assert.False(m10.IsOverride);
            Assert.Null(i1.FindImplementationForInterfaceMember(m10));
        }

        [Fact]
        public void OperatorModifiers_02()
        {
            var source1 =
@"
public interface I1
{
    abstract static I1 operator+ (I1 x)
    {throw null;} 

    virtual static I1 operator- (I1 x)
    {throw null;} 

    sealed static I1 operator++ (I1 x)
    {throw null;} 

    override static I1 operator-- (I1 x)
    {throw null;} 

    abstract virtual static I1 operator! (I1 x)
    {throw null;} 

    abstract sealed static I1 operator~ (I1 x)
    {throw null;} 

    abstract override static I1 operator+ (I1 x, I1 y)
    {throw null;} 

    virtual sealed static I1 operator- (I1 x, I1 y)
    {throw null;} 

    virtual override static I1 operator* (I1 x, I1 y) 
    {throw null;} 

    sealed override static I1 operator/ (I1 x, I1 y)
    {throw null;} 
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,32): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract static I1 operator+ (I1 x)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "+").WithArguments("abstract", "10.0", "11.0").WithLocation(4, 32),
                // (4,32): error CS0500: 'I1.operator +(I1)' cannot declare a body because it is marked abstract
                //     abstract static I1 operator+ (I1 x)
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "+").WithArguments("I1.operator +(I1)").WithLocation(4, 32),
                // (7,31): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual static I1 operator- (I1 x)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "-").WithArguments("virtual", "10.0", "11.0").WithLocation(7, 31),
                // (10,30): error CS8703: The modifier 'sealed' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     sealed static I1 operator++ (I1 x)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "++").WithArguments("sealed", "10.0", "11.0").WithLocation(10, 30),
                // (13,32): error CS0106: The modifier 'override' is not valid for this item
                //     override static I1 operator-- (I1 x)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "--").WithArguments("override").WithLocation(13, 32),
                // (16,40): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract virtual static I1 operator! (I1 x)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "!").WithArguments("abstract", "10.0", "11.0").WithLocation(16, 40),
                // (16,40): error CS0503: The abstract method 'I1.operator !(I1)' cannot be marked virtual
                //     abstract virtual static I1 operator! (I1 x)
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "!").WithArguments("method", "I1.operator !(I1)").WithLocation(16, 40),
                // (19,39): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static I1 operator~ (I1 x)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "~").WithArguments("sealed").WithLocation(19, 39),
                // (19,39): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract sealed static I1 operator~ (I1 x)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "~").WithArguments("abstract", "10.0", "11.0").WithLocation(19, 39),
                // (19,39): error CS0500: 'I1.operator ~(I1)' cannot declare a body because it is marked abstract
                //     abstract sealed static I1 operator~ (I1 x)
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "~").WithArguments("I1.operator ~(I1)").WithLocation(19, 39),
                // (22,41): error CS0106: The modifier 'override' is not valid for this item
                //     abstract override static I1 operator+ (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "+").WithArguments("override").WithLocation(22, 41),
                // (22,41): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract override static I1 operator+ (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "+").WithArguments("abstract", "10.0", "11.0").WithLocation(22, 41),
                // (22,41): error CS0500: 'I1.operator +(I1, I1)' cannot declare a body because it is marked abstract
                //     abstract override static I1 operator+ (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "+").WithArguments("I1.operator +(I1, I1)").WithLocation(22, 41),
                // (25,38): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static I1 operator- (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "-").WithArguments("sealed").WithLocation(25, 38),
                // (25,38): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual sealed static I1 operator- (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "-").WithArguments("virtual", "10.0", "11.0").WithLocation(25, 38),
                // (28,40): error CS0106: The modifier 'override' is not valid for this item
                //     virtual override static I1 operator* (I1 x, I1 y) 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "*").WithArguments("override").WithLocation(28, 40),
                // (28,40): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual override static I1 operator* (I1 x, I1 y) 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "*").WithArguments("virtual", "10.0", "11.0").WithLocation(28, 40),
                // (31,39): error CS0106: The modifier 'override' is not valid for this item
                //     sealed override static I1 operator/ (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "/").WithArguments("override").WithLocation(31, 39),
                // (31,39): error CS8703: The modifier 'sealed' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     sealed override static I1 operator/ (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "/").WithArguments("sealed", "10.0", "11.0").WithLocation(31, 39)
                );

            ValidateOperatorModifiers_01(compilation1);
        }

        [Fact]
        public void OperatorModifiers_03()
        {
            var source1 =
@"
public interface I1
{
    abstract static I1 operator+ (I1 x)
    ; 

    virtual static I1 operator- (I1 x)
    ; 

    sealed static I1 operator++ (I1 x)
    ; 

    override static I1 operator-- (I1 x)
    ; 

    abstract virtual static I1 operator! (I1 x)
    ; 

    abstract sealed static I1 operator~ (I1 x)
    ; 

    abstract override static I1 operator+ (I1 x, I1 y)
    ; 

    virtual sealed static I1 operator- (I1 x, I1 y)
    ; 

    virtual override static I1 operator* (I1 x, I1 y) 
    ; 

    sealed override static I1 operator/ (I1 x, I1 y)
    ; 
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (7,31): error CS0501: 'I1.operator -(I1)' must declare a body because it is not marked abstract, extern, or partial
                //     virtual static I1 operator- (I1 x)
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "-").WithArguments("I1.operator -(I1)").WithLocation(7, 31),
                // (10,30): error CS0501: 'I1.operator ++(I1)' must declare a body because it is not marked abstract, extern, or partial
                //     sealed static I1 operator++ (I1 x)
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "++").WithArguments("I1.operator ++(I1)").WithLocation(10, 30),
                // (13,32): error CS0106: The modifier 'override' is not valid for this item
                //     override static I1 operator-- (I1 x)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "--").WithArguments("override").WithLocation(13, 32),
                // (13,32): error CS0501: 'I1.operator --(I1)' must declare a body because it is not marked abstract, extern, or partial
                //     override static I1 operator-- (I1 x)
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "--").WithArguments("I1.operator --(I1)").WithLocation(13, 32),
                // (16,40): error CS0503: The abstract method 'I1.operator !(I1)' cannot be marked virtual
                //     abstract virtual static I1 operator! (I1 x)
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "!").WithArguments("method", "I1.operator !(I1)").WithLocation(16, 40),
                // (19,39): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static I1 operator~ (I1 x)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "~").WithArguments("sealed").WithLocation(19, 39),
                // (22,41): error CS0106: The modifier 'override' is not valid for this item
                //     abstract override static I1 operator+ (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "+").WithArguments("override").WithLocation(22, 41),
                // (25,38): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static I1 operator- (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "-").WithArguments("sealed").WithLocation(25, 38),
                // (25,38): error CS0501: 'I1.operator -(I1, I1)' must declare a body because it is not marked abstract, extern, or partial
                //     virtual sealed static I1 operator- (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "-").WithArguments("I1.operator -(I1, I1)").WithLocation(25, 38),
                // (28,40): error CS0106: The modifier 'override' is not valid for this item
                //     virtual override static I1 operator* (I1 x, I1 y) 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "*").WithArguments("override").WithLocation(28, 40),
                // (28,40): error CS0501: 'I1.operator *(I1, I1)' must declare a body because it is not marked abstract, extern, or partial
                //     virtual override static I1 operator* (I1 x, I1 y) 
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "*").WithArguments("I1.operator *(I1, I1)").WithLocation(28, 40),
                // (31,39): error CS0106: The modifier 'override' is not valid for this item
                //     sealed override static I1 operator/ (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "/").WithArguments("override").WithLocation(31, 39),
                // (31,39): error CS0501: 'I1.operator /(I1, I1)' must declare a body because it is not marked abstract, extern, or partial
                //     sealed override static I1 operator/ (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "/").WithArguments("I1.operator /(I1, I1)").WithLocation(31, 39)
                );

            ValidateOperatorModifiers_01(compilation1);
        }

        [Fact]
        public void OperatorModifiers_04()
        {
            var source1 =
@"
public interface I1
{
    abstract static I1 operator+ (I1 x)
    {throw null;} 

    virtual static I1 operator- (I1 x)
    {throw null;} 

    sealed static I1 operator++ (I1 x)
    {throw null;} 

    override static I1 operator-- (I1 x)
    {throw null;} 

    abstract virtual static I1 operator! (I1 x)
    {throw null;} 

    abstract sealed static I1 operator~ (I1 x)
    {throw null;} 

    abstract override static I1 operator+ (I1 x, I1 y)
    {throw null;} 

    virtual sealed static I1 operator- (I1 x, I1 y)
    {throw null;} 

    virtual override static I1 operator* (I1 x, I1 y) 
    {throw null;} 

    sealed override static I1 operator/ (I1 x, I1 y)
    {throw null;} 
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,32): error CS0500: 'I1.operator +(I1)' cannot declare a body because it is marked abstract
                //     abstract static I1 operator+ (I1 x)
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "+").WithArguments("I1.operator +(I1)").WithLocation(4, 32),
                // (13,32): error CS0106: The modifier 'override' is not valid for this item
                //     override static I1 operator-- (I1 x)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "--").WithArguments("override").WithLocation(13, 32),
                // (16,40): error CS0503: The abstract method 'I1.operator !(I1)' cannot be marked virtual
                //     abstract virtual static I1 operator! (I1 x)
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "!").WithArguments("method", "I1.operator !(I1)").WithLocation(16, 40),
                // (19,39): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static I1 operator~ (I1 x)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "~").WithArguments("sealed").WithLocation(19, 39),
                // (19,39): error CS0500: 'I1.operator ~(I1)' cannot declare a body because it is marked abstract
                //     abstract sealed static I1 operator~ (I1 x)
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "~").WithArguments("I1.operator ~(I1)").WithLocation(19, 39),
                // (22,41): error CS0106: The modifier 'override' is not valid for this item
                //     abstract override static I1 operator+ (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "+").WithArguments("override").WithLocation(22, 41),
                // (22,41): error CS0500: 'I1.operator +(I1, I1)' cannot declare a body because it is marked abstract
                //     abstract override static I1 operator+ (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "+").WithArguments("I1.operator +(I1, I1)").WithLocation(22, 41),
                // (25,38): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static I1 operator- (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "-").WithArguments("sealed").WithLocation(25, 38),
                // (28,40): error CS0106: The modifier 'override' is not valid for this item
                //     virtual override static I1 operator* (I1 x, I1 y) 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "*").WithArguments("override").WithLocation(28, 40),
                // (31,39): error CS0106: The modifier 'override' is not valid for this item
                //     sealed override static I1 operator/ (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "/").WithArguments("override").WithLocation(31, 39)
                );

            ValidateOperatorModifiers_01(compilation1);
        }

        [Fact]
        public void OperatorModifiers_05()
        {
            var source1 =
@"
public interface I1
{
    abstract static I1 operator+ (I1 x)
    ; 

    virtual static I1 operator- (I1 x)
    ; 

    sealed static I1 operator++ (I1 x)
    ; 

    override static I1 operator-- (I1 x)
    ; 

    abstract virtual static I1 operator! (I1 x)
    ; 

    abstract sealed static I1 operator~ (I1 x)
    ; 

    abstract override static I1 operator+ (I1 x, I1 y)
    ; 

    virtual sealed static I1 operator- (I1 x, I1 y)
    ; 

    virtual override static I1 operator* (I1 x, I1 y) 
    ; 

    sealed override static I1 operator/ (I1 x, I1 y)
    ; 
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular7_3,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,32): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract static I1 operator+ (I1 x)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "+").WithArguments("abstract", "7.3", "11.0").WithLocation(4, 32),
                // (7,31): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual static I1 operator- (I1 x)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "-").WithArguments("virtual", "7.3", "11.0").WithLocation(7, 31),
                // (7,31): error CS0501: 'I1.operator -(I1)' must declare a body because it is not marked abstract, extern, or partial
                //     virtual static I1 operator- (I1 x)
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "-").WithArguments("I1.operator -(I1)").WithLocation(7, 31),
                // (10,30): error CS8703: The modifier 'sealed' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     sealed static I1 operator++ (I1 x)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "++").WithArguments("sealed", "7.3", "11.0").WithLocation(10, 30),
                // (10,30): error CS0501: 'I1.operator ++(I1)' must declare a body because it is not marked abstract, extern, or partial
                //     sealed static I1 operator++ (I1 x)
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "++").WithArguments("I1.operator ++(I1)").WithLocation(10, 30),
                // (13,32): error CS0106: The modifier 'override' is not valid for this item
                //     override static I1 operator-- (I1 x)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "--").WithArguments("override").WithLocation(13, 32),
                // (13,32): error CS8370: Feature 'default interface implementation' is not available in C# 7.3. Please use language version 8.0 or greater.
                //     override static I1 operator-- (I1 x)
                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion7_3, "--").WithArguments("default interface implementation", "8.0").WithLocation(13, 32),
                // (13,32): error CS0501: 'I1.operator --(I1)' must declare a body because it is not marked abstract, extern, or partial
                //     override static I1 operator-- (I1 x)
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "--").WithArguments("I1.operator --(I1)").WithLocation(13, 32),
                // (16,40): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract virtual static I1 operator! (I1 x)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "!").WithArguments("abstract", "7.3", "11.0").WithLocation(16, 40),
                // (16,40): error CS0503: The abstract method 'I1.operator !(I1)' cannot be marked virtual
                //     abstract virtual static I1 operator! (I1 x)
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "!").WithArguments("method", "I1.operator !(I1)").WithLocation(16, 40),
                // (19,39): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static I1 operator~ (I1 x)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "~").WithArguments("sealed").WithLocation(19, 39),
                // (19,39): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract sealed static I1 operator~ (I1 x)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "~").WithArguments("abstract", "7.3", "11.0").WithLocation(19, 39),
                // (22,41): error CS0106: The modifier 'override' is not valid for this item
                //     abstract override static I1 operator+ (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "+").WithArguments("override").WithLocation(22, 41),
                // (22,41): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract override static I1 operator+ (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "+").WithArguments("abstract", "7.3", "11.0").WithLocation(22, 41),
                // (25,38): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static I1 operator- (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "-").WithArguments("sealed").WithLocation(25, 38),
                // (25,38): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual sealed static I1 operator- (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "-").WithArguments("virtual", "7.3", "11.0").WithLocation(25, 38),
                // (25,38): error CS0501: 'I1.operator -(I1, I1)' must declare a body because it is not marked abstract, extern, or partial
                //     virtual sealed static I1 operator- (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "-").WithArguments("I1.operator -(I1, I1)").WithLocation(25, 38),
                // (28,40): error CS0106: The modifier 'override' is not valid for this item
                //     virtual override static I1 operator* (I1 x, I1 y) 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "*").WithArguments("override").WithLocation(28, 40),
                // (28,40): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual override static I1 operator* (I1 x, I1 y) 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "*").WithArguments("virtual", "7.3", "11.0").WithLocation(28, 40),
                // (28,40): error CS0501: 'I1.operator *(I1, I1)' must declare a body because it is not marked abstract, extern, or partial
                //     virtual override static I1 operator* (I1 x, I1 y) 
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "*").WithArguments("I1.operator *(I1, I1)").WithLocation(28, 40),
                // (31,39): error CS0106: The modifier 'override' is not valid for this item
                //     sealed override static I1 operator/ (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "/").WithArguments("override").WithLocation(31, 39),
                // (31,39): error CS8703: The modifier 'sealed' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     sealed override static I1 operator/ (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "/").WithArguments("sealed", "7.3", "11.0").WithLocation(31, 39),
                // (31,39): error CS0501: 'I1.operator /(I1, I1)' must declare a body because it is not marked abstract, extern, or partial
                //     sealed override static I1 operator/ (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "/").WithArguments("I1.operator /(I1, I1)").WithLocation(31, 39)
                );

            ValidateOperatorModifiers_01(compilation1);
        }

        [Fact]
        public void OperatorModifiers_06()
        {
            var source1 =
@"
public interface I1
{
    abstract static I1 operator+ (I1 x)
    {throw null;} 

    virtual static I1 operator- (I1 x)
    {throw null;} 

    sealed static I1 operator++ (I1 x)
    {throw null;} 

    override static I1 operator-- (I1 x)
    {throw null;} 

    abstract virtual static I1 operator! (I1 x)
    {throw null;} 

    abstract sealed static I1 operator~ (I1 x)
    {throw null;} 

    abstract override static I1 operator+ (I1 x, I1 y)
    {throw null;} 

    virtual sealed static I1 operator- (I1 x, I1 y)
    {throw null;} 

    virtual override static I1 operator* (I1 x, I1 y) 
    {throw null;} 

    sealed override static I1 operator/ (I1 x, I1 y)
    {throw null;} 
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular7_3,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,32): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract static I1 operator+ (I1 x)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "+").WithArguments("abstract", "7.3", "11.0").WithLocation(4, 32),
                // (4,32): error CS0500: 'I1.operator +(I1)' cannot declare a body because it is marked abstract
                //     abstract static I1 operator+ (I1 x)
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "+").WithArguments("I1.operator +(I1)").WithLocation(4, 32),
                // (7,31): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual static I1 operator- (I1 x)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "-").WithArguments("virtual", "7.3", "11.0").WithLocation(7, 31),
                // (10,30): error CS8703: The modifier 'sealed' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     sealed static I1 operator++ (I1 x)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "++").WithArguments("sealed", "7.3", "11.0").WithLocation(10, 30),
                // (13,32): error CS0106: The modifier 'override' is not valid for this item
                //     override static I1 operator-- (I1 x)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "--").WithArguments("override").WithLocation(13, 32),
                // (13,32): error CS8370: Feature 'default interface implementation' is not available in C# 7.3. Please use language version 8.0 or greater.
                //     override static I1 operator-- (I1 x)
                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion7_3, "--").WithArguments("default interface implementation", "8.0").WithLocation(13, 32),
                // (16,40): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract virtual static I1 operator! (I1 x)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "!").WithArguments("abstract", "7.3", "11.0").WithLocation(16, 40),
                // (16,40): error CS0503: The abstract method 'I1.operator !(I1)' cannot be marked virtual
                //     abstract virtual static I1 operator! (I1 x)
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "!").WithArguments("method", "I1.operator !(I1)").WithLocation(16, 40),
                // (19,39): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static I1 operator~ (I1 x)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "~").WithArguments("sealed").WithLocation(19, 39),
                // (19,39): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract sealed static I1 operator~ (I1 x)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "~").WithArguments("abstract", "7.3", "11.0").WithLocation(19, 39),
                // (19,39): error CS0500: 'I1.operator ~(I1)' cannot declare a body because it is marked abstract
                //     abstract sealed static I1 operator~ (I1 x)
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "~").WithArguments("I1.operator ~(I1)").WithLocation(19, 39),
                // (22,41): error CS0106: The modifier 'override' is not valid for this item
                //     abstract override static I1 operator+ (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "+").WithArguments("override").WithLocation(22, 41),
                // (22,41): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract override static I1 operator+ (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "+").WithArguments("abstract", "7.3", "11.0").WithLocation(22, 41),
                // (22,41): error CS0500: 'I1.operator +(I1, I1)' cannot declare a body because it is marked abstract
                //     abstract override static I1 operator+ (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "+").WithArguments("I1.operator +(I1, I1)").WithLocation(22, 41),
                // (25,38): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static I1 operator- (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "-").WithArguments("sealed").WithLocation(25, 38),
                // (25,38): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual sealed static I1 operator- (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "-").WithArguments("virtual", "7.3", "11.0").WithLocation(25, 38),
                // (28,40): error CS0106: The modifier 'override' is not valid for this item
                //     virtual override static I1 operator* (I1 x, I1 y) 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "*").WithArguments("override").WithLocation(28, 40),
                // (28,40): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual override static I1 operator* (I1 x, I1 y) 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "*").WithArguments("virtual", "7.3", "11.0").WithLocation(28, 40),
                // (31,39): error CS0106: The modifier 'override' is not valid for this item
                //     sealed override static I1 operator/ (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "/").WithArguments("override").WithLocation(31, 39),
                // (31,39): error CS8703: The modifier 'sealed' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     sealed override static I1 operator/ (I1 x, I1 y)
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "/").WithArguments("sealed", "7.3", "11.0").WithLocation(31, 39)
                );

            ValidateOperatorModifiers_01(compilation1);
        }

        [Fact]
        public void OperatorModifiers_07()
        {
            var source1 =
@"
public interface I1
{
    abstract static bool operator== (I1 x, I1 y); 

    abstract static bool operator!= (I1 x, I1 y) {return false;} 
}

public interface I2
{
    sealed static bool operator== (I2 x, I2 y);

    sealed static bool operator!= (I2 x, I2 y) {return false;} 
}

public interface I3
{
    abstract sealed static bool operator== (I3 x, I3 y);

    abstract sealed static bool operator!= (I3 x, I3 y) {return false;} 
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular7_3,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_BadAbstractEqualityOperatorSignature).Verify(
                // (4,34): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract static bool operator== (I1 x, I1 y); 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "==").WithArguments("abstract", "7.3", "11.0").WithLocation(4, 34),
                // (6,34): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract static bool operator!= (I1 x, I1 y) {return false;} 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "!=").WithArguments("abstract", "7.3", "11.0").WithLocation(6, 34),
                // (6,34): error CS0500: 'I1.operator !=(I1, I1)' cannot declare a body because it is marked abstract
                //     abstract static bool operator!= (I1 x, I1 y) {return false;} 
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "!=").WithArguments("I1.operator !=(I1, I1)").WithLocation(6, 34),
                // (11,32): error CS0106: The modifier 'sealed' is not valid for this item
                //     sealed static bool operator== (I2 x, I2 y);
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "==").WithArguments("sealed").WithLocation(11, 32),
                // (11,32): error CS0567: Conversion, equality, or inequality operators declared in interfaces must be abstract or virtual
                //     sealed static bool operator== (I2 x, I2 y);
                Diagnostic(ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators, "==").WithLocation(11, 32),
                // (13,32): error CS0106: The modifier 'sealed' is not valid for this item
                //     sealed static bool operator!= (I2 x, I2 y) {return false;} 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "!=").WithArguments("sealed").WithLocation(13, 32),
                // (13,32): error CS0567: Conversion, equality, or inequality operators declared in interfaces must be abstract or virtual
                //     sealed static bool operator!= (I2 x, I2 y) {return false;} 
                Diagnostic(ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators, "!=").WithLocation(13, 32),
                // (18,41): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static bool operator== (I3 x, I3 y);
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "==").WithArguments("sealed").WithLocation(18, 41),
                // (18,41): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract sealed static bool operator== (I3 x, I3 y);
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "==").WithArguments("abstract", "7.3", "11.0").WithLocation(18, 41),
                // (20,41): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static bool operator!= (I3 x, I3 y) {return false;} 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "!=").WithArguments("sealed").WithLocation(20, 41),
                // (20,41): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract sealed static bool operator!= (I3 x, I3 y) {return false;} 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "!=").WithArguments("abstract", "7.3", "11.0").WithLocation(20, 41),
                // (20,41): error CS0500: 'I3.operator !=(I3, I3)' cannot declare a body because it is marked abstract
                //     abstract sealed static bool operator!= (I3 x, I3 y) {return false;} 
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "!=").WithArguments("I3.operator !=(I3, I3)").WithLocation(20, 41)
                );

            validate();

            compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_BadAbstractEqualityOperatorSignature).Verify(
                // (4,34): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract static bool operator== (I1 x, I1 y); 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "==").WithArguments("abstract", "10.0", "11.0").WithLocation(4, 34),
                // (6,34): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract static bool operator!= (I1 x, I1 y) {return false;} 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "!=").WithArguments("abstract", "10.0", "11.0").WithLocation(6, 34),
                // (6,34): error CS0500: 'I1.operator !=(I1, I1)' cannot declare a body because it is marked abstract
                //     abstract static bool operator!= (I1 x, I1 y) {return false;} 
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "!=").WithArguments("I1.operator !=(I1, I1)").WithLocation(6, 34),
                // (11,32): error CS0106: The modifier 'sealed' is not valid for this item
                //     sealed static bool operator== (I2 x, I2 y);
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "==").WithArguments("sealed").WithLocation(11, 32),
                // (11,32): error CS0567: Conversion, equality, or inequality operators declared in interfaces must be abstract or virtual
                //     sealed static bool operator== (I2 x, I2 y);
                Diagnostic(ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators, "==").WithLocation(11, 32),
                // (13,32): error CS0106: The modifier 'sealed' is not valid for this item
                //     sealed static bool operator!= (I2 x, I2 y) {return false;} 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "!=").WithArguments("sealed").WithLocation(13, 32),
                // (13,32): error CS0567: Conversion, equality, or inequality operators declared in interfaces must be abstract or virtual
                //     sealed static bool operator!= (I2 x, I2 y) {return false;} 
                Diagnostic(ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators, "!=").WithLocation(13, 32),
                // (18,41): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static bool operator== (I3 x, I3 y);
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "==").WithArguments("sealed").WithLocation(18, 41),
                // (18,41): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract sealed static bool operator== (I3 x, I3 y);
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "==").WithArguments("abstract", "10.0", "11.0").WithLocation(18, 41),
                // (20,41): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static bool operator!= (I3 x, I3 y) {return false;} 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "!=").WithArguments("sealed").WithLocation(20, 41),
                // (20,41): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract sealed static bool operator!= (I3 x, I3 y) {return false;} 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "!=").WithArguments("abstract", "10.0", "11.0").WithLocation(20, 41),
                // (20,41): error CS0500: 'I3.operator !=(I3, I3)' cannot declare a body because it is marked abstract
                //     abstract sealed static bool operator!= (I3 x, I3 y) {return false;} 
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "!=").WithArguments("I3.operator !=(I3, I3)").WithLocation(20, 41)
                );

            validate();

            compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_BadAbstractEqualityOperatorSignature).Verify(
                // (6,34): error CS0500: 'I1.operator !=(I1, I1)' cannot declare a body because it is marked abstract
                //     abstract static bool operator!= (I1 x, I1 y) {return false;} 
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "!=").WithArguments("I1.operator !=(I1, I1)").WithLocation(6, 34),
                // (11,32): error CS0106: The modifier 'sealed' is not valid for this item
                //     sealed static bool operator== (I2 x, I2 y);
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "==").WithArguments("sealed").WithLocation(11, 32),
                // (11,32): error CS0567: Conversion, equality, or inequality operators declared in interfaces must be abstract or virtual
                //     sealed static bool operator== (I2 x, I2 y);
                Diagnostic(ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators, "==").WithLocation(11, 32),
                // (13,32): error CS0106: The modifier 'sealed' is not valid for this item
                //     sealed static bool operator!= (I2 x, I2 y) {return false;} 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "!=").WithArguments("sealed").WithLocation(13, 32),
                // (13,32): error CS0567: Conversion, equality, or inequality operators declared in interfaces must be abstract or virtual
                //     sealed static bool operator!= (I2 x, I2 y) {return false;} 
                Diagnostic(ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators, "!=").WithLocation(13, 32),
                // (18,41): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static bool operator== (I3 x, I3 y);
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "==").WithArguments("sealed").WithLocation(18, 41),
                // (20,41): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static bool operator!= (I3 x, I3 y) {return false;} 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "!=").WithArguments("sealed").WithLocation(20, 41),
                // (20,41): error CS0500: 'I3.operator !=(I3, I3)' cannot declare a body because it is marked abstract
                //     abstract sealed static bool operator!= (I3 x, I3 y) {return false;} 
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "!=").WithArguments("I3.operator !=(I3, I3)").WithLocation(20, 41)
                );

            validate();

            void validate()
            {
                foreach (MethodSymbol m01 in compilation1.GetTypeByMetadataName("I1").GetMembers())
                {
                    Assert.True(m01.IsAbstract);
                    Assert.False(m01.IsVirtual);
                    Assert.True(m01.IsMetadataVirtual());
                    Assert.False(m01.IsSealed);
                    Assert.True(m01.IsStatic);
                    Assert.False(m01.IsExtern);
                    Assert.False(m01.IsAsync);
                    Assert.False(m01.IsOverride);
                    Assert.Null(m01.ContainingType.FindImplementationForInterfaceMember(m01));
                }

                foreach (MethodSymbol m01 in compilation1.GetTypeByMetadataName("I2").GetMembers())
                {
                    Assert.False(m01.IsAbstract);
                    Assert.False(m01.IsVirtual);
                    Assert.False(m01.IsMetadataVirtual());
                    Assert.False(m01.IsSealed);
                    Assert.True(m01.IsStatic);
                    Assert.False(m01.IsExtern);
                    Assert.False(m01.IsAsync);
                    Assert.False(m01.IsOverride);
                    Assert.Null(m01.ContainingType.FindImplementationForInterfaceMember(m01));
                }

                foreach (MethodSymbol m01 in compilation1.GetTypeByMetadataName("I3").GetMembers())
                {
                    Assert.True(m01.IsAbstract);
                    Assert.False(m01.IsVirtual);
                    Assert.True(m01.IsMetadataVirtual());
                    Assert.False(m01.IsSealed);
                    Assert.True(m01.IsStatic);
                    Assert.False(m01.IsExtern);
                    Assert.False(m01.IsAsync);
                    Assert.False(m01.IsOverride);
                    Assert.Null(m01.ContainingType.FindImplementationForInterfaceMember(m01));
                }
            }
        }

        [Fact]
        public void OperatorModifiers_08()
        {
            var source1 =
@"
public interface I1
{
    abstract static implicit operator int(I1 x); 

    abstract static explicit operator I1(bool x) {return null;} 
}

public interface I2
{
    sealed static implicit operator int(I2 x);

    sealed static explicit operator I2(bool x) {return null;} 
}

public interface I3
{
    abstract sealed static implicit operator int(I3 x);

    abstract sealed static explicit operator I3(bool x) {return null;} 
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular7_3,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,39): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract static implicit operator int(I1 x); 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "int").WithArguments("abstract", "7.3", "11.0").WithLocation(4, 39),
                // (4,39): error CS0552: 'I1.implicit operator int(I1)': user-defined conversions to or from an interface are not allowed
                //     abstract static implicit operator int(I1 x); 
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "int").WithArguments("I1.implicit operator int(I1)").WithLocation(4, 39),
                // (6,39): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract static explicit operator I1(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "I1").WithArguments("abstract", "7.3", "11.0").WithLocation(6, 39),
                // (6,39): error CS0500: 'I1.explicit operator I1(bool)' cannot declare a body because it is marked abstract
                //     abstract static explicit operator I1(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "I1").WithArguments("I1.explicit operator I1(bool)").WithLocation(6, 39),
                // (6,39): error CS0552: 'I1.explicit operator I1(bool)': user-defined conversions to or from an interface are not allowed
                //     abstract static explicit operator I1(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "I1").WithArguments("I1.explicit operator I1(bool)").WithLocation(6, 39),
                // (11,37): error CS0106: The modifier 'sealed' is not valid for this item
                //     sealed static implicit operator int(I2 x);
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "int").WithArguments("sealed").WithLocation(11, 37),
                // (11,37): error CS0567: Conversion, equality, or inequality operators declared in interfaces must be abstract or virtual
                //     sealed static implicit operator int(I2 x);
                Diagnostic(ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators, "int").WithLocation(11, 37),
                // (11,37): error CS0552: 'I2.implicit operator int(I2)': user-defined conversions to or from an interface are not allowed
                //     sealed static implicit operator int(I2 x);
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "int").WithArguments("I2.implicit operator int(I2)").WithLocation(11, 37),
                // (13,37): error CS0106: The modifier 'sealed' is not valid for this item
                //     sealed static explicit operator I2(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "I2").WithArguments("sealed").WithLocation(13, 37),
                // (13,37): error CS0567: Conversion, equality, or inequality operators declared in interfaces must be abstract or virtual
                //     sealed static explicit operator I2(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators, "I2").WithLocation(13, 37),
                // (13,37): error CS0552: 'I2.explicit operator I2(bool)': user-defined conversions to or from an interface are not allowed
                //     sealed static explicit operator I2(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "I2").WithArguments("I2.explicit operator I2(bool)").WithLocation(13, 37),
                // (18,46): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static implicit operator int(I3 x);
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "int").WithArguments("sealed").WithLocation(18, 46),
                // (18,46): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract sealed static implicit operator int(I3 x);
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "int").WithArguments("abstract", "7.3", "11.0").WithLocation(18, 46),
                // (18,46): error CS0552: 'I3.implicit operator int(I3)': user-defined conversions to or from an interface are not allowed
                //     abstract sealed static implicit operator int(I3 x);
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "int").WithArguments("I3.implicit operator int(I3)").WithLocation(18, 46),
                // (20,46): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static explicit operator I3(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "I3").WithArguments("sealed").WithLocation(20, 46),
                // (20,46): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract sealed static explicit operator I3(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "I3").WithArguments("abstract", "7.3", "11.0").WithLocation(20, 46),
                // (20,46): error CS0500: 'I3.explicit operator I3(bool)' cannot declare a body because it is marked abstract
                //     abstract sealed static explicit operator I3(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "I3").WithArguments("I3.explicit operator I3(bool)").WithLocation(20, 46),
                // (20,46): error CS0552: 'I3.explicit operator I3(bool)': user-defined conversions to or from an interface are not allowed
                //     abstract sealed static explicit operator I3(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "I3").WithArguments("I3.explicit operator I3(bool)").WithLocation(20, 46)
                );

            validate();

            compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                             parseOptions: TestOptions.Regular10,
                                             targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,39): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract static implicit operator int(I1 x); 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "int").WithArguments("abstract", "10.0", "11.0").WithLocation(4, 39),
                // (4,39): error CS0552: 'I1.implicit operator int(I1)': user-defined conversions to or from an interface are not allowed
                //     abstract static implicit operator int(I1 x); 
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "int").WithArguments("I1.implicit operator int(I1)").WithLocation(4, 39),
                // (6,39): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract static explicit operator I1(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "I1").WithArguments("abstract", "10.0", "11.0").WithLocation(6, 39),
                // (6,39): error CS0500: 'I1.explicit operator I1(bool)' cannot declare a body because it is marked abstract
                //     abstract static explicit operator I1(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "I1").WithArguments("I1.explicit operator I1(bool)").WithLocation(6, 39),
                // (6,39): error CS0552: 'I1.explicit operator I1(bool)': user-defined conversions to or from an interface are not allowed
                //     abstract static explicit operator I1(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "I1").WithArguments("I1.explicit operator I1(bool)").WithLocation(6, 39),
                // (11,37): error CS0106: The modifier 'sealed' is not valid for this item
                //     sealed static implicit operator int(I2 x);
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "int").WithArguments("sealed").WithLocation(11, 37),
                // (11,37): error CS0567: Conversion, equality, or inequality operators declared in interfaces must be abstract or virtual
                //     sealed static implicit operator int(I2 x);
                Diagnostic(ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators, "int").WithLocation(11, 37),
                // (11,37): error CS0552: 'I2.implicit operator int(I2)': user-defined conversions to or from an interface are not allowed
                //     sealed static implicit operator int(I2 x);
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "int").WithArguments("I2.implicit operator int(I2)").WithLocation(11, 37),
                // (13,37): error CS0106: The modifier 'sealed' is not valid for this item
                //     sealed static explicit operator I2(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "I2").WithArguments("sealed").WithLocation(13, 37),
                // (13,37): error CS0567: Conversion, equality, or inequality operators declared in interfaces must be abstract or virtual
                //     sealed static explicit operator I2(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators, "I2").WithLocation(13, 37),
                // (13,37): error CS0552: 'I2.explicit operator I2(bool)': user-defined conversions to or from an interface are not allowed
                //     sealed static explicit operator I2(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "I2").WithArguments("I2.explicit operator I2(bool)").WithLocation(13, 37),
                // (18,46): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static implicit operator int(I3 x);
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "int").WithArguments("sealed").WithLocation(18, 46),
                // (18,46): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract sealed static implicit operator int(I3 x);
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "int").WithArguments("abstract", "10.0", "11.0").WithLocation(18, 46),
                // (18,46): error CS0552: 'I3.implicit operator int(I3)': user-defined conversions to or from an interface are not allowed
                //     abstract sealed static implicit operator int(I3 x);
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "int").WithArguments("I3.implicit operator int(I3)").WithLocation(18, 46),
                // (20,46): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static explicit operator I3(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "I3").WithArguments("sealed").WithLocation(20, 46),
                // (20,46): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract sealed static explicit operator I3(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "I3").WithArguments("abstract", "10.0", "11.0").WithLocation(20, 46),
                // (20,46): error CS0500: 'I3.explicit operator I3(bool)' cannot declare a body because it is marked abstract
                //     abstract sealed static explicit operator I3(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "I3").WithArguments("I3.explicit operator I3(bool)").WithLocation(20, 46),
                // (20,46): error CS0552: 'I3.explicit operator I3(bool)': user-defined conversions to or from an interface are not allowed
                //     abstract sealed static explicit operator I3(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "I3").WithArguments("I3.explicit operator I3(bool)").WithLocation(20, 46)
                );

            validate();

            compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                             parseOptions: TestOptions.RegularPreview,
                                             targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,39): error CS0552: 'I1.implicit operator int(I1)': user-defined conversions to or from an interface are not allowed
                //     abstract static implicit operator int(I1 x); 
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "int").WithArguments("I1.implicit operator int(I1)").WithLocation(4, 39),
                // (6,39): error CS0500: 'I1.explicit operator I1(bool)' cannot declare a body because it is marked abstract
                //     abstract static explicit operator I1(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "I1").WithArguments("I1.explicit operator I1(bool)").WithLocation(6, 39),
                // (6,39): error CS0552: 'I1.explicit operator I1(bool)': user-defined conversions to or from an interface are not allowed
                //     abstract static explicit operator I1(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "I1").WithArguments("I1.explicit operator I1(bool)").WithLocation(6, 39),
                // (11,37): error CS0106: The modifier 'sealed' is not valid for this item
                //     sealed static implicit operator int(I2 x);
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "int").WithArguments("sealed").WithLocation(11, 37),
                // (11,37): error CS0552: 'I2.implicit operator int(I2)': user-defined conversions to or from an interface are not allowed
                //     sealed static implicit operator int(I2 x);
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "int").WithArguments("I2.implicit operator int(I2)").WithLocation(11, 37),
                // (11,37): error CS0567: Conversion, equality, or inequality operators declared in interfaces must be abstract or virtual
                //     sealed static implicit operator int(I2 x);
                Diagnostic(ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators, "int").WithLocation(11, 37),
                // (13,37): error CS0106: The modifier 'sealed' is not valid for this item
                //     sealed static explicit operator I2(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "I2").WithArguments("sealed").WithLocation(13, 37),
                // (13,37): error CS0552: 'I2.explicit operator I2(bool)': user-defined conversions to or from an interface are not allowed
                //     sealed static explicit operator I2(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "I2").WithArguments("I2.explicit operator I2(bool)").WithLocation(13, 37),
                // (13,37): error CS0567: Conversion, equality, or inequality operators declared in interfaces must be abstract or virtual
                //     sealed static explicit operator I2(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators, "I2").WithLocation(13, 37),
                // (18,46): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static implicit operator int(I3 x);
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "int").WithArguments("sealed").WithLocation(18, 46),
                // (18,46): error CS0552: 'I3.implicit operator int(I3)': user-defined conversions to or from an interface are not allowed
                //     abstract sealed static implicit operator int(I3 x);
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "int").WithArguments("I3.implicit operator int(I3)").WithLocation(18, 46),
                // (20,46): error CS0106: The modifier 'sealed' is not valid for this item
                //     abstract sealed static explicit operator I3(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "I3").WithArguments("sealed").WithLocation(20, 46),
                // (20,46): error CS0500: 'I3.explicit operator I3(bool)' cannot declare a body because it is marked abstract
                //     abstract sealed static explicit operator I3(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_AbstractHasBody, "I3").WithArguments("I3.explicit operator I3(bool)").WithLocation(20, 46),
                // (20,46): error CS0552: 'I3.explicit operator I3(bool)': user-defined conversions to or from an interface are not allowed
                //     abstract sealed static explicit operator I3(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "I3").WithArguments("I3.explicit operator I3(bool)").WithLocation(20, 46)
                );

            validate();

            void validate()
            {
                foreach (MethodSymbol m01 in compilation1.GetTypeByMetadataName("I1").GetMembers())
                {
                    Assert.True(m01.IsAbstract);
                    Assert.False(m01.IsVirtual);
                    Assert.True(m01.IsMetadataVirtual());
                    Assert.False(m01.IsSealed);
                    Assert.True(m01.IsStatic);
                    Assert.False(m01.IsExtern);
                    Assert.False(m01.IsAsync);
                    Assert.False(m01.IsOverride);
                    Assert.Null(m01.ContainingType.FindImplementationForInterfaceMember(m01));
                }

                foreach (MethodSymbol m01 in compilation1.GetTypeByMetadataName("I2").GetMembers())
                {
                    Assert.False(m01.IsAbstract);
                    Assert.False(m01.IsVirtual);
                    Assert.False(m01.IsMetadataVirtual());
                    Assert.False(m01.IsSealed);
                    Assert.True(m01.IsStatic);
                    Assert.False(m01.IsExtern);
                    Assert.False(m01.IsAsync);
                    Assert.False(m01.IsOverride);
                    Assert.Null(m01.ContainingType.FindImplementationForInterfaceMember(m01));
                }

                foreach (MethodSymbol m01 in compilation1.GetTypeByMetadataName("I3").GetMembers())
                {
                    Assert.True(m01.IsAbstract);
                    Assert.False(m01.IsVirtual);
                    Assert.True(m01.IsMetadataVirtual());
                    Assert.False(m01.IsSealed);
                    Assert.True(m01.IsStatic);
                    Assert.False(m01.IsExtern);
                    Assert.False(m01.IsAsync);
                    Assert.False(m01.IsOverride);
                    Assert.Null(m01.ContainingType.FindImplementationForInterfaceMember(m01));
                }
            }
        }

        [Fact]
        public void OperatorModifiers_09()
        {
            var source1 =
@"
public interface I1
{
    virtual static bool operator== (I1 x, I1 y); 

    virtual static bool operator!= (I1 x, I1 y) {return false;} 
}

public interface I2
{
    virtual sealed static bool operator== (I2 x, I2 y);

    virtual sealed static bool operator!= (I2 x, I2 y) {return false;} 
}

public interface I3
{
    abstract virtual static bool operator== (I3 x, I3 y);

    abstract virtual static bool operator!= (I3 x, I3 y) {return false;} 
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular7_3,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_BadAbstractEqualityOperatorSignature).Verify(
                // (4,33): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual static bool operator== (I1 x, I1 y); 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "==").WithArguments("virtual", "7.3", "11.0").WithLocation(4, 33),
                // (4,33): error CS0501: 'I1.operator ==(I1, I1)' must declare a body because it is not marked abstract, extern, or partial
                //     virtual static bool operator== (I1 x, I1 y); 
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "==").WithArguments("I1.operator ==(I1, I1)").WithLocation(4, 33),
                // (6,33): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual static bool operator!= (I1 x, I1 y) {return false;} 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "!=").WithArguments("virtual", "7.3", "11.0").WithLocation(6, 33),
                // (11,40): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static bool operator== (I2 x, I2 y);
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "==").WithArguments("sealed").WithLocation(11, 40),
                // (11,40): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual sealed static bool operator== (I2 x, I2 y);
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "==").WithArguments("virtual", "7.3", "11.0").WithLocation(11, 40),
                // (11,40): error CS0501: 'I2.operator ==(I2, I2)' must declare a body because it is not marked abstract, extern, or partial
                //     virtual sealed static bool operator== (I2 x, I2 y);
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "==").WithArguments("I2.operator ==(I2, I2)").WithLocation(11, 40),
                // (13,40): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static bool operator!= (I2 x, I2 y) {return false;} 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "!=").WithArguments("sealed").WithLocation(13, 40),
                // (13,40): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual sealed static bool operator!= (I2 x, I2 y) {return false;} 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "!=").WithArguments("virtual", "7.3", "11.0").WithLocation(13, 40),
                // (18,42): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract virtual static bool operator== (I3 x, I3 y);
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "==").WithArguments("abstract", "7.3", "11.0").WithLocation(18, 42),
                // (18,42): error CS0503: The abstract method 'I3.operator ==(I3, I3)' cannot be marked virtual
                //     abstract virtual static bool operator== (I3 x, I3 y);
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "==").WithArguments("method", "I3.operator ==(I3, I3)").WithLocation(18, 42),
                // (20,42): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract virtual static bool operator!= (I3 x, I3 y) {return false;} 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "!=").WithArguments("abstract", "7.3", "11.0").WithLocation(20, 42),
                // (20,42): error CS0503: The abstract method 'I3.operator !=(I3, I3)' cannot be marked virtual
                //     abstract virtual static bool operator!= (I3 x, I3 y) {return false;} 
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "!=").WithArguments("method", "I3.operator !=(I3, I3)").WithLocation(20, 42)
                );

            validate();

            compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                             parseOptions: TestOptions.Regular10,
                                             targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_BadAbstractEqualityOperatorSignature).Verify(
                // (4,33): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual static bool operator== (I1 x, I1 y); 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "==").WithArguments("virtual", "10.0", "11.0").WithLocation(4, 33),
                // (4,33): error CS0501: 'I1.operator ==(I1, I1)' must declare a body because it is not marked abstract, extern, or partial
                //     virtual static bool operator== (I1 x, I1 y); 
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "==").WithArguments("I1.operator ==(I1, I1)").WithLocation(4, 33),
                // (6,33): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual static bool operator!= (I1 x, I1 y) {return false;} 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "!=").WithArguments("virtual", "10.0", "11.0").WithLocation(6, 33),
                // (11,40): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static bool operator== (I2 x, I2 y);
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "==").WithArguments("sealed").WithLocation(11, 40),
                // (11,40): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual sealed static bool operator== (I2 x, I2 y);
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "==").WithArguments("virtual", "10.0", "11.0").WithLocation(11, 40),
                // (11,40): error CS0501: 'I2.operator ==(I2, I2)' must declare a body because it is not marked abstract, extern, or partial
                //     virtual sealed static bool operator== (I2 x, I2 y);
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "==").WithArguments("I2.operator ==(I2, I2)").WithLocation(11, 40),
                // (13,40): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static bool operator!= (I2 x, I2 y) {return false;} 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "!=").WithArguments("sealed").WithLocation(13, 40),
                // (13,40): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual sealed static bool operator!= (I2 x, I2 y) {return false;} 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "!=").WithArguments("virtual", "10.0", "11.0").WithLocation(13, 40),
                // (18,42): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract virtual static bool operator== (I3 x, I3 y);
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "==").WithArguments("abstract", "10.0", "11.0").WithLocation(18, 42),
                // (18,42): error CS0503: The abstract method 'I3.operator ==(I3, I3)' cannot be marked virtual
                //     abstract virtual static bool operator== (I3 x, I3 y);
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "==").WithArguments("method", "I3.operator ==(I3, I3)").WithLocation(18, 42),
                // (20,42): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract virtual static bool operator!= (I3 x, I3 y) {return false;} 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "!=").WithArguments("abstract", "10.0", "11.0").WithLocation(20, 42),
                // (20,42): error CS0503: The abstract method 'I3.operator !=(I3, I3)' cannot be marked virtual
                //     abstract virtual static bool operator!= (I3 x, I3 y) {return false;} 
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "!=").WithArguments("method", "I3.operator !=(I3, I3)").WithLocation(20, 42)
                );

            validate();

            compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_BadAbstractEqualityOperatorSignature).Verify(
                // (4,33): error CS0501: 'I1.operator ==(I1, I1)' must declare a body because it is not marked abstract, extern, or partial
                //     virtual static bool operator== (I1 x, I1 y); 
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "==").WithArguments("I1.operator ==(I1, I1)").WithLocation(4, 33),
                // (11,40): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static bool operator== (I2 x, I2 y);
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "==").WithArguments("sealed").WithLocation(11, 40),
                // (11,40): error CS0501: 'I2.operator ==(I2, I2)' must declare a body because it is not marked abstract, extern, or partial
                //     virtual sealed static bool operator== (I2 x, I2 y);
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "==").WithArguments("I2.operator ==(I2, I2)").WithLocation(11, 40),
                // (13,40): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static bool operator!= (I2 x, I2 y) {return false;} 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "!=").WithArguments("sealed").WithLocation(13, 40),
                // (18,42): error CS0503: The abstract method 'I3.operator ==(I3, I3)' cannot be marked virtual
                //     abstract virtual static bool operator== (I3 x, I3 y);
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "==").WithArguments("method", "I3.operator ==(I3, I3)").WithLocation(18, 42),
                // (20,42): error CS0503: The abstract method 'I3.operator !=(I3, I3)' cannot be marked virtual
                //     abstract virtual static bool operator!= (I3 x, I3 y) {return false;} 
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "!=").WithArguments("method", "I3.operator !=(I3, I3)").WithLocation(20, 42)
                );

            validate();

            void validate()
            {
                foreach (MethodSymbol m01 in compilation1.GetTypeByMetadataName("I1").GetMembers())
                {
                    Assert.False(m01.IsAbstract);
                    Assert.True(m01.IsVirtual);
                    Assert.True(m01.IsMetadataVirtual());
                    Assert.False(m01.IsSealed);
                    Assert.True(m01.IsStatic);
                    Assert.False(m01.IsExtern);
                    Assert.False(m01.IsAsync);
                    Assert.False(m01.IsOverride);
                    Assert.Same(m01, m01.ContainingType.FindImplementationForInterfaceMember(m01));
                }

                foreach (MethodSymbol m01 in compilation1.GetTypeByMetadataName("I2").GetMembers())
                {
                    Assert.False(m01.IsAbstract);
                    Assert.True(m01.IsVirtual);
                    Assert.True(m01.IsMetadataVirtual());
                    Assert.False(m01.IsSealed);
                    Assert.True(m01.IsStatic);
                    Assert.False(m01.IsExtern);
                    Assert.False(m01.IsAsync);
                    Assert.False(m01.IsOverride);
                    Assert.Same(m01, m01.ContainingType.FindImplementationForInterfaceMember(m01));
                }

                foreach (MethodSymbol m01 in compilation1.GetTypeByMetadataName("I3").GetMembers())
                {
                    Assert.True(m01.IsAbstract);
                    Assert.True(m01.IsVirtual);
                    Assert.True(m01.IsMetadataVirtual());
                    Assert.False(m01.IsSealed);
                    Assert.True(m01.IsStatic);
                    Assert.False(m01.IsExtern);
                    Assert.False(m01.IsAsync);
                    Assert.False(m01.IsOverride);
                    Assert.Null(m01.ContainingType.FindImplementationForInterfaceMember(m01));
                }
            }
        }

        [Fact]
        public void OperatorModifiers_10()
        {
            var source1 =
@"
public interface I1
{
    virtual static implicit operator int(I1 x); 

    virtual static explicit operator I1(bool x) {return null;} 
}

public interface I2
{
    virtual sealed static implicit operator int(I2 x);

    virtual sealed static explicit operator I2(bool x) {return null;} 
}

public interface I3
{
    abstract virtual static implicit operator int(I3 x);

    abstract virtual static explicit operator I3(bool x) {return null;} 
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular7_3,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,38): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual static implicit operator int(I1 x); 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "int").WithArguments("virtual", "7.3", "11.0").WithLocation(4, 38),
                // (4,38): error CS0501: 'I1.implicit operator int(I1)' must declare a body because it is not marked abstract, extern, or partial
                //     virtual static implicit operator int(I1 x); 
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "int").WithArguments("I1.implicit operator int(I1)").WithLocation(4, 38),
                // (4,38): error CS0552: 'I1.implicit operator int(I1)': user-defined conversions to or from an interface are not allowed
                //     virtual static implicit operator int(I1 x); 
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "int").WithArguments("I1.implicit operator int(I1)").WithLocation(4, 38),
                // (6,38): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual static explicit operator I1(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "I1").WithArguments("virtual", "7.3", "11.0").WithLocation(6, 38),
                // (6,38): error CS0552: 'I1.explicit operator I1(bool)': user-defined conversions to or from an interface are not allowed
                //     virtual static explicit operator I1(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "I1").WithArguments("I1.explicit operator I1(bool)").WithLocation(6, 38),
                // (11,45): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static implicit operator int(I2 x);
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "int").WithArguments("sealed").WithLocation(11, 45),
                // (11,45): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual sealed static implicit operator int(I2 x);
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "int").WithArguments("virtual", "7.3", "11.0").WithLocation(11, 45),
                // (11,45): error CS0501: 'I2.implicit operator int(I2)' must declare a body because it is not marked abstract, extern, or partial
                //     virtual sealed static implicit operator int(I2 x);
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "int").WithArguments("I2.implicit operator int(I2)").WithLocation(11, 45),
                // (11,45): error CS0552: 'I2.implicit operator int(I2)': user-defined conversions to or from an interface are not allowed
                //     virtual sealed static implicit operator int(I2 x);
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "int").WithArguments("I2.implicit operator int(I2)").WithLocation(11, 45),
                // (13,45): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static explicit operator I2(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "I2").WithArguments("sealed").WithLocation(13, 45),
                // (13,45): error CS8703: The modifier 'virtual' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     virtual sealed static explicit operator I2(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "I2").WithArguments("virtual", "7.3", "11.0").WithLocation(13, 45),
                // (13,45): error CS0552: 'I2.explicit operator I2(bool)': user-defined conversions to or from an interface are not allowed
                //     virtual sealed static explicit operator I2(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "I2").WithArguments("I2.explicit operator I2(bool)").WithLocation(13, 45),
                // (18,47): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract virtual static implicit operator int(I3 x);
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "int").WithArguments("abstract", "7.3", "11.0").WithLocation(18, 47),
                // (18,47): error CS0503: The abstract method 'I3.implicit operator int(I3)' cannot be marked virtual
                //     abstract virtual static implicit operator int(I3 x);
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "int").WithArguments("method", "I3.implicit operator int(I3)").WithLocation(18, 47),
                // (18,47): error CS0552: 'I3.implicit operator int(I3)': user-defined conversions to or from an interface are not allowed
                //     abstract virtual static implicit operator int(I3 x);
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "int").WithArguments("I3.implicit operator int(I3)").WithLocation(18, 47),
                // (20,47): error CS8703: The modifier 'abstract' is not valid for this item in C# 7.3. Please use language version '11.0' or greater.
                //     abstract virtual static explicit operator I3(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "I3").WithArguments("abstract", "7.3", "11.0").WithLocation(20, 47),
                // (20,47): error CS0503: The abstract method 'I3.explicit operator I3(bool)' cannot be marked virtual
                //     abstract virtual static explicit operator I3(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "I3").WithArguments("method", "I3.explicit operator I3(bool)").WithLocation(20, 47),
                // (20,47): error CS0552: 'I3.explicit operator I3(bool)': user-defined conversions to or from an interface are not allowed
                //     abstract virtual static explicit operator I3(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "I3").WithArguments("I3.explicit operator I3(bool)").WithLocation(20, 47)
                );

            validate();

            compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                             parseOptions: TestOptions.Regular10,
                                             targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,38): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual static implicit operator int(I1 x); 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "int").WithArguments("virtual", "10.0", "11.0").WithLocation(4, 38),
                // (4,38): error CS0501: 'I1.implicit operator int(I1)' must declare a body because it is not marked abstract, extern, or partial
                //     virtual static implicit operator int(I1 x); 
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "int").WithArguments("I1.implicit operator int(I1)").WithLocation(4, 38),
                // (4,38): error CS0552: 'I1.implicit operator int(I1)': user-defined conversions to or from an interface are not allowed
                //     virtual static implicit operator int(I1 x); 
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "int").WithArguments("I1.implicit operator int(I1)").WithLocation(4, 38),
                // (6,38): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual static explicit operator I1(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "I1").WithArguments("virtual", "10.0", "11.0").WithLocation(6, 38),
                // (6,38): error CS0552: 'I1.explicit operator I1(bool)': user-defined conversions to or from an interface are not allowed
                //     virtual static explicit operator I1(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "I1").WithArguments("I1.explicit operator I1(bool)").WithLocation(6, 38),
                // (11,45): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static implicit operator int(I2 x);
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "int").WithArguments("sealed").WithLocation(11, 45),
                // (11,45): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual sealed static implicit operator int(I2 x);
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "int").WithArguments("virtual", "10.0", "11.0").WithLocation(11, 45),
                // (11,45): error CS0501: 'I2.implicit operator int(I2)' must declare a body because it is not marked abstract, extern, or partial
                //     virtual sealed static implicit operator int(I2 x);
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "int").WithArguments("I2.implicit operator int(I2)").WithLocation(11, 45),
                // (11,45): error CS0552: 'I2.implicit operator int(I2)': user-defined conversions to or from an interface are not allowed
                //     virtual sealed static implicit operator int(I2 x);
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "int").WithArguments("I2.implicit operator int(I2)").WithLocation(11, 45),
                // (13,45): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static explicit operator I2(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "I2").WithArguments("sealed").WithLocation(13, 45),
                // (13,45): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual sealed static explicit operator I2(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "I2").WithArguments("virtual", "10.0", "11.0").WithLocation(13, 45),
                // (13,45): error CS0552: 'I2.explicit operator I2(bool)': user-defined conversions to or from an interface are not allowed
                //     virtual sealed static explicit operator I2(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "I2").WithArguments("I2.explicit operator I2(bool)").WithLocation(13, 45),
                // (18,47): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract virtual static implicit operator int(I3 x);
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "int").WithArguments("abstract", "10.0", "11.0").WithLocation(18, 47),
                // (18,47): error CS0503: The abstract method 'I3.implicit operator int(I3)' cannot be marked virtual
                //     abstract virtual static implicit operator int(I3 x);
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "int").WithArguments("method", "I3.implicit operator int(I3)").WithLocation(18, 47),
                // (18,47): error CS0552: 'I3.implicit operator int(I3)': user-defined conversions to or from an interface are not allowed
                //     abstract virtual static implicit operator int(I3 x);
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "int").WithArguments("I3.implicit operator int(I3)").WithLocation(18, 47),
                // (20,47): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     abstract virtual static explicit operator I3(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "I3").WithArguments("abstract", "10.0", "11.0").WithLocation(20, 47),
                // (20,47): error CS0503: The abstract method 'I3.explicit operator I3(bool)' cannot be marked virtual
                //     abstract virtual static explicit operator I3(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "I3").WithArguments("method", "I3.explicit operator I3(bool)").WithLocation(20, 47),
                // (20,47): error CS0552: 'I3.explicit operator I3(bool)': user-defined conversions to or from an interface are not allowed
                //     abstract virtual static explicit operator I3(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "I3").WithArguments("I3.explicit operator I3(bool)").WithLocation(20, 47)
                );

            validate();

            compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,38): error CS0501: 'I1.implicit operator int(I1)' must declare a body because it is not marked abstract, extern, or partial
                //     virtual static implicit operator int(I1 x); 
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "int").WithArguments("I1.implicit operator int(I1)").WithLocation(4, 38),
                // (4,38): error CS0552: 'I1.implicit operator int(I1)': user-defined conversions to or from an interface are not allowed
                //     virtual static implicit operator int(I1 x); 
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "int").WithArguments("I1.implicit operator int(I1)").WithLocation(4, 38),
                // (6,38): error CS0552: 'I1.explicit operator I1(bool)': user-defined conversions to or from an interface are not allowed
                //     virtual static explicit operator I1(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "I1").WithArguments("I1.explicit operator I1(bool)").WithLocation(6, 38),
                // (11,45): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static implicit operator int(I2 x);
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "int").WithArguments("sealed").WithLocation(11, 45),
                // (11,45): error CS0501: 'I2.implicit operator int(I2)' must declare a body because it is not marked abstract, extern, or partial
                //     virtual sealed static implicit operator int(I2 x);
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "int").WithArguments("I2.implicit operator int(I2)").WithLocation(11, 45),
                // (11,45): error CS0552: 'I2.implicit operator int(I2)': user-defined conversions to or from an interface are not allowed
                //     virtual sealed static implicit operator int(I2 x);
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "int").WithArguments("I2.implicit operator int(I2)").WithLocation(11, 45),
                // (13,45): error CS0106: The modifier 'sealed' is not valid for this item
                //     virtual sealed static explicit operator I2(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "I2").WithArguments("sealed").WithLocation(13, 45),
                // (13,45): error CS0552: 'I2.explicit operator I2(bool)': user-defined conversions to or from an interface are not allowed
                //     virtual sealed static explicit operator I2(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "I2").WithArguments("I2.explicit operator I2(bool)").WithLocation(13, 45),
                // (18,47): error CS0503: The abstract method 'I3.implicit operator int(I3)' cannot be marked virtual
                //     abstract virtual static implicit operator int(I3 x);
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "int").WithArguments("method", "I3.implicit operator int(I3)").WithLocation(18, 47),
                // (18,47): error CS0552: 'I3.implicit operator int(I3)': user-defined conversions to or from an interface are not allowed
                //     abstract virtual static implicit operator int(I3 x);
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "int").WithArguments("I3.implicit operator int(I3)").WithLocation(18, 47),
                // (20,47): error CS0503: The abstract method 'I3.explicit operator I3(bool)' cannot be marked virtual
                //     abstract virtual static explicit operator I3(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_AbstractNotVirtual, "I3").WithArguments("method", "I3.explicit operator I3(bool)").WithLocation(20, 47),
                // (20,47): error CS0552: 'I3.explicit operator I3(bool)': user-defined conversions to or from an interface are not allowed
                //     abstract virtual static explicit operator I3(bool x) {return null;} 
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "I3").WithArguments("I3.explicit operator I3(bool)").WithLocation(20, 47)
                );

            validate();

            void validate()
            {
                foreach (MethodSymbol m01 in compilation1.GetTypeByMetadataName("I1").GetMembers())
                {
                    Assert.False(m01.IsAbstract);
                    Assert.True(m01.IsVirtual);
                    Assert.True(m01.IsMetadataVirtual());
                    Assert.False(m01.IsSealed);
                    Assert.True(m01.IsStatic);
                    Assert.False(m01.IsExtern);
                    Assert.False(m01.IsAsync);
                    Assert.False(m01.IsOverride);
                    Assert.Same(m01, m01.ContainingType.FindImplementationForInterfaceMember(m01));
                }

                foreach (MethodSymbol m01 in compilation1.GetTypeByMetadataName("I2").GetMembers())
                {
                    Assert.False(m01.IsAbstract);
                    Assert.True(m01.IsVirtual);
                    Assert.True(m01.IsMetadataVirtual());
                    Assert.False(m01.IsSealed);
                    Assert.True(m01.IsStatic);
                    Assert.False(m01.IsExtern);
                    Assert.False(m01.IsAsync);
                    Assert.False(m01.IsOverride);
                    Assert.Same(m01, m01.ContainingType.FindImplementationForInterfaceMember(m01));
                }

                foreach (MethodSymbol m01 in compilation1.GetTypeByMetadataName("I3").GetMembers())
                {
                    Assert.True(m01.IsAbstract);
                    Assert.True(m01.IsVirtual);
                    Assert.True(m01.IsMetadataVirtual());
                    Assert.False(m01.IsSealed);
                    Assert.True(m01.IsStatic);
                    Assert.False(m01.IsExtern);
                    Assert.False(m01.IsAsync);
                    Assert.False(m01.IsOverride);
                    Assert.Null(m01.ContainingType.FindImplementationForInterfaceMember(m01));
                }
            }
        }

        [Fact]
        public void FieldModifiers_01()
        {
            var source1 =
@"
public interface I1
{
    abstract static int F1; 
    sealed static int F2; 
    abstract int F3; 
    sealed int F4; 
    virtual static int F5;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,25): error CS0681: The modifier 'abstract' is not valid on fields. Try using a property instead.
                //     abstract static int F1; 
                Diagnostic(ErrorCode.ERR_AbstractField, "F1").WithLocation(4, 25),
                // (5,23): error CS0106: The modifier 'sealed' is not valid for this item
                //     sealed static int F2; 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "F2").WithArguments("sealed").WithLocation(5, 23),
                // (6,18): error CS0681: The modifier 'abstract' is not valid on fields. Try using a property instead.
                //     abstract int F3; 
                Diagnostic(ErrorCode.ERR_AbstractField, "F3").WithLocation(6, 18),
                // (6,18): error CS0525: Interfaces cannot contain instance fields
                //     abstract int F3; 
                Diagnostic(ErrorCode.ERR_InterfacesCantContainFields, "F3").WithLocation(6, 18),
                // (7,16): error CS0106: The modifier 'sealed' is not valid for this item
                //     sealed int F4; 
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "F4").WithArguments("sealed").WithLocation(7, 16),
                // (7,16): error CS0525: Interfaces cannot contain instance fields
                //     sealed int F4; 
                Diagnostic(ErrorCode.ERR_InterfacesCantContainFields, "F4").WithLocation(7, 16),
                // (8,24): error CS0106: The modifier 'virtual' is not valid for this item
                //     virtual static int F5;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "F5").WithArguments("virtual").WithLocation(8, 24)
                );
        }

        [Fact]
        public void ExternAbstractStatic_01()
        {
            var source1 =
@"
interface I1
{
    extern abstract static void M01();
    extern abstract static bool P01 { get; }
    extern abstract static event System.Action E01;
    extern abstract static I1 operator+ (I1 x);
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,33): error CS0180: 'I1.M01()' cannot be both extern and abstract
                //     extern abstract static void M01();
                Diagnostic(ErrorCode.ERR_AbstractAndExtern, "M01").WithArguments("I1.M01()").WithLocation(4, 33),
                // (5,33): error CS0180: 'I1.P01' cannot be both extern and abstract
                //     extern abstract static bool P01 { get; }
                Diagnostic(ErrorCode.ERR_AbstractAndExtern, "P01").WithArguments("I1.P01").WithLocation(5, 33),
                // (6,48): error CS0180: 'I1.E01' cannot be both extern and abstract
                //     extern abstract static event System.Action E01;
                Diagnostic(ErrorCode.ERR_AbstractAndExtern, "E01").WithArguments("I1.E01").WithLocation(6, 48),
                // (7,39): error CS0180: 'I1.operator +(I1)' cannot be both extern and abstract
                //     extern abstract static I1 operator+ (I1 x);
                Diagnostic(ErrorCode.ERR_AbstractAndExtern, "+").WithArguments("I1.operator +(I1)").WithLocation(7, 39)
                );
        }

        [Fact]
        public void ExternVirtualStatic_01()
        {
            var source1 =
@"
interface I1
{
    extern virtual static void M01();
    extern virtual static bool P01 { get; }
    extern virtual static event System.Action E01;
    extern virtual static I1 operator+ (I1 x);
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,32): warning CS0626: Method, operator, or accessor 'I1.M01()' is marked external and has no attributes on it. Consider adding a DllImport attribute to specify the external implementation.
                //     extern virtual static void M01();
                Diagnostic(ErrorCode.WRN_ExternMethodNoImplementation, "M01").WithArguments("I1.M01()").WithLocation(4, 32),
                // (5,38): warning CS0626: Method, operator, or accessor 'I1.P01.get' is marked external and has no attributes on it. Consider adding a DllImport attribute to specify the external implementation.
                //     extern virtual static bool P01 { get; }
                Diagnostic(ErrorCode.WRN_ExternMethodNoImplementation, "get").WithArguments("I1.P01.get").WithLocation(5, 38),
                // (6,47): warning CS0626: Method, operator, or accessor 'I1.E01.remove' is marked external and has no attributes on it. Consider adding a DllImport attribute to specify the external implementation.
                //     extern virtual static event System.Action E01;
                Diagnostic(ErrorCode.WRN_ExternMethodNoImplementation, "E01").WithArguments("I1.E01.remove").WithLocation(6, 47),
                // (7,38): warning CS0626: Method, operator, or accessor 'I1.operator +(I1)' is marked external and has no attributes on it. Consider adding a DllImport attribute to specify the external implementation.
                //     extern virtual static I1 operator+ (I1 x);
                Diagnostic(ErrorCode.WRN_ExternMethodNoImplementation, "+").WithArguments("I1.operator +(I1)").WithLocation(7, 38)
                );
        }

        [Fact]
        public void ExternAbstractStatic_02()
        {
            var source1 =
@"
interface I1
{
    extern abstract static void M01() {}
    extern abstract static bool P01 { get => false; }
    extern abstract static event System.Action E01 { add {} remove {} }
    extern abstract static I1 operator+ (I1 x) => null;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,33): error CS0180: 'I1.M01()' cannot be both extern and abstract
                //     extern abstract static void M01() {}
                Diagnostic(ErrorCode.ERR_AbstractAndExtern, "M01").WithArguments("I1.M01()").WithLocation(4, 33),
                // (5,33): error CS0180: 'I1.P01' cannot be both extern and abstract
                //     extern abstract static bool P01 { get => false; }
                Diagnostic(ErrorCode.ERR_AbstractAndExtern, "P01").WithArguments("I1.P01").WithLocation(5, 33),
                // (6,48): error CS0180: 'I1.E01' cannot be both extern and abstract
                //     extern abstract static event System.Action E01 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_AbstractAndExtern, "E01").WithArguments("I1.E01").WithLocation(6, 48),
                // (6,52): error CS8712: 'I1.E01': abstract event cannot use event accessor syntax
                //     extern abstract static event System.Action E01 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_AbstractEventHasAccessors, "{").WithArguments("I1.E01").WithLocation(6, 52),
                // (7,39): error CS0180: 'I1.operator +(I1)' cannot be both extern and abstract
                //     extern abstract static I1 operator+ (I1 x) => null;
                Diagnostic(ErrorCode.ERR_AbstractAndExtern, "+").WithArguments("I1.operator +(I1)").WithLocation(7, 39)
                );
        }

        [Fact]
        public void ExternVirtualStatic_02()
        {
            var source1 =
@"
interface I1
{
    extern virtual static void M01() {}
    extern virtual static bool P01 { get => false; }
    extern virtual static event System.Action E01 { add {} remove {} }
    extern virtual static I1 operator+ (I1 x) => null;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,32): error CS0179: 'I1.M01()' cannot be extern and declare a body
                //     extern virtual static void M01() {}
                Diagnostic(ErrorCode.ERR_ExternHasBody, "M01").WithArguments("I1.M01()").WithLocation(4, 32),
                // (5,38): error CS0179: 'I1.P01.get' cannot be extern and declare a body
                //     extern virtual static bool P01 { get => false; }
                Diagnostic(ErrorCode.ERR_ExternHasBody, "get").WithArguments("I1.P01.get").WithLocation(5, 38),
                // (6,53): error CS0179: 'I1.E01.add' cannot be extern and declare a body
                //     extern virtual static event System.Action E01 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_ExternHasBody, "add").WithArguments("I1.E01.add").WithLocation(6, 53),
                // (6,60): error CS0179: 'I1.E01.remove' cannot be extern and declare a body
                //     extern virtual static event System.Action E01 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_ExternHasBody, "remove").WithArguments("I1.E01.remove").WithLocation(6, 60),
                // (7,38): error CS0179: 'I1.operator +(I1)' cannot be extern and declare a body
                //     extern virtual static I1 operator+ (I1 x) => null;
                Diagnostic(ErrorCode.ERR_ExternHasBody, "+").WithArguments("I1.operator +(I1)").WithLocation(7, 38)
                );
        }

        [Fact]
        public void ExternSealedStatic_01()
        {
            var source1 =
@"
#pragma warning disable CS0626 // Method, operator, or accessor is marked external and has no attributes on it. Consider adding a DllImport attribute to specify the external implementation.

interface I1
{
    extern sealed static void M01();
    extern sealed static bool P01 { get; }
    extern sealed static event System.Action E01;
    extern sealed static I1 operator+ (I1 x);
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();
        }

        [Fact]
        public void AbstractStaticInClass_01()
        {
            var source1 =
@"
abstract class C1
{
    public abstract static void M01();
    public abstract static bool P01 { get; }
    public abstract static event System.Action E01;
    public abstract static C1 operator+ (C1 x);
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,33): error CS0112: A static member cannot be marked as 'abstract'
                //     public abstract static void M01();
                Diagnostic(ErrorCode.ERR_StaticNotVirtual, "M01").WithArguments("abstract").WithLocation(4, 33),
                // (4,33): error CS0501: 'C1.M01()' must declare a body because it is not marked abstract, extern, or partial
                //     public abstract static void M01();
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "M01").WithArguments("C1.M01()").WithLocation(4, 33),
                // (5,33): error CS0112: A static member cannot be marked as 'abstract'
                //     public abstract static bool P01 { get; }
                Diagnostic(ErrorCode.ERR_StaticNotVirtual, "P01").WithArguments("abstract").WithLocation(5, 33),
                // (6,48): error CS0112: A static member cannot be marked as 'abstract'
                //     public abstract static event System.Action E01;
                Diagnostic(ErrorCode.ERR_StaticNotVirtual, "E01").WithArguments("abstract").WithLocation(6, 48),
                // (6,48): warning CS0067: The event 'C1.E01' is never used
                //     public abstract static event System.Action E01;
                Diagnostic(ErrorCode.WRN_UnreferencedEvent, "E01").WithArguments("C1.E01").WithLocation(6, 48),
                // (7,39): error CS0106: The modifier 'abstract' is not valid for this item
                //     public abstract static C1 operator+ (C1 x);
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "+").WithArguments("abstract").WithLocation(7, 39),
                // (7,39): error CS0501: 'C1.operator +(C1)' must declare a body because it is not marked abstract, extern, or partial
                //     public abstract static C1 operator+ (C1 x);
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "+").WithArguments("C1.operator +(C1)").WithLocation(7, 39)
                );
        }

        [Fact]
        public void VirtualStaticInClass_01()
        {
            var source1 =
@"
abstract class C1
{
    public virtual static void M01();
    public virtual static bool P01 { get; }
    public virtual static event System.Action E01;
    public virtual static C1 operator+ (C1 x);
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,32): error CS0112: A static member cannot be marked as 'virtual'
                //     public virtual static void M01();
                Diagnostic(ErrorCode.ERR_StaticNotVirtual, "M01").WithArguments("virtual").WithLocation(4, 32),
                // (4,32): error CS0501: 'C1.M01()' must declare a body because it is not marked abstract, extern, or partial
                //     public virtual static void M01();
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "M01").WithArguments("C1.M01()").WithLocation(4, 32),
                // (5,32): error CS0112: A static member cannot be marked as 'virtual'
                //     public virtual static bool P01 { get; }
                Diagnostic(ErrorCode.ERR_StaticNotVirtual, "P01").WithArguments("virtual").WithLocation(5, 32),
                // (6,47): error CS0112: A static member cannot be marked as 'virtual'
                //     public virtual static event System.Action E01;
                Diagnostic(ErrorCode.ERR_StaticNotVirtual, "E01").WithArguments("virtual").WithLocation(6, 47),
                // (6,47): warning CS0067: The event 'C1.E01' is never used
                //     public virtual static event System.Action E01;
                Diagnostic(ErrorCode.WRN_UnreferencedEvent, "E01").WithArguments("C1.E01").WithLocation(6, 47),
                // (7,38): error CS0106: The modifier 'virtual' is not valid for this item
                //     public virtual static C1 operator+ (C1 x);
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "+").WithArguments("virtual").WithLocation(7, 38),
                // (7,38): error CS0501: 'C1.operator +(C1)' must declare a body because it is not marked abstract, extern, or partial
                //     public virtual static C1 operator+ (C1 x);
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "+").WithArguments("C1.operator +(C1)").WithLocation(7, 38)
                );
        }

        [Fact]
        public void SealedStaticInClass_01()
        {
            var source1 =
@"
class C1
{
    sealed static void M01() {}
    sealed static bool P01 { get => false; }
    sealed static event System.Action E01 { add {} remove {} }
    public sealed static C1 operator+ (C1 x) => null;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,24): error CS0238: 'C1.M01()' cannot be sealed because it is not an override
                //     sealed static void M01() {}
                Diagnostic(ErrorCode.ERR_SealedNonOverride, "M01").WithArguments("C1.M01()").WithLocation(4, 24),
                // (5,24): error CS0238: 'C1.P01' cannot be sealed because it is not an override
                //     sealed static bool P01 { get => false; }
                Diagnostic(ErrorCode.ERR_SealedNonOverride, "P01").WithArguments("C1.P01").WithLocation(5, 24),
                // (6,39): error CS0238: 'C1.E01' cannot be sealed because it is not an override
                //     sealed static event System.Action E01 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_SealedNonOverride, "E01").WithArguments("C1.E01").WithLocation(6, 39),
                // (7,37): error CS0106: The modifier 'sealed' is not valid for this item
                //     public sealed static C1 operator+ (C1 x) => null;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "+").WithArguments("sealed").WithLocation(7, 37)
                );
        }

        [Fact]
        public void AbstractStaticInStruct_01()
        {
            var source1 =
@"
struct C1
{
    public abstract static void M01();
    public abstract static bool P01 { get; }
    public abstract static event System.Action E01;
    public abstract static C1 operator+ (C1 x);
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,33): error CS0112: A static member cannot be marked as 'abstract'
                //     public abstract static void M01();
                Diagnostic(ErrorCode.ERR_StaticNotVirtual, "M01").WithArguments("abstract").WithLocation(4, 33),
                // (4,33): error CS0501: 'C1.M01()' must declare a body because it is not marked abstract, extern, or partial
                //     public abstract static void M01();
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "M01").WithArguments("C1.M01()").WithLocation(4, 33),
                // (5,33): error CS0112: A static member cannot be marked as 'abstract'
                //     public abstract static bool P01 { get; }
                Diagnostic(ErrorCode.ERR_StaticNotVirtual, "P01").WithArguments("abstract").WithLocation(5, 33),
                // (6,48): error CS0112: A static member cannot be marked as 'abstract'
                //     public abstract static event System.Action E01;
                Diagnostic(ErrorCode.ERR_StaticNotVirtual, "E01").WithArguments("abstract").WithLocation(6, 48),
                // (6,48): warning CS0067: The event 'C1.E01' is never used
                //     public abstract static event System.Action E01;
                Diagnostic(ErrorCode.WRN_UnreferencedEvent, "E01").WithArguments("C1.E01").WithLocation(6, 48),
                // (7,39): error CS0106: The modifier 'abstract' is not valid for this item
                //     public abstract static C1 operator+ (C1 x);
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "+").WithArguments("abstract").WithLocation(7, 39),
                // (7,39): error CS0501: 'C1.operator +(C1)' must declare a body because it is not marked abstract, extern, or partial
                //     public abstract static C1 operator+ (C1 x);
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "+").WithArguments("C1.operator +(C1)").WithLocation(7, 39)
                );
        }

        [Fact]
        public void VirtualStaticInStruct_01()
        {
            var source1 =
@"
struct C1
{
    public virtual static void M01();
    public virtual static bool P01 { get; }
    public virtual static event System.Action E01;
    public virtual static C1 operator+ (C1 x);
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,32): error CS0112: A static member cannot be marked as 'virtual'
                //     public virtual static void M01();
                Diagnostic(ErrorCode.ERR_StaticNotVirtual, "M01").WithArguments("virtual").WithLocation(4, 32),
                // (4,32): error CS0501: 'C1.M01()' must declare a body because it is not marked abstract, extern, or partial
                //     public virtual static void M01();
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "M01").WithArguments("C1.M01()").WithLocation(4, 32),
                // (5,32): error CS0112: A static member cannot be marked as 'virtual'
                //     public virtual static bool P01 { get; }
                Diagnostic(ErrorCode.ERR_StaticNotVirtual, "P01").WithArguments("virtual").WithLocation(5, 32),
                // (6,47): error CS0112: A static member cannot be marked as 'virtual'
                //     public virtual static event System.Action E01;
                Diagnostic(ErrorCode.ERR_StaticNotVirtual, "E01").WithArguments("virtual").WithLocation(6, 47),
                // (6,47): warning CS0067: The event 'C1.E01' is never used
                //     public virtual static event System.Action E01;
                Diagnostic(ErrorCode.WRN_UnreferencedEvent, "E01").WithArguments("C1.E01").WithLocation(6, 47),
                // (7,38): error CS0106: The modifier 'virtual' is not valid for this item
                //     public virtual static C1 operator+ (C1 x);
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "+").WithArguments("virtual").WithLocation(7, 38),
                // (7,38): error CS0501: 'C1.operator +(C1)' must declare a body because it is not marked abstract, extern, or partial
                //     public virtual static C1 operator+ (C1 x);
                Diagnostic(ErrorCode.ERR_ConcreteMissingBody, "+").WithArguments("C1.operator +(C1)").WithLocation(7, 38)
                );
        }

        [Fact]
        public void SealedStaticInStruct_01()
        {
            var source1 =
@"
struct C1
{
    sealed static void M01() {}
    sealed static bool P01 { get => false; }
    sealed static event System.Action E01 { add {} remove {} }
    public sealed static C1 operator+ (C1 x) => default;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,24): error CS0238: 'C1.M01()' cannot be sealed because it is not an override
                //     sealed static void M01() {}
                Diagnostic(ErrorCode.ERR_SealedNonOverride, "M01").WithArguments("C1.M01()").WithLocation(4, 24),
                // (5,24): error CS0238: 'C1.P01' cannot be sealed because it is not an override
                //     sealed static bool P01 { get => false; }
                Diagnostic(ErrorCode.ERR_SealedNonOverride, "P01").WithArguments("C1.P01").WithLocation(5, 24),
                // (6,39): error CS0238: 'C1.E01' cannot be sealed because it is not an override
                //     sealed static event System.Action E01 { add {} remove {} }
                Diagnostic(ErrorCode.ERR_SealedNonOverride, "E01").WithArguments("C1.E01").WithLocation(6, 39),
                // (7,37): error CS0106: The modifier 'sealed' is not valid for this item
                //     public sealed static C1 operator+ (C1 x) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "+").WithArguments("sealed").WithLocation(7, 37)
                );
        }

        [Fact]
        public void DefineAbstractStaticMethod_01()
        {
            var source1 =
@"
interface I1
{
    abstract static void M01();
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            Assert.True(compilation1.Assembly.RuntimeSupportsDefaultInterfaceImplementation);
            Assert.True(compilation1.Assembly.RuntimeSupportsStaticAbstractMembersInInterfaces);
            Assert.True(compilation1.SupportsRuntimeCapability(RuntimeCapability.DefaultImplementationsOfInterfaces));
            Assert.True(compilation1.SupportsRuntimeCapability(RuntimeCapability.VirtualStaticsInInterfaces));

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var m01 = module.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<MethodSymbol>().Single();

                Assert.False(m01.IsMetadataNewSlot());
                Assert.True(m01.IsAbstract);
                Assert.True(m01.IsMetadataVirtual());
                Assert.False(m01.IsMetadataFinal);
                Assert.False(m01.IsVirtual);
                Assert.False(m01.IsSealed);
                Assert.True(m01.IsStatic);
                Assert.False(m01.IsOverride);
            }
        }

        [Fact]
        public void DefineVirtualStaticMethod_01()
        {
            var source1 =
@"
interface I1
{
    virtual static void M01(){}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            Assert.True(compilation1.Assembly.RuntimeSupportsDefaultInterfaceImplementation);
            Assert.True(compilation1.Assembly.RuntimeSupportsStaticAbstractMembersInInterfaces);
            Assert.True(compilation1.SupportsRuntimeCapability(RuntimeCapability.DefaultImplementationsOfInterfaces));
            Assert.True(compilation1.SupportsRuntimeCapability(RuntimeCapability.VirtualStaticsInInterfaces));

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var m01 = module.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<MethodSymbol>().Single();

                Assert.False(m01.IsMetadataNewSlot());
                Assert.False(m01.IsAbstract);
                Assert.True(m01.IsMetadataVirtual());
                Assert.False(m01.IsMetadataFinal);
                Assert.True(m01.IsVirtual);
                Assert.False(m01.IsSealed);
                Assert.True(m01.IsStatic);
                Assert.False(m01.IsOverride);
            }
        }

        [Fact]
        public void DefineAbstractStaticMethod_02()
        {
            var source1 =
@"
interface I1
{
    abstract static void M01();
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation1.VerifyDiagnostics(
                // (4,26): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static void M01();
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "M01").WithLocation(4, 26)
                );

            Assert.False(compilation1.Assembly.RuntimeSupportsDefaultInterfaceImplementation);
            Assert.False(compilation1.Assembly.RuntimeSupportsStaticAbstractMembersInInterfaces);
            Assert.False(compilation1.SupportsRuntimeCapability(RuntimeCapability.DefaultImplementationsOfInterfaces));
            Assert.False(compilation1.SupportsRuntimeCapability(RuntimeCapability.VirtualStaticsInInterfaces));

            var compilation2 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Net50);

            compilation2.VerifyDiagnostics(
                // (4,26): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static void M01();
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "M01").WithLocation(4, 26)
                );

            Assert.True(compilation2.Assembly.RuntimeSupportsDefaultInterfaceImplementation);
            Assert.False(compilation2.Assembly.RuntimeSupportsStaticAbstractMembersInInterfaces);
            Assert.True(compilation2.SupportsRuntimeCapability(RuntimeCapability.DefaultImplementationsOfInterfaces));
            Assert.False(compilation2.SupportsRuntimeCapability(RuntimeCapability.VirtualStaticsInInterfaces));
        }

        [Fact]
        public void DefineVirtualStaticMethod_02()
        {
            var source1 =
@"
interface I1
{
    virtual  static void M01(){}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation1.VerifyDiagnostics(
                // (4,26): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     virtual  static void M01(){}
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "M01").WithLocation(4, 26)
                );

            Assert.False(compilation1.Assembly.RuntimeSupportsDefaultInterfaceImplementation);
            Assert.False(compilation1.Assembly.RuntimeSupportsStaticAbstractMembersInInterfaces);
            Assert.False(compilation1.SupportsRuntimeCapability(RuntimeCapability.DefaultImplementationsOfInterfaces));
            Assert.False(compilation1.SupportsRuntimeCapability(RuntimeCapability.VirtualStaticsInInterfaces));

            var compilation2 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Net50);

            compilation2.VerifyDiagnostics(
                // (4,26): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     virtual  static void M01(){}
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "M01").WithLocation(4, 26)
                );

            Assert.True(compilation2.Assembly.RuntimeSupportsDefaultInterfaceImplementation);
            Assert.False(compilation2.Assembly.RuntimeSupportsStaticAbstractMembersInInterfaces);
            Assert.True(compilation2.SupportsRuntimeCapability(RuntimeCapability.DefaultImplementationsOfInterfaces));
            Assert.False(compilation2.SupportsRuntimeCapability(RuntimeCapability.VirtualStaticsInInterfaces));
        }

        [Theory]
        [InlineData("I1", "+", "(I1 x)")]
        [InlineData("I1", "-", "(I1 x)")]
        [InlineData("I1", "!", "(I1 x)")]
        [InlineData("I1", "~", "(I1 x)")]
        [InlineData("I1", "++", "(I1 x)")]
        [InlineData("I1", "--", "(I1 x)")]
        [InlineData("I1", "+", "(I1 x, I1 y)")]
        [InlineData("I1", "-", "(I1 x, I1 y)")]
        [InlineData("I1", "*", "(I1 x, I1 y)")]
        [InlineData("I1", "/", "(I1 x, I1 y)")]
        [InlineData("I1", "%", "(I1 x, I1 y)")]
        [InlineData("I1", "&", "(I1 x, I1 y)")]
        [InlineData("I1", "|", "(I1 x, I1 y)")]
        [InlineData("I1", "^", "(I1 x, I1 y)")]
        [InlineData("I1", "<<", "(I1 x, int y)")]
        [InlineData("I1", ">>", "(I1 x, int y)")]
        [InlineData("I1", ">>>", "(I1 x, int y)")]
        [InlineData("I1", "checked -", "(I1 x)")]
        [InlineData("I1", "checked ++", "(I1 x)")]
        [InlineData("I1", "checked --", "(I1 x)")]
        [InlineData("I1", "checked +", "(I1 x, I1 y)")]
        [InlineData("I1", "checked -", "(I1 x, I1 y)")]
        [InlineData("I1", "checked *", "(I1 x, I1 y)")]
        [InlineData("I1", "checked /", "(I1 x, I1 y)")]
        public void DefineAbstractStaticOperator_01(string type, string op, string paramList)
        {
            var source1 =
@"
partial interface I1
{
    abstract static " + type + " operator " + op + " " + paramList + @";
}
";

            if (op.StartsWith("checked "))
            {
                source1 +=
@"
partial interface I1
{
    abstract static " + type + " operator " + op.Substring(8) + " " + paramList + @";
}
";
            }

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                foreach (var m01 in module.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<MethodSymbol>())
                {
                    Assert.False(m01.IsMetadataNewSlot());
                    Assert.True(m01.IsAbstract);
                    Assert.True(m01.IsMetadataVirtual());
                    Assert.False(m01.IsMetadataFinal);
                    Assert.False(m01.IsVirtual);
                    Assert.False(m01.IsSealed);
                    Assert.True(m01.IsStatic);
                    Assert.False(m01.IsOverride);
                }
            }
        }

        [Theory]
        [InlineData("I1", "+", "(I1 x)")]
        [InlineData("I1", "-", "(I1 x)")]
        [InlineData("I1", "!", "(I1 x)")]
        [InlineData("I1", "~", "(I1 x)")]
        [InlineData("I1", "++", "(I1 x)")]
        [InlineData("I1", "--", "(I1 x)")]
        [InlineData("I1", "+", "(I1 x, I1 y)")]
        [InlineData("I1", "-", "(I1 x, I1 y)")]
        [InlineData("I1", "*", "(I1 x, I1 y)")]
        [InlineData("I1", "/", "(I1 x, I1 y)")]
        [InlineData("I1", "%", "(I1 x, I1 y)")]
        [InlineData("I1", "&", "(I1 x, I1 y)")]
        [InlineData("I1", "|", "(I1 x, I1 y)")]
        [InlineData("I1", "^", "(I1 x, I1 y)")]
        [InlineData("I1", "<<", "(I1 x, int y)")]
        [InlineData("I1", ">>", "(I1 x, int y)")]
        [InlineData("I1", ">>>", "(I1 x, int y)")]
        [InlineData("I1", "checked -", "(I1 x)")]
        [InlineData("I1", "checked ++", "(I1 x)")]
        [InlineData("I1", "checked --", "(I1 x)")]
        [InlineData("I1", "checked +", "(I1 x, I1 y)")]
        [InlineData("I1", "checked -", "(I1 x, I1 y)")]
        [InlineData("I1", "checked *", "(I1 x, I1 y)")]
        [InlineData("I1", "checked /", "(I1 x, I1 y)")]
        public void DefineVirtualStaticOperator_01(string type, string op, string paramList)
        {
            var source1 =
@"
partial interface I1
{
    virtual static " + type + " operator " + op + " " + paramList + @" => throw null;
}
";

            if (op.StartsWith("checked "))
            {
                source1 +=
@"
partial interface I1
{
    virtual static " + type + " operator " + op.Substring(8) + " " + paramList + @" => throw null;
}
";
            }

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                foreach (var m01 in module.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<MethodSymbol>())
                {
                    Assert.False(m01.IsMetadataNewSlot());
                    Assert.False(m01.IsAbstract);
                    Assert.True(m01.IsMetadataVirtual());
                    Assert.False(m01.IsMetadataFinal);
                    Assert.True(m01.IsVirtual);
                    Assert.False(m01.IsSealed);
                    Assert.True(m01.IsStatic);
                    Assert.False(m01.IsOverride);
                }
            }
        }

        [Fact]
        public void DefineAbstractStaticOperator_02()
        {
            var source1 =
@"
interface I1<T> where T : I1<T>
{
    abstract static bool operator true (I1<T> x);
    abstract static bool operator false (I1<T> x);
    abstract static I1<T> operator > (I1<T> x, I1<T> y);
    abstract static I1<T> operator < (I1<T> x, I1<T> y);
    abstract static I1<T> operator >= (I1<T> x, I1<T> y);
    abstract static I1<T> operator <= (I1<T> x, I1<T> y);
    abstract static T operator == (T x, T y);
    abstract static T operator != (T x, T y);
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                int count = 0;
                foreach (var m01 in module.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<MethodSymbol>())
                {
                    Assert.False(m01.IsMetadataNewSlot());
                    Assert.True(m01.IsAbstract);
                    Assert.True(m01.IsMetadataVirtual());
                    Assert.False(m01.IsMetadataFinal);
                    Assert.False(m01.IsVirtual);
                    Assert.False(m01.IsSealed);
                    Assert.True(m01.IsStatic);
                    Assert.False(m01.IsOverride);

                    count++;
                }

                Assert.Equal(8, count);
            }
        }

        [Fact]
        public void DefineVirtualStaticOperator_02()
        {
            var source1 =
@"
interface I1<T> where T : I1<T>
{
    virtual  static bool operator true (I1<T> x) => throw null;
    virtual  static bool operator false (I1<T> x) => throw null;
    virtual  static I1<T> operator > (I1<T> x, I1<T> y) => throw null;
    virtual  static I1<T> operator < (I1<T> x, I1<T> y) => throw null;
    virtual  static I1<T> operator >= (I1<T> x, I1<T> y) => throw null;
    virtual  static I1<T> operator <= (I1<T> x, I1<T> y) => throw null;
    virtual  static T operator == (T x, T y) => throw null;
    virtual  static T operator != (T x, T y) => throw null;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                int count = 0;
                foreach (var m01 in module.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<MethodSymbol>())
                {
                    Assert.False(m01.IsMetadataNewSlot());
                    Assert.False(m01.IsAbstract);
                    Assert.True(m01.IsMetadataVirtual());
                    Assert.False(m01.IsMetadataFinal);
                    Assert.True(m01.IsVirtual);
                    Assert.False(m01.IsSealed);
                    Assert.True(m01.IsStatic);
                    Assert.False(m01.IsOverride);

                    count++;
                }

                Assert.Equal(8, count);
            }
        }

        [Theory]
        [InlineData("I1", "+", "(I1 x)")]
        [InlineData("I1", "-", "(I1 x)")]
        [InlineData("I1", "!", "(I1 x)")]
        [InlineData("I1", "~", "(I1 x)")]
        [InlineData("I1", "++", "(I1 x)")]
        [InlineData("I1", "--", "(I1 x)")]
        [InlineData("I1", "+", "(I1 x, I1 y)")]
        [InlineData("I1", "-", "(I1 x, I1 y)")]
        [InlineData("I1", "*", "(I1 x, I1 y)")]
        [InlineData("I1", "/", "(I1 x, I1 y)")]
        [InlineData("I1", "%", "(I1 x, I1 y)")]
        [InlineData("I1", "&", "(I1 x, I1 y)")]
        [InlineData("I1", "|", "(I1 x, I1 y)")]
        [InlineData("I1", "^", "(I1 x, I1 y)")]
        [InlineData("I1", "<<", "(I1 x, int y)")]
        [InlineData("I1", ">>", "(I1 x, int y)")]
        [InlineData("I1", ">>>", "(I1 x, int y)")]
        [InlineData("I1", "checked -", "(I1 x)")]
        [InlineData("I1", "checked ++", "(I1 x)")]
        [InlineData("I1", "checked --", "(I1 x)")]
        [InlineData("I1", "checked +", "(I1 x, I1 y)")]
        [InlineData("I1", "checked -", "(I1 x, I1 y)")]
        [InlineData("I1", "checked *", "(I1 x, I1 y)")]
        [InlineData("I1", "checked /", "(I1 x, I1 y)")]
        public void DefineAbstractStaticOperator_03(string type, string op, string paramList)
        {
            var source1 =
@"
interface I1
{
    abstract static " + type + " operator " + op + " " + paramList + @";
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            bool isChecked = op.StartsWith("checked ");

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (4,33): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static I1 operator + (I1 x);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, op.Substring(isChecked ? 8 : 0)).WithLocation(4, 31 + type.Length + (isChecked ? 8 : 0))
                );
        }

        [Theory]
        [InlineData("I1", "+", "(I1 x)")]
        [InlineData("I1", "-", "(I1 x)")]
        [InlineData("I1", "!", "(I1 x)")]
        [InlineData("I1", "~", "(I1 x)")]
        [InlineData("I1", "++", "(I1 x)")]
        [InlineData("I1", "--", "(I1 x)")]
        [InlineData("I1", "+", "(I1 x, I1 y)")]
        [InlineData("I1", "-", "(I1 x, I1 y)")]
        [InlineData("I1", "*", "(I1 x, I1 y)")]
        [InlineData("I1", "/", "(I1 x, I1 y)")]
        [InlineData("I1", "%", "(I1 x, I1 y)")]
        [InlineData("I1", "&", "(I1 x, I1 y)")]
        [InlineData("I1", "|", "(I1 x, I1 y)")]
        [InlineData("I1", "^", "(I1 x, I1 y)")]
        [InlineData("I1", "<<", "(I1 x, int y)")]
        [InlineData("I1", ">>", "(I1 x, int y)")]
        [InlineData("I1", ">>>", "(I1 x, int y)")]
        [InlineData("I1", "checked -", "(I1 x)")]
        [InlineData("I1", "checked ++", "(I1 x)")]
        [InlineData("I1", "checked --", "(I1 x)")]
        [InlineData("I1", "checked +", "(I1 x, I1 y)")]
        [InlineData("I1", "checked -", "(I1 x, I1 y)")]
        [InlineData("I1", "checked *", "(I1 x, I1 y)")]
        [InlineData("I1", "checked /", "(I1 x, I1 y)")]
        public void DefineVirtualStaticOperator_03(string type, string op, string paramList)
        {
            var source1 =
@"
interface I1
{
    virtual  static " + type + " operator " + op + " " + paramList + @" => throw null;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            bool isChecked = op.StartsWith("checked ");

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (4,33): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     virtual  static I1 operator + (I1 x);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, op.Substring(isChecked ? 8 : 0)).WithLocation(4, 31 + type.Length + (isChecked ? 8 : 0))
                );
        }

        [Fact]
        public void DefineAbstractStaticOperator_04()
        {
            var source1 =
@"
interface I1
{
    abstract static bool operator true (I1 x);
    abstract static bool operator false (I1 x);
    abstract static I1 operator > (I1 x, I1 y);
    abstract static I1 operator < (I1 x, I1 y);
    abstract static I1 operator >= (I1 x, I1 y);
    abstract static I1 operator <= (I1 x, I1 y);
    abstract static I1 operator == (I1 x, I1 y);
    abstract static I1 operator != (I1 x, I1 y);
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_BadAbstractEqualityOperatorSignature).Verify(
                // (4,35): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static bool operator true (I1 x);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "true").WithLocation(4, 35),
                // (5,35): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static bool operator false (I1 x);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "false").WithLocation(5, 35),
                // (6,33): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static I1 operator > (I1 x, I1 y);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, ">").WithLocation(6, 33),
                // (7,33): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static I1 operator < (I1 x, I1 y);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "<").WithLocation(7, 33),
                // (8,33): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static I1 operator >= (I1 x, I1 y);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, ">=").WithLocation(8, 33),
                // (9,33): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static I1 operator <= (I1 x, I1 y);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "<=").WithLocation(9, 33),
                // (10,33): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static I1 operator == (I1 x, I1 y);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "==").WithLocation(10, 33),
                // (11,33): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static I1 operator != (I1 x, I1 y);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "!=").WithLocation(11, 33)
                );
        }

        [Fact]
        public void DefineVirtualStaticOperator_04()
        {
            var source1 =
@"
interface I1
{
    virtual  static bool operator true (I1 x) => throw null;
    virtual  static bool operator false (I1 x) => throw null;
    virtual  static I1 operator > (I1 x, I1 y) => throw null;
    virtual  static I1 operator < (I1 x, I1 y) => throw null;
    virtual  static I1 operator >= (I1 x, I1 y) => throw null;
    virtual  static I1 operator <= (I1 x, I1 y) => throw null;
    virtual  static I1 operator == (I1 x, I1 y) => throw null;
    virtual  static I1 operator != (I1 x, I1 y) => throw null;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_BadAbstractEqualityOperatorSignature).Verify(
                // (4,35): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     virtual  static bool operator true (I1 x);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "true").WithLocation(4, 35),
                // (5,35): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     virtual  static bool operator false (I1 x);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "false").WithLocation(5, 35),
                // (6,33): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     virtual  static I1 operator > (I1 x, I1 y);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, ">").WithLocation(6, 33),
                // (7,33): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     virtual  static I1 operator < (I1 x, I1 y);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "<").WithLocation(7, 33),
                // (8,33): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     virtual  static I1 operator >= (I1 x, I1 y);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, ">=").WithLocation(8, 33),
                // (9,33): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     virtual  static I1 operator <= (I1 x, I1 y);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "<=").WithLocation(9, 33),
                // (10,33): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     virtual  static I1 operator == (I1 x, I1 y) => throw null;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "==").WithLocation(10, 33),
                // (11,33): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     virtual  static I1 operator != (I1 x, I1 y) => throw null;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "!=").WithLocation(11, 33)
                );
        }

        [Fact]
        public void DefineAbstractStaticConversion_01()
        {
            var source1 =
@"
interface I1<T> where T : I1<T>
{
    abstract static implicit operator int(T x);
    abstract static explicit operator T(int x);
    abstract static explicit operator checked T(int x);
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                int count = 0;
                foreach (var m01 in module.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<MethodSymbol>())
                {
                    Assert.False(m01.IsMetadataNewSlot());
                    Assert.True(m01.IsAbstract);
                    Assert.True(m01.IsMetadataVirtual());
                    Assert.False(m01.IsMetadataFinal);
                    Assert.False(m01.IsVirtual);
                    Assert.False(m01.IsSealed);
                    Assert.True(m01.IsStatic);
                    Assert.False(m01.IsOverride);

                    count++;
                }

                Assert.Equal(3, count);
            }
        }

        [Fact]
        public void DefineVirtualStaticConversion_01()
        {
            var source1 =
@"
interface I1<T> where T : I1<T>
{
    virtual static implicit operator int(T x) => default;
    virtual static explicit operator T(int x) => default;
    virtual static explicit operator checked T(int x) => default;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                int count = 0;
                foreach (var m01 in module.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<MethodSymbol>())
                {
                    Assert.False(m01.IsMetadataNewSlot());
                    Assert.False(m01.IsAbstract);
                    Assert.True(m01.IsMetadataVirtual());
                    Assert.False(m01.IsMetadataFinal);
                    Assert.True(m01.IsVirtual);
                    Assert.False(m01.IsSealed);
                    Assert.True(m01.IsStatic);
                    Assert.False(m01.IsOverride);

                    count++;
                }

                Assert.Equal(3, count);
            }
        }

        [Theory]
        [CombinatorialData]
        public void DefineAbstractStaticConversion_03(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
interface I1<T> where T : I1<T>
{
    " + modifier + @" static implicit operator int(T x)" + body + @"
    " + modifier + @" static explicit operator T(int x)" + body + @"
    " + modifier + @" static explicit operator checked T(int x)" + body + @"
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation1.VerifyDiagnostics(
                // (4,39): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static implicit operator int(T x);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "int").WithLocation(4, 39),
                // (5,39): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static explicit operator T(int x);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "T").WithLocation(5, 39),
                // (6,47): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static explicit operator checked T(int x);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "T").WithLocation(6, 47)
                );
        }

        [Fact]
        public void DefineAbstractStaticProperty_01()
        {
            var source1 =
@"
interface I1
{
    abstract static int P01 { get; set; }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var p01 = module.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<PropertySymbol>().Single();

                Assert.True(p01.IsAbstract);
                Assert.False(p01.IsVirtual);
                Assert.False(p01.IsSealed);
                Assert.True(p01.IsStatic);
                Assert.False(p01.IsOverride);

                int count = 0;
                foreach (var m01 in module.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<MethodSymbol>())
                {
                    Assert.False(m01.IsMetadataNewSlot());
                    Assert.True(m01.IsAbstract);
                    Assert.True(m01.IsMetadataVirtual());
                    Assert.False(m01.IsMetadataFinal);
                    Assert.False(m01.IsVirtual);
                    Assert.False(m01.IsSealed);
                    Assert.True(m01.IsStatic);
                    Assert.False(m01.IsOverride);

                    count++;
                }

                Assert.Equal(2, count);
            }
        }

        [Fact]
        public void DefineVirtualStaticProperty_01()
        {
            var source1 =
@"
interface I1
{
    virtual static int P01 { get; set; }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var p01 = module.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<PropertySymbol>().Single();

                Assert.False(p01.IsAbstract);
                Assert.True(p01.IsVirtual);
                Assert.False(p01.IsSealed);
                Assert.True(p01.IsStatic);
                Assert.False(p01.IsOverride);

                int count = 0;
                foreach (var m01 in module.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<MethodSymbol>())
                {
                    Assert.False(m01.IsMetadataNewSlot());
                    Assert.False(m01.IsAbstract);
                    Assert.True(m01.IsMetadataVirtual());
                    Assert.False(m01.IsMetadataFinal);
                    Assert.True(m01.IsVirtual);
                    Assert.False(m01.IsSealed);
                    Assert.True(m01.IsStatic);
                    Assert.False(m01.IsOverride);

                    count++;
                }

                Assert.Equal(2, count);
            }
        }

        [Fact]
        public void DefineAbstractStaticProperty_02()
        {
            var source1 =
@"
interface I1
{
    abstract static int P01 { get; set; }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation1.VerifyDiagnostics(
                // (4,31): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static int P01 { get; set; }
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "get").WithLocation(4, 31),
                // (4,36): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static int P01 { get; set; }
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "set").WithLocation(4, 36)
                );
        }

        [Fact]
        public void DefineVirtualStaticProperty_02()
        {
            var source1 =
@"
interface I1
{
    virtual  static int P01 { get; set; }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation1.VerifyDiagnostics(
                // (4,31): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     virtual  static int P01 { get; set; }
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "get").WithLocation(4, 31),
                // (4,36): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     virtual  static int P01 { get; set; }
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "set").WithLocation(4, 36)
                );
        }

        [Fact]
        public void DefineAbstractStaticEvent_01()
        {
            var source1 =
@"
interface I1
{
    abstract static event System.Action E01;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var e01 = module.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<EventSymbol>().Single();

                Assert.True(e01.IsAbstract);
                Assert.False(e01.IsVirtual);
                Assert.False(e01.IsSealed);
                Assert.True(e01.IsStatic);
                Assert.False(e01.IsOverride);

                int count = 0;
                foreach (var m01 in module.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<MethodSymbol>())
                {
                    Assert.False(m01.IsMetadataNewSlot());
                    Assert.True(m01.IsAbstract);
                    Assert.True(m01.IsMetadataVirtual());
                    Assert.False(m01.IsMetadataFinal);
                    Assert.False(m01.IsVirtual);
                    Assert.False(m01.IsSealed);
                    Assert.True(m01.IsStatic);
                    Assert.False(m01.IsOverride);

                    count++;
                }

                Assert.Equal(2, count);
            }
        }

        [Fact]
        public void DefineVirtualStaticEvent_01()
        {
            var source1 =
@"
#pragma warning disable CS0067 // The event 'I1.E01' is never used
interface I1
{
    virtual static event System.Action E01;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var e01 = module.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<EventSymbol>().Single();

                Assert.False(e01.IsAbstract);
                Assert.True(e01.IsVirtual);
                Assert.False(e01.IsSealed);
                Assert.True(e01.IsStatic);
                Assert.False(e01.IsOverride);

                int count = 0;
                foreach (var m01 in module.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<MethodSymbol>())
                {
                    Assert.False(m01.IsMetadataNewSlot());
                    Assert.False(m01.IsAbstract);
                    Assert.True(m01.IsMetadataVirtual());
                    Assert.False(m01.IsMetadataFinal);
                    Assert.True(m01.IsVirtual);
                    Assert.False(m01.IsSealed);
                    Assert.True(m01.IsStatic);
                    Assert.False(m01.IsOverride);

                    count++;
                }

                Assert.Equal(2, count);
            }
        }

        [Fact]
        public void DefineAbstractStaticEvent_02()
        {
            var source1 =
@"
interface I1
{
    abstract static event System.Action E01;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation1.VerifyDiagnostics(
                // (4,41): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static event System.Action E01;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "E01").WithLocation(4, 41)
                );
        }

        [Fact]
        public void DefineVirtualStaticEvent_02()
        {
            var source1 =
@"#pragma warning disable CS0067 // The event 'I1.E01' is never used
interface I1
{
    virtual  static event System.Action E01;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation1.VerifyDiagnostics(
                // (4,41): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     virtual  static event System.Action E01;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "E01").WithLocation(4, 41)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConstraintChecks_01(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static void M01()" + body + @"
}

public interface I2 : I1
{
}

public interface I3 : I2
{
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var source2 =
@"
class C1<T1> where T1 : I1
{
    void Test(C1<I2> x)
    {
    }
}

class C2
{
    void M<T2>() where T2 : I1 {}

    void Test(C2 x)
    {
        x.M<I2>();
    }
}

class C3<T3> where T3 : I2
{
    void Test(C3<I2> x, C3<I3> y)
    {
    }
}

class C4
{
    void M<T4>() where T4 : I2 {}

    void Test(C4 x)
    {
        x.M<I2>();
        x.M<I3>();
    }
}

class C5<T5> where T5 : I3
{
    void Test(C5<I3> y)
    {
    }
}

class C6
{
    void M<T6>() where T6 : I3 {}

    void Test(C6 x)
    {
        x.M<I3>();
    }
}

class C7<T7> where T7 : I1
{
    void Test(C7<I1> y)
    {
    }
}

class C8
{
    void M<T8>() where T8 : I1 {}

    void Test(C8 x)
    {
        x.M<I1>();
    }
}
";
            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.ToMetadataReference() });

            DiagnosticDescription[] expected;

            if (!isVirtual)
            {
                expected = new[] {
                    // (4,22): error CS8920: The interface 'I2' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                    //     void Test(C1<I2> x)
                    Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "x").WithArguments("I2", "I1.M01()").WithLocation(4, 22),
                    // (15,11): error CS8920: The interface 'I2' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                    //         x.M<I2>();
                    Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "M<I2>").WithArguments("I2", "I1.M01()").WithLocation(15, 11),
                    // (21,22): error CS8920: The interface 'I2' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                    //     void Test(C3<I2> x, C3<I3> y)
                    Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "x").WithArguments("I2", "I1.M01()").WithLocation(21, 22),
                    // (21,32): error CS8920: The interface 'I3' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                    //     void Test(C3<I2> x, C3<I3> y)
                    Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "y").WithArguments("I3", "I1.M01()").WithLocation(21, 32),
                    // (32,11): error CS8920: The interface 'I2' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                    //         x.M<I2>();
                    Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "M<I2>").WithArguments("I2", "I1.M01()").WithLocation(32, 11),
                    // (33,11): error CS8920: The interface 'I3' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                    //         x.M<I3>();
                    Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "M<I3>").WithArguments("I3", "I1.M01()").WithLocation(33, 11),
                    // (39,22): error CS8920: The interface 'I3' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                    //     void Test(C5<I3> y)
                    Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "y").WithArguments("I3", "I1.M01()").WithLocation(39, 22),
                    // (50,11): error CS8920: The interface 'I3' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                    //         x.M<I3>();
                    Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "M<I3>").WithArguments("I3", "I1.M01()").WithLocation(50, 11),
                    // (56,22): error CS8920: The interface 'I1' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                    //     void Test(C7<I1> y)
                    Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "y").WithArguments("I1", "I1.M01()").WithLocation(56, 22),
                    // (67,11): error CS8920: The interface 'I1' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                    //         x.M<I1>();
                    Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "M<I1>").WithArguments("I1", "I1.M01()").WithLocation(67, 11)
                };
            }
            else
            {
                expected = Array.Empty<DiagnosticDescription>();
            }

            compilation2.VerifyDiagnostics(expected);

            compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.EmitToImageReference() });

            compilation2.VerifyDiagnostics(expected);
        }

        [Theory]
        [CombinatorialData]
        public void ConstraintChecks_02(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static void M01()" + body + @"
}

public class C : I1
{
    public static void M01() {}
}

public struct S : I1
{
    public static void M01() {}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var source2 =
@"
class C1<T1> where T1 : I1
{
    void Test(C1<C> x, C1<S> y, C1<T1> z)
    {
    }
}

class C2
{
    public void M<T2>(C2 x) where T2 : I1
    {
        x.M<T2>(x);
    }

    void Test(C2 x)
    {
        x.M<C>(x);
        x.M<S>(x);
    }
}

class C3<T3> where T3 : I1
{
    void Test(C1<T3> z)
    {
    }
}

class C4
{
    void M<T4>(C2 x) where T4 : I1
    {
        x.M<T4>(x);
    }
}

class C5<T5>
{
    internal virtual void M<U5>() where U5 : T5 { }
}

class C6 : C5<I1>
{
    internal override void M<U6>() { base.M<U6>(); }
}
";
            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.ToMetadataReference() });

            if (isVirtual)
            {
                compilation2.VerifyEmitDiagnostics();
            }
            else
            {
                compilation2.VerifyEmitDiagnostics(
                    // (43,7): error CS8920: The interface 'I1' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                    // class C6 : C5<I1>
                    Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "C6").WithArguments("I1", "I1.M01()").WithLocation(43, 7)
                    );
            }

            compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.EmitToImageReference() });

            if (isVirtual)
            {
                compilation2.VerifyEmitDiagnostics();
            }
            else
            {
                compilation2.VerifyEmitDiagnostics(
                    // (43,7): error CS8920: The interface 'I1' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                    // class C6 : C5<I1>
                    Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "C6").WithArguments("I1", "I1.M01()").WithLocation(43, 7)
                    );
            }
        }

        [Fact]
        public void ConstraintChecks_03()
        {
            var source1 =
@"
public interface I1
{
    abstract static void M01();
}

public interface I2 : I1
{
    static void I1.M01() {}
}

public interface I3 : I2
{
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var source2 =
@"
class C1<T1> where T1 : I1
{
    void Test(C1<I2> x)
    {
    }
}

class C2
{
    void M<T2>() where T2 : I1 {}

    void Test(C2 x)
    {
        x.M<I2>();
    }
}

class C3<T3> where T3 : I2
{
    void Test(C3<I2> x, C3<I3> y)
    {
    }
}

class C4
{
    void M<T4>() where T4 : I2 {}

    void Test(C4 x)
    {
        x.M<I2>();
        x.M<I3>();
    }
}

class C5<T5> where T5 : I3
{
    void Test(C5<I3> y)
    {
    }
}

class C6
{
    void M<T6>() where T6 : I3 {}

    void Test(C6 x)
    {
        x.M<I3>();
    }
}

class C7<T7> where T7 : I1
{
    void Test(C7<I1> y)
    {
    }
}

class C8
{
    void M<T8>() where T8 : I1 {}

    void Test(C8 x)
    {
        x.M<I1>();
    }
}
";
            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.ToMetadataReference() });

            var expected = new[] {
                // (56,22): error CS8920: The interface 'I1' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                //     void Test(C7<I1> y)
                Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "y").WithArguments("I1", "I1.M01()").WithLocation(56, 22),
                // (67,11): error CS8920: The interface 'I1' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                //         x.M<I1>();
                Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "M<I1>").WithArguments("I1", "I1.M01()").WithLocation(67, 11)
                };

            compilation2.VerifyDiagnostics(expected);

            compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.EmitToImageReference() });

            compilation2.VerifyDiagnostics(expected);
        }

        [Fact]
        public void ConstraintChecks_04()
        {
            var source1 =
@"
public interface I1
{
    virtual static void M01(){}
}

public interface I2 : I1
{
    abstract static void I1.M01();
}

public interface I3 : I2
{
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var source2 =
@"
class C1<T1> where T1 : I1
{
    void Test(C1<I2> x)
    {
    }
}

class C2
{
    void M<T2>() where T2 : I1 {}

    void Test(C2 x)
    {
        x.M<I2>();
    }
}

class C3<T3> where T3 : I2
{
    void Test(C3<I2> x, C3<I3> y)
    {
    }
}

class C4
{
    void M<T4>() where T4 : I2 {}

    void Test(C4 x)
    {
        x.M<I2>();
        x.M<I3>();
    }
}

class C5<T5> where T5 : I3
{
    void Test(C5<I3> y)
    {
    }
}

class C6
{
    void M<T6>() where T6 : I3 {}

    void Test(C6 x)
    {
        x.M<I3>();
    }
}

class C7<T7> where T7 : I1
{
    void Test(C7<I1> y)
    {
    }
}

class C8
{
    void M<T8>() where T8 : I1 {}

    void Test(C8 x)
    {
        x.M<I1>();
    }
}
";
            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.ToMetadataReference() });

            var expected = new[] {
                // (4,22): error CS8920: The interface 'I2' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                //     void Test(C1<I2> x)
                Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "x").WithArguments("I2", "I1.M01()").WithLocation(4, 22),
                // (15,11): error CS8920: The interface 'I2' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                //         x.M<I2>();
                Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "M<I2>").WithArguments("I2", "I1.M01()").WithLocation(15, 11),
                // (21,22): error CS8920: The interface 'I2' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                //     void Test(C3<I2> x, C3<I3> y)
                Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "x").WithArguments("I2", "I1.M01()").WithLocation(21, 22),
                // (21,32): error CS8920: The interface 'I3' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                //     void Test(C3<I2> x, C3<I3> y)
                Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "y").WithArguments("I3", "I1.M01()").WithLocation(21, 32),
                // (32,11): error CS8920: The interface 'I2' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                //         x.M<I2>();
                Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "M<I2>").WithArguments("I2", "I1.M01()").WithLocation(32, 11),
                // (33,11): error CS8920: The interface 'I3' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                //         x.M<I3>();
                Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "M<I3>").WithArguments("I3", "I1.M01()").WithLocation(33, 11),
                // (39,22): error CS8920: The interface 'I3' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                //     void Test(C5<I3> y)
                Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "y").WithArguments("I3", "I1.M01()").WithLocation(39, 22),
                // (50,11): error CS8920: The interface 'I3' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                //         x.M<I3>();
                Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "M<I3>").WithArguments("I3", "I1.M01()").WithLocation(50, 11)
                };

            compilation2.VerifyDiagnostics(expected);

            compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.EmitToImageReference() });

            compilation2.VerifyDiagnostics(expected);
        }

        [Fact]
        public void ConstraintChecks_05()
        {
            var source1 =
@"
public interface I1
{
    virtual static void M01(){}
}

public interface I2 : I1
{
    static void I1.M01(){}
}

public interface I4 : I1
{
    abstract static void I1.M01();
}

public interface I3 : I2, I4
{
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var source2 =
@"
class C1<T1> where T1 : I1
{
    void Test(C1<I2> x)
    {
    }
}

class C2
{
    void M<T2>() where T2 : I1 {}

    void Test(C2 x)
    {
        x.M<I2>();
    }
}

class C3<T3> where T3 : I2
{
    void Test(C3<I2> x, C3<I3> y)
    {
    }
}

class C4
{
    void M<T4>() where T4 : I2 {}

    void Test(C4 x)
    {
        x.M<I2>();
        x.M<I3>();
    }
}

class C5<T5> where T5 : I3
{
    void Test(C5<I3> y)
    {
    }
}

class C6
{
    void M<T6>() where T6 : I3 {}

    void Test(C6 x)
    {
        x.M<I3>();
    }
}

class C7<T7> where T7 : I1
{
    void Test(C7<I1> y)
    {
    }
}

class C8
{
    void M<T8>() where T8 : I1 {}

    void Test(C8 x)
    {
        x.M<I1>();
    }
}
";
            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.ToMetadataReference() });

            var expected = new[] {
                // (21,32): error CS8920: The interface 'I3' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                //     void Test(C3<I2> x, C3<I3> y)
                Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "y").WithArguments("I3", "I1.M01()").WithLocation(21, 32),
                // (33,11): error CS8920: The interface 'I3' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                //         x.M<I3>();
                Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "M<I3>").WithArguments("I3", "I1.M01()").WithLocation(33, 11),
                // (39,22): error CS8920: The interface 'I3' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                //     void Test(C5<I3> y)
                Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "y").WithArguments("I3", "I1.M01()").WithLocation(39, 22),
                // (50,11): error CS8920: The interface 'I3' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                //         x.M<I3>();
                Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "M<I3>").WithArguments("I3", "I1.M01()").WithLocation(50, 11)
                };

            compilation2.VerifyDiagnostics(expected);

            compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.EmitToImageReference() });

            compilation2.VerifyDiagnostics(expected);
        }

        [Fact]
        public void ConstraintChecks_06()
        {
            var source1 =
@"
public interface I1
{
    virtual static void M01(){}
}

public interface I2 : I1
{
    static void I1.M01(){}
}

public interface I4 : I1
{
    static void I1.M01(){}
}

public interface I3 : I2, I4
{
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var source2 =
@"
class C1<T1> where T1 : I1
{
    void Test(C1<I2> x)
    {
    }
}

class C2
{
    void M<T2>() where T2 : I1 {}

    void Test(C2 x)
    {
        x.M<I2>();
    }
}

class C3<T3> where T3 : I2
{
    void Test(C3<I2> x, C3<I3> y)
    {
    }
}

class C4
{
    void M<T4>() where T4 : I2 {}

    void Test(C4 x)
    {
        x.M<I2>();
        x.M<I3>();
    }
}

class C5<T5> where T5 : I3
{
    void Test(C5<I3> y)
    {
    }
}

class C6
{
    void M<T6>() where T6 : I3 {}

    void Test(C6 x)
    {
        x.M<I3>();
    }
}

class C7<T7> where T7 : I1
{
    void Test(C7<I1> y)
    {
    }
}

class C8
{
    void M<T8>() where T8 : I1 {}

    void Test(C8 x)
    {
        x.M<I1>();
    }
}
";
            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.ToMetadataReference() });

            var expected = new[] {
                // (21,32): error CS8920: The interface 'I3' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                //     void Test(C3<I2> x, C3<I3> y)
                Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "y").WithArguments("I3", "I1.M01()").WithLocation(21, 32),
                // (33,11): error CS8920: The interface 'I3' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                //         x.M<I3>();
                Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "M<I3>").WithArguments("I3", "I1.M01()").WithLocation(33, 11),
                // (39,22): error CS8920: The interface 'I3' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                //     void Test(C5<I3> y)
                Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "y").WithArguments("I3", "I1.M01()").WithLocation(39, 22),
                // (50,11): error CS8920: The interface 'I3' cannot be used as type argument. Static member 'I1.M01()' does not have a most specific implementation in the interface.
                //         x.M<I3>();
                Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "M<I3>").WithArguments("I3", "I1.M01()").WithLocation(50, 11)
                };

            compilation2.VerifyDiagnostics(expected);

            compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.EmitToImageReference() });

            compilation2.VerifyDiagnostics(expected);
        }

        [Fact]
        public void ConstraintChecks_07()
        {
            var source1 =
@"
abstract class C<T>
{
    public abstract void M<U>() where U : T;
    public void M0() { M<T>(); }
}
interface I
{
    static abstract string P { get; }
}
class D : C<I>
{
    public override void M<U>() => System.Console.WriteLine(U.P);
    
    static void Main()
    {
        new D().M0();
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (11,7): error CS8920: The interface 'I' cannot be used as type argument. Static member 'I.P' does not have a most specific implementation in the interface.
                // class D : C<I>
                Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "D").WithArguments("I", "I.P").WithLocation(11, 7)
                );
        }

        [Theory]
        [CombinatorialData]
        public void VarianceSafety_01(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
interface I2<out T1, in T2>
{
    " + modifier + @" static T1 P1 { get" + body + @" }
    " + modifier + @" static T2 P2 { get" + body + @" }
    " + modifier + @" static T1 P3 { set" + body + @" }
    " + modifier + @" static T2 P4 { set" + body + @" }
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);
            compilation1.VerifyDiagnostics(
                // (5,21): error CS1961: Invalid variance: The type parameter 'T2' must be covariantly valid on 'I2<T1, T2>.P2'. 'T2' is contravariant.
                //     abstract static T2 P2 { get; }
                Diagnostic(ErrorCode.ERR_UnexpectedVariance, "T2").WithArguments("I2<T1, T2>.P2", "T2", "contravariant", "covariantly").WithLocation(5, 21),
                // (6,21): error CS1961: Invalid variance: The type parameter 'T1' must be contravariantly valid on 'I2<T1, T2>.P3'. 'T1' is covariant.
                //     abstract static T1 P3 { set; }
                Diagnostic(ErrorCode.ERR_UnexpectedVariance, "T1").WithArguments("I2<T1, T2>.P3", "T1", "covariant", "contravariantly").WithLocation(6, 21)
                );
        }

        [Theory]
        [CombinatorialData]
        public void VarianceSafety_02(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
interface I2<out T1, in T2>
{
    " + modifier + @" static T1 M1()" + body + @"
    " + modifier + @" static T2 M2()" + body + @"
    " + modifier + @" static void M3(T1 x)" + body + @"
    " + modifier + @" static void M4(T2 x)" + body + @"
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);
            compilation1.VerifyDiagnostics(
                // (5,21): error CS1961: Invalid variance: The type parameter 'T2' must be covariantly valid on 'I2<T1, T2>.M2()'. 'T2' is contravariant.
                //     abstract static T2 M2();
                Diagnostic(ErrorCode.ERR_UnexpectedVariance, "T2").WithArguments("I2<T1, T2>.M2()", "T2", "contravariant", "covariantly").WithLocation(5, 21),
                // (6,29): error CS1961: Invalid variance: The type parameter 'T1' must be contravariantly valid on 'I2<T1, T2>.M3(T1)'. 'T1' is covariant.
                //     abstract static void M3(T1 x);
                Diagnostic(ErrorCode.ERR_UnexpectedVariance, "T1").WithArguments("I2<T1, T2>.M3(T1)", "T1", "covariant", "contravariantly").WithLocation(6, 29)
                );
        }

        [Theory]
        [CombinatorialData]
        public void VarianceSafety_03(bool isVirtual)
        {
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"#pragma warning disable CS0067 // The event 'I2<T1, T2>.E1' is never used
interface I2<out T1, in T2>
{
    " + modifier + @" static event System.Action<System.Func<T1>> E1;
    " + modifier + @" static event System.Action<System.Func<T2>> E2;
    " + modifier + @" static event System.Action<System.Action<T1>> E3;
    " + modifier + @" static event System.Action<System.Action<T2>> E4;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);
            compilation1.VerifyDiagnostics(
                // (5,58): error CS1961: Invalid variance: The type parameter 'T2' must be covariantly valid on 'I2<T1, T2>.E2'. 'T2' is contravariant.
                //     abstract static event System.Action<System.Func<T2>> E2;
                Diagnostic(ErrorCode.ERR_UnexpectedVariance, "E2").WithArguments("I2<T1, T2>.E2", "T2", "contravariant", "covariantly").WithLocation(5, 58),
                // (6,60): error CS1961: Invalid variance: The type parameter 'T1' must be contravariantly valid on 'I2<T1, T2>.E3'. 'T1' is covariant.
                //     abstract static event System.Action<System.Action<T1>> E3;
                Diagnostic(ErrorCode.ERR_UnexpectedVariance, "E3").WithArguments("I2<T1, T2>.E3", "T1", "covariant", "contravariantly").WithLocation(6, 60)
                );
        }

        [Theory]
        [CombinatorialData]
        public void VarianceSafety_04(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
interface I2<out T2>
{
    " + modifier + @" static int operator +(I2<T2> x)" + body + @"
}

interface I3<out T3>
{
    " + modifier + @" static int operator +(I3<T3> x)" + body + @"
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);
            compilation1.VerifyDiagnostics(
                // (4,36): error CS1961: Invalid variance: The type parameter 'T2' must be contravariantly valid on 'I2<T2>.operator +(I2<T2>)'. 'T2' is covariant.
                //     abstract static int operator +(I2<T2> x);
                Diagnostic(ErrorCode.ERR_UnexpectedVariance, "I2<T2>").WithArguments("I2<T2>.operator +(I2<T2>)", "T2", "covariant", "contravariantly").WithLocation(4, 36),
                // (9,36): error CS1961: Invalid variance: The type parameter 'T3' must be contravariantly valid on 'I3<T3>.operator +(I3<T3>)'. 'T3' is covariant.
                //     abstract static int operator +(I3<T3> x);
                Diagnostic(ErrorCode.ERR_UnexpectedVariance, "I3<T3>").WithArguments("I3<T3>.operator +(I3<T3>)", "T3", "covariant", "contravariantly").WithLocation(9, 36)
                );
        }

        [Theory]
        [CombinatorialData]
        public void OperatorSignature_01([CombinatorialValues("+", "-", "!", "~", "true", "false")] string op, bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
interface I1<T1> where T1 : I1<T1>
{
    static bool operator " + op + @"(T1 x) => throw null;
}

interface I2<T2> where T2 : struct, I2<T2>
{
    static bool operator " + op + @"(T2? x) => throw null;
}

interface I3<T3> where T3 : I3<T3>
{
    static " + modifier + @" bool operator " + op + @"(T3 x)" + body + @"
}

interface I4<T4> where T4 : struct, I4<T4>
{
    static " + modifier + @" bool operator " + op + @"(T4? x)" + body + @"
}

class C5<T5> where T5 : C5<T5>.I6
{
    public interface I6
    {
        static " + modifier + @" bool operator " + op + @"(T5 x)" + body + @"
    }
}

interface I7<T71, T72> where T72 : I7<T71, T72> where T71 : T72
{
    static " + modifier + @" bool operator " + op + @"(T71 x)" + body + @"
}

interface I8<T8> where T8 : I9<T8>
{
    static " + modifier + @" bool operator " + op + @"(T8 x)" + body + @"
}

interface I9<T9> : I8<T9> where T9 : I9<T9> {}

interface I10<T10> where T10 : C11<T10>
{
    static " + modifier + @" bool operator " + op + @"(T10 x)" + body + @"
}

class C11<T11> : I10<T11> where T11 : C11<T11> {}

interface I12
{
    static " + modifier + @" bool operator " + op + @"(int x)" + body + @"
}

interface I13
{
    static " + modifier + @" bool operator " + op + @"(I13 x)" + body + @"
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);
            compilation1.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_UnimplementedInterfaceMember)).Verify(
                // (4,26): error CS0562: The parameter of a unary operator must be the containing type
                //     static bool operator +(T1 x) => throw null;
                Diagnostic(ErrorCode.ERR_BadUnaryOperatorSignature, op).WithLocation(4, 26),
                // (9,26): error CS0562: The parameter of a unary operator must be the containing type
                //     static bool operator +(T2? x) => throw null;
                Diagnostic(ErrorCode.ERR_BadUnaryOperatorSignature, op).WithLocation(9, 26),
                // (26,39): error CS8921: The parameter of a unary operator must be the containing type, or its type parameter constrained to it.
                //         static abstract bool operator +(T5 x);
                Diagnostic(ErrorCode.ERR_BadAbstractUnaryOperatorSignature, op).WithLocation(26, 39),
                // (32,35): error CS8921: The parameter of a unary operator must be the containing type, or its type parameter constrained to it.
                //     static abstract bool operator +(T71 x);
                Diagnostic(ErrorCode.ERR_BadAbstractUnaryOperatorSignature, op).WithLocation(32, 35),
                // (37,35): error CS8921: The parameter of a unary operator must be the containing type, or its type parameter constrained to it.
                //     static abstract bool operator +(T8 x);
                Diagnostic(ErrorCode.ERR_BadAbstractUnaryOperatorSignature, op).WithLocation(37, 35),
                // (44,35): error CS8921: The parameter of a unary operator must be the containing type, or its type parameter constrained to it.
                //     static abstract bool operator +(T10 x);
                Diagnostic(ErrorCode.ERR_BadAbstractUnaryOperatorSignature, op).WithLocation(44, 35),
                // (51,35): error CS8921: The parameter of a unary operator must be the containing type, or its type parameter constrained to it.
                //     static abstract bool operator false(int x);
                Diagnostic(ErrorCode.ERR_BadAbstractUnaryOperatorSignature, op).WithLocation(51, 35)
                );
        }

        [Theory]
        [CombinatorialData]
        public void OperatorSignature_02([CombinatorialValues("++", "--")] string op, bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
interface I1<T1> where T1 : I1<T1>
{
    static T1 operator " + op + @"(T1 x) => throw null;
}

interface I2<T2> where T2 : struct, I2<T2>
{
    static T2? operator " + op + @"(T2? x) => throw null;
}

interface I3<T3> where T3 : I3<T3>
{
    static " + modifier + @" T3 operator " + op + @"(T3 x)" + body + @"
}

interface I4<T4> where T4 : struct, I4<T4>
{
    static " + modifier + @" T4? operator " + op + @"(T4? x)" + body + @"
}

class C5<T5> where T5 : C5<T5>.I6
{
    public interface I6
    {
        static " + modifier + @" T5 operator " + op + @"(T5 x)" + body + @"
    }
}

interface I7<T71, T72> where T72 : I7<T71, T72> where T71 : T72
{
    static " + modifier + @" T71 operator " + op + @"(T71 x)" + body + @"
}

interface I8<T8> where T8 : I9<T8>
{
    static " + modifier + @" T8 operator " + op + @"(T8 x)" + body + @"
}

interface I9<T9> : I8<T9> where T9 : I9<T9> {}

interface I10<T10> where T10 : C11<T10>
{
    static " + modifier + @" T10 operator " + op + @"(T10 x)" + body + @"
}

class C11<T11> : I10<T11> where T11 : C11<T11> {}

interface I12
{
    static " + modifier + @" int operator " + op + @"(int x)" + body + @"
}

interface I13
{
    static " + modifier + @" I13 operator " + op + @"(I13 x)" + body + @"
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);
            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_UnimplementedInterfaceMember).Verify(
                // (4,24): error CS0559: The parameter type for ++ or -- operator must be the containing type
                //     static T1 operator ++(T1 x) => throw null;
                Diagnostic(ErrorCode.ERR_BadIncDecSignature, op).WithLocation(4, 24),
                // (9,25): error CS0559: The parameter type for ++ or -- operator must be the containing type
                //     static T2? operator ++(T2? x) => throw null;
                Diagnostic(ErrorCode.ERR_BadIncDecSignature, op).WithLocation(9, 25),
                // (26,37): error CS8922: The parameter type for ++ or -- operator must be the containing type, or its type parameter constrained to it.
                //         static abstract T5 operator ++(T5 x);
                Diagnostic(ErrorCode.ERR_BadAbstractIncDecSignature, op).WithLocation(26, 37),
                // (32,34): error CS8922: The parameter type for ++ or -- operator must be the containing type, or its type parameter constrained to it.
                //     static abstract T71 operator ++(T71 x);
                Diagnostic(ErrorCode.ERR_BadAbstractIncDecSignature, op).WithLocation(32, 34),
                // (37,33): error CS8922: The parameter type for ++ or -- operator must be the containing type, or its type parameter constrained to it.
                //     static abstract T8 operator ++(T8 x);
                Diagnostic(ErrorCode.ERR_BadAbstractIncDecSignature, op).WithLocation(37, 33),
                // (44,34): error CS8922: The parameter type for ++ or -- operator must be the containing type, or its type parameter constrained to it.
                //     static abstract T10 operator ++(T10 x);
                Diagnostic(ErrorCode.ERR_BadAbstractIncDecSignature, op).WithLocation(44, 34),
                // (51,34): error CS8922: The parameter type for ++ or -- operator must be the containing type, or its type parameter constrained to it.
                //     static abstract int operator ++(int x);
                Diagnostic(ErrorCode.ERR_BadAbstractIncDecSignature, op).WithLocation(51, 34)
                );
        }

        [Theory]
        [CombinatorialData]
        public void OperatorSignature_03([CombinatorialValues("++", "--")] string op, bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
interface I1<T1> where T1 : I1<T1>
{
    static T1 operator " + op + @"(I1<T1> x) => throw null;
}

interface I2<T2> where T2 : struct, I2<T2>
{
    static T2? operator " + op + @"(I2<T2> x) => throw null;
}

interface I3<T3> where T3 : I3<T3>
{
    static " + modifier + @" T3 operator " + op + @"(I3<T3> x)" + body + @"
}

interface I4<T4> where T4 : struct, I4<T4>
{
    static " + modifier + @" T4? operator " + op + @"(I4<T4> x)" + body + @"
}

class C5<T5> where T5 : C5<T5>.I6
{
    public interface I6
    {
        static " + modifier + @" T5 operator " + op + @"(I6 x)" + body + @"
    }
}

interface I7<T71, T72> where T72 : I7<T71, T72> where T71 : T72
{
    static " + modifier + @" T71 operator " + op + @"(I7<T71, T72> x)" + body + @"
}

interface I8<T8> where T8 : I9<T8>
{
    static " + modifier + @" T8 operator " + op + @"(I8<T8> x)" + body + @"
}

interface I9<T9> : I8<T9> where T9 : I9<T9> {}

interface I10<T10> where T10 : C11<T10>
{
    static " + modifier + @" T10 operator " + op + @"(I10<T10> x)" + body + @"
}

class C11<T11> : I10<T11> where T11 : C11<T11> {}

interface I12
{
    static " + modifier + @" int operator " + op + @"(I12 x)" + body + @"
}

interface I13<T13> where T13 : struct, I13<T13>
{
    static " + modifier + @" T13? operator " + op + @"(T13 x)" + body + @"
}

interface I14<T14> where T14 : struct, I14<T14>
{
    static " + modifier + @" T14 operator " + op + @"(T14? x)" + body + @"
}

interface I15<T151, T152> where T151 : I15<T151, T152> where T152 : I15<T151, T152>
{
    static " + modifier + @" T151 operator " + op + @"(T152 x)" + body + @"
}

";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);
            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_UnimplementedInterfaceMember).Verify(
                // (4,24): error CS0448: The return type for ++ or -- operator must match the parameter type or be derived from the parameter type
                //     static T1 operator ++(I1<T1> x) => throw null;
                Diagnostic(ErrorCode.ERR_BadIncDecRetType, op).WithLocation(4, 24),
                // (9,25): error CS0448: The return type for ++ or -- operator must match the parameter type or be derived from the parameter type
                //     static T2? operator ++(I2<T2> x) => throw null;
                Diagnostic(ErrorCode.ERR_BadIncDecRetType, op).WithLocation(9, 25),
                // (19,34): error CS8923: The return type for ++ or -- operator must either match the parameter type, or be derived from the parameter type, or be the containing type's type parameter constrained to it unless the parameter type is a different type parameter.
                //     static abstract T4? operator ++(I4<T4> x);
                Diagnostic(ErrorCode.ERR_BadAbstractIncDecRetType, op).WithLocation(19, 34),
                // (26,37): error CS8923: The return type for ++ or -- operator must either match the parameter type, or be derived from the parameter type, or be the containing type's type parameter constrained to it unless the parameter type is a different type parameter.
                //         static abstract T5 operator ++(I6 x);
                Diagnostic(ErrorCode.ERR_BadAbstractIncDecRetType, op).WithLocation(26, 37),
                // (32,34): error CS8923: The return type for ++ or -- operator must either match the parameter type, or be derived from the parameter type, or be the containing type's type parameter constrained to it unless the parameter type is a different type parameter.
                //     static abstract T71 operator ++(I7<T71, T72> x);
                Diagnostic(ErrorCode.ERR_BadAbstractIncDecRetType, op).WithLocation(32, 34),
                // (37,33): error CS8923: The return type for ++ or -- operator must either match the parameter type, or be derived from the parameter type, or be the containing type's type parameter constrained to it unless the parameter type is a different type parameter.
                //     static abstract T8 operator ++(I8<T8> x);
                Diagnostic(ErrorCode.ERR_BadAbstractIncDecRetType, op).WithLocation(37, 33),
                // (44,34): error CS8923: The return type for ++ or -- operator must either match the parameter type, or be derived from the parameter type, or be the containing type's type parameter constrained to it unless the parameter type is a different type parameter.
                //     static abstract T10 operator ++(I10<T10> x);
                Diagnostic(ErrorCode.ERR_BadAbstractIncDecRetType, op).WithLocation(44, 34),
                // (51,34): error CS8923: The return type for ++ or -- operator must either match the parameter type, or be derived from the parameter type, or be the containing type's type parameter constrained to it unless the parameter type is a different type parameter.
                //     static abstract int operator ++(I12 x);
                Diagnostic(ErrorCode.ERR_BadAbstractIncDecRetType, op).WithLocation(51, 34),
                // (56,35): error CS8923: The return type for ++ or -- operator must either match the parameter type, or be derived from the parameter type, or be the containing type's type parameter constrained to it unless the parameter type is a different type parameter.
                //     static abstract T13? operator ++(T13 x);
                Diagnostic(ErrorCode.ERR_BadAbstractIncDecRetType, op).WithLocation(56, 35),
                // (61,34): error CS8923: The return type for ++ or -- operator must either match the parameter type, or be derived from the parameter type, or be the containing type's type parameter constrained to it unless the parameter type is a different type parameter.
                //     static abstract T14 operator ++(T14? x);
                Diagnostic(ErrorCode.ERR_BadAbstractIncDecRetType, op).WithLocation(61, 34),
                // (66,35): error CS8923: The return type for ++ or -- operator must either match the parameter type, or be derived from the parameter type, or be the containing type's type parameter constrained to it unless the parameter type is a different type parameter.
                //     static abstract T151 operator ++(T152 x);
                Diagnostic(ErrorCode.ERR_BadAbstractIncDecRetType, op).WithLocation(66, 35)
                );
        }

        [Theory]
        [CombinatorialData]
        public void OperatorSignature_04([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<", ">", "<=", ">=")] string op, bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
interface I1<T1> where T1 : I1<T1>
{
    static bool operator " + op + @"(T1 x, bool y) => throw null;
}

interface I2<T2> where T2 : struct, I2<T2>
{
    static bool operator " + op + @"(T2? x, bool y) => throw null;
}

interface I3<T3> where T3 : I3<T3>
{
    static " + modifier + @" bool operator " + op + @"(T3 x, bool y)" + body + @"
}

interface I4<T4> where T4 : struct, I4<T4>
{
    static " + modifier + @" bool operator " + op + @"(T4? x, bool y)" + body + @"
}

class C5<T5> where T5 : C5<T5>.I6
{
    public interface I6
    {
        static " + modifier + @" bool operator " + op + @"(T5 x, bool y)" + body + @"
    }
}

interface I7<T71, T72> where T72 : I7<T71, T72> where T71 : T72
{
    static " + modifier + @" bool operator " + op + @"(T71 x, bool y)" + body + @"
}

interface I8<T8> where T8 : I9<T8>
{
    static " + modifier + @" bool operator " + op + @"(T8 x, bool y)" + body + @"
}

interface I9<T9> : I8<T9> where T9 : I9<T9> {}

interface I10<T10> where T10 : C11<T10>
{
    static " + modifier + @" bool operator " + op + @"(T10 x, bool y)" + body + @"
}

class C11<T11> : I10<T11> where T11 : C11<T11> {}

interface I12
{
    static " + modifier + @" bool operator " + op + @"(int x, bool y)" + body + @"
}

interface I13
{
    static " + modifier + @" bool operator " + op + @"(I13 x, bool y)" + body + @"
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);
            compilation1.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators or (int)ErrorCode.ERR_UnimplementedInterfaceMember)).Verify(
                // (4,26): error CS0563: One of the parameters of a binary operator must be the containing type
                //     static bool operator +(T1 x, bool y) => throw null;
                Diagnostic(ErrorCode.ERR_BadBinaryOperatorSignature, op).WithLocation(4, 26),
                // (9,26): error CS0563: One of the parameters of a binary operator must be the containing type
                //     static bool operator +(T2? x, bool y) => throw null;
                Diagnostic(ErrorCode.ERR_BadBinaryOperatorSignature, op).WithLocation(9, 26),
                // (26,39): error CS8924: One of the parameters of a binary operator must be the containing type, or its type parameter constrained to it.
                //         static abstract bool operator +(T5 x, bool y);
                Diagnostic(ErrorCode.ERR_BadAbstractBinaryOperatorSignature, op).WithLocation(26, 39),
                // (32,35): error CS8924: One of the parameters of a binary operator must be the containing type, or its type parameter constrained to it.
                //     static abstract bool operator +(T71 x, bool y);
                Diagnostic(ErrorCode.ERR_BadAbstractBinaryOperatorSignature, op).WithLocation(32, 35),
                // (37,35): error CS8924: One of the parameters of a binary operator must be the containing type, or its type parameter constrained to it.
                //     static abstract bool operator +(T8 x, bool y);
                Diagnostic(ErrorCode.ERR_BadAbstractBinaryOperatorSignature, op).WithLocation(37, 35),
                // (44,35): error CS8924: One of the parameters of a binary operator must be the containing type, or its type parameter constrained to it.
                //     static abstract bool operator +(T10 x, bool y);
                Diagnostic(ErrorCode.ERR_BadAbstractBinaryOperatorSignature, op).WithLocation(44, 35),
                // (51,35): error CS8924: One of the parameters of a binary operator must be the containing type, or its type parameter constrained to it.
                //     static abstract bool operator +(int x, bool y);
                Diagnostic(ErrorCode.ERR_BadAbstractBinaryOperatorSignature, op).WithLocation(51, 35)
                );
        }

        [Theory]
        [CombinatorialData]
        public void OperatorSignature_05([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<", ">", "<=", ">=")] string op, bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
interface I1<T1> where T1 : I1<T1>
{
    static bool operator " + op + @"(bool y, T1 x) => throw null;
}

interface I2<T2> where T2 : struct, I2<T2>
{
    static bool operator " + op + @"(bool y, T2? x) => throw null;
}

interface I3<T3> where T3 : I3<T3>
{
    static " + modifier + @" bool operator " + op + @"(bool y, T3 x)" + body + @"
}

interface I4<T4> where T4 : struct, I4<T4>
{
    static " + modifier + @" bool operator " + op + @"(bool y, T4? x)" + body + @"
}

class C5<T5> where T5 : C5<T5>.I6
{
    public interface I6
    {
        static " + modifier + @" bool operator " + op + @"(bool y, T5 x)" + body + @"
    }
}

interface I7<T71, T72> where T72 : I7<T71, T72> where T71 : T72
{
    static " + modifier + @" bool operator " + op + @"(bool y, T71 x)" + body + @"
}

interface I8<T8> where T8 : I9<T8>
{
    static " + modifier + @" bool operator " + op + @"(bool y, T8 x)" + body + @"
}

interface I9<T9> : I8<T9> where T9 : I9<T9> {}

interface I10<T10> where T10 : C11<T10>
{
    static " + modifier + @" bool operator " + op + @"(bool y, T10 x)" + body + @"
}

class C11<T11> : I10<T11> where T11 : C11<T11> {}

interface I12
{
    static " + modifier + @" bool operator " + op + @"(bool y, int x)" + body + @"
}

interface I13
{
    static " + modifier + @" bool operator " + op + @"(bool y, I13 x)" + body + @"
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);
            compilation1.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators or (int)ErrorCode.ERR_UnimplementedInterfaceMember)).Verify(
                // (4,26): error CS0563: One of the parameters of a binary operator must be the containing type
                //     static bool operator +(bool y, T1 x) => throw null;
                Diagnostic(ErrorCode.ERR_BadBinaryOperatorSignature, op).WithLocation(4, 26),
                // (9,26): error CS0563: One of the parameters of a binary operator must be the containing type
                //     static bool operator +(bool y, T2? x) => throw null;
                Diagnostic(ErrorCode.ERR_BadBinaryOperatorSignature, op).WithLocation(9, 26),
                // (26,39): error CS8924: One of the parameters of a binary operator must be the containing type, or its type parameter constrained to it.
                //         static abstract bool operator +(bool y, T5 x);
                Diagnostic(ErrorCode.ERR_BadAbstractBinaryOperatorSignature, op).WithLocation(26, 39),
                // (32,35): error CS8924: One of the parameters of a binary operator must be the containing type, or its type parameter constrained to it.
                //     static abstract bool operator +(bool y, T71 x);
                Diagnostic(ErrorCode.ERR_BadAbstractBinaryOperatorSignature, op).WithLocation(32, 35),
                // (37,35): error CS8924: One of the parameters of a binary operator must be the containing type, or its type parameter constrained to it.
                //     static abstract bool operator +(bool y, T8 x);
                Diagnostic(ErrorCode.ERR_BadAbstractBinaryOperatorSignature, op).WithLocation(37, 35),
                // (44,35): error CS8924: One of the parameters of a binary operator must be the containing type, or its type parameter constrained to it.
                //     static abstract bool operator +(bool y, T10 x);
                Diagnostic(ErrorCode.ERR_BadAbstractBinaryOperatorSignature, op).WithLocation(44, 35),
                // (51,35): error CS8924: One of the parameters of a binary operator must be the containing type, or its type parameter constrained to it.
                //     static abstract bool operator +(bool y, int x);
                Diagnostic(ErrorCode.ERR_BadAbstractBinaryOperatorSignature, op).WithLocation(51, 35)
                );
        }

        [Theory]
        [CombinatorialData]
        public void OperatorSignature_06([CombinatorialValues("<<", ">>", ">>>")] string op, bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
interface I1<T1> where T1 : I1<T1>
{
    static bool operator " + op + @"(T1 x, int y) => throw null;
}

interface I2<T2> where T2 : struct, I2<T2>
{
    static bool operator " + op + @"(T2? x, int y) => throw null;
}

interface I3<T3> where T3 : I3<T3>
{
    static " + modifier + @" bool operator " + op + @"(T3 x, int y)" + body + @"
}

interface I4<T4> where T4 : struct, I4<T4>
{
    static " + modifier + @" bool operator " + op + @"(T4? x, int y)" + body + @"
}

class C5<T5> where T5 : C5<T5>.I6
{
    public interface I6
    {
        static " + modifier + @" bool operator " + op + @"(T5 x, int y)" + body + @"
    }
}

interface I7<T71, T72> where T72 : I7<T71, T72> where T71 : T72
{
    static " + modifier + @" bool operator " + op + @"(T71 x, int y)" + body + @"
}

interface I8<T8> where T8 : I9<T8>
{
    static " + modifier + @" bool operator " + op + @"(T8 x, int y)" + body + @"
}

interface I9<T9> : I8<T9> where T9 : I9<T9> {}

interface I10<T10> where T10 : C11<T10>
{
    static " + modifier + @" bool operator " + op + @"(T10 x, int y)" + body + @"
}

class C11<T11> : I10<T11> where T11 : C11<T11> {}

interface I12
{
    static " + modifier + @" bool operator " + op + @"(int x, int y)" + body + @"
}

interface I13
{
    static " + modifier + @" bool operator " + op + @"(I13 x, int y)" + body + @"
}

interface I14
{
    static " + modifier + @" bool operator " + op + @"(I14 x, bool y)" + body + @"
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);
            compilation1.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_UnimplementedInterfaceMember)).Verify(
                // (4,26): error CS0564: The first operand of an overloaded shift operator must have the same type as the containing type
                //     static bool operator <<(T1 x, int y) => throw null;
                Diagnostic(ErrorCode.ERR_BadShiftOperatorSignature, op).WithLocation(4, 26),
                // (9,26): error CS0564: The first operand of an overloaded shift operator must have the same type as the containing type
                //     static bool operator <<(T2? x, int y) => throw null;
                Diagnostic(ErrorCode.ERR_BadShiftOperatorSignature, op).WithLocation(9, 26),
                // (26,39): error CS8925: The first operand of an overloaded shift operator must have the same type as the containing type or its type parameter constrained to it
                //         static abstract bool operator <<(T5 x, int y);
                Diagnostic(ErrorCode.ERR_BadAbstractShiftOperatorSignature, op).WithLocation(26, 39),
                // (32,35): error CS8925: The first operand of an overloaded shift operator must have the same type as the containing type or its type parameter constrained to it
                //     static abstract bool operator <<(T71 x, int y);
                Diagnostic(ErrorCode.ERR_BadAbstractShiftOperatorSignature, op).WithLocation(32, 35),
                // (37,35): error CS8925: The first operand of an overloaded shift operator must have the same type as the containing type or its type parameter constrained to it
                //     static abstract bool operator <<(T8 x, int y);
                Diagnostic(ErrorCode.ERR_BadAbstractShiftOperatorSignature, op).WithLocation(37, 35),
                // (44,35): error CS8925: The first operand of an overloaded shift operator must have the same type as the containing type or its type parameter constrained to it
                //     static abstract bool operator <<(T10 x, int y);
                Diagnostic(ErrorCode.ERR_BadAbstractShiftOperatorSignature, op).WithLocation(44, 35),
                // (51,35): error CS8925: The first operand of an overloaded shift operator must have the same type as the containing type or its type parameter constrained to it
                //     static abstract bool operator <<(int x, int y);
                Diagnostic(ErrorCode.ERR_BadAbstractShiftOperatorSignature, op).WithLocation(51, 35)
                );
        }

        [Theory]
        [CombinatorialData]
        public void OperatorSignature_07([CombinatorialValues("implicit", "explicit")] string op, bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
interface I1<T1> where T1 : I1<T1>
{
    " + modifier + @" static " + op + @" operator T1(T1 y)" + body + @"
}

interface I2<T2> where T2 : I2<T2>
{
    " + modifier + @" static " + op + @" operator dynamic(T2 y)" + body + @"
}

interface I3<T3> where T3 : I3<T3>
{
    static " + modifier + @" " + op + @" operator T3(bool y)" + body + @"
}

interface I4<T4> where T4 : struct, I4<T4>
{
    static " + modifier + @" " + op + @" operator T4?(bool y)" + body + @"
}

class C5<T5> where T5 : C5<T5>.I6
{
    public interface I6
    {
        static " + modifier + @" " + op + @" operator T5 (bool y)" + body + @"
    }
}

interface I7<T71, T72> where T72 : I7<T71, T72> where T71 : T72
{
    static " + modifier + @" " + op + @" operator T71 (bool y)" + body + @"
}

interface I8<T8> where T8 : I9<T8>
{
    static " + modifier + @" " + op + @" operator T8(bool y)" + body + @"
}

interface I9<T9> : I8<T9> where T9 : I9<T9> {}

interface I10<T10> where T10 : C11<T10>
{
    static " + modifier + @" " + op + @" operator T10(bool y)" + body + @"
}

class C11<T11> : I10<T11> where T11 : C11<T11> {}

interface I12
{
    static " + modifier + @" " + op + @" operator int(bool y)" + body + @"
}

interface I13
{
    static " + modifier + @" " + op + @" operator I13(bool y)" + body + @"
}

interface I14<T14> where T14 : I14<T14>
{
    " + modifier + @" static " + op + @" operator object(T14 y)" + body + @"
}

class C15 {}
class C16 : C15 {}

interface I17<T17> where T17 : C15, I17<T17>
{
    " + modifier + @" static " + op + @" operator C16(T17 y)" + body + @"
}

interface I18<T18> where T18 : C16, I18<T18>
{
    " + modifier + @" static " + op + @" operator C15(T18 y)" + body + @"
}

interface I19<T19_1, T19_2> where T19_1 : I19<T19_1, T19_2>, T19_2
{
    " + modifier + @" static " + op + @" operator T19_1(T19_2 y)" + body + @"
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);
            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_UnimplementedInterfaceMember).Verify(
                // (4,39): error CS0555: User-defined operator cannot convert a type to itself
                //     abstract static explicit operator T1(T1 y);
                Diagnostic(ErrorCode.ERR_IdentityConversion, "T1").WithLocation(4, 39),
                // (9,39): error CS1964: 'I2<T2>.explicit operator dynamic(T2)': user-defined conversions to or from the dynamic type are not allowed
                //     abstract static explicit operator dynamic(T2 y);
                Diagnostic(ErrorCode.ERR_BadDynamicConversion, "dynamic").WithArguments("I2<T2>." + op + " operator dynamic(T2)").WithLocation(9, 39),
                // (26,43): error CS8931: User-defined conversion in an interface must convert to or from a type parameter on the enclosing type constrained to the enclosing type
                //         static abstract explicit operator T5 (bool y);
                Diagnostic(ErrorCode.ERR_AbstractConversionNotInvolvingContainedType, "T5").WithLocation(26, 43),
                // (32,39): error CS8931: User-defined conversion in an interface must convert to or from a type parameter on the enclosing type constrained to the enclosing type
                //     static abstract explicit operator T71 (bool y);
                Diagnostic(ErrorCode.ERR_AbstractConversionNotInvolvingContainedType, "T71").WithLocation(32, 39),
                // (37,39): error CS8931: User-defined conversion in an interface must convert to or from a type parameter on the enclosing type constrained to the enclosing type
                //     static abstract explicit operator T8(bool y);
                Diagnostic(ErrorCode.ERR_AbstractConversionNotInvolvingContainedType, "T8").WithLocation(37, 39),
                // (44,39): error CS8931: User-defined conversion in an interface must convert to or from a type parameter on the enclosing type constrained to the enclosing type
                //     static abstract explicit operator T10(bool y);
                Diagnostic(ErrorCode.ERR_AbstractConversionNotInvolvingContainedType, "T10").WithLocation(44, 39),
                // (51,39): error CS8931: User-defined conversion in an interface must convert to or from a type parameter on the enclosing type constrained to the enclosing type
                //     static abstract explicit operator int(bool y);
                Diagnostic(ErrorCode.ERR_AbstractConversionNotInvolvingContainedType, "int").WithLocation(51, 39),
                // (56,39): error CS0552: 'I13.explicit operator I13(bool)': user-defined conversions to or from an interface are not allowed
                //     static abstract explicit operator I13(bool y);
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "I13").WithArguments("I13." + op + " operator I13(bool)").WithLocation(56, 39)
                );
        }

        [Theory]
        [CombinatorialData]
        public void OperatorSignature_08([CombinatorialValues("implicit", "explicit")] string op, bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
interface I1<T1> where T1 : I1<T1>
{
    " + modifier + @" static " + op + @" operator T1(T1 y)" + body + @"
}

interface I2<T2> where T2 : I2<T2>
{
    " + modifier + @" static " + op + @" operator T2(dynamic y)" + body + @"
}

interface I3<T3> where T3 : I3<T3>
{
    static " + modifier + @" " + op + @" operator bool(T3 y)" + body + @"
}

interface I4<T4> where T4 : struct, I4<T4>
{
    static " + modifier + @" " + op + @" operator bool(T4? y)" + body + @"
}

class C5<T5> where T5 : C5<T5>.I6
{
    public interface I6
    {
        static " + modifier + @" " + op + @" operator bool(T5 y)" + body + @"
    }
}

interface I7<T71, T72> where T72 : I7<T71, T72> where T71 : T72
{
    static " + modifier + @" " + op + @" operator bool(T71 y)" + body + @"
}

interface I8<T8> where T8 : I9<T8>
{
    static " + modifier + @" " + op + @" operator bool(T8 y)" + body + @"
}

interface I9<T9> : I8<T9> where T9 : I9<T9> {}

interface I10<T10> where T10 : C11<T10>
{
    static " + modifier + @" " + op + @" operator bool(T10 y)" + body + @"
}

class C11<T11> : I10<T11> where T11 : C11<T11> {}

interface I12
{
    static " + modifier + @" " + op + @" operator bool(int y)" + body + @"
}

interface I13
{
    static " + modifier + @" " + op + @" operator bool(I13 y)" + body + @"
}

interface I14<T14> where T14 : I14<T14>
{
    " + modifier + @" static " + op + @" operator T14(object y)" + body + @"
}

class C15 {}
class C16 : C15 {}

interface I17<T17> where T17 : C15, I17<T17>
{
    " + modifier + @" static " + op + @" operator T17(C16 y)" + body + @"
}

interface I18<T18> where T18 : C16, I18<T18>
{
    " + modifier + @" static " + op + @" operator T18(C15 y)" + body + @"
}

interface I19<T19_1, T19_2> where T19_1 : I19<T19_1, T19_2>, T19_2
{
    " + modifier + @" static " + op + @" operator T19_2(T19_1 y)" + body + @"
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);
            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_UnimplementedInterfaceMember).Verify(
                // (4,39): error CS0555: User-defined operator cannot convert a type to itself
                //     abstract static explicit operator T1(T1 y);
                Diagnostic(ErrorCode.ERR_IdentityConversion, "T1").WithLocation(4, 39),
                // (9,39): error CS1964: 'I2<T2>.explicit operator T2(dynamic)': user-defined conversions to or from the dynamic type are not allowed
                //     abstract static explicit operator T2(dynamic y);
                Diagnostic(ErrorCode.ERR_BadDynamicConversion, "T2").WithArguments("I2<T2>." + op + " operator T2(dynamic)").WithLocation(9, 39),
                // (26,43): error CS8931: User-defined conversion in an interface must convert to or from a type parameter on the enclosing type constrained to the enclosing type
                //         static abstract explicit operator bool(T5 y);
                Diagnostic(ErrorCode.ERR_AbstractConversionNotInvolvingContainedType, "bool").WithLocation(26, 43),
                // (32,39): error CS8931: User-defined conversion in an interface must convert to or from a type parameter on the enclosing type constrained to the enclosing type
                //     static abstract explicit operator bool(T71 y);
                Diagnostic(ErrorCode.ERR_AbstractConversionNotInvolvingContainedType, "bool").WithLocation(32, 39),
                // (37,39): error CS8931: User-defined conversion in an interface must convert to or from a type parameter on the enclosing type constrained to the enclosing type
                //     static abstract explicit operator bool(T8 y);
                Diagnostic(ErrorCode.ERR_AbstractConversionNotInvolvingContainedType, "bool").WithLocation(37, 39),
                // (44,39): error CS8931: User-defined conversion in an interface must convert to or from a type parameter on the enclosing type constrained to the enclosing type
                //     static abstract explicit operator bool(T10 y);
                Diagnostic(ErrorCode.ERR_AbstractConversionNotInvolvingContainedType, "bool").WithLocation(44, 39),
                // (51,39): error CS8931: User-defined conversion in an interface must convert to or from a type parameter on the enclosing type constrained to the enclosing type
                //     static abstract explicit operator bool(int y);
                Diagnostic(ErrorCode.ERR_AbstractConversionNotInvolvingContainedType, "bool").WithLocation(51, 39),
                // (56,39): error CS0552: 'I13.explicit operator bool(I13)': user-defined conversions to or from an interface are not allowed
                //     static abstract explicit operator bool(I13 y);
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "bool").WithArguments("I13." + op + " operator bool(I13)").WithLocation(56, 39)
                );
        }

        [Theory]
        [CombinatorialData]
        public void OperatorSignature_09([CombinatorialValues("==", "!=")] string op, bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
interface I1<T1> where T1 : I1<T1>
{
    static bool operator " + op + @"(T1 x, bool y) => throw null;
}

interface I2<T2> where T2 : struct, I2<T2>
{
    static bool operator " + op + @"(T2? x, bool y) => throw null;
}

interface I3<T3> where T3 : I3<T3>
{
    static " + modifier + @" bool operator " + op + @"(T3 x, bool y)" + body + @"
}

interface I4<T4> where T4 : struct, I4<T4>
{
    static " + modifier + @" bool operator " + op + @"(T4? x, bool y)" + body + @"
}

class C5<T5> where T5 : C5<T5>.I6
{
    public interface I6
    {
        static " + modifier + @" bool operator " + op + @"(T5 x, bool y)" + body + @"
    }
}

interface I7<T71, T72> where T72 : I7<T71, T72> where T71 : T72
{
    static " + modifier + @" bool operator " + op + @"(T71 x, bool y)" + body + @"
}

interface I8<T8> where T8 : I9<T8>
{
    static " + modifier + @" bool operator " + op + @"(T8 x, bool y)" + body + @"
}

interface I9<T9> : I8<T9> where T9 : I9<T9> {}

interface I10<T10> where T10 : C11<T10>
{
    static " + modifier + @" bool operator " + op + @"(T10 x, bool y)" + body + @"
}

class C11<T11> : I10<T11> where T11 : C11<T11> {}

interface I12
{
    static " + modifier + @" bool operator " + op + @"(int x, bool y)" + body + @"
}

interface I13
{
    static " + modifier + @" bool operator " + op + @"(I13 x, bool y)" + body + @"
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);
            compilation1.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators or (int)ErrorCode.ERR_UnimplementedInterfaceMember)).Verify(
                // (4,26): error CS0563: One of the parameters of a binary operator must be the containing type
                //     static bool operator ==(T1 x, bool y) => throw null;
                Diagnostic(ErrorCode.ERR_BadBinaryOperatorSignature, op).WithLocation(4, 26),
                // (9,26): error CS0563: One of the parameters of a binary operator must be the containing type
                //     static bool operator ==(T2? x, bool y) => throw null;
                Diagnostic(ErrorCode.ERR_BadBinaryOperatorSignature, op).WithLocation(9, 26),
                // (26,39): error CS9046: One of the parameters of an equality, or inequality operator declared in interface 'C5<T5>.I6' must be a type parameter on 'C5<T5>.I6' constrained to 'C5<T5>.I6'
                //         static abstract bool operator ==(T5 x, bool y);
                Diagnostic(ErrorCode.ERR_BadAbstractEqualityOperatorSignature, op).WithArguments("C5<T5>.I6").WithLocation(26, 39),
                // (32,35): error CS9046: One of the parameters of an equality, or inequality operator declared in interface 'I7<T71, T72>' must be a type parameter on 'I7<T71, T72>' constrained to 'I7<T71, T72>'
                //     static abstract bool operator ==(T71 x, bool y);
                Diagnostic(ErrorCode.ERR_BadAbstractEqualityOperatorSignature, op).WithArguments("I7<T71, T72>").WithLocation(32, 35),
                // (37,35): error CS9046: One of the parameters of an equality, or inequality operator declared in interface 'I8<T8>' must be a type parameter on 'I8<T8>' constrained to 'I8<T8>'
                //     static abstract bool operator ==(T8 x, bool y);
                Diagnostic(ErrorCode.ERR_BadAbstractEqualityOperatorSignature, op).WithArguments("I8<T8>").WithLocation(37, 35),
                // (44,35): error CS9046: One of the parameters of an equality, or inequality operator declared in interface 'I10<T10>' must be a type parameter on 'I10<T10>' constrained to 'I10<T10>'
                //     static abstract bool operator ==(T10 x, bool y);
                Diagnostic(ErrorCode.ERR_BadAbstractEqualityOperatorSignature, op).WithArguments("I10<T10>").WithLocation(44, 35),
                // (51,35): error CS9046: One of the parameters of an equality, or inequality operator declared in interface 'I12' must be a type parameter on 'I12' constrained to 'I12'
                //     static abstract bool operator ==(int x, bool y);
                Diagnostic(ErrorCode.ERR_BadAbstractEqualityOperatorSignature, op).WithArguments("I12").WithLocation(51, 35),
                // (56,35): error CS9046: One of the parameters of an equality, or inequality operator declared in interface 'I13' must be a type parameter on 'I13' constrained to 'I13'
                //     static abstract bool operator ==(I13 x, bool y);
                Diagnostic(ErrorCode.ERR_BadAbstractEqualityOperatorSignature, op).WithArguments("I13").WithLocation(56, 35)
                );
        }

        [Theory]
        [CombinatorialData]
        public void OperatorSignature_10([CombinatorialValues("==", "!=")] string op, bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
interface I1<T1> where T1 : I1<T1>
{
    static bool operator " + op + @"(bool y, T1 x) => throw null;
}

interface I2<T2> where T2 : struct, I2<T2>
{
    static bool operator " + op + @"(bool y, T2? x) => throw null;
}

interface I3<T3> where T3 : I3<T3>
{
    static " + modifier + @" bool operator " + op + @"(bool y, T3 x)" + body + @"
}

interface I4<T4> where T4 : struct, I4<T4>
{
    static " + modifier + @" bool operator " + op + @"(bool y, T4? x)" + body + @"
}

class C5<T5> where T5 : C5<T5>.I6
{
    public interface I6
    {
        static " + modifier + @" bool operator " + op + @"(bool y, T5 x)" + body + @"
    }
}

interface I7<T71, T72> where T72 : I7<T71, T72> where T71 : T72
{
    static " + modifier + @" bool operator " + op + @"(bool y, T71 x)" + body + @"
}

interface I8<T8> where T8 : I9<T8>
{
    static " + modifier + @" bool operator " + op + @"(bool y, T8 x)" + body + @"
}

interface I9<T9> : I8<T9> where T9 : I9<T9> {}

interface I10<T10> where T10 : C11<T10>
{
    static " + modifier + @" bool operator " + op + @"(bool y, T10 x)" + body + @"
}

class C11<T11> : I10<T11> where T11 : C11<T11> {}

interface I12
{
    static " + modifier + @" bool operator " + op + @"(bool y, int x)" + body + @"
}

interface I13
{
    static " + modifier + @" bool operator " + op + @"(bool y, I13 x)" + body + @"
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);
            compilation1.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators or (int)ErrorCode.ERR_UnimplementedInterfaceMember)).Verify(
                // (4,26): error CS0563: One of the parameters of a binary operator must be the containing type
                //     static bool operator ==(bool y, T1 x) => throw null;
                Diagnostic(ErrorCode.ERR_BadBinaryOperatorSignature, op).WithLocation(4, 26),
                // (9,26): error CS0563: One of the parameters of a binary operator must be the containing type
                //     static bool operator ==(bool y, T2? x) => throw null;
                Diagnostic(ErrorCode.ERR_BadBinaryOperatorSignature, op).WithLocation(9, 26),
                // (26,39): error CS9046: One of the parameters of an equality, or inequality operator declared in interface 'C5<T5>.I6' must be a type parameter on 'C5<T5>.I6' constrained to 'C5<T5>.I6'
                //         static abstract bool operator ==(bool y, T5 x);
                Diagnostic(ErrorCode.ERR_BadAbstractEqualityOperatorSignature, op).WithArguments("C5<T5>.I6").WithLocation(26, 39),
                // (32,35): error CS9046: One of the parameters of an equality, or inequality operator declared in interface 'I7<T71, T72>' must be a type parameter on 'I7<T71, T72>' constrained to 'I7<T71, T72>'
                //     static abstract bool operator ==(bool y, T71 x);
                Diagnostic(ErrorCode.ERR_BadAbstractEqualityOperatorSignature, op).WithArguments("I7<T71, T72>").WithLocation(32, 35),
                // (37,35): error CS9046: One of the parameters of an equality, or inequality operator declared in interface 'I8<T8>' must be a type parameter on 'I8<T8>' constrained to 'I8<T8>'
                //     static abstract bool operator ==(bool y, T8 x);
                Diagnostic(ErrorCode.ERR_BadAbstractEqualityOperatorSignature, op).WithArguments("I8<T8>").WithLocation(37, 35),
                // (44,35): error CS9046: One of the parameters of an equality, or inequality operator declared in interface 'I10<T10>' must be a type parameter on 'I10<T10>' constrained to 'I10<T10>'
                //     static abstract bool operator ==(bool y, T10 x);
                Diagnostic(ErrorCode.ERR_BadAbstractEqualityOperatorSignature, op).WithArguments("I10<T10>").WithLocation(44, 35),
                // (51,35): error CS9046: One of the parameters of an equality, or inequality operator declared in interface 'I12' must be a type parameter on 'I12' constrained to 'I12'
                //     static abstract bool operator ==(bool y, int x);
                Diagnostic(ErrorCode.ERR_BadAbstractEqualityOperatorSignature, op).WithArguments("I12").WithLocation(51, 35),
                // (56,35): error CS9046: One of the parameters of an equality, or inequality operator declared in interface 'I13' must be a type parameter on 'I13' constrained to 'I13'
                //     static abstract bool operator ==(bool y, I13 x);
                Diagnostic(ErrorCode.ERR_BadAbstractEqualityOperatorSignature, op).WithArguments("I13").WithLocation(56, 35)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticMethod_01(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
interface I1
{
    " + modifier + @" static void M01()" + body + @"

    static void M02()
    {
        M01();
        M04();
    }

    void M03()
    {
        this.M01();
        this.M04();
    }

    static void M04() {}

    protected " + modifier + @" static void M05()" + body + @"
}

class Test
{
    static void MT1(I1 x)
    {
        I1.M01();
        x.M01();
        I1.M04();
        x.M04();
    }

    static void MT2<T>() where T : I1
    {
        T.M03();
        T.M04();
        T.M00();
        T.M05();

        _ = (System.Linq.Expressions.Expression<System.Action>)(() => T.M01());
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (8,9): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         M01();
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "M01").WithLocation(8, 9),
                // (14,9): error CS0176: Member 'I1.M01()' cannot be accessed with an instance reference; qualify it with a type name instead
                //         this.M01();
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "this.M01").WithArguments("I1.M01()").WithLocation(14, 9),
                // (15,9): error CS0176: Member 'I1.M04()' cannot be accessed with an instance reference; qualify it with a type name instead
                //         this.M04();
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "this.M04").WithArguments("I1.M04()").WithLocation(15, 9),
                // (27,9): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         I1.M01();
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "I1.M01").WithLocation(27, 9),
                // (28,9): error CS0176: Member 'I1.M01()' cannot be accessed with an instance reference; qualify it with a type name instead
                //         x.M01();
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "x.M01").WithArguments("I1.M01()").WithLocation(28, 9),
                // (30,9): error CS0176: Member 'I1.M04()' cannot be accessed with an instance reference; qualify it with a type name instead
                //         x.M04();
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "x.M04").WithArguments("I1.M04()").WithLocation(30, 9),
                // (35,9): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         T.M03();
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(35, 9),
                // (36,9): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         T.M04();
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(36, 9),
                // (37,9): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         T.M00();
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(37, 9),
                // (38,11): error CS0122: 'I1.M05()' is inaccessible due to its protection level
                //         T.M05();
                Diagnostic(ErrorCode.ERR_BadAccess, "M05").WithArguments("I1.M05()").WithLocation(38, 11),
                // (40,71): error CS8927: An expression tree may not contain an access of static virtual or abstract interface member
                //         _ = (System.Linq.Expressions.Expression<System.Action>)(() => T.M01());
                Diagnostic(ErrorCode.ERR_ExpressionTreeContainsAbstractStaticMemberAccess, "T.M01()").WithLocation(40, 71)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticMethod_02(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
interface I1
{
    " + modifier + @" static void M01()" + body + @"

    static void M02()
    {
        _ = nameof(M01);
        _ = nameof(M04);
    }

    void M03()
    {
        _ = nameof(this.M01);
        _ = nameof(this.M04);
    }

    static void M04() {}

    protected " + modifier + @" static void M05()" + body + @"
}

class Test
{
    static void MT1(I1 x)
    {
        _ = nameof(I1.M01);
        _ = nameof(x.M01);
        _ = nameof(I1.M04);
        _ = nameof(x.M04);
    }

    static void MT2<T>() where T : I1
    {
        _ = nameof(T.M03);
        _ = nameof(T.M04);
        _ = nameof(T.M00);
        _ = nameof(T.M05);
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (35,20): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         _ = nameof(T.M03);
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(35, 20),
                // (36,20): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         _ = nameof(T.M04);
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(36, 20),
                // (37,20): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         _ = nameof(T.M00);
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(37, 20),
                // (38,22): error CS0122: 'I1.M05()' is inaccessible due to its protection level
                //         _ = nameof(T.M05);
                Diagnostic(ErrorCode.ERR_BadAccess, "M05").WithArguments("I1.M05()").WithLocation(38, 22)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticMethod_03(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static void M01()" + body + @"
    " + modifier + @" static void M04(int x)" + body + @"
}

class Test
{
    static void M02<T, U>() where T : U where U : I1
    {
        T.M01();
    }

    static string M03<T, U>() where T : U where U : I1
    {
        return nameof(T.M01);
    }

    static async void M05<T, U>() where T : U where U : I1
    {
        T.M04(await System.Threading.Tasks.Task.FromResult(1));
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>()",
@"
{
  // Code size       14 (0xe)
  .maxstack  0
  IL_0000:  nop
  IL_0001:  constrained. ""T""
  IL_0007:  call       ""void I1.M01()""
  IL_000c:  nop
  IL_000d:  ret
}
");

            verifier.VerifyIL("Test.M03<T, U>()",
@"
{
  // Code size       11 (0xb)
  .maxstack  1
  .locals init (string V_0)
  IL_0000:  nop
  IL_0001:  ldstr      ""M01""
  IL_0006:  stloc.0
  IL_0007:  br.s       IL_0009
  IL_0009:  ldloc.0
  IL_000a:  ret
}
");

            compilation1 = CreateCompilation(source1, options: TestOptions.ReleaseDll,
                                             parseOptions: TestOptions.RegularPreview,
                                             targetFramework: _supportingFramework);

            verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>()",
@"
{
  // Code size       12 (0xc)
  .maxstack  0
  IL_0000:  constrained. ""T""
  IL_0006:  call       ""void I1.M01()""
  IL_000b:  ret
}
");

            verifier.VerifyIL("Test.M03<T, U>()",
@"
{
  // Code size        6 (0x6)
  .maxstack  1
  IL_0000:  ldstr      ""M01""
  IL_0005:  ret
}
");

            var tree = compilation1.SyntaxTrees.Single();
            var model = compilation1.GetSemanticModel(tree);
            var node = tree.GetRoot().DescendantNodes().OfType<InvocationExpressionSyntax>().First();

            Assert.Equal("T.M01()", node.ToString());
            VerifyOperationTreeForNode(compilation1, model, node,
@"
IInvocationOperation (virtual void I1.M01() ConstrainedToType: T) (OperationKind.Invocation, Type: System.Void) (Syntax: 'T.M01()')
  Instance Receiver: 
    null
  Arguments(0)
");

            var m02 = compilation1.GetMember<MethodSymbol>("Test.M02");

            Assert.Equal("void I1.M01()", ((CSharpSemanticModel)model).LookupSymbols(node.SpanStart, m02.TypeParameters[0], "M01").Single().ToTestDisplayString());
            Assert.Contains("void I1.M01()", ((CSharpSemanticModel)model).LookupSymbols(node.SpanStart, m02.TypeParameters[0]).ToTestDisplayStrings());
            Assert.Equal("void I1.M01()", ((CSharpSemanticModel)model).LookupStaticMembers(node.SpanStart, m02.TypeParameters[0], "M01").Single().ToTestDisplayString());
            Assert.Contains("void I1.M01()", ((CSharpSemanticModel)model).LookupStaticMembers(node.SpanStart, m02.TypeParameters[0]).ToTestDisplayStrings());

            Assert.Equal("void I1.M01()", model.LookupSymbols(node.SpanStart, m02.TypeParameters[0].GetPublicSymbol(), "M01").Single().ToTestDisplayString());
            Assert.Contains("void I1.M01()", model.LookupSymbols(node.SpanStart, m02.TypeParameters[0].GetPublicSymbol()).ToTestDisplayStrings());
            Assert.Equal("void I1.M01()", model.LookupStaticMembers(node.SpanStart, m02.TypeParameters[0].GetPublicSymbol(), "M01").Single().ToTestDisplayString());
            Assert.Contains("void I1.M01()", model.LookupStaticMembers(node.SpanStart, m02.TypeParameters[0].GetPublicSymbol()).ToTestDisplayStrings());

            Assert.Contains("M01", model.LookupNames(node.SpanStart, m02.TypeParameters[0].GetPublicSymbol()));
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticMethod_04(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static void M01()" + body + @"
}
";
            var source2 =
@"
class Test
{
    static void M02<T>() where T : I1
    {
        T.M01();
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (6,9): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //         T.M01();
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "T.M01").WithLocation(6, 9)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation3.VerifyDiagnostics(
                // (12,26): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static void M01();
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "M01").WithLocation(12, 26)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticMethod_05(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static I1 Select(System.Func<int, int> p)" + body + @"
}

class Test
{
    static void M02<T>() where T : I1
    {
        _ = from t in T select t + 1;
        _ = from t in I1 select t + 1;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (11,23): error CS0119: 'T' is a type parameter, which is not valid in the given context
                //         _ = from t in T select t + 1;
                Diagnostic(ErrorCode.ERR_BadSKunknown, "T").WithArguments("T", "type parameter").WithLocation(11, 23),
                // (12,26): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         _ = from t in I1 select t + 1;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "select t + 1").WithLocation(12, 26)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticMethod_06(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static void M01()" + body + @"
}
";
            var source2 =
@"
class Test
{
    static void M02<T>() where T : I1
    {
        T.M01();
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (6,9): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                //         T.M01();
                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "T").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 9)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation3.VerifyDiagnostics(
                // (6,9): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                //         T.M01();
                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "T").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 9),
                // (12,26): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual  static void M01() => throw null;
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M01").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(12, 26)
                );
        }

        [Theory]
        [InlineData("+", "", false)]
        [InlineData("-", "", false)]
        [InlineData("!", "", false)]
        [InlineData("~", "", false)]
        [InlineData("++", "", false)]
        [InlineData("--", "", false)]
        [InlineData("", "++", false)]
        [InlineData("", "--", false)]
        [InlineData("-", "", true)]
        [InlineData("++", "", true)]
        [InlineData("--", "", true)]
        [InlineData("", "++", true)]
        [InlineData("", "--", true)]
        public void ConsumeAbstractUnaryOperator_01(string prefixOp, string postfixOp, bool isChecked)
        {
            consumeAbstractUnaryOperator_01(prefixOp, postfixOp, isChecked, isVirtual: false);
            consumeAbstractUnaryOperator_01(prefixOp, postfixOp, isChecked, isVirtual: true);

            void consumeAbstractUnaryOperator_01(string prefixOp, string postfixOp, bool isChecked, bool isVirtual)
            {
                var (modifier, body) = GetModifierAndBody(isVirtual);

                string checkedKeyword = isChecked ? " checked " : "";

                var source1 =
@"
partial interface I1<T> where T : I1<T>
{
    " + modifier + @" static T operator" + checkedKeyword + prefixOp + postfixOp + @" (T x)" + body + @"
    " + modifier + @" static I1<T> operator" + checkedKeyword + prefixOp + postfixOp + @" (I1<T> x)" + body + @"
    static void M02(I1<T> x)
    {" + checkedKeyword + @"{
        _ = " + prefixOp + "x" + postfixOp + @";
    }}

    void M03(I1<T> y)
    {" + checkedKeyword + @"{
        _ = " + prefixOp + "y" + postfixOp + @";
    }}
}

class Test<T> where T : I1<T>
{
    static void MT1(I1<T> a)
    {" + checkedKeyword + @"{
        _ = " + prefixOp + "a" + postfixOp + @";
    }}

    static void MT2()
    {" + checkedKeyword + @"{
        _ = (System.Linq.Expressions.Expression<System.Action<T>>)((T b) => (" + prefixOp + "b" + postfixOp + @").ToString());
    }}
}
";

                var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                    // (8,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                    //         _ = -x;
                    Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, prefixOp + "x" + postfixOp).WithLocation(8, 13),
                    // (13,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                    //         _ = -y;
                    Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, prefixOp + "y" + postfixOp).WithLocation(13, 13),
                    // (21,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                    //         _ = -a;
                    Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, prefixOp + "a" + postfixOp).WithLocation(21, 13),
                    (prefixOp + postfixOp).Length == 1 ?
                        // (26,78): error CS8927: An expression tree may not contain an access of static virtual or abstract interface member
                        //         _ = (System.Linq.Expressions.Expression<System.Action<T>>)((T b) => (-b).ToString());
                        Diagnostic(ErrorCode.ERR_ExpressionTreeContainsAbstractStaticMemberAccess, prefixOp + "b" + postfixOp).WithLocation(26, 78)
                        :
                        // (26,78): error CS0832: An expression tree may not contain an assignment operator
                        //         _ = (System.Linq.Expressions.Expression<System.Action<T>>)((T b) => (b--).ToString());
                        Diagnostic(ErrorCode.ERR_ExpressionTreeContainsAssignment, prefixOp + "b" + postfixOp).WithLocation(26, 78)
                    );
            }
        }

        [Theory]
        [InlineData("+", "", "op_UnaryPlus", "Plus", false, false)]
        [InlineData("-", "", "op_UnaryNegation", "Minus", false, false)]
        [InlineData("!", "", "op_LogicalNot", "Not", false, false)]
        [InlineData("~", "", "op_OnesComplement", "BitwiseNegation", false, false)]
        [InlineData("++", "", "op_Increment", "Increment", false, false)]
        [InlineData("--", "", "op_Decrement", "Decrement", false, false)]
        [InlineData("", "++", "op_Increment", "Increment", false, false)]
        [InlineData("", "--", "op_Decrement", "Decrement", false, false)]
        [InlineData("+", "", "op_UnaryPlus", "Plus", false, true)]
        [InlineData("-", "", "op_UnaryNegation", "Minus", false, true)]
        [InlineData("!", "", "op_LogicalNot", "Not", false, true)]
        [InlineData("~", "", "op_OnesComplement", "BitwiseNegation", false, true)]
        [InlineData("++", "", "op_Increment", "Increment", false, true)]
        [InlineData("--", "", "op_Decrement", "Decrement", false, true)]
        [InlineData("", "++", "op_Increment", "Increment", false, true)]
        [InlineData("", "--", "op_Decrement", "Decrement", false, true)]
        [InlineData("-", "", "op_UnaryNegation", "Minus", true, false)]
        [InlineData("++", "", "op_Increment", "Increment", true, false)]
        [InlineData("--", "", "op_Decrement", "Decrement", true, false)]
        [InlineData("", "++", "op_Increment", "Increment", true, false)]
        [InlineData("", "--", "op_Decrement", "Decrement", true, false)]
        [InlineData("-", "", "op_CheckedUnaryNegation", "Minus", true, true)]
        [InlineData("++", "", "op_CheckedIncrement", "Increment", true, true)]
        [InlineData("--", "", "op_CheckedDecrement", "Decrement", true, true)]
        [InlineData("", "++", "op_CheckedIncrement", "Increment", true, true)]
        [InlineData("", "--", "op_CheckedDecrement", "Decrement", true, true)]
        public void ConsumeAbstractUnaryOperator_03(string prefixOp, string postfixOp, string metadataName, string opKind, bool isCheckedOperator, bool isCheckedContext)
        {
            consumeAbstractUnaryOperator_03(prefixOp, postfixOp, metadataName, opKind, isCheckedOperator, isCheckedContext, isVirtual: false);
            consumeAbstractUnaryOperator_03(prefixOp, postfixOp, metadataName, opKind, isCheckedOperator, isCheckedContext, isVirtual: true);

            void consumeAbstractUnaryOperator_03(string prefixOp, string postfixOp, string metadataName, string opKind, bool isCheckedOperator, bool isCheckedContext, bool isVirtual)
            {
                string contextKeyword = isCheckedContext ? " checked " : " unchecked ";
                var (modifier, body) = GetModifierAndBody(isVirtual);

                var source1 =
@"
public interface I1<T> where T : I1<T>
{
    " + modifier + @" static T operator " + prefixOp + postfixOp + @" (T x)" + body + @"
"
    ;
                if (isCheckedOperator)
                {
                    source1 +=
@"
    " + modifier + @" static T operator checked " + prefixOp + postfixOp + @" (T x)" + body + @"
"
    ;
                }

                source1 +=
@"}

class Test
{
    static T M02<T, U>(T x) where T : U where U : I1<T>
    {" + contextKeyword + @"{
        return " + prefixOp + "x" + postfixOp + @";
    }}

    static T? M03<T, U>(T? y) where T : struct, U where U : I1<T>
    {" + contextKeyword + @"{
        return " + prefixOp + "y" + postfixOp + @";
    }}
}
";
                var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

                compilation1 = CreateCompilation(source1, options: TestOptions.ReleaseDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                var verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

                switch ((prefixOp, postfixOp))
                {
                    case ("++", ""):
                    case ("--", ""):
                        verifier.VerifyIL("Test.M02<T, U>(T)",
@"
{
  // Code size       16 (0x10)
  .maxstack  2
  IL_0000:  ldarg.0
  IL_0001:  constrained. ""T""
  IL_0007:  call       ""T I1<T>." + metadataName + @"(T)""
  IL_000c:  dup
  IL_000d:  starg.s    V_0
  IL_000f:  ret
}
");
                        verifier.VerifyIL("Test.M03<T, U>(T?)",
@"
{
  // Code size       49 (0x31)
  .maxstack  2
  .locals init (T? V_0,
                T? V_1)
  IL_0000:  ldarg.0
  IL_0001:  stloc.0
  IL_0002:  ldloca.s   V_0
  IL_0004:  call       ""readonly bool T?.HasValue.get""
  IL_0009:  brtrue.s   IL_0016
  IL_000b:  ldloca.s   V_1
  IL_000d:  initobj    ""T?""
  IL_0013:  ldloc.1
  IL_0014:  br.s       IL_002d
  IL_0016:  ldloca.s   V_0
  IL_0018:  call       ""readonly T T?.GetValueOrDefault()""
  IL_001d:  constrained. ""T""
  IL_0023:  call       ""T I1<T>." + metadataName + @"(T)""
  IL_0028:  newobj     ""T?..ctor(T)""
  IL_002d:  dup
  IL_002e:  starg.s    V_0
  IL_0030:  ret
}
");
                        break;

                    case ("", "++"):
                    case ("", "--"):
                        verifier.VerifyIL("Test.M02<T, U>(T)",
@"
{
  // Code size       16 (0x10)
  .maxstack  2
  IL_0000:  ldarg.0
  IL_0001:  dup
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""T I1<T>." + metadataName + @"(T)""
  IL_000d:  starg.s    V_0
  IL_000f:  ret
}
");
                        verifier.VerifyIL("Test.M03<T, U>(T?)",
@"
{
  // Code size       49 (0x31)
  .maxstack  2
  .locals init (T? V_0,
                T? V_1)
  IL_0000:  ldarg.0
  IL_0001:  dup
  IL_0002:  stloc.0
  IL_0003:  ldloca.s   V_0
  IL_0005:  call       ""readonly bool T?.HasValue.get""
  IL_000a:  brtrue.s   IL_0017
  IL_000c:  ldloca.s   V_1
  IL_000e:  initobj    ""T?""
  IL_0014:  ldloc.1
  IL_0015:  br.s       IL_002e
  IL_0017:  ldloca.s   V_0
  IL_0019:  call       ""readonly T T?.GetValueOrDefault()""
  IL_001e:  constrained. ""T""
  IL_0024:  call       ""T I1<T>." + metadataName + @"(T)""
  IL_0029:  newobj     ""T?..ctor(T)""
  IL_002e:  starg.s    V_0
  IL_0030:  ret
}
");
                        break;

                    default:
                        verifier.VerifyIL("Test.M02<T, U>(T)",
@"
{
  // Code size       13 (0xd)
  .maxstack  1
  IL_0000:  ldarg.0
  IL_0001:  constrained. ""T""
  IL_0007:  call       ""T I1<T>." + metadataName + @"(T)""
  IL_000c:  ret
}
");
                        verifier.VerifyIL("Test.M03<T, U>(T?)",
@"
{
  // Code size       45 (0x2d)
  .maxstack  1
  .locals init (T? V_0,
                T? V_1)
  IL_0000:  ldarg.0
  IL_0001:  stloc.0
  IL_0002:  ldloca.s   V_0
  IL_0004:  call       ""readonly bool T?.HasValue.get""
  IL_0009:  brtrue.s   IL_0015
  IL_000b:  ldloca.s   V_1
  IL_000d:  initobj    ""T?""
  IL_0013:  ldloc.1
  IL_0014:  ret
  IL_0015:  ldloca.s   V_0
  IL_0017:  call       ""readonly T T?.GetValueOrDefault()""
  IL_001c:  constrained. ""T""
  IL_0022:  call       ""T I1<T>." + metadataName + @"(T)""
  IL_0027:  newobj     ""T?..ctor(T)""
  IL_002c:  ret
}
");
                        break;
                }

                compilation1 = CreateCompilation(source1, options: TestOptions.ReleaseDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

                verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

                switch ((prefixOp, postfixOp))
                {
                    case ("++", ""):
                    case ("--", ""):
                        verifier.VerifyIL("Test.M02<T, U>(T)",
@"
{
  // Code size       16 (0x10)
  .maxstack  2
  IL_0000:  ldarg.0
  IL_0001:  constrained. ""T""
  IL_0007:  call       ""T I1<T>." + metadataName + @"(T)""
  IL_000c:  dup
  IL_000d:  starg.s    V_0
  IL_000f:  ret
}
");
                        verifier.VerifyIL("Test.M03<T, U>(T?)",
@"
{
  // Code size       49 (0x31)
  .maxstack  2
  .locals init (T? V_0,
                T? V_1)
  IL_0000:  ldarg.0
  IL_0001:  stloc.0
  IL_0002:  ldloca.s   V_0
  IL_0004:  call       ""readonly bool T?.HasValue.get""
  IL_0009:  brtrue.s   IL_0016
  IL_000b:  ldloca.s   V_1
  IL_000d:  initobj    ""T?""
  IL_0013:  ldloc.1
  IL_0014:  br.s       IL_002d
  IL_0016:  ldloca.s   V_0
  IL_0018:  call       ""readonly T T?.GetValueOrDefault()""
  IL_001d:  constrained. ""T""
  IL_0023:  call       ""T I1<T>." + metadataName + @"(T)""
  IL_0028:  newobj     ""T?..ctor(T)""
  IL_002d:  dup
  IL_002e:  starg.s    V_0
  IL_0030:  ret
}
");
                        break;

                    case ("", "++"):
                    case ("", "--"):
                        verifier.VerifyIL("Test.M02<T, U>(T)",
@"
{
  // Code size       16 (0x10)
  .maxstack  2
  IL_0000:  ldarg.0
  IL_0001:  dup
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""T I1<T>." + metadataName + @"(T)""
  IL_000d:  starg.s    V_0
  IL_000f:  ret
}
");
                        verifier.VerifyIL("Test.M03<T, U>(T?)",
@"
{
  // Code size       49 (0x31)
  .maxstack  2
  .locals init (T? V_0,
                T? V_1)
  IL_0000:  ldarg.0
  IL_0001:  dup
  IL_0002:  stloc.0
  IL_0003:  ldloca.s   V_0
  IL_0005:  call       ""readonly bool T?.HasValue.get""
  IL_000a:  brtrue.s   IL_0017
  IL_000c:  ldloca.s   V_1
  IL_000e:  initobj    ""T?""
  IL_0014:  ldloc.1
  IL_0015:  br.s       IL_002e
  IL_0017:  ldloca.s   V_0
  IL_0019:  call       ""readonly T T?.GetValueOrDefault()""
  IL_001e:  constrained. ""T""
  IL_0024:  call       ""T I1<T>." + metadataName + @"(T)""
  IL_0029:  newobj     ""T?..ctor(T)""
  IL_002e:  starg.s    V_0
  IL_0030:  ret
}
");
                        break;

                    default:
                        verifier.VerifyIL("Test.M02<T, U>(T)",
@"
{
  // Code size       13 (0xd)
  .maxstack  1
  IL_0000:  ldarg.0
  IL_0001:  constrained. ""T""
  IL_0007:  call       ""T I1<T>." + metadataName + @"(T)""
  IL_000c:  ret
}
");
                        verifier.VerifyIL("Test.M03<T, U>(T?)",
@"
{
  // Code size       45 (0x2d)
  .maxstack  1
  .locals init (T? V_0,
                T? V_1)
  IL_0000:  ldarg.0
  IL_0001:  stloc.0
  IL_0002:  ldloca.s   V_0
  IL_0004:  call       ""readonly bool T?.HasValue.get""
  IL_0009:  brtrue.s   IL_0015
  IL_000b:  ldloca.s   V_1
  IL_000d:  initobj    ""T?""
  IL_0013:  ldloc.1
  IL_0014:  ret
  IL_0015:  ldloca.s   V_0
  IL_0017:  call       ""readonly T T?.GetValueOrDefault()""
  IL_001c:  constrained. ""T""
  IL_0022:  call       ""T I1<T>." + metadataName + @"(T)""
  IL_0027:  newobj     ""T?..ctor(T)""
  IL_002c:  ret
}
");
                        break;
                }

                var tree = compilation1.SyntaxTrees.Single();
                var model = compilation1.GetSemanticModel(tree);
                var node = postfixOp != "" ? (ExpressionSyntax)tree.GetRoot().DescendantNodes().OfType<PostfixUnaryExpressionSyntax>().First() : tree.GetRoot().DescendantNodes().OfType<PrefixUnaryExpressionSyntax>().First();

                Assert.Equal(prefixOp + "x" + postfixOp, node.ToString());

                switch ((prefixOp, postfixOp))
                {
                    case ("++", ""):
                    case ("--", ""):
                    case ("", "++"):
                    case ("", "--"):
                        VerifyOperationTreeForNode(compilation1, model, node,
@"
IIncrementOrDecrementOperation (" + (prefixOp != "" ? "Prefix" : "Postfix") + (isCheckedOperator && isCheckedContext ? ", Checked" : "") + @") (OperatorMethod: T I1<T>." + metadataName + @"(T x) ConstrainedToType: T) (OperationKind." + opKind + @", Type: T) (Syntax: '" + prefixOp + "x" + postfixOp + @"')
  Target: 
    IParameterReferenceOperation: x (OperationKind.ParameterReference, Type: T) (Syntax: 'x')
");
                        break;

                    default:
                        VerifyOperationTreeForNode(compilation1, model, node,
@"
IUnaryOperation (UnaryOperatorKind." + opKind + (isCheckedOperator && isCheckedContext ? ", Checked" : "") + @") (OperatorMethod: T I1<T>." + metadataName + @"(T x) ConstrainedToType: T) (OperationKind.Unary, Type: T) (Syntax: '" + prefixOp + "x" + postfixOp + @"')
  Operand: 
    IParameterReferenceOperation: x (OperationKind.ParameterReference, Type: T) (Syntax: 'x')
");
                        break;
                }
            }
        }

        [Theory]
        [InlineData("+", "", false)]
        [InlineData("-", "", false)]
        [InlineData("!", "", false)]
        [InlineData("~", "", false)]
        [InlineData("++", "", false)]
        [InlineData("--", "", false)]
        [InlineData("", "++", false)]
        [InlineData("", "--", false)]
        [InlineData("-", "", true)]
        [InlineData("++", "", true)]
        [InlineData("--", "", true)]
        [InlineData("", "++", true)]
        [InlineData("", "--", true)]
        public void ConsumeAbstractUnaryOperator_04(string prefixOp, string postfixOp, bool isChecked)
        {
            consumeAbstractUnaryOperator_04(prefixOp, postfixOp, isChecked, isVirtual: false);
            consumeAbstractUnaryOperator_04(prefixOp, postfixOp, isChecked, isVirtual: true);

            void consumeAbstractUnaryOperator_04(string prefixOp, string postfixOp, bool isChecked, bool isVirtual)
            {
                var (modifier, body) = GetModifierAndBody(isVirtual);
                string checkedKeyword = isChecked ? " checked " : "";

                var source1 =
@"
public interface I1<T> where T : I1<T>
{
    " + modifier + @" static T operator" + checkedKeyword + prefixOp + postfixOp + @" (T x)" + body + @"
}
";
                var source2 =
@"
class Test
{
    static void M02<T>(T x) where T : I1<T>
    {" + checkedKeyword + @"{
        _ = " + prefixOp + "x" + postfixOp + @";
    }}
}
";
                var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: TargetFramework.Mscorlib461Extended,
                                                     references: new[] { compilation1.ToMetadataReference() });

                compilation2.VerifyDiagnostics(
                    // (6,13): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                    //         _ = -x;
                    Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, prefixOp + "x" + postfixOp).WithLocation(6, 13)
                    );

                var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: TargetFramework.Mscorlib461Extended);

                compilation3.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                    // (12,32): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                    //     abstract static T operator- (T x);
                    Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, prefixOp + postfixOp).WithLocation(12, 31 + checkedKeyword.Length)
                    );
            }
        }

        [Theory]
        [InlineData("+", "", false)]
        [InlineData("-", "", false)]
        [InlineData("!", "", false)]
        [InlineData("~", "", false)]
        [InlineData("++", "", false)]
        [InlineData("--", "", false)]
        [InlineData("", "++", false)]
        [InlineData("", "--", false)]
        [InlineData("-", "", true)]
        [InlineData("++", "", true)]
        [InlineData("--", "", true)]
        [InlineData("", "++", true)]
        [InlineData("", "--", true)]
        public void ConsumeAbstractUnaryOperator_06(string prefixOp, string postfixOp, bool isChecked)
        {
            consumeAbstractUnaryOperator_06(prefixOp, postfixOp, isChecked, isVirtual: false);
            consumeAbstractUnaryOperator_06(prefixOp, postfixOp, isChecked, isVirtual: true);

            void consumeAbstractUnaryOperator_06(string prefixOp, string postfixOp, bool isChecked, bool isVirtual)
            {
                var (modifier, body) = GetModifierAndBody(isVirtual);
                string checkedKeyword = isChecked ? " checked " : "";

                var source1 =
@"
public interface I1<T> where T : I1<T>
{
    " + modifier + @" static T operator" + checkedKeyword + prefixOp + postfixOp + @" (T x)" + body + @"
}
";
                var source2 =
@"
class Test
{
    static void M02<T>(T x) where T : I1<T>
    {" + checkedKeyword + @"{
        _ = " + prefixOp + "x" + postfixOp + @";
    }}
}
";
                var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.Regular10,
                                                     targetFramework: _supportingFramework,
                                                     references: new[] { compilation1.ToMetadataReference() });

                if (isChecked)
                {
                    compilation2.VerifyDiagnostics(
                        // (6,13): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                        //         _ = ++x;
                        Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, prefixOp + "x" + postfixOp).WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 13),
                        // (6,13): error CS8936: Feature 'checked user-defined operators' is not available in C# 10.0. Please use language version 11.0 or greater.
                        //         _ = ++x;
                        Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, prefixOp + "x" + postfixOp).WithArguments("checked user-defined operators", "11.0").WithLocation(6, 13)
                        );
                }
                else
                {
                    compilation2.VerifyDiagnostics(
                        // (6,13): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                        //         _ = ++x;
                        Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, prefixOp + "x" + postfixOp).WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 13)
                        );
                }

                var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.Regular10,
                                                     targetFramework: _supportingFramework);

                if (isChecked)
                {
                    compilation3.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                        // (12,32): error CS8936: Feature 'checked user-defined operators' is not available in C# 10.0. Please use language version 11.0 or greater.
                        //     abstract static T operator checked ++ (T x);
                        Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "checked").WithArguments("checked user-defined operators", "11.0").WithLocation(12, 32),
                        // (12,40): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                        //     abstract static T operator checked ++ (T x);
                        Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, prefixOp + postfixOp).WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(12, 40)
                        );
                }
                else
                {
                    compilation3.VerifyDiagnostics(
                        // (12,31): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                        //     abstract static T operator+ (T x);
                        Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, prefixOp + postfixOp).WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(12, 31)
                        );
                }
            }
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractTrueOperator_01(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
interface I1
{
    " + modifier + @" static bool operator true (I1 x)" + body + @"
    " + modifier + @" static bool operator false (I1 x)" + body + @"

    static void M02(I1 x)
    {
        _ = x ? true : false;
    }

    void M03(I1 y)
    {
        _ = y ? true : false;
    }
}

class Test
{
    static void MT1(I1 a)
    {
        _ = a ? true : false;
    }

    static void MT2<T>() where T : I1
    {
        _ = (System.Linq.Expressions.Expression<System.Action<T>>)((T b) => (b ? true : false).ToString());
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (9,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         _ = x ? true : false;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "x").WithLocation(9, 13),
                // (14,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         _ = y ? true : false;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "y").WithLocation(14, 13),
                // (22,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         _ = a ? true : false;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "a").WithLocation(22, 13),
                // (27,78): error CS8927: An expression tree may not contain an access of static virtual or abstract interface member
                //         _ = (System.Linq.Expressions.Expression<System.Action<T>>)((T b) => (b ? true : false).ToString());
                Diagnostic(ErrorCode.ERR_ExpressionTreeContainsAbstractStaticMemberAccess, "b").WithLocation(27, 78)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractTrueOperator_03(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    " + modifier + @" static bool operator true (T x)" + body + @"
    " + modifier + @" static bool operator false (T x)" + body + @"
}

class Test
{
    static void M02<T, U>(T x) where T : U where U : I1<T>
    {
        _ = x ? true : false;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>(T)",
@"
{
  // Code size       18 (0x12)
  .maxstack  1
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""bool I1<T>.op_True(T)""
  IL_000d:  brtrue.s   IL_0011
  IL_000f:  br.s       IL_0011
  IL_0011:  ret
}
");

            compilation1 = CreateCompilation(source1, options: TestOptions.ReleaseDll,
                                             parseOptions: TestOptions.RegularPreview,
                                             targetFramework: _supportingFramework);

            verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>(T)",
@"
{
  // Code size       14 (0xe)
  .maxstack  1
  IL_0000:  ldarg.0
  IL_0001:  constrained. ""T""
  IL_0007:  call       ""bool I1<T>.op_True(T)""
  IL_000c:  pop
  IL_000d:  ret
}
");

            var tree = compilation1.SyntaxTrees.Single();
            var model = compilation1.GetSemanticModel(tree);
            var node = tree.GetRoot().DescendantNodes().OfType<ConditionalExpressionSyntax>().First();

            Assert.Equal("x ? true : false", node.ToString());
            VerifyOperationTreeForNode(compilation1, model, node,
@"
IConditionalOperation (OperationKind.Conditional, Type: System.Boolean) (Syntax: 'x ? true : false')
  Condition: 
    IUnaryOperation (UnaryOperatorKind.True) (OperatorMethod: System.Boolean I1<T>.op_True(T x) ConstrainedToType: T) (OperationKind.Unary, Type: System.Boolean, IsImplicit) (Syntax: 'x')
      Operand: 
        IParameterReferenceOperation: x (OperationKind.ParameterReference, Type: T) (Syntax: 'x')
  WhenTrue: 
    ILiteralOperation (OperationKind.Literal, Type: System.Boolean, Constant: True) (Syntax: 'true')
  WhenFalse: 
    ILiteralOperation (OperationKind.Literal, Type: System.Boolean, Constant: False) (Syntax: 'false')
");
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractTrueOperator_04(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static bool operator true (I1 x)" + body + @"
    " + modifier + @" static bool operator false (I1 x)" + body + @"
}
";
            var source2 =
@"
class Test
{
    static void M02<T>(T x) where T : I1
    {
        _ = x ? true : false;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (6,13): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //         _ = x ? true : false;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "x").WithLocation(6, 13)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation3.VerifyDiagnostics(
                // (12,35): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static bool operator true (I1 x);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "true").WithLocation(12, 35),
                // (13,35): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static bool operator false (I1 x);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "false").WithLocation(13, 35)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractTrueOperator_06(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static bool operator true (I1 x)" + body + @"
    " + modifier + @" static bool operator false (I1 x)" + body + @"
}
";
            var source2 =
@"
class Test
{
    static void M02<T>(T x) where T : I1
    {
        _ = x ? true : false;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (6,13): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                //         _ = x ? true : false;
                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "x").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 13)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation3.VerifyDiagnostics(
                // (12,35): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual  static bool operator true (I1 x) => throw null;
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "true").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(12, 35),
                // (13,35): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual  static bool operator false (I1 x) => throw null;
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "false").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(13, 35)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractTrueFalseOperatorForTupleEquality_01([CombinatorialValues("==", "!=")] string op, bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
interface I1
{
    " + modifier + @" static bool operator true (I1 x)" + body + @"
    " + modifier + @" static bool operator false (I1 x)" + body + @"

    static void M02((int, C<I1>) x)
    {
        _ = x " + op + @" x;
    }

    void M03((int, C<I1>) y)
    {
        _ = y " + op + @" y;
    }
}

class Test
{
    static void MT1((int, C<I1>) a)
    {
        _ = a " + op + @" a;
    }

    static void MT2<T>() where T : I1
    {
        _ = (System.Linq.Expressions.Expression<System.Action<(int, C<T>)>>)(((int, C<T>) b) => (b " + op + @" b).ToString());
    }
}

#pragma warning disable CS0660 // 'C<T>' defines operator == or operator != but does not override Object.Equals(object o)
#pragma warning disable CS0661 // 'C<T>' defines operator == or operator != but does not override Object.GetHashCode()

class C<T>
{
    public static T operator == (C<T> x, C<T> y) => default;
    public static T operator != (C<T> x, C<T> y) => default;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            if (isVirtual)
            {
                compilation1.VerifyDiagnostics(
                    // (9,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                    //         _ = x == x;
                    Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "x " + op + " x").WithLocation(9, 13),
                    // (14,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                    //         _ = y == y;
                    Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "y " + op + " y").WithLocation(14, 13),
                    // (22,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                    //         _ = a == a;
                    Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "a " + op + " a").WithLocation(22, 13),
                    // (27,98): error CS8382: An expression tree may not contain a tuple == or != operator
                    //         _ = (System.Linq.Expressions.Expression<System.Action<(int, C<T>)>>)(((int, C<T>) b) => (b == b).ToString());
                    Diagnostic(ErrorCode.ERR_ExpressionTreeContainsTupleBinOp, "b " + op + " b").WithLocation(27, 98)
                    );
            }
            else
            {
                compilation1.VerifyDiagnostics(
                    // (7,34): error CS8920: The interface 'I1' cannot be used as type argument. Static member 'I1.operator true(I1)' does not have a most specific implementation in the interface.
                    //     static void M02((int, C<I1>) x)
                    Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "x").WithArguments("I1", "I1.operator true(I1)").WithLocation(7, 34),
                    // (12,27): error CS8920: The interface 'I1' cannot be used as type argument. Static member 'I1.operator true(I1)' does not have a most specific implementation in the interface.
                    //     void M03((int, C<I1>) y)
                    Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "y").WithArguments("I1", "I1.operator true(I1)").WithLocation(12, 27),
                    // (20,34): error CS8920: The interface 'I1' cannot be used as type argument. Static member 'I1.operator true(I1)' does not have a most specific implementation in the interface.
                    //     static void MT1((int, C<I1>) a)
                    Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers, "a").WithArguments("I1", "I1.operator true(I1)").WithLocation(20, 34),
                    // (9,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                    //         _ = x == x;
                    Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "x " + op + " x").WithLocation(9, 13),
                    // (14,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                    //         _ = y == y;
                    Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "y " + op + " y").WithLocation(14, 13),
                    // (22,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                    //         _ = a == a;
                    Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "a " + op + " a").WithLocation(22, 13),
                    // (27,98): error CS8382: An expression tree may not contain a tuple == or != operator
                    //         _ = (System.Linq.Expressions.Expression<System.Action<(int, C<T>)>>)(((int, C<T>) b) => (b == b).ToString());
                    Diagnostic(ErrorCode.ERR_ExpressionTreeContainsTupleBinOp, "b " + op + " b").WithLocation(27, 98)
                    );
            }
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractTrueFalseOperatorForTupleEquality_03([CombinatorialValues("==", "!=")] string op, bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    " + modifier + @" static bool operator true (T x)" + body + @"
    " + modifier + @" static bool operator false (T x)" + body + @"
}

class Test
{
    static void M02<T, U>((int, C<T>) x) where T : U where U : I1<T>
    {
        _ = x " + op + @" x;
    }
}

#pragma warning disable CS0660 // 'C<T>' defines operator == or operator != but does not override Object.Equals(object o)
#pragma warning disable CS0661 // 'C<T>' defines operator == or operator != but does not override Object.GetHashCode()

class C<T>
{
    public static T operator == (C<T> x, C<T> y) => default;
    public static T operator != (C<T> x, C<T> y) => default;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            if (op == "==")
            {
                verifier.VerifyIL("Test.M02<T, U>(System.ValueTuple<int, C<T>>)",
@"
{
  // Code size       55 (0x37)
  .maxstack  2
  .locals init (System.ValueTuple<int, C<T>> V_0,
                System.ValueTuple<int, C<T>> V_1)
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  stloc.0
  IL_0003:  ldarg.0
  IL_0004:  stloc.1
  IL_0005:  ldloc.0
  IL_0006:  ldfld      ""int System.ValueTuple<int, C<T>>.Item1""
  IL_000b:  ldloc.1
  IL_000c:  ldfld      ""int System.ValueTuple<int, C<T>>.Item1""
  IL_0011:  bne.un.s   IL_0034
  IL_0013:  ldloc.0
  IL_0014:  ldfld      ""C<T> System.ValueTuple<int, C<T>>.Item2""
  IL_0019:  ldloc.1
  IL_001a:  ldfld      ""C<T> System.ValueTuple<int, C<T>>.Item2""
  IL_001f:  call       ""T C<T>.op_Equality(C<T>, C<T>)""
  IL_0024:  constrained. ""T""
  IL_002a:  call       ""bool I1<T>.op_False(T)""
  IL_002f:  ldc.i4.0
  IL_0030:  ceq
  IL_0032:  br.s       IL_0035
  IL_0034:  ldc.i4.0
  IL_0035:  pop
  IL_0036:  ret
}
");
            }
            else
            {
                verifier.VerifyIL("Test.M02<T, U>(System.ValueTuple<int, C<T>>)",
@"
{
  // Code size       52 (0x34)
  .maxstack  2
  .locals init (System.ValueTuple<int, C<T>> V_0,
                System.ValueTuple<int, C<T>> V_1)
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  stloc.0
  IL_0003:  ldarg.0
  IL_0004:  stloc.1
  IL_0005:  ldloc.0
  IL_0006:  ldfld      ""int System.ValueTuple<int, C<T>>.Item1""
  IL_000b:  ldloc.1
  IL_000c:  ldfld      ""int System.ValueTuple<int, C<T>>.Item1""
  IL_0011:  bne.un.s   IL_0031
  IL_0013:  ldloc.0
  IL_0014:  ldfld      ""C<T> System.ValueTuple<int, C<T>>.Item2""
  IL_0019:  ldloc.1
  IL_001a:  ldfld      ""C<T> System.ValueTuple<int, C<T>>.Item2""
  IL_001f:  call       ""T C<T>.op_Inequality(C<T>, C<T>)""
  IL_0024:  constrained. ""T""
  IL_002a:  call       ""bool I1<T>.op_True(T)""
  IL_002f:  br.s       IL_0032
  IL_0031:  ldc.i4.1
  IL_0032:  pop
  IL_0033:  ret
}
");
            }

            compilation1 = CreateCompilation(source1, options: TestOptions.ReleaseDll,
                                             parseOptions: TestOptions.RegularPreview,
                                             targetFramework: _supportingFramework);

            verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            if (op == "==")
            {
                verifier.VerifyIL("Test.M02<T, U>(System.ValueTuple<int, C<T>>)",
@"
{
  // Code size       54 (0x36)
  .maxstack  2
  .locals init (System.ValueTuple<int, C<T>> V_0,
                System.ValueTuple<int, C<T>> V_1)
  IL_0000:  ldarg.0
  IL_0001:  stloc.0
  IL_0002:  ldarg.0
  IL_0003:  stloc.1
  IL_0004:  ldloc.0
  IL_0005:  ldfld      ""int System.ValueTuple<int, C<T>>.Item1""
  IL_000a:  ldloc.1
  IL_000b:  ldfld      ""int System.ValueTuple<int, C<T>>.Item1""
  IL_0010:  bne.un.s   IL_0033
  IL_0012:  ldloc.0
  IL_0013:  ldfld      ""C<T> System.ValueTuple<int, C<T>>.Item2""
  IL_0018:  ldloc.1
  IL_0019:  ldfld      ""C<T> System.ValueTuple<int, C<T>>.Item2""
  IL_001e:  call       ""T C<T>.op_Equality(C<T>, C<T>)""
  IL_0023:  constrained. ""T""
  IL_0029:  call       ""bool I1<T>.op_False(T)""
  IL_002e:  ldc.i4.0
  IL_002f:  ceq
  IL_0031:  br.s       IL_0034
  IL_0033:  ldc.i4.0
  IL_0034:  pop
  IL_0035:  ret
}
");
            }
            else
            {
                verifier.VerifyIL("Test.M02<T, U>(System.ValueTuple<int, C<T>>)",
@"
{
  // Code size       51 (0x33)
  .maxstack  2
  .locals init (System.ValueTuple<int, C<T>> V_0,
                System.ValueTuple<int, C<T>> V_1)
  IL_0000:  ldarg.0
  IL_0001:  stloc.0
  IL_0002:  ldarg.0
  IL_0003:  stloc.1
  IL_0004:  ldloc.0
  IL_0005:  ldfld      ""int System.ValueTuple<int, C<T>>.Item1""
  IL_000a:  ldloc.1
  IL_000b:  ldfld      ""int System.ValueTuple<int, C<T>>.Item1""
  IL_0010:  bne.un.s   IL_0030
  IL_0012:  ldloc.0
  IL_0013:  ldfld      ""C<T> System.ValueTuple<int, C<T>>.Item2""
  IL_0018:  ldloc.1
  IL_0019:  ldfld      ""C<T> System.ValueTuple<int, C<T>>.Item2""
  IL_001e:  call       ""T C<T>.op_Inequality(C<T>, C<T>)""
  IL_0023:  constrained. ""T""
  IL_0029:  call       ""bool I1<T>.op_True(T)""
  IL_002e:  br.s       IL_0031
  IL_0030:  ldc.i4.1
  IL_0031:  pop
  IL_0032:  ret
}
");
            }

            var tree = compilation1.SyntaxTrees.Single();
            var model = compilation1.GetSemanticModel(tree);
            var node = tree.GetRoot().DescendantNodes().OfType<BinaryExpressionSyntax>().First();

            Assert.Equal("x " + op + " x", node.ToString());
            VerifyOperationTreeForNode(compilation1, model, node,
// Information about user-defined operators isn't exposed today.
@"
ITupleBinaryOperation (BinaryOperatorKind." + (op == "==" ? "Equals" : "NotEquals") + @") (OperationKind.TupleBinary, Type: System.Boolean) (Syntax: 'x " + op + @" x')
  Left: 
    IParameterReferenceOperation: x (OperationKind.ParameterReference, Type: (System.Int32, C<T>)) (Syntax: 'x')
  Right: 
    IParameterReferenceOperation: x (OperationKind.ParameterReference, Type: (System.Int32, C<T>)) (Syntax: 'x')
");
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractTrueFalseOperatorForTupleEquality_04([CombinatorialValues("==", "!=")] string op, bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static bool operator true (I1 x)" + body + @"
    " + modifier + @" static bool operator false (I1 x)" + body + @"
}
";
            var source2 =
@"
class Test
{
    static void M02<T>((int, C<T>) x) where T : I1
    {
        _ = x " + op + @" x;
    }
}

#pragma warning disable CS0660 // 'C<T>' defines operator == or operator != but does not override Object.Equals(object o)
#pragma warning disable CS0661 // 'C<T>' defines operator == or operator != but does not override Object.GetHashCode()

class C<T>
{
    public static T operator == (C<T> x, C<T> y) => default;
    public static T operator != (C<T> x, C<T> y) => default;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (6,13): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //         _ = x == x;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "x " + op + " x").WithLocation(6, 13)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation3.VerifyDiagnostics(
                // (21,35): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static bool operator true (I1 x);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "true").WithLocation(21, 35),
                // (22,35): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static bool operator false (I1 x);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "false").WithLocation(22, 35)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractTrueFalseOperatorForTupleEquality_06([CombinatorialValues("==", "!=")] string op, bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static bool operator true (I1 x)" + body + @"
    " + modifier + @" static bool operator false (I1 x)" + body + @"
}
";
            var source2 =
@"
class Test
{
    static void M02<T>((int, C<T>) x) where T : I1
    {
        _ = x " + op + @" x;
    }
}

#pragma warning disable CS0660 // 'C<T>' defines operator == or operator != but does not override Object.Equals(object o)
#pragma warning disable CS0661 // 'C<T>' defines operator == or operator != but does not override Object.GetHashCode()

class C<T>
{
    public static T operator == (C<T> x, C<T> y) => default;
    public static T operator != (C<T> x, C<T> y) => default;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (6,13): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                //         _ = x == x;
                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "x " + op + " x").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 13)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation3.VerifyDiagnostics(
                // (21,35): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual  static bool operator true (I1 x) => throw null;
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "true").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(21, 35),
                // (22,35): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual  static bool operator false (I1 x) => throw null;
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "false").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(22, 35)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractBinaryOperator_01([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<<", ">>", ">>>", "<", ">", "<=", ">=", "==", "!=")] string op, bool isChecked, bool isVirtual)
        {
            if (GetBinaryOperatorName(op, isChecked, out string checkedKeyword) is null)
            {
                return;
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
partial interface I1
{
    " + modifier + @" static I1 operator " + checkedKeyword + op + @" (I1 x, int y)" + body + @"

    static void M02(I1 x)
    {" + checkedKeyword + @"{
        _ = x " + op + @" 1;
    }}

    void M03(I1 y)
    {" + checkedKeyword + @"{
        _ = y " + op + @" 2;
    }}
}

class Test
{
    static void MT1(I1 a)
    {" + checkedKeyword + @"{
        _ = a " + op + @" 3;
    }}

    static void MT2<T>() where T : I1
    {" + checkedKeyword + @"{
        _ = (System.Linq.Expressions.Expression<System.Action<T>>)((T b) => (b " + op + @" 4).ToString());
    }}
}
";

            string matchingOp = isChecked ? op : MatchingBinaryOperator(op);

            if (matchingOp is object)
            {
                source1 +=
@"
public partial interface I1
{
    " + modifier + @" static I1 operator" + matchingOp + @" (I1 x, int y)" + body + @"
}
";
            }

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            if (isChecked && op == "/")
            {
                compilation1.VerifyDiagnostics(
                    // (8,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                    //         _ = x - 1;
                    Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "x " + op + " 1").WithLocation(8, 13),
                    // (13,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                    //         _ = y - 2;
                    Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "y " + op + " 2").WithLocation(13, 13),
                    // (21,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                    //         _ = a - 3;
                    Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "a " + op + " 3").WithLocation(21, 13),
                    // (26,78): error CS7053: An expression tree may not contain 'I1.operator checked /(I1, int)'
                    //         _ = (System.Linq.Expressions.Expression<System.Action<T>>)((T b) => (b / 4).ToString());
                    Diagnostic(ErrorCode.ERR_FeatureNotValidInExpressionTree, "b / 4").WithArguments("I1.operator checked /(I1, int)").WithLocation(26, 78)
                    );
            }
            else if (op == ">>>")
            {
                compilation1.VerifyDiagnostics(
                    // (8,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                    //         _ = x >>> 1;
                    Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "x >>> 1").WithLocation(8, 13),
                    // (13,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                    //         _ = y >>> 2;
                    Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "y >>> 2").WithLocation(13, 13),
                    // (21,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                    //         _ = a >>> 3;
                    Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "a >>> 3").WithLocation(21, 13),
                    // (26,78): error CS8927: An expression tree may not contain an access of static virtual or abstract interface member
                    //         _ = (System.Linq.Expressions.Expression<System.Action<T>>)((T b) => (b >>> 4).ToString());
                    Diagnostic(ErrorCode.ERR_ExpressionTreeContainsAbstractStaticMemberAccess, "b >>> 4").WithLocation(26, 78),
                    // (26,78): error CS7053: An expression tree may not contain '>>>'
                    //         _ = (System.Linq.Expressions.Expression<System.Action<T>>)((T b) => (b >>> 4).ToString());
                    Diagnostic(ErrorCode.ERR_FeatureNotValidInExpressionTree, "b >>> 4").WithArguments(">>>").WithLocation(26, 78)
                    );
            }
            else
            {
                compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_BadAbstractEqualityOperatorSignature).Verify(
                    // (8,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                    //         _ = x - 1;
                    Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "x " + op + " 1").WithLocation(8, 13),
                    // (13,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                    //         _ = y - 2;
                    Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "y " + op + " 2").WithLocation(13, 13),
                    // (21,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                    //         _ = a - 3;
                    Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "a " + op + " 3").WithLocation(21, 13),
                    // (26,78): error CS8927: An expression tree may not contain an access of static virtual or abstract interface member
                    //         _ = (System.Linq.Expressions.Expression<System.Action<T>>)((T b) => (b - 4).ToString());
                    Diagnostic(ErrorCode.ERR_ExpressionTreeContainsAbstractStaticMemberAccess, "b " + op + " 4").WithLocation(26, 78)
                    );
            }
        }

        [Theory]
        [InlineData("&", true, false, false, false)]
        [InlineData("|", true, false, false, false)]
        [InlineData("&", false, false, true, false)]
        [InlineData("|", false, true, false, false)]
        [InlineData("&", true, false, true, false)]
        [InlineData("|", true, true, false, false)]
        [InlineData("&", false, true, false, true)]
        [InlineData("|", false, false, true, true)]
        public void ConsumeAbstractLogicalBinaryOperator_01(string op, bool binaryIsAbstract, bool trueIsAbstract, bool falseIsAbstract, bool success)
        {
            consumeAbstractLogicalBinaryOperator_01(op, binaryIsAbstract, trueIsAbstract, falseIsAbstract, success, isVirtual: false);
            consumeAbstractLogicalBinaryOperator_01(op, binaryIsAbstract, trueIsAbstract, falseIsAbstract, success, isVirtual: true);

            void consumeAbstractLogicalBinaryOperator_01(string op, bool binaryIsAbstract, bool trueIsAbstract, bool falseIsAbstract, bool success, bool isVirtual)
            {
                var (modifier, body) = GetModifierAndBody(isVirtual);

                var source1 =
@"
interface I1
{
    " + (binaryIsAbstract ? modifier : "") + @" static I1 operator" + op + @" (I1 x, I1 y)" + (binaryIsAbstract ? body : " => throw null;") + @"
    " + (trueIsAbstract ? modifier : "") + @" static bool operator true (I1 x)" + (trueIsAbstract ? body : " => throw null;") + @"
    " + (falseIsAbstract ? modifier : "") + @" static bool operator false (I1 x)" + (falseIsAbstract ? body : " => throw null;") + @"

    static void M02(I1 x)
    {
        _ = x " + op + op + @" x;
    }

    void M03(I1 y)
    {
        _ = y " + op + op + @" y;
    }
}

class Test
{
    static void MT1(I1 a)
    {
        _ = a " + op + op + @" a;
    }

    static void MT2<T>() where T : I1
    {
        _ = (System.Linq.Expressions.Expression<System.Action<T>>)((T b) => (b " + op + op + @" b).ToString());
    }
}
";
                var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                if (success)
                {
                    Assert.False(binaryIsAbstract);
                    Assert.False(op == "&" ? falseIsAbstract : trueIsAbstract);
                    var binaryMetadataName = op == "&" ? "op_BitwiseAnd" : "op_BitwiseOr";
                    var unaryMetadataName = op == "&" ? "op_False" : "op_True";

                    var verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

                    verifier.VerifyIL("Test.MT1(I1)",
@"
{
  // Code size       22 (0x16)
  .maxstack  2
  .locals init (I1 V_0)
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  stloc.0
  IL_0003:  ldloc.0
  IL_0004:  call       ""bool I1." + unaryMetadataName + @"(I1)""
  IL_0009:  brtrue.s   IL_0015
  IL_000b:  ldloc.0
  IL_000c:  ldarg.0
  IL_000d:  call       ""I1 I1." + binaryMetadataName + @"(I1, I1)""
  IL_0012:  pop
  IL_0013:  br.s       IL_0015
  IL_0015:  ret
}
");
                }
                else
                {
                    compilation1.VerifyDiagnostics(
                        // (10,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                        //         _ = x && x;
                        Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "x " + op + op + " x").WithLocation(10, 13),
                        // (15,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                        //         _ = y && y;
                        Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "y " + op + op + " y").WithLocation(15, 13),
                        // (23,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                        //         _ = a && a;
                        Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "a " + op + op + " a").WithLocation(23, 13),
                        // (28,78): error CS8927: An expression tree may not contain an access of static virtual or abstract interface member
                        //         _ = (System.Linq.Expressions.Expression<System.Action<T>>)((T b) => (b && b).ToString());
                        Diagnostic(ErrorCode.ERR_ExpressionTreeContainsAbstractStaticMemberAccess, "b " + op + op + " b").WithLocation(28, 78)
                        );
                }
            }
        }

        [Theory]
        [InlineData("&", true, false, false)]
        [InlineData("|", true, false, false)]
        [InlineData("&", false, false, true)]
        [InlineData("|", false, true, false)]
        [InlineData("&", true, false, true)]
        [InlineData("|", true, true, false)]
        [InlineData("&", false, true, false)]
        [InlineData("|", false, false, true)]
        public void ConsumeAbstractLogicalBinaryOperator_01_Dynamic(string op, bool binaryIsAbstract, bool trueIsAbstract, bool falseIsAbstract)
        {
            consumeAbstractLogicalBinaryOperator_01_Dynamic(op, binaryIsAbstract, trueIsAbstract, falseIsAbstract, isVirtual: false);
            consumeAbstractLogicalBinaryOperator_01_Dynamic(op, binaryIsAbstract, trueIsAbstract, falseIsAbstract, isVirtual: true);

            void consumeAbstractLogicalBinaryOperator_01_Dynamic(string op, bool binaryIsAbstract, bool trueIsAbstract, bool falseIsAbstract, bool isVirtual)
            {
                var (modifier, body) = GetModifierAndBody(isVirtual);

                var source1 =
@"
interface I1
{
    " + (binaryIsAbstract ? modifier : "") + @" static I1 operator" + op + @" (I1 x, I1 y)" + (binaryIsAbstract ? body : " => throw null;") + @"
    " + (trueIsAbstract ? modifier : "") + @" static bool operator true (I1 x)" + (trueIsAbstract ? body : " => throw null;") + @"
    " + (falseIsAbstract ? modifier : "") + @" static bool operator false (I1 x)" + (falseIsAbstract ? body : " => throw null;") + @"
}

class Test
{
    static void MT3(I1 b, dynamic c)
    {
        _ = b " + op + op + @" c;
    }

    static void MT4<T>() where T : I1
    {
        _ = (System.Linq.Expressions.Expression<System.Action<T, dynamic>>)((T d, dynamic e) => (d " + op + op + @" e).ToString());
    }
}
";
                var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation1.VerifyDiagnostics(
                    // (13,13): error CS7083: Expression must be implicitly convertible to Boolean or its type 'I1' must not be an interface and must define operator 'false'.
                    //         _ = b && c;
                    Diagnostic(ErrorCode.ERR_InvalidDynamicCondition, "b").WithArguments("I1", op == "&" ? "false" : "true").WithLocation(13, 13),
                    // (18,98): error CS7083: Expression must be implicitly convertible to Boolean or its type 'T' must not be an interface and must define operator 'false'.
                    //         _ = (System.Linq.Expressions.Expression<System.Action<T, dynamic>>)((T d, dynamic e) => (d && e).ToString());
                    Diagnostic(ErrorCode.ERR_InvalidDynamicCondition, "d").WithArguments("T", op == "&" ? "false" : "true").WithLocation(18, 98)
                    );
            }
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractCompoundBinaryOperator_01([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<<", ">>", ">>>")] string op, bool isChecked, bool isVirtual)
        {
            if (GetBinaryOperatorName(op, isChecked, out string checkedKeyword) is null)
            {
                return;
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
interface I1
{
    " + modifier + @" static I1 operator " + checkedKeyword + op + @" (I1 x, int y)" + body + @"

    static void M02(I1 x)
    {" + checkedKeyword + @"{
        x " + op + @"= 1;
    }}

    void M03(I1 y)
    {" + checkedKeyword + @"{
        y " + op + @"= 2;
    }}
}

interface I2<T> where T : I2<T>
{
    " + modifier + @" static T operator " + checkedKeyword + op + @" (T x, int y)" + body + @"
}

class Test
{
    static void MT1(I1 a)
    {" + checkedKeyword + @"{
        a " + op + @"= 3;
    }}

    static void MT2<T>() where T : I2<T>
    {" + checkedKeyword + @"{
        _ = (System.Linq.Expressions.Expression<System.Action<T>>)((T b) => (b " + op + @"= 4).ToString());
    }}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (8,9): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         x /= 1;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "x " + op + "= 1").WithLocation(8, 9),
                // (13,9): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         y /= 2;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "y " + op + "= 2").WithLocation(13, 9),
                // (26,9): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         a /= 3;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "a " + op + "= 3").WithLocation(26, 9),
                // (31,78): error CS0832: An expression tree may not contain an assignment operator
                //         _ = (System.Linq.Expressions.Expression<System.Action<T>>)((T b) => (b /= 4).ToString());
                Diagnostic(ErrorCode.ERR_ExpressionTreeContainsAssignment, "b " + op + "= 4").WithLocation(31, 78)
                );
        }

        private static string BinaryOperatorKind(string op)
        {
            switch (op)
            {
                case "+":
                    return "Add";

                case "-":
                    return "Subtract";

                case "*":
                    return "Multiply";

                case "/":
                    return "Divide";

                case "%":
                    return "Remainder";

                case "<<":
                    return "LeftShift";

                case ">>":
                    return "RightShift";

                case ">>>":
                    return "UnsignedRightShift";

                case "&":
                    return "And";

                case "|":
                    return "Or";

                case "^":
                    return "ExclusiveOr";

                case "<":
                    return "LessThan";

                case "<=":
                    return "LessThanOrEqual";

                case "==":
                    return "Equals";

                case "!=":
                    return "NotEquals";

                case ">=":
                    return "GreaterThanOrEqual";

                case ">":
                    return "GreaterThan";

            }

            throw TestExceptionUtilities.UnexpectedValue(op);
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractBinaryOperatorForTupleEquality_01([CombinatorialValues("==", "!=")] string op, bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
interface I1<T> where T : I1<T>
{
    " + modifier + @" static bool operator == (T x, T y)" + body + @"
    " + modifier + @" static bool operator != (T x, T y)" + body + @"

    " + modifier + @" static bool operator == (I1<T> x, I1<T> y)" + body + @"
    " + modifier + @" static bool operator != (I1<T> x, I1<T> y)" + body + @"

    static void M02((int, I1<T>) x)
    {
        _ = x " + op + @" x;
    }

    void M03((int, I1<T>) y)
    {
        _ = y " + op + @" y;
    }
}

class Test
{
    static void MT1<T>((int, I1<T>) a) where T : I1<T>
    {
        _ = a " + op + @" a;
    }

    static void MT2<T>() where T : I1<T>
    {
        _ = (System.Linq.Expressions.Expression<System.Action<(int, T)>>)(((int, T) b) => (b " + op + @" b).ToString());
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_BadAbstractEqualityOperatorSignature or (int)ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers)).Verify(
                // (12,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         _ = x != x;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "x " + op + " x").WithLocation(12, 13),
                // (17,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         _ = y != y;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "y " + op + " y").WithLocation(17, 13),
                // (25,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         _ = a != a;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "a " + op + " a").WithLocation(25, 13),
                // (30,92): error CS8382: An expression tree may not contain a tuple == or != operator
                //         _ = (System.Linq.Expressions.Expression<System.Action<(int, T)>>)(((int, T) b) => (b != b).ToString());
                Diagnostic(ErrorCode.ERR_ExpressionTreeContainsTupleBinOp, "b " + op + " b").WithLocation(30, 92)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractBinaryOperator_03([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<<", ">>", ">>>")] string op, bool isCheckedOperator, bool isCheckedContext, bool isVirtual)
        {
            string metadataName = GetBinaryOperatorName(op, isCheckedOperator, out string checkedKeyword);

            if (metadataName is null)
            {
                return;
            }

            if (isCheckedOperator && !isCheckedContext)
            {
                metadataName = BinaryOperatorName(op, isChecked: false);
            }

            string contextKeyword = isCheckedContext ? " checked " : " unchecked ";
            bool isShiftOperator = op is "<<" or ">>" or ">>>";
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public partial interface I1<T0> where T0 : I1<T0>
{
    " + modifier + @" static T0 operator" + op + @" (T0 x, int a)" + body + @"
"
;
            if (isCheckedOperator)
            {
                source1 +=
@"
    " + modifier + @" static T0 operator checked" + op + @" (T0 x, int a)" + body + @"
"
;
            }

            source1 +=
@"
}

partial class Test
{
    static void M03<T, U>(T x) where T : U where U : I1<T>
    {" + contextKeyword + @"{
        _ = x " + op + @" 1;
    }}

    static void M05<T, U>(T? y) where T : struct, U where U : I1<T>
    {" + contextKeyword + @"{
        _ = y " + op + @" 1;
    }}
}
";

            if (!isShiftOperator)
            {
                source1 += @"
public partial interface I1<T0>
{
    " + modifier + @" static T0 operator" + op + @" (int a, T0 x)" + body + @"
    " + modifier + @" static T0 operator" + op + @" (I1<T0> x, T0 a)" + body + @"
    " + modifier + @" static T0 operator" + op + @" (T0 x, I1<T0> a)" + body + @"
"
;
                if (isCheckedOperator)
                {
                    source1 +=
@"
    " + modifier + @" static T0 operator checked " + op + @" (int a, T0 x)" + body + @"
    " + modifier + @" static T0 operator checked " + op + @" (I1<T0> x, T0 a)" + body + @"
    " + modifier + @" static T0 operator checked " + op + @" (T0 x, I1<T0> a)" + body + @"
"
    ;
                }

                source1 +=
@"}

partial class Test
{
    static void M02<T, U>(T x) where T : U where U : I1<T>
    {" + contextKeyword + @"{
        _ = 1 " + op + @" x;
    }}

    static void M04<T, U>(T? y) where T : struct, U where U : I1<T>
    {" + contextKeyword + @"{
        _ = 1 " + op + @" y;
    }}

    static void M06<T, U>(I1<T> x, T y) where T : U where U : I1<T>
    {" + contextKeyword + @"{
        _ = x " + op + @" y;
    }}

    static void M07<T, U>(T x, I1<T> y) where T : U where U : I1<T>
    {" + contextKeyword + @"{
        _ = x " + op + @" y;
    }}
}
";
            }

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            compilation1 = CreateCompilation(source1, options: TestOptions.ReleaseDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            if (!isShiftOperator)
            {
                verifier.VerifyIL("Test.M02<T, U>(T)",
@"
{
  // Code size       15 (0xf)
  .maxstack  2
  IL_0000:  ldc.i4.1
  IL_0001:  ldarg.0
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""T I1<T>." + metadataName + @"(int, T)""
  IL_000d:  pop
  IL_000e:  ret
}
");
                verifier.VerifyIL("Test.M04<T, U>(T?)",
@"
{
  // Code size       32 (0x20)
  .maxstack  2
  .locals init (T? V_0)
  IL_0000:  ldarg.0
  IL_0001:  stloc.0
  IL_0002:  ldloca.s   V_0
  IL_0004:  call       ""readonly bool T?.HasValue.get""
  IL_0009:  brfalse.s  IL_001f
  IL_000b:  ldc.i4.1
  IL_000c:  ldloca.s   V_0
  IL_000e:  call       ""readonly T T?.GetValueOrDefault()""
  IL_0013:  constrained. ""T""
  IL_0019:  call       ""T I1<T>." + metadataName + @"(int, T)""
  IL_001e:  pop
  IL_001f:  ret
}
");
                verifier.VerifyIL("Test.M06<T, U>(I1<T>, T)",
@"
{
  // Code size       15 (0xf)
  .maxstack  2
  IL_0000:  ldarg.0
  IL_0001:  ldarg.1
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""T I1<T>." + metadataName + @"(I1<T>, T)""
  IL_000d:  pop
  IL_000e:  ret
}
");

                verifier.VerifyIL("Test.M07<T, U>(T, I1<T>)",
@"
{
  // Code size       15 (0xf)
  .maxstack  2
  IL_0000:  ldarg.0
  IL_0001:  ldarg.1
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""T I1<T>." + metadataName + @"(T, I1<T>)""
  IL_000d:  pop
  IL_000e:  ret
}
");
            }

            verifier.VerifyIL("Test.M03<T, U>(T)",
@"
{
  // Code size       15 (0xf)
  .maxstack  2
  IL_0000:  ldarg.0
  IL_0001:  ldc.i4.1
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""T I1<T>." + metadataName + @"(T, int)""
  IL_000d:  pop
  IL_000e:  ret
}
");

            verifier.VerifyIL("Test.M05<T, U>(T?)",
@"
{
  // Code size       32 (0x20)
  .maxstack  2
  .locals init (T? V_0)
  IL_0000:  ldarg.0
  IL_0001:  stloc.0
  IL_0002:  ldloca.s   V_0
  IL_0004:  call       ""readonly bool T?.HasValue.get""
  IL_0009:  brfalse.s  IL_001f
  IL_000b:  ldloca.s   V_0
  IL_000d:  call       ""readonly T T?.GetValueOrDefault()""
  IL_0012:  ldc.i4.1
  IL_0013:  constrained. ""T""
  IL_0019:  call       ""T I1<T>." + metadataName + @"(T, int)""
  IL_001e:  pop
  IL_001f:  ret
}
");

            compilation1 = CreateCompilation(source1, options: TestOptions.ReleaseDll,
                                             parseOptions: TestOptions.RegularPreview,
                                             targetFramework: _supportingFramework);

            verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            if (!isShiftOperator)
            {
                verifier.VerifyIL("Test.M02<T, U>(T)",
@"
{
  // Code size       15 (0xf)
  .maxstack  2
  IL_0000:  ldc.i4.1
  IL_0001:  ldarg.0
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""T I1<T>." + metadataName + @"(int, T)""
  IL_000d:  pop
  IL_000e:  ret
}
");
                verifier.VerifyIL("Test.M04<T, U>(T?)",
@"
{
  // Code size       32 (0x20)
  .maxstack  2
  .locals init (T? V_0)
  IL_0000:  ldarg.0
  IL_0001:  stloc.0
  IL_0002:  ldloca.s   V_0
  IL_0004:  call       ""readonly bool T?.HasValue.get""
  IL_0009:  brfalse.s  IL_001f
  IL_000b:  ldc.i4.1
  IL_000c:  ldloca.s   V_0
  IL_000e:  call       ""readonly T T?.GetValueOrDefault()""
  IL_0013:  constrained. ""T""
  IL_0019:  call       ""T I1<T>." + metadataName + @"(int, T)""
  IL_001e:  pop
  IL_001f:  ret
}
");
                verifier.VerifyIL("Test.M06<T, U>(I1<T>, T)",
@"
{
  // Code size       15 (0xf)
  .maxstack  2
  IL_0000:  ldarg.0
  IL_0001:  ldarg.1
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""T I1<T>." + metadataName + @"(I1<T>, T)""
  IL_000d:  pop
  IL_000e:  ret
}
");

                verifier.VerifyIL("Test.M07<T, U>(T, I1<T>)",
@"
{
  // Code size       15 (0xf)
  .maxstack  2
  IL_0000:  ldarg.0
  IL_0001:  ldarg.1
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""T I1<T>." + metadataName + @"(T, I1<T>)""
  IL_000d:  pop
  IL_000e:  ret
}
");
            }

            verifier.VerifyIL("Test.M03<T, U>(T)",
@"
{
  // Code size       15 (0xf)
  .maxstack  2
  IL_0000:  ldarg.0
  IL_0001:  ldc.i4.1
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""T I1<T>." + metadataName + @"(T, int)""
  IL_000d:  pop
  IL_000e:  ret
}
");

            verifier.VerifyIL("Test.M05<T, U>(T?)",
@"
{
  // Code size       32 (0x20)
  .maxstack  2
  .locals init (T? V_0)
  IL_0000:  ldarg.0
  IL_0001:  stloc.0
  IL_0002:  ldloca.s   V_0
  IL_0004:  call       ""readonly bool T?.HasValue.get""
  IL_0009:  brfalse.s  IL_001f
  IL_000b:  ldloca.s   V_0
  IL_000d:  call       ""readonly T T?.GetValueOrDefault()""
  IL_0012:  ldc.i4.1
  IL_0013:  constrained. ""T""
  IL_0019:  call       ""T I1<T>." + metadataName + @"(T, int)""
  IL_001e:  pop
  IL_001f:  ret
}
");

            var tree = compilation1.SyntaxTrees.Single();
            var model = compilation1.GetSemanticModel(tree);
            var node = tree.GetRoot().DescendantNodes().OfType<BinaryExpressionSyntax>().Where(n => n.ToString() == "x " + op + " 1").Single();

            Assert.Equal("x " + op + " 1", node.ToString());
            VerifyOperationTreeForNode(compilation1, model, node,
@"
IBinaryOperation (BinaryOperatorKind." + BinaryOperatorKind(op) + (isCheckedOperator && isCheckedContext ? ", Checked" : "") + @") (OperatorMethod: T I1<T>." + metadataName + @"(T x, System.Int32 a) ConstrainedToType: T) (OperationKind.Binary, Type: T) (Syntax: 'x " + op + @" 1')
  Left: 
    IParameterReferenceOperation: x (OperationKind.ParameterReference, Type: T) (Syntax: 'x')
  Right: 
    ILiteralOperation (OperationKind.Literal, Type: System.Int32, Constant: 1) (Syntax: '1')
");
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractComparisonBinaryOperator_03([CombinatorialValues("<", ">", "<=", ">=", "==", "!=")] string op, bool isVirtual)
        {
            string metadataName = BinaryOperatorName(op);
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public partial interface I1<T0> where T0 : I1<T0>
{
    " + modifier + @" static bool operator" + op + @" (T0 x, int a)" + body + @"
    " + modifier + @" static bool operator" + op + @" (int a, T0 x)" + body + @"
    " + modifier + @" static bool operator" + op + @" (I1<T0> x, T0 a)" + body + @"
    " + modifier + @" static bool operator" + op + @" (T0 x, I1<T0> a)" + body + @"
}

partial class Test
{
    static void M02<T, U>(T x) where T : U where U : I1<T>
    {
        _ = 1 " + op + @" x;
    }

    static void M03<T, U>(T x) where T : U where U : I1<T>
    {
        _ = x " + op + @" 1;
    }

    static void M06<T, U>(I1<T> x, T y) where T : U where U : I1<T>
    {
        _ = x " + op + @" y;
    }

    static void M07<T, U>(T x, I1<T> y) where T : U where U : I1<T>
    {
        _ = x " + op + @" y;
    }
}
";
            string matchingOp = MatchingBinaryOperator(op);

            source1 +=
@"
public partial interface I1<T0>
{
    " + modifier + @" static bool operator" + matchingOp + @" (T0 x, int a)" + body + @"
    " + modifier + @" static bool operator" + matchingOp + @" (int a, T0 x)" + body + @"
    " + modifier + @" static bool operator" + matchingOp + @" (I1<T0> x, T0 a)" + body + @"
    " + modifier + @" static bool operator" + matchingOp + @" (T0 x, I1<T0> a)" + body + @"
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>(T)",
@"
{
  // Code size       16 (0x10)
  .maxstack  2
  IL_0000:  nop
  IL_0001:  ldc.i4.1
  IL_0002:  ldarg.0
  IL_0003:  constrained. ""T""
  IL_0009:  call       ""bool I1<T>." + metadataName + @"(int, T)""
  IL_000e:  pop
  IL_000f:  ret
}
");
            verifier.VerifyIL("Test.M06<T, U>(I1<T>, T)",
@"
{
  // Code size       16 (0x10)
  .maxstack  2
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  ldarg.1
  IL_0003:  constrained. ""T""
  IL_0009:  call       ""bool I1<T>." + metadataName + @"(I1<T>, T)""
  IL_000e:  pop
  IL_000f:  ret
}
");

            verifier.VerifyIL("Test.M07<T, U>(T, I1<T>)",
@"
{
  // Code size       16 (0x10)
  .maxstack  2
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  ldarg.1
  IL_0003:  constrained. ""T""
  IL_0009:  call       ""bool I1<T>." + metadataName + @"(T, I1<T>)""
  IL_000e:  pop
  IL_000f:  ret
}
");

            verifier.VerifyIL("Test.M03<T, U>(T)",
@"
{
  // Code size       16 (0x10)
  .maxstack  2
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  ldc.i4.1
  IL_0003:  constrained. ""T""
  IL_0009:  call       ""bool I1<T>." + metadataName + @"(T, int)""
  IL_000e:  pop
  IL_000f:  ret
}
");

            compilation1 = CreateCompilation(source1, options: TestOptions.ReleaseDll,
                                             parseOptions: TestOptions.RegularPreview,
                                             targetFramework: _supportingFramework);

            verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>(T)",
@"
{
  // Code size       15 (0xf)
  .maxstack  2
  IL_0000:  ldc.i4.1
  IL_0001:  ldarg.0
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""bool I1<T>." + metadataName + @"(int, T)""
  IL_000d:  pop
  IL_000e:  ret
}
");
            verifier.VerifyIL("Test.M06<T, U>(I1<T>, T)",
@"
{
  // Code size       15 (0xf)
  .maxstack  2
  IL_0000:  ldarg.0
  IL_0001:  ldarg.1
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""bool I1<T>." + metadataName + @"(I1<T>, T)""
  IL_000d:  pop
  IL_000e:  ret
}
");

            verifier.VerifyIL("Test.M07<T, U>(T, I1<T>)",
@"
{
  // Code size       15 (0xf)
  .maxstack  2
  IL_0000:  ldarg.0
  IL_0001:  ldarg.1
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""bool I1<T>." + metadataName + @"(T, I1<T>)""
  IL_000d:  pop
  IL_000e:  ret
}
");

            verifier.VerifyIL("Test.M03<T, U>(T)",
@"
{
  // Code size       15 (0xf)
  .maxstack  2
  IL_0000:  ldarg.0
  IL_0001:  ldc.i4.1
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""bool I1<T>." + metadataName + @"(T, int)""
  IL_000d:  pop
  IL_000e:  ret
}
");

            var tree = compilation1.SyntaxTrees.Single();
            var model = compilation1.GetSemanticModel(tree);
            var node = tree.GetRoot().DescendantNodes().OfType<BinaryExpressionSyntax>().Where(n => n.ToString() == "x " + op + " 1").Single();

            Assert.Equal("x " + op + " 1", node.ToString());
            VerifyOperationTreeForNode(compilation1, model, node,
@"
IBinaryOperation (BinaryOperatorKind." + BinaryOperatorKind(op) + @") (OperatorMethod: System.Boolean I1<T>." + metadataName + @"(T x, System.Int32 a) ConstrainedToType: T) (OperationKind.Binary, Type: System.Boolean) (Syntax: 'x " + op + @" 1')
  Left: 
    IParameterReferenceOperation: x (OperationKind.ParameterReference, Type: T) (Syntax: 'x')
  Right: 
    ILiteralOperation (OperationKind.Literal, Type: System.Int32, Constant: 1) (Syntax: '1')
");
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractLiftedComparisonBinaryOperator_03([CombinatorialValues("<", ">", "<=", ">=", "==", "!=")] string op, bool isVirtual)
        {
            string metadataName = BinaryOperatorName(op);
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public partial interface I1<T0> where T0 : I1<T0>
{
    " + modifier + @" static bool operator" + op + @" (T0 x, T0 a)" + body + @"
}

partial class Test
{
    static void M04<T, U>(T? x, T? y) where T : struct, U where U : I1<T>
    {
        _ = x " + op + @" y;
    }
}
";
            string matchingOp = MatchingBinaryOperator(op);

            source1 +=
@"
public partial interface I1<T0>
{
    " + modifier + @" static bool operator" + matchingOp + @" (T0 x, T0 a)" + body + @"
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            if (op is "==" or "!=")
            {
                verifier.VerifyIL("Test.M04<T, U>(T?, T?)",
@"
{
  // Code size       61 (0x3d)
  .maxstack  2
  .locals init (T? V_0,
                T? V_1)
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  stloc.0
  IL_0003:  ldarg.1
  IL_0004:  stloc.1
  IL_0005:  ldloca.s   V_0
  IL_0007:  call       ""readonly bool T?.HasValue.get""
  IL_000c:  ldloca.s   V_1
  IL_000e:  call       ""readonly bool T?.HasValue.get""
  IL_0013:  beq.s      IL_0017
  IL_0015:  br.s       IL_003c
  IL_0017:  ldloca.s   V_0
  IL_0019:  call       ""readonly bool T?.HasValue.get""
  IL_001e:  brtrue.s   IL_0022
  IL_0020:  br.s       IL_003c
  IL_0022:  ldloca.s   V_0
  IL_0024:  call       ""readonly T T?.GetValueOrDefault()""
  IL_0029:  ldloca.s   V_1
  IL_002b:  call       ""readonly T T?.GetValueOrDefault()""
  IL_0030:  constrained. ""T""
  IL_0036:  call       ""bool I1<T>." + metadataName + @"(T, T)""
  IL_003b:  pop
  IL_003c:  ret
}
");
            }
            else
            {
                verifier.VerifyIL("Test.M04<T, U>(T?, T?)",
@"
{
  // Code size       51 (0x33)
  .maxstack  2
  .locals init (T? V_0,
                T? V_1)
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  stloc.0
  IL_0003:  ldarg.1
  IL_0004:  stloc.1
  IL_0005:  ldloca.s   V_0
  IL_0007:  call       ""readonly bool T?.HasValue.get""
  IL_000c:  ldloca.s   V_1
  IL_000e:  call       ""readonly bool T?.HasValue.get""
  IL_0013:  and
  IL_0014:  brtrue.s   IL_0018
  IL_0016:  br.s       IL_0032
  IL_0018:  ldloca.s   V_0
  IL_001a:  call       ""readonly T T?.GetValueOrDefault()""
  IL_001f:  ldloca.s   V_1
  IL_0021:  call       ""readonly T T?.GetValueOrDefault()""
  IL_0026:  constrained. ""T""
  IL_002c:  call       ""bool I1<T>." + metadataName + @"(T, T)""
  IL_0031:  pop
  IL_0032:  ret
}
");
            }

            compilation1 = CreateCompilation(source1, options: TestOptions.ReleaseDll,
                                             parseOptions: TestOptions.RegularPreview,
                                             targetFramework: _supportingFramework);

            verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            if (op is "==" or "!=")
            {
                verifier.VerifyIL("Test.M04<T, U>(T?, T?)",
@"
{
  // Code size       56 (0x38)
  .maxstack  2
  .locals init (T? V_0,
                T? V_1)
  IL_0000:  ldarg.0
  IL_0001:  stloc.0
  IL_0002:  ldarg.1
  IL_0003:  stloc.1
  IL_0004:  ldloca.s   V_0
  IL_0006:  call       ""readonly bool T?.HasValue.get""
  IL_000b:  ldloca.s   V_1
  IL_000d:  call       ""readonly bool T?.HasValue.get""
  IL_0012:  bne.un.s   IL_0037
  IL_0014:  ldloca.s   V_0
  IL_0016:  call       ""readonly bool T?.HasValue.get""
  IL_001b:  brfalse.s  IL_0037
  IL_001d:  ldloca.s   V_0
  IL_001f:  call       ""readonly T T?.GetValueOrDefault()""
  IL_0024:  ldloca.s   V_1
  IL_0026:  call       ""readonly T T?.GetValueOrDefault()""
  IL_002b:  constrained. ""T""
  IL_0031:  call       ""bool I1<T>." + metadataName + @"(T, T)""
  IL_0036:  pop
  IL_0037:  ret
}
");

            }
            else
            {
                verifier.VerifyIL("Test.M04<T, U>(T?, T?)",
@"
{
  // Code size       48 (0x30)
  .maxstack  2
  .locals init (T? V_0,
                T? V_1)
  IL_0000:  ldarg.0
  IL_0001:  stloc.0
  IL_0002:  ldarg.1
  IL_0003:  stloc.1
  IL_0004:  ldloca.s   V_0
  IL_0006:  call       ""readonly bool T?.HasValue.get""
  IL_000b:  ldloca.s   V_1
  IL_000d:  call       ""readonly bool T?.HasValue.get""
  IL_0012:  and
  IL_0013:  brfalse.s  IL_002f
  IL_0015:  ldloca.s   V_0
  IL_0017:  call       ""readonly T T?.GetValueOrDefault()""
  IL_001c:  ldloca.s   V_1
  IL_001e:  call       ""readonly T T?.GetValueOrDefault()""
  IL_0023:  constrained. ""T""
  IL_0029:  call       ""bool I1<T>." + metadataName + @"(T, T)""
  IL_002e:  pop
  IL_002f:  ret
}
");
            }

            var tree = compilation1.SyntaxTrees.Single();
            var model = compilation1.GetSemanticModel(tree);
            var node = tree.GetRoot().DescendantNodes().OfType<BinaryExpressionSyntax>().Where(n => n.ToString() == "x " + op + " y").Single();

            Assert.Equal("x " + op + " y", node.ToString());
            VerifyOperationTreeForNode(compilation1, model, node,
@"
IBinaryOperation (BinaryOperatorKind." + BinaryOperatorKind(op) + @", IsLifted) (OperatorMethod: System.Boolean I1<T>." + metadataName + @"(T x, T a) ConstrainedToType: T) (OperationKind.Binary, Type: System.Boolean) (Syntax: 'x " + op + @" y')
  Left: 
    IParameterReferenceOperation: x (OperationKind.ParameterReference, Type: T?) (Syntax: 'x')
  Right: 
    IParameterReferenceOperation: y (OperationKind.ParameterReference, Type: T?) (Syntax: 'y')
");
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractLogicalBinaryOperator_03([CombinatorialValues("&", "|")] string op, bool binaryIsAbstract, bool unaryIsAbstract, bool isVirtual)
        {
            if (!binaryIsAbstract && !unaryIsAbstract)
            {
                return;
            }

            var binaryMetadataName = op == "&" ? "op_BitwiseAnd" : "op_BitwiseOr";
            var unaryMetadataName = op == "&" ? "op_False" : "op_True";
            var opKind = op == "&" ? "ConditionalAnd" : "ConditionalOr";
            var (modifier, body) = GetModifierAndBody(isVirtual);

            if (binaryIsAbstract && unaryIsAbstract)
            {
                consumeAbstract(op);
            }
            else
            {
                consumeMixed(op, binaryIsAbstract, unaryIsAbstract);
            }

            void consumeAbstract(string op)
            {
                var source1 =
@"
public interface I1<T0> where T0 : I1<T0>
{
    " + modifier + @" static T0 operator" + op + @" (T0 a, T0 x)" + body + @"
    " + modifier + @" static bool operator true (T0 x)" + body + @"
    " + modifier + @" static bool operator false (T0 x)" + body + @"
}

public interface I2<T0> where T0 : struct, I2<T0>
{
    " + modifier + @" static T0 operator" + op + @" (T0 a, T0 x)" + body + @"
    " + modifier + @" static bool operator true (T0? x)" + body + @"
    " + modifier + @" static bool operator false (T0? x)" + body + @"
}

class Test
{
    static void M03<T, U>(T x, T y) where T : U where U : I1<T>
    {
        _ = x " + op + op + @" y;
    }

    static void M04<T, U>(T? x, T? y) where T : struct, U where U : I2<T>
    {
        _ = x " + op + op + @" y;
    }
}
";
                var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                var verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();
                verifier.VerifyIL("Test.M03<T, U>(T, T)",
@"
{
  // Code size       34 (0x22)
  .maxstack  2
  .locals init (T V_0)
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  stloc.0
  IL_0003:  ldloc.0
  IL_0004:  constrained. ""T""
  IL_000a:  call       ""bool I1<T>." + unaryMetadataName + @"(T)""
  IL_000f:  brtrue.s   IL_0021
  IL_0011:  ldloc.0
  IL_0012:  ldarg.1
  IL_0013:  constrained. ""T""
  IL_0019:  call       ""T I1<T>." + binaryMetadataName + @"(T, T)""
  IL_001e:  pop
  IL_001f:  br.s       IL_0021
  IL_0021:  ret
}
");
                verifier.VerifyIL("Test.M04<T, U>(T?, T?)",
@"
{
  // Code size       69 (0x45)
  .maxstack  2
  .locals init (T? V_0,
                T? V_1,
                T? V_2)
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  stloc.0
  IL_0003:  ldloc.0
  IL_0004:  constrained. ""T""
  IL_000a:  call       ""bool I2<T>." + unaryMetadataName + @"(T?)""
  IL_000f:  brtrue.s   IL_0044
  IL_0011:  ldloc.0
  IL_0012:  stloc.1
  IL_0013:  ldarg.1
  IL_0014:  stloc.2
  IL_0015:  ldloca.s   V_1
  IL_0017:  call       ""readonly bool T?.HasValue.get""
  IL_001c:  ldloca.s   V_2
  IL_001e:  call       ""readonly bool T?.HasValue.get""
  IL_0023:  and
  IL_0024:  brtrue.s   IL_0028
  IL_0026:  br.s       IL_0042
  IL_0028:  ldloca.s   V_1
  IL_002a:  call       ""readonly T T?.GetValueOrDefault()""
  IL_002f:  ldloca.s   V_2
  IL_0031:  call       ""readonly T T?.GetValueOrDefault()""
  IL_0036:  constrained. ""T""
  IL_003c:  call       ""T I2<T>." + binaryMetadataName + @"(T, T)""
  IL_0041:  pop
  IL_0042:  br.s       IL_0044
  IL_0044:  ret
}
");

                compilation1 = CreateCompilation(source1, options: TestOptions.ReleaseDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

                verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();
                verifier.VerifyIL("Test.M03<T, U>(T, T)",
@"
{
  // Code size       31 (0x1f)
  .maxstack  2
  .locals init (T V_0)
  IL_0000:  ldarg.0
  IL_0001:  stloc.0
  IL_0002:  ldloc.0
  IL_0003:  constrained. ""T""
  IL_0009:  call       ""bool I1<T>." + unaryMetadataName + @"(T)""
  IL_000e:  brtrue.s   IL_001e
  IL_0010:  ldloc.0
  IL_0011:  ldarg.1
  IL_0012:  constrained. ""T""
  IL_0018:  call       ""T I1<T>." + binaryMetadataName + @"(T, T)""
  IL_001d:  pop
  IL_001e:  ret
}
");
                verifier.VerifyIL("Test.M04<T, U>(T?, T?)",
@"
{
  // Code size       64 (0x40)
  .maxstack  2
  .locals init (T? V_0,
                T? V_1,
                T? V_2)
  IL_0000:  ldarg.0
  IL_0001:  stloc.0
  IL_0002:  ldloc.0
  IL_0003:  constrained. ""T""
  IL_0009:  call       ""bool I2<T>." + unaryMetadataName + @"(T?)""
  IL_000e:  brtrue.s   IL_003f
  IL_0010:  ldloc.0
  IL_0011:  stloc.1
  IL_0012:  ldarg.1
  IL_0013:  stloc.2
  IL_0014:  ldloca.s   V_1
  IL_0016:  call       ""readonly bool T?.HasValue.get""
  IL_001b:  ldloca.s   V_2
  IL_001d:  call       ""readonly bool T?.HasValue.get""
  IL_0022:  and
  IL_0023:  brfalse.s  IL_003f
  IL_0025:  ldloca.s   V_1
  IL_0027:  call       ""readonly T T?.GetValueOrDefault()""
  IL_002c:  ldloca.s   V_2
  IL_002e:  call       ""readonly T T?.GetValueOrDefault()""
  IL_0033:  constrained. ""T""
  IL_0039:  call       ""T I2<T>." + binaryMetadataName + @"(T, T)""
  IL_003e:  pop
  IL_003f:  ret
}
");

                var tree = compilation1.SyntaxTrees.Single();
                var model = compilation1.GetSemanticModel(tree);
                var node1 = tree.GetRoot().DescendantNodes().OfType<BinaryExpressionSyntax>().Where(n => n.ToString() == "x " + op + op + " y").First();

                Assert.Equal("x " + op + op + " y", node1.ToString());

                VerifyOperationTreeForNode(compilation1, model, node1,
@"
IBinaryOperation (BinaryOperatorKind." + opKind + @") (OperatorMethod: T I1<T>." + binaryMetadataName + @"(T a, T x) ConstrainedToType: T) (OperationKind.Binary, Type: T) (Syntax: 'x " + op + op + @" y')
  Left: 
    IParameterReferenceOperation: x (OperationKind.ParameterReference, Type: T) (Syntax: 'x')
  Right: 
    IParameterReferenceOperation: y (OperationKind.ParameterReference, Type: T) (Syntax: 'y')
");
            }

            void consumeMixed(string op, bool binaryIsAbstract, bool unaryIsAbstract)
            {
                var source1 =
@"
public interface I1
{
    " + (binaryIsAbstract ? modifier : "") + @" static I1 operator" + op + @" (I1 a, I1 x)" + (binaryIsAbstract ? body : " => throw null;") + @"
    " + (unaryIsAbstract ? modifier : "") + @" static bool operator true (I1 x)" + (unaryIsAbstract ? body : " => throw null;") + @"
    " + (unaryIsAbstract ? modifier : "") + @" static bool operator false (I1 x)" + (unaryIsAbstract ? body : " => throw null;") + @"
}

class Test
{
    static void M03<T, U>(T x, T y) where T : U where U : I1
    {
        _ = x " + op + op + @" y;
    }

    static void M04<T, U>(T? x, T? y) where T : struct, U where U : I1
    {
        _ = x " + op + op + @" y;
    }
}
";
                var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                var verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

                switch (binaryIsAbstract, unaryIsAbstract)
                {
                    case (true, false):
                        verifier.VerifyIL("Test.M03<T, U>(T, T)",
@"
{
  // Code size       38 (0x26)
  .maxstack  2
  .locals init (I1 V_0)
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  box        ""T""
  IL_0007:  stloc.0
  IL_0008:  ldloc.0
  IL_0009:  call       ""bool I1." + unaryMetadataName + @"(I1)""
  IL_000e:  brtrue.s   IL_0025
  IL_0010:  ldloc.0
  IL_0011:  ldarg.1
  IL_0012:  box        ""T""
  IL_0017:  constrained. ""T""
  IL_001d:  call       ""I1 I1." + binaryMetadataName + @"(I1, I1)""
  IL_0022:  pop
  IL_0023:  br.s       IL_0025
  IL_0025:  ret
}
");
                        verifier.VerifyIL("Test.M04<T, U>(T?, T?)",
@"
{
  // Code size       38 (0x26)
  .maxstack  2
  .locals init (I1 V_0)
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  box        ""T?""
  IL_0007:  stloc.0
  IL_0008:  ldloc.0
  IL_0009:  call       ""bool I1." + unaryMetadataName + @"(I1)""
  IL_000e:  brtrue.s   IL_0025
  IL_0010:  ldloc.0
  IL_0011:  ldarg.1
  IL_0012:  box        ""T?""
  IL_0017:  constrained. ""T""
  IL_001d:  call       ""I1 I1." + binaryMetadataName + @"(I1, I1)""
  IL_0022:  pop
  IL_0023:  br.s       IL_0025
  IL_0025:  ret
}
");
                        break;

                    case (false, true):
                        verifier.VerifyIL("Test.M03<T, U>(T, T)",
@"
{
  // Code size       38 (0x26)
  .maxstack  2
  .locals init (I1 V_0)
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  box        ""T""
  IL_0007:  stloc.0
  IL_0008:  ldloc.0
  IL_0009:  constrained. ""T""
  IL_000f:  call       ""bool I1." + unaryMetadataName + @"(I1)""
  IL_0014:  brtrue.s   IL_0025
  IL_0016:  ldloc.0
  IL_0017:  ldarg.1
  IL_0018:  box        ""T""
  IL_001d:  call       ""I1 I1." + binaryMetadataName + @"(I1, I1)""
  IL_0022:  pop
  IL_0023:  br.s       IL_0025
  IL_0025:  ret
}
");
                        verifier.VerifyIL("Test.M04<T, U>(T?, T?)",
@"
{
  // Code size       38 (0x26)
  .maxstack  2
  .locals init (I1 V_0)
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  box        ""T?""
  IL_0007:  stloc.0
  IL_0008:  ldloc.0
  IL_0009:  constrained. ""T""
  IL_000f:  call       ""bool I1." + unaryMetadataName + @"(I1)""
  IL_0014:  brtrue.s   IL_0025
  IL_0016:  ldloc.0
  IL_0017:  ldarg.1
  IL_0018:  box        ""T?""
  IL_001d:  call       ""I1 I1." + binaryMetadataName + @"(I1, I1)""
  IL_0022:  pop
  IL_0023:  br.s       IL_0025
  IL_0025:  ret
}
");
                        break;

                    default:
                        Assert.True(false);
                        break;
                }

                compilation1 = CreateCompilation(source1, options: TestOptions.ReleaseDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

                verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

                switch (binaryIsAbstract, unaryIsAbstract)
                {
                    case (true, false):
                        verifier.VerifyIL("Test.M03<T, U>(T, T)",
@"
{
  // Code size       35 (0x23)
  .maxstack  2
  .locals init (I1 V_0)
  IL_0000:  ldarg.0
  IL_0001:  box        ""T""
  IL_0006:  stloc.0
  IL_0007:  ldloc.0
  IL_0008:  call       ""bool I1." + unaryMetadataName + @"(I1)""
  IL_000d:  brtrue.s   IL_0022
  IL_000f:  ldloc.0
  IL_0010:  ldarg.1
  IL_0011:  box        ""T""
  IL_0016:  constrained. ""T""
  IL_001c:  call       ""I1 I1." + binaryMetadataName + @"(I1, I1)""
  IL_0021:  pop
  IL_0022:  ret
}
");
                        verifier.VerifyIL("Test.M04<T, U>(T?, T?)",
@"
{
  // Code size       35 (0x23)
  .maxstack  2
  .locals init (I1 V_0)
  IL_0000:  ldarg.0
  IL_0001:  box        ""T?""
  IL_0006:  stloc.0
  IL_0007:  ldloc.0
  IL_0008:  call       ""bool I1." + unaryMetadataName + @"(I1)""
  IL_000d:  brtrue.s   IL_0022
  IL_000f:  ldloc.0
  IL_0010:  ldarg.1
  IL_0011:  box        ""T?""
  IL_0016:  constrained. ""T""
  IL_001c:  call       ""I1 I1." + binaryMetadataName + @"(I1, I1)""
  IL_0021:  pop
  IL_0022:  ret
}
");
                        break;

                    case (false, true):
                        verifier.VerifyIL("Test.M03<T, U>(T, T)",
@"
{
  // Code size       35 (0x23)
  .maxstack  2
  .locals init (I1 V_0)
  IL_0000:  ldarg.0
  IL_0001:  box        ""T""
  IL_0006:  stloc.0
  IL_0007:  ldloc.0
  IL_0008:  constrained. ""T""
  IL_000e:  call       ""bool I1." + unaryMetadataName + @"(I1)""
  IL_0013:  brtrue.s   IL_0022
  IL_0015:  ldloc.0
  IL_0016:  ldarg.1
  IL_0017:  box        ""T""
  IL_001c:  call       ""I1 I1." + binaryMetadataName + @"(I1, I1)""
  IL_0021:  pop
  IL_0022:  ret
}
");
                        verifier.VerifyIL("Test.M04<T, U>(T?, T?)",
@"
{
  // Code size       35 (0x23)
  .maxstack  2
  .locals init (I1 V_0)
  IL_0000:  ldarg.0
  IL_0001:  box        ""T?""
  IL_0006:  stloc.0
  IL_0007:  ldloc.0
  IL_0008:  constrained. ""T""
  IL_000e:  call       ""bool I1." + unaryMetadataName + @"(I1)""
  IL_0013:  brtrue.s   IL_0022
  IL_0015:  ldloc.0
  IL_0016:  ldarg.1
  IL_0017:  box        ""T?""
  IL_001c:  call       ""I1 I1." + binaryMetadataName + @"(I1, I1)""
  IL_0021:  pop
  IL_0022:  ret
}
");
                        break;

                    default:
                        Assert.True(false);
                        break;
                }

                var tree = compilation1.SyntaxTrees.Single();
                var model = compilation1.GetSemanticModel(tree);
                var node1 = tree.GetRoot().DescendantNodes().OfType<BinaryExpressionSyntax>().Where(n => n.ToString() == "x " + op + op + " y").First();

                Assert.Equal("x " + op + op + " y", node1.ToString());

                VerifyOperationTreeForNode(compilation1, model, node1,
@"
IBinaryOperation (BinaryOperatorKind." + opKind + @") (OperatorMethod: I1 I1." + binaryMetadataName + @"(I1 a, I1 x) ConstrainedToType: T) (OperationKind.Binary, Type: I1) (Syntax: 'x " + op + op + @" y')
  Left: 
    IConversionOperation (TryCast: False, Unchecked) (OperationKind.Conversion, Type: I1, IsImplicit) (Syntax: 'x')
      Conversion: CommonConversion (Exists: True, IsIdentity: False, IsNumeric: False, IsReference: False, IsUserDefined: False) (MethodSymbol: null)
      Operand: 
        IParameterReferenceOperation: x (OperationKind.ParameterReference, Type: T) (Syntax: 'x')
  Right: 
    IConversionOperation (TryCast: False, Unchecked) (OperationKind.Conversion, Type: I1, IsImplicit) (Syntax: 'y')
      Conversion: CommonConversion (Exists: True, IsIdentity: False, IsNumeric: False, IsReference: False, IsUserDefined: False) (MethodSymbol: null)
      Operand: 
        IParameterReferenceOperation: y (OperationKind.ParameterReference, Type: T) (Syntax: 'y')
");
            }
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractCompoundBinaryOperator_03([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<<", ">>", ">>>")] string op, bool isCheckedOperator, bool isCheckedContext, bool isVirtual)
        {
            string metadataName = GetBinaryOperatorName(op, isCheckedOperator, out string checkedKeyword);

            if (metadataName is null)
            {
                return;
            }

            if (isCheckedOperator && !isCheckedContext)
            {
                metadataName = BinaryOperatorName(op, isChecked: false);
            }

            string contextKeyword = isCheckedContext ? " checked " : " unchecked ";
            bool isShiftOperator = op is "<<" or ">>" or ">>>";
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1<T0> where T0 : I1<T0>
{
";
            if (!isShiftOperator)
            {
                source1 += @"
    " + modifier + @" static int operator" + op + @" (int a, T0 x)" + body + @"
    " + modifier + @" static I1<T0> operator" + op + @" (I1<T0> x, T0 a)" + body + @"
    " + modifier + @" static T0 operator" + op + @" (T0 x, I1<T0> a)" + body + @"
";

                if (isCheckedOperator)
                {
                    source1 +=
@"
    " + modifier + @" static int operator checked " + op + @" (int a, T0 x)" + body + @"
    " + modifier + @" static I1<T0> operator checked " + op + @" (I1<T0> x, T0 a)" + body + @"
    " + modifier + @" static T0 operator checked " + op + @" (T0 x, I1<T0> a)" + body + @"
"
    ;
                }
            }

            source1 += @"
    " + modifier + @" static T0 operator" + op + @" (T0 x, int a)" + body + @"
";
            if (isCheckedOperator)
            {
                source1 +=
@"
    " + modifier + @" static T0 operator checked " + op + @" (T0 x, int a)" + body + @"
"
;
            }

            source1 += @"
}

class Test
{
";
            if (!isShiftOperator)
            {
                source1 += @"
    static void M02<T, U>(int a, T x) where T : U where U : I1<T>
    {" + contextKeyword + @"{
        a " + op + @"= x;
    }}

    static void M04<T, U>(int? a, T? y) where T : struct, U where U : I1<T>
    {" + contextKeyword + @"{
        a " + op + @"= y;
    }}

    static void M06<T, U>(I1<T> x, T y) where T : U where U : I1<T>
    {" + contextKeyword + @"{
        x " + op + @"= y;
    }}

    static void M07<T, U>(T x, I1<T> y) where T : U where U : I1<T>
    {" + contextKeyword + @"{
        x " + op + @"= y;
    }}
";
            }

            source1 += @"
    static void M03<T, U>(T x) where T : U where U : I1<T>
    {" + contextKeyword + @"{
        x " + op + @"= 1;
    }}

    static void M05<T, U>(T? y) where T : struct, U where U : I1<T>
    {" + contextKeyword + @"{
        y " + op + @"= 1;
    }}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            compilation1 = CreateCompilation(source1, options: TestOptions.ReleaseDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            if (!isShiftOperator)
            {
                verifier.VerifyIL("Test.M02<T, U>(int, T)",
@"
{
  // Code size       16 (0x10)
  .maxstack  2
  IL_0000:  ldarg.0
  IL_0001:  ldarg.1
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""int I1<T>." + metadataName + @"(int, T)""
  IL_000d:  starg.s    V_0
  IL_000f:  ret
}
");
                verifier.VerifyIL("Test.M04<T, U>(int?, T?)",
@"
{
  // Code size       65 (0x41)
  .maxstack  2
  .locals init (int? V_0,
                T? V_1,
                int? V_2)
  IL_0000:  ldarg.0
  IL_0001:  stloc.0
  IL_0002:  ldarg.1
  IL_0003:  stloc.1
  IL_0004:  ldloca.s   V_0
  IL_0006:  call       ""readonly bool int?.HasValue.get""
  IL_000b:  ldloca.s   V_1
  IL_000d:  call       ""readonly bool T?.HasValue.get""
  IL_0012:  and
  IL_0013:  brtrue.s   IL_0020
  IL_0015:  ldloca.s   V_2
  IL_0017:  initobj    ""int?""
  IL_001d:  ldloc.2
  IL_001e:  br.s       IL_003e
  IL_0020:  ldloca.s   V_0
  IL_0022:  call       ""readonly int int?.GetValueOrDefault()""
  IL_0027:  ldloca.s   V_1
  IL_0029:  call       ""readonly T T?.GetValueOrDefault()""
  IL_002e:  constrained. ""T""
  IL_0034:  call       ""int I1<T>." + metadataName + @"(int, T)""
  IL_0039:  newobj     ""int?..ctor(int)""
  IL_003e:  starg.s    V_0
  IL_0040:  ret
}
");
                verifier.VerifyIL("Test.M06<T, U>(I1<T>, T)",
@"
{
  // Code size       16 (0x10)
  .maxstack  2
  IL_0000:  ldarg.0
  IL_0001:  ldarg.1
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""I1<T> I1<T>." + metadataName + @"(I1<T>, T)""
  IL_000d:  starg.s    V_0
  IL_000f:  ret
}
");

                verifier.VerifyIL("Test.M07<T, U>(T, I1<T>)",
@"
{
  // Code size       16 (0x10)
  .maxstack  2
  IL_0000:  ldarg.0
  IL_0001:  ldarg.1
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""T I1<T>." + metadataName + @"(T, I1<T>)""
  IL_000d:  starg.s    V_0
  IL_000f:  ret
}
");
            }

            verifier.VerifyIL("Test.M03<T, U>(T)",
@"
{
  // Code size       16 (0x10)
  .maxstack  2
  IL_0000:  ldarg.0
  IL_0001:  ldc.i4.1
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""T I1<T>." + metadataName + @"(T, int)""
  IL_000d:  starg.s    V_0
  IL_000f:  ret
}
");

            verifier.VerifyIL("Test.M05<T, U>(T?)",
@"
{
  // Code size       49 (0x31)
  .maxstack  2
  .locals init (T? V_0,
                T? V_1)
  IL_0000:  ldarg.0
  IL_0001:  stloc.0
  IL_0002:  ldloca.s   V_0
  IL_0004:  call       ""readonly bool T?.HasValue.get""
  IL_0009:  brtrue.s   IL_0016
  IL_000b:  ldloca.s   V_1
  IL_000d:  initobj    ""T?""
  IL_0013:  ldloc.1
  IL_0014:  br.s       IL_002e
  IL_0016:  ldloca.s   V_0
  IL_0018:  call       ""readonly T T?.GetValueOrDefault()""
  IL_001d:  ldc.i4.1
  IL_001e:  constrained. ""T""
  IL_0024:  call       ""T I1<T>." + metadataName + @"(T, int)""
  IL_0029:  newobj     ""T?..ctor(T)""
  IL_002e:  starg.s    V_0
  IL_0030:  ret
}
");

            compilation1 = CreateCompilation(source1, options: TestOptions.ReleaseDll,
                                             parseOptions: TestOptions.RegularPreview,
                                             targetFramework: _supportingFramework);

            verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            if (!isShiftOperator)
            {
                verifier.VerifyIL("Test.M02<T, U>(int, T)",
@"
{
  // Code size       16 (0x10)
  .maxstack  2
  IL_0000:  ldarg.0
  IL_0001:  ldarg.1
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""int I1<T>." + metadataName + @"(int, T)""
  IL_000d:  starg.s    V_0
  IL_000f:  ret
}
");
                verifier.VerifyIL("Test.M04<T, U>(int?, T?)",
@"
{
  // Code size       65 (0x41)
  .maxstack  2
  .locals init (int? V_0,
                T? V_1,
                int? V_2)
  IL_0000:  ldarg.0
  IL_0001:  stloc.0
  IL_0002:  ldarg.1
  IL_0003:  stloc.1
  IL_0004:  ldloca.s   V_0
  IL_0006:  call       ""readonly bool int?.HasValue.get""
  IL_000b:  ldloca.s   V_1
  IL_000d:  call       ""readonly bool T?.HasValue.get""
  IL_0012:  and
  IL_0013:  brtrue.s   IL_0020
  IL_0015:  ldloca.s   V_2
  IL_0017:  initobj    ""int?""
  IL_001d:  ldloc.2
  IL_001e:  br.s       IL_003e
  IL_0020:  ldloca.s   V_0
  IL_0022:  call       ""readonly int int?.GetValueOrDefault()""
  IL_0027:  ldloca.s   V_1
  IL_0029:  call       ""readonly T T?.GetValueOrDefault()""
  IL_002e:  constrained. ""T""
  IL_0034:  call       ""int I1<T>." + metadataName + @"(int, T)""
  IL_0039:  newobj     ""int?..ctor(int)""
  IL_003e:  starg.s    V_0
  IL_0040:  ret
}
");
                verifier.VerifyIL("Test.M06<T, U>(I1<T>, T)",
@"
{
  // Code size       16 (0x10)
  .maxstack  2
  IL_0000:  ldarg.0
  IL_0001:  ldarg.1
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""I1<T> I1<T>." + metadataName + @"(I1<T>, T)""
  IL_000d:  starg.s    V_0
  IL_000f:  ret
}
");

                verifier.VerifyIL("Test.M07<T, U>(T, I1<T>)",
@"
{
  // Code size       16 (0x10)
  .maxstack  2
  IL_0000:  ldarg.0
  IL_0001:  ldarg.1
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""T I1<T>." + metadataName + @"(T, I1<T>)""
  IL_000d:  starg.s    V_0
  IL_000f:  ret
}
");
            }

            verifier.VerifyIL("Test.M03<T, U>(T)",
@"
{
  // Code size       16 (0x10)
  .maxstack  2
  IL_0000:  ldarg.0
  IL_0001:  ldc.i4.1
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""T I1<T>." + metadataName + @"(T, int)""
  IL_000d:  starg.s    V_0
  IL_000f:  ret
}
");

            verifier.VerifyIL("Test.M05<T, U>(T?)",
@"
{
  // Code size       49 (0x31)
  .maxstack  2
  .locals init (T? V_0,
                T? V_1)
  IL_0000:  ldarg.0
  IL_0001:  stloc.0
  IL_0002:  ldloca.s   V_0
  IL_0004:  call       ""readonly bool T?.HasValue.get""
  IL_0009:  brtrue.s   IL_0016
  IL_000b:  ldloca.s   V_1
  IL_000d:  initobj    ""T?""
  IL_0013:  ldloc.1
  IL_0014:  br.s       IL_002e
  IL_0016:  ldloca.s   V_0
  IL_0018:  call       ""readonly T T?.GetValueOrDefault()""
  IL_001d:  ldc.i4.1
  IL_001e:  constrained. ""T""
  IL_0024:  call       ""T I1<T>." + metadataName + @"(T, int)""
  IL_0029:  newobj     ""T?..ctor(T)""
  IL_002e:  starg.s    V_0
  IL_0030:  ret
}
");

            var tree = compilation1.SyntaxTrees.Single();
            var model = compilation1.GetSemanticModel(tree);
            var node = tree.GetRoot().DescendantNodes().OfType<AssignmentExpressionSyntax>().Where(n => n.ToString() == "x " + op + "= 1").Single();

            Assert.Equal("x " + op + "= 1", node.ToString());
            VerifyOperationTreeForNode(compilation1, model, node,
@"
ICompoundAssignmentOperation (BinaryOperatorKind." + BinaryOperatorKind(op) + (isCheckedOperator && isCheckedContext ? ", Checked" : "") + @") (OperatorMethod: T I1<T>." + metadataName + @"(T x, System.Int32 a) ConstrainedToType: T) (OperationKind.CompoundAssignment, Type: T) (Syntax: 'x " + op + @"= 1')
  InConversion: CommonConversion (Exists: True, IsIdentity: True, IsNumeric: False, IsReference: False, IsUserDefined: False) (MethodSymbol: null)
  OutConversion: CommonConversion (Exists: True, IsIdentity: True, IsNumeric: False, IsReference: False, IsUserDefined: False) (MethodSymbol: null)
  Left: 
    IParameterReferenceOperation: x (OperationKind.ParameterReference, Type: T) (Syntax: 'x')
  Right: 
    ILiteralOperation (OperationKind.Literal, Type: System.Int32, Constant: 1) (Syntax: '1')
");
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractBinaryOperatorForTupleEquality_03([CombinatorialValues("==", "!=")] string op, bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    " + modifier + @" static bool operator == (T x, T y)" + body + @"
    " + modifier + @" static bool operator != (T x, T y)" + body + @"
}

class Test
{
    static void M02<T, U>((int, T) x) where T : U where U : I1<T>
    {
        _ = x " + op + @" x;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            if (op == "==")
            {
                verifier.VerifyIL("Test.M02<T, U>(System.ValueTuple<int, T>)",
@"
{
  // Code size       47 (0x2f)
  .maxstack  2
  .locals init (System.ValueTuple<int, T> V_0,
                System.ValueTuple<int, T> V_1)
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  stloc.0
  IL_0003:  ldarg.0
  IL_0004:  stloc.1
  IL_0005:  ldloc.0
  IL_0006:  ldfld      ""int System.ValueTuple<int, T>.Item1""
  IL_000b:  ldloc.1
  IL_000c:  ldfld      ""int System.ValueTuple<int, T>.Item1""
  IL_0011:  bne.un.s   IL_002c
  IL_0013:  ldloc.0
  IL_0014:  ldfld      ""T System.ValueTuple<int, T>.Item2""
  IL_0019:  ldloc.1
  IL_001a:  ldfld      ""T System.ValueTuple<int, T>.Item2""
  IL_001f:  constrained. ""T""
  IL_0025:  call       ""bool I1<T>.op_Equality(T, T)""
  IL_002a:  br.s       IL_002d
  IL_002c:  ldc.i4.0
  IL_002d:  pop
  IL_002e:  ret
}
");
            }
            else
            {
                verifier.VerifyIL("Test.M02<T, U>(System.ValueTuple<int, T>)",
@"
{
  // Code size       47 (0x2f)
  .maxstack  2
  .locals init (System.ValueTuple<int, T> V_0,
                System.ValueTuple<int, T> V_1)
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  stloc.0
  IL_0003:  ldarg.0
  IL_0004:  stloc.1
  IL_0005:  ldloc.0
  IL_0006:  ldfld      ""int System.ValueTuple<int, T>.Item1""
  IL_000b:  ldloc.1
  IL_000c:  ldfld      ""int System.ValueTuple<int, T>.Item1""
  IL_0011:  bne.un.s   IL_002c
  IL_0013:  ldloc.0
  IL_0014:  ldfld      ""T System.ValueTuple<int, T>.Item2""
  IL_0019:  ldloc.1
  IL_001a:  ldfld      ""T System.ValueTuple<int, T>.Item2""
  IL_001f:  constrained. ""T""
  IL_0025:  call       ""bool I1<T>.op_Inequality(T, T)""
  IL_002a:  br.s       IL_002d
  IL_002c:  ldc.i4.1
  IL_002d:  pop
  IL_002e:  ret
}
");
            }

            compilation1 = CreateCompilation(source1, options: TestOptions.ReleaseDll,
                                             parseOptions: TestOptions.RegularPreview,
                                             targetFramework: _supportingFramework);

            verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            if (op == "==")
            {
                verifier.VerifyIL("Test.M02<T, U>(System.ValueTuple<int, T>)",
@"
{
  // Code size       46 (0x2e)
  .maxstack  2
  .locals init (System.ValueTuple<int, T> V_0,
                System.ValueTuple<int, T> V_1)
  IL_0000:  ldarg.0
  IL_0001:  stloc.0
  IL_0002:  ldarg.0
  IL_0003:  stloc.1
  IL_0004:  ldloc.0
  IL_0005:  ldfld      ""int System.ValueTuple<int, T>.Item1""
  IL_000a:  ldloc.1
  IL_000b:  ldfld      ""int System.ValueTuple<int, T>.Item1""
  IL_0010:  bne.un.s   IL_002b
  IL_0012:  ldloc.0
  IL_0013:  ldfld      ""T System.ValueTuple<int, T>.Item2""
  IL_0018:  ldloc.1
  IL_0019:  ldfld      ""T System.ValueTuple<int, T>.Item2""
  IL_001e:  constrained. ""T""
  IL_0024:  call       ""bool I1<T>.op_Equality(T, T)""
  IL_0029:  br.s       IL_002c
  IL_002b:  ldc.i4.0
  IL_002c:  pop
  IL_002d:  ret
}
");
            }
            else
            {
                verifier.VerifyIL("Test.M02<T, U>(System.ValueTuple<int, T>)",
@"
{
  // Code size       46 (0x2e)
  .maxstack  2
  .locals init (System.ValueTuple<int, T> V_0,
                System.ValueTuple<int, T> V_1)
  IL_0000:  ldarg.0
  IL_0001:  stloc.0
  IL_0002:  ldarg.0
  IL_0003:  stloc.1
  IL_0004:  ldloc.0
  IL_0005:  ldfld      ""int System.ValueTuple<int, T>.Item1""
  IL_000a:  ldloc.1
  IL_000b:  ldfld      ""int System.ValueTuple<int, T>.Item1""
  IL_0010:  bne.un.s   IL_002b
  IL_0012:  ldloc.0
  IL_0013:  ldfld      ""T System.ValueTuple<int, T>.Item2""
  IL_0018:  ldloc.1
  IL_0019:  ldfld      ""T System.ValueTuple<int, T>.Item2""
  IL_001e:  constrained. ""T""
  IL_0024:  call       ""bool I1<T>.op_Inequality(T, T)""
  IL_0029:  br.s       IL_002c
  IL_002b:  ldc.i4.1
  IL_002c:  pop
  IL_002d:  ret
}
");
            }

            var tree = compilation1.SyntaxTrees.Single();
            var model = compilation1.GetSemanticModel(tree);
            var node = tree.GetRoot().DescendantNodes().OfType<BinaryExpressionSyntax>().First();

            Assert.Equal("x " + op + " x", node.ToString());
            VerifyOperationTreeForNode(compilation1, model, node,
// Information about user-defined operators isn't exposed today.
@"
ITupleBinaryOperation (BinaryOperatorKind." + (op == "==" ? "Equals" : "NotEquals") + @") (OperationKind.TupleBinary, Type: System.Boolean) (Syntax: 'x " + op + @" x')
  Left: 
    IParameterReferenceOperation: x (OperationKind.ParameterReference, Type: (System.Int32, T)) (Syntax: 'x')
  Right: 
    IParameterReferenceOperation: x (OperationKind.ParameterReference, Type: (System.Int32, T)) (Syntax: 'x')
");
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractBinaryOperator_04([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<<", ">>", ">>>", "<", ">", "<=", ">=", "==", "!=")] string op, bool isChecked, bool isVirtual)
        {
            if (GetBinaryOperatorName(op, isChecked, out string checkedKeyword) is null)
            {
                return;
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static I1 operator " + checkedKeyword + op + @" (I1 x, int y)" + body + @"
}
";
            var source2 =
@"
class Test
{
    static void M02<T>(T x, int y) where T : I1
    {" + checkedKeyword + @"{
        _ = x " + op + @" y;
    }}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (6,13): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //         _ = x - y;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "x " + op + " y").WithLocation(6, 13)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation3.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_CheckedOperatorNeedsMatch or (int)ErrorCode.ERR_BadAbstractEqualityOperatorSignature)).Verify(
                // (12,33): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static I1 operator - (I1 x, int y);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, op).WithLocation(12, 33 + checkedKeyword.Length)
                );
        }

        [Theory]
        [InlineData("&", true, false, false, false)]
        [InlineData("|", true, false, false, false)]
        [InlineData("&", false, false, true, false)]
        [InlineData("|", false, true, false, false)]
        [InlineData("&", true, false, true, false)]
        [InlineData("|", true, true, false, false)]
        [InlineData("&", false, true, false, true)]
        [InlineData("|", false, false, true, true)]
        public void ConsumeAbstractLogicalBinaryOperator_04(string op, bool binaryIsAbstract, bool trueIsAbstract, bool falseIsAbstract, bool success)
        {
            consumeAbstractLogicalBinaryOperator_04(op, binaryIsAbstract, trueIsAbstract, falseIsAbstract, success, isVirtual: false);
            consumeAbstractLogicalBinaryOperator_04(op, binaryIsAbstract, trueIsAbstract, falseIsAbstract, success, isVirtual: true);

            void consumeAbstractLogicalBinaryOperator_04(string op, bool binaryIsAbstract, bool trueIsAbstract, bool falseIsAbstract, bool success, bool isVirtual)
            {
                var (modifier, body) = GetModifierAndBody(isVirtual);

                var source1 =
@"
public interface I1
{
    " + (binaryIsAbstract ? modifier : "") + @" static I1 operator" + op + @" (I1 x, I1 y)" + (binaryIsAbstract ? body : " => throw null;") + @"
    " + (trueIsAbstract ? modifier : "") + @" static bool operator true (I1 x)" + (trueIsAbstract ? body : " => throw null;") + @"
    " + (falseIsAbstract ? modifier : "") + @" static bool operator false (I1 x)" + (falseIsAbstract ? body : " => throw null;") + @"
}
";
                var source2 =
@"
class Test
{
    static void M02<T>(T x, T y) where T : I1
    {
        _ = x " + op + op + @" y;
    }
}
";
                var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: TargetFramework.Mscorlib461Extended,
                                                     references: new[] { compilation1.ToMetadataReference() });

                if (success)
                {
                    compilation2.VerifyDiagnostics();
                }
                else
                {
                    compilation2.VerifyDiagnostics(
                        // (6,13): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                        //         _ = x && y;
                        Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "x " + op + op + " y").WithLocation(6, 13)
                        );
                }

                var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: TargetFramework.Mscorlib461Extended);

                var builder = ArrayBuilder<DiagnosticDescription>.GetInstance();

                if (binaryIsAbstract)
                {
                    builder.Add(
                        // (12,32): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                        //     abstract static I1 operator& (I1 x, I1 y);
                        Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, op).WithLocation(12, 32)
                        );
                }

                if (trueIsAbstract)
                {
                    builder.Add(
                        // (13,35): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                        //     abstract static bool operator true (I1 x);
                        Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "true").WithLocation(13, 35)
                        );
                }

                if (falseIsAbstract)
                {
                    builder.Add(
                        // (14,35): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                        //     abstract static bool operator false (I1 x);
                        Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "false").WithLocation(14, 35)
                        );
                }

                compilation3.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_RuntimeDoesNotSupportDefaultInterfaceImplementation).Verify(builder.ToArrayAndFree());
            }
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractCompoundBinaryOperator_04([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<<", ">>", ">>>")] string op, bool isChecked, bool isVirtual)
        {
            if (GetBinaryOperatorName(op, isChecked, out string checkedKeyword) is null)
            {
                return;
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    " + modifier + @" static T operator " + checkedKeyword + op + @" (T x, int y)" + body + @"
}
";
            var source2 =
@"
class Test
{
    static void M02<T>(T x, int y) where T : I1<T>
    {" + checkedKeyword + @"{
        x " + op + @"= y;
    }}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (6,9): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //         x *= y;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "x " + op + "= y").WithLocation(6, 9)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation3.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (12,32): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static T operator * (T x, int y);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, op).WithLocation(12, 32 + checkedKeyword.Length)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractBinaryOperatorForTupleEquality_04([CombinatorialValues("==", "!=")] string op, bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    " + modifier + @" static bool operator == (T x, T y)" + body + @"
    " + modifier + @" static bool operator != (T x, T y)" + body + @"
}
";
            var source2 =
@"
class Test
{
    static void M02<T>((int, T) x) where T : I1<T>
    {
        _ = x " + op + @" x;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (6,13): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //         _ = x == x;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "x " + op + " x").WithLocation(6, 13)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation3.VerifyDiagnostics(
                // (12,35): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static bool operator == (T x, T y);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "==").WithLocation(12, 35),
                // (13,35): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static bool operator != (T x, T y);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "!=").WithLocation(13, 35)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractBinaryOperator_06([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<<", ">>", ">>>", "<", ">", "<=", ">=", "==", "!=")] string op, bool isChecked, bool isVirtual)
        {
            if (GetBinaryOperatorName(op, isChecked, out string checkedKeyword) is null)
            {
                return;
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static I1 operator " + checkedKeyword + op + @" (I1 x, int y)" + body + @"
}
";
            var source2 =
@"
class Test
{
    static void M02<T>(T x, int y) where T : I1
    {" + checkedKeyword + @"{
        _ = x " + op + @" y;
    }}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.ToMetadataReference() });

            if (isChecked)
            {
                compilation2.VerifyDiagnostics(
                    // (6,13): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //         _ = x + y;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "x " + op + " y").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 13),
                    // (6,13): error CS8936: Feature 'checked user-defined operators' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //         _ = x + y;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "x " + op + " y").WithArguments("checked user-defined operators", "11.0").WithLocation(6, 13)
                    );
            }
            else if (op != ">>>")
            {
                compilation2.VerifyDiagnostics(
                    // (6,13): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //         _ = x >> y;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "x " + op + " y").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 13)
                    );
            }
            else
            {
                compilation2.VerifyDiagnostics(
                    // (6,13): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //         _ = x >>> y;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "x >>> y").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 13),
                    // (6,13): error CS8936: Feature 'unsigned right shift' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //         _ = x >>> y;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "x >>> y").WithArguments("unsigned right shift", "11.0").WithLocation(6, 13)
                    );
            }

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            if (isChecked)
            {
                compilation3.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                    // (12,33): error CS8936: Feature 'checked user-defined operators' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     virtual  static I1 operator checked + (I1 x, int y) => throw null;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "checked").WithArguments("checked user-defined operators", "11.0").WithLocation(12, 33),
                    // (12,41): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                    //     virtual  static I1 operator checked + (I1 x, int y) => throw null;
                    Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, op).WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(12, 41)
                    );
            }
            else if (op != ">>>")
            {
                compilation3.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_BadAbstractEqualityOperatorSignature)).Verify(
                    // (12,33): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                    //     virtual  static I1 operator >= (I1 x, int y) => throw null;
                    Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, op).WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(12, 33)
                    );
            }
            else
            {
                compilation3.VerifyDiagnostics(
                    // (12,33): error CS8936: Feature 'unsigned right shift' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     virtual  static I1 operator >>> (I1 x, int y) => throw null;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, ">>>").WithArguments("unsigned right shift", "11.0").WithLocation(12, 33),
                    // (12,33): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                    //     virtual  static I1 operator >>> (I1 x, int y) => throw null;
                    Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, ">>>").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(12, 33)
                    );
            }
        }

        [Theory]
        [InlineData("&", true, false, false, false)]
        [InlineData("|", true, false, false, false)]
        [InlineData("&", false, false, true, false)]
        [InlineData("|", false, true, false, false)]
        [InlineData("&", true, false, true, false)]
        [InlineData("|", true, true, false, false)]
        [InlineData("&", false, true, false, true)]
        [InlineData("|", false, false, true, true)]
        public void ConsumeAbstractLogicalBinaryOperator_06(string op, bool binaryIsAbstract, bool trueIsAbstract, bool falseIsAbstract, bool success)
        {
            consumeAbstractLogicalBinaryOperator_06(op, binaryIsAbstract, trueIsAbstract, falseIsAbstract, success, isVirtual: false);
            consumeAbstractLogicalBinaryOperator_06(op, binaryIsAbstract, trueIsAbstract, falseIsAbstract, success, isVirtual: true);

            void consumeAbstractLogicalBinaryOperator_06(string op, bool binaryIsAbstract, bool trueIsAbstract, bool falseIsAbstract, bool success, bool isVirtual)
            {
                var (modifier, body) = GetModifierAndBody(isVirtual);

                var source1 =
@"
public interface I1
{
    " + (binaryIsAbstract ? modifier : "") + @" static I1 operator" + op + @" (I1 x, I1 y)" + (binaryIsAbstract ? body : " => throw null;") + @"
    " + (trueIsAbstract ? modifier : "") + @" static bool operator true (I1 x)" + (trueIsAbstract ? body : " => throw null;") + @"
    " + (falseIsAbstract ? modifier : "") + @" static bool operator false (I1 x)" + (falseIsAbstract ? body : " => throw null;") + @"
}
";
                var source2 =
@"
class Test
{
    static void M02<T>(T x, T y) where T : I1
    {
        _ = x " + op + op + @" y;
    }
}
";
                var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.Regular10,
                                                     targetFramework: _supportingFramework,
                                                     references: new[] { compilation1.ToMetadataReference() });

                if (success)
                {
                    compilation2.VerifyDiagnostics();
                }
                else
                {
                    compilation2.VerifyDiagnostics(
                        // (6,13): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                        //         _ = x || y;
                        Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "x " + op + op + " y").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 13)
                        );
                }

                var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.Regular10,
                                                     targetFramework: _supportingFramework);

                var builder = ArrayBuilder<DiagnosticDescription>.GetInstance();

                if (binaryIsAbstract)
                {
                    builder.Add(
                        // (12,32): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                        //     abstract static I1 operator& (I1 x, I1 y);
                        Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, op).WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(12, 32)
                        );
                }

                if (trueIsAbstract)
                {
                    builder.Add(
                        // (13,35): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                        //     abstract static bool operator true (I1 x);
                        Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "true").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(13, 35)
                        );
                }

                if (falseIsAbstract)
                {
                    builder.Add(
                        // (14,35): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                        //     abstract static bool operator false (I1 x);
                        Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "false").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(14, 35)
                        );
                }

                compilation3.VerifyDiagnostics(builder.ToArrayAndFree());
            }
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractCompoundBinaryOperator_06([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<<", ">>", ">>>")] string op, bool isChecked, bool isVirtual)
        {
            if (GetBinaryOperatorName(op, isChecked, out string checkedKeyword) is null)
            {
                return;
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    " + modifier + @" static T operator " + checkedKeyword + op + @" (T x, int y)" + body + @"
}
";
            var source2 =
@"
class Test
{
    static void M02<T>(T x, int y) where T : I1<T>
    {" + checkedKeyword + @"{
        x " + op + @"= y;
    }}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.ToMetadataReference() });

            if (isChecked)
            {
                compilation2.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                    // (6,9): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //         x += y;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "x " + op + "= y").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 9),
                    // (6,9): error CS8936: Feature 'checked user-defined operators' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //         x += y;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "x " + op + "= y").WithArguments("checked user-defined operators", "11.0").WithLocation(6, 9)
                    );
            }
            else if (op != ">>>")
            {
                compilation2.VerifyDiagnostics(
                    // (6,9): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //         x >>>= y;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "x " + op + "= y").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 9)
                    );
            }
            else
            {
                compilation2.VerifyDiagnostics(
                    // (6,9): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //         x >>>= y;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "x >>>= y").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 9),
                    // (6,9): error CS8936: Feature 'unsigned right shift' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //         x >>>= y;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "x >>>= y").WithArguments("unsigned right shift", "11.0").WithLocation(6, 9)
                    );
            }

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            if (isChecked)
            {
                compilation3.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                    // (12,32): error CS8936: Feature 'checked user-defined operators' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     virtual  static T operator checked + (T x, int y) => throw null;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "checked").WithArguments("checked user-defined operators", "11.0").WithLocation(12, 32),
                    // (12,40): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                    //     virtual  static T operator checked + (T x, int y) => throw null;
                    Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, op).WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(12, 40)
                    );
            }
            else if (op != ">>>")
            {
                compilation3.VerifyDiagnostics(
                    // (12,32): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                    //     abstract static T operator << (T x, int y);
                    Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, op).WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(12, 32)
                    );
            }
            else
            {
                compilation3.VerifyDiagnostics(
                    // (12,32): error CS8936: Feature 'unsigned right shift' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     virtual  static T operator >>> (T x, int y) => throw null;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, ">>>").WithArguments("unsigned right shift", "11.0").WithLocation(12, 32),
                    // (12,32): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                    //     virtual  static T operator >>> (T x, int y) => throw null;
                    Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, ">>>").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(12, 32)
                    );
            }
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractBinaryOperatorForTupleEquality_06([CombinatorialValues("==", "!=")] string op, bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    " + modifier + @" static bool operator == (T x, T y)" + body + @"
    " + modifier + @" static bool operator != (T x, T y)" + body + @"
}
";
            var source2 =
@"
class Test
{
    static void M02<T>((int, T) x) where T : I1<T>
    {
        _ = x " + op + @" x;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (6,13): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                //         _ = x == x;
                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "x " + op + " x").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 13)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation3.VerifyDiagnostics(
                // (12,35): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual  static bool operator == (T x, T y) => throw null;
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "==").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(12, 35),
                // (13,35): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual  static bool operator != (T x, T y) => throw null;
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "!=").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(13, 35)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticPropertyGet_01(bool isVirtual)
        {
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"
interface I1
{
    " + modifier + @" static int P01 { get; set;}

    static void M02()
    {
        _ = P01;
        _ = P04;
    }

    void M03()
    {
        _ = this.P01;
        _ = this.P04;
    }

    static int P04 { get; set; }

    protected " + modifier + @" static int P05 { get; set; }
}

class Test
{
    static void MT1(I1 x)
    {
        _ = I1.P01;
        _ = x.P01;
        _ = I1.P04;
        _ = x.P04;
    }

    static void MT2<T>() where T : I1
    {
        _ = T.P03;
        _ = T.P04;
        _ = T.P00;
        _ = T.P05;

        _ = (System.Linq.Expressions.Expression<System.Action>)(() => T.P01.ToString());
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (8,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         _ = P01;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "P01").WithLocation(8, 13),
                // (14,13): error CS0176: Member 'I1.P01' cannot be accessed with an instance reference; qualify it with a type name instead
                //         _ = this.P01;
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "this.P01").WithArguments("I1.P01").WithLocation(14, 13),
                // (15,13): error CS0176: Member 'I1.P04' cannot be accessed with an instance reference; qualify it with a type name instead
                //         _ = this.P04;
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "this.P04").WithArguments("I1.P04").WithLocation(15, 13),
                // (27,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         _ = I1.P01;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "I1.P01").WithLocation(27, 13),
                // (28,13): error CS0176: Member 'I1.P01' cannot be accessed with an instance reference; qualify it with a type name instead
                //         _ = x.P01;
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "x.P01").WithArguments("I1.P01").WithLocation(28, 13),
                // (30,13): error CS0176: Member 'I1.P04' cannot be accessed with an instance reference; qualify it with a type name instead
                //         _ = x.P04;
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "x.P04").WithArguments("I1.P04").WithLocation(30, 13),
                // (35,13): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         _ = T.P03;
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(35, 13),
                // (36,13): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         _ = T.P04;
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(36, 13),
                // (37,13): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         _ = T.P00;
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(37, 13),
                // (38,15): error CS0122: 'I1.P05' is inaccessible due to its protection level
                //         _ = T.P05;
                Diagnostic(ErrorCode.ERR_BadAccess, "P05").WithArguments("I1.P05").WithLocation(38, 15),
                // (40,71): error CS8927: An expression tree may not contain an access of static virtual or abstract interface member
                //         _ = (System.Linq.Expressions.Expression<System.Action>)(() => T.P01.ToString());
                Diagnostic(ErrorCode.ERR_ExpressionTreeContainsAbstractStaticMemberAccess, "T.P01").WithLocation(40, 71)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticPropertySet_01(bool isVirtual)
        {
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"
interface I1
{
    " + modifier + @" static int P01 { get; set;}

    static void M02()
    {
        P01 = 1;
        P04 = 1;
    }

    void M03()
    {
        this.P01 = 1;
        this.P04 = 1;
    }

    static int P04 { get; set; }

    protected " + modifier + @" static int P05 { get; set; }
}

class Test
{
    static void MT1(I1 x)
    {
        I1.P01 = 1;
        x.P01 = 1;
        I1.P04 = 1;
        x.P04 = 1;
    }

    static void MT2<T>() where T : I1
    {
        T.P03 = 1;
        T.P04 = 1;
        T.P00 = 1;
        T.P05 = 1;

        _ = (System.Linq.Expressions.Expression<System.Action>)(() => T.P01 = 1);
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (8,9): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         P01 = 1;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "P01").WithLocation(8, 9),
                // (14,9): error CS0176: Member 'I1.P01' cannot be accessed with an instance reference; qualify it with a type name instead
                //         this.P01 = 1;
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "this.P01").WithArguments("I1.P01").WithLocation(14, 9),
                // (15,9): error CS0176: Member 'I1.P04' cannot be accessed with an instance reference; qualify it with a type name instead
                //         this.P04 = 1;
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "this.P04").WithArguments("I1.P04").WithLocation(15, 9),
                // (27,9): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         I1.P01 = 1;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "I1.P01").WithLocation(27, 9),
                // (28,9): error CS0176: Member 'I1.P01' cannot be accessed with an instance reference; qualify it with a type name instead
                //         x.P01 = 1;
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "x.P01").WithArguments("I1.P01").WithLocation(28, 9),
                // (30,9): error CS0176: Member 'I1.P04' cannot be accessed with an instance reference; qualify it with a type name instead
                //         x.P04 = 1;
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "x.P04").WithArguments("I1.P04").WithLocation(30, 9),
                // (35,9): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         T.P03 = 1;
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(35, 9),
                // (36,9): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         T.P04 = 1;
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(36, 9),
                // (37,9): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         T.P00 = 1;
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(37, 9),
                // (38,11): error CS0122: 'I1.P05' is inaccessible due to its protection level
                //         T.P05 = 1;
                Diagnostic(ErrorCode.ERR_BadAccess, "P05").WithArguments("I1.P05").WithLocation(38, 11),
                // (40,71): error CS0832: An expression tree may not contain an assignment operator
                //         _ = (System.Linq.Expressions.Expression<System.Action>)(() => T.P01 = 1);
                Diagnostic(ErrorCode.ERR_ExpressionTreeContainsAssignment, "T.P01 = 1").WithLocation(40, 71),
                // (40,71): error CS8927: An expression tree may not contain an access of static virtual or abstract interface member
                //         _ = (System.Linq.Expressions.Expression<System.Action>)(() => T.P01 = 1);
                Diagnostic(ErrorCode.ERR_ExpressionTreeContainsAbstractStaticMemberAccess, "T.P01").WithLocation(40, 71)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticPropertyCompound_01(bool isVirtual)
        {
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"
interface I1
{
    " + modifier + @" static int P01 { get; set;}

    static void M02()
    {
        P01 += 1;
        P04 += 1;
    }

    void M03()
    {
        this.P01 += 1;
        this.P04 += 1;
    }

    static int P04 { get; set; }

    protected " + modifier + @" static int P05 { get; set; }
}

class Test
{
    static void MT1(I1 x)
    {
        I1.P01 += 1;
        x.P01 += 1;
        I1.P04 += 1;
        x.P04 += 1;
    }

    static void MT2<T>() where T : I1
    {
        T.P03 += 1;
        T.P04 += 1;
        T.P00 += 1;
        T.P05 += 1;

        _ = (System.Linq.Expressions.Expression<System.Action>)(() => T.P01 += 1);
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (8,9): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         P01 += 1;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "P01").WithLocation(8, 9),
                // (8,9): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         P01 += 1;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "P01").WithLocation(8, 9),
                // (14,9): error CS0176: Member 'I1.P01' cannot be accessed with an instance reference; qualify it with a type name instead
                //         this.P01 += 1;
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "this.P01").WithArguments("I1.P01").WithLocation(14, 9),
                // (15,9): error CS0176: Member 'I1.P04' cannot be accessed with an instance reference; qualify it with a type name instead
                //         this.P04 += 1;
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "this.P04").WithArguments("I1.P04").WithLocation(15, 9),
                // (27,9): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         I1.P01 += 1;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "I1.P01").WithLocation(27, 9),
                // (27,9): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         I1.P01 += 1;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "I1.P01").WithLocation(27, 9),
                // (28,9): error CS0176: Member 'I1.P01' cannot be accessed with an instance reference; qualify it with a type name instead
                //         x.P01 += 1;
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "x.P01").WithArguments("I1.P01").WithLocation(28, 9),
                // (30,9): error CS0176: Member 'I1.P04' cannot be accessed with an instance reference; qualify it with a type name instead
                //         x.P04 += 1;
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "x.P04").WithArguments("I1.P04").WithLocation(30, 9),
                // (35,9): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         T.P03 += 1;
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(35, 9),
                // (36,9): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         T.P04 += 1;
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(36, 9),
                // (37,9): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         T.P00 += 1;
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(37, 9),
                // (38,11): error CS0122: 'I1.P05' is inaccessible due to its protection level
                //         T.P05 += 1;
                Diagnostic(ErrorCode.ERR_BadAccess, "P05").WithArguments("I1.P05").WithLocation(38, 11),
                // (40,71): error CS0832: An expression tree may not contain an assignment operator
                //         _ = (System.Linq.Expressions.Expression<System.Action>)(() => T.P01 += 1);
                Diagnostic(ErrorCode.ERR_ExpressionTreeContainsAssignment, "T.P01 += 1").WithLocation(40, 71),
                // (40,71): error CS8927: An expression tree may not contain an access of static virtual or abstract interface member
                //         _ = (System.Linq.Expressions.Expression<System.Action>)(() => T.P01 += 1);
                Diagnostic(ErrorCode.ERR_ExpressionTreeContainsAbstractStaticMemberAccess, "T.P01").WithLocation(40, 71)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticProperty_02(bool isVirtual)
        {
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"
interface I1
{
    " + modifier + @" static int P01 { get; set; }

    static void M02()
    {
        _ = nameof(P01);
        _ = nameof(P04);
    }

    void M03()
    {
        _ = nameof(this.P01);
        _ = nameof(this.P04);
    }

    static int P04 { get; set; }

    protected " + modifier + @" static int P05 { get; set; }
}

class Test
{
    static void MT1(I1 x)
    {
        _ = nameof(I1.P01);
        _ = nameof(x.P01);
        _ = nameof(I1.P04);
        _ = nameof(x.P04);
    }

    static void MT2<T>() where T : I1
    {
        _ = nameof(T.P03);
        _ = nameof(T.P04);
        _ = nameof(T.P00);
        _ = nameof(T.P05);
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (35,20): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         _ = nameof(T.P03);
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(35, 20),
                // (36,20): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         _ = nameof(T.P04);
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(36, 20),
                // (37,20): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         _ = nameof(T.P00);
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(37, 20),
                // (38,22): error CS0122: 'I1.P05' is inaccessible due to its protection level
                //         _ = nameof(T.P05);
                Diagnostic(ErrorCode.ERR_BadAccess, "P05").WithArguments("I1.P05").WithLocation(38, 22)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticPropertyGet_03(bool isVirtual)
        {
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static int P01 { get; set; }
}

class Test
{
    static void M02<T, U>() where T : U where U : I1
    {
        _ = T.P01;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>()",
@"
{
  // Code size       14 (0xe)
  .maxstack  1
  IL_0000:  nop
  IL_0001:  constrained. ""T""
  IL_0007:  call       ""int I1.P01.get""
  IL_000c:  pop
  IL_000d:  ret
}
");

            compilation1 = CreateCompilation(source1, options: TestOptions.ReleaseDll,
                                             parseOptions: TestOptions.RegularPreview,
                                             targetFramework: _supportingFramework);

            verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>()",
@"
{
  // Code size       13 (0xd)
  .maxstack  1
  IL_0000:  constrained. ""T""
  IL_0006:  call       ""int I1.P01.get""
  IL_000b:  pop
  IL_000c:  ret
}
");

            var tree = compilation1.SyntaxTrees.Single();
            var model = compilation1.GetSemanticModel(tree);
            var node = tree.GetRoot().DescendantNodes().OfType<AssignmentExpressionSyntax>().First().Right;

            Assert.Equal("T.P01", node.ToString());
            VerifyOperationTreeForNode(compilation1, model, node,
@"
IPropertyReferenceOperation: System.Int32 I1.P01 { get; set; } (ConstrainedToType: T) (Static) (OperationKind.PropertyReference, Type: System.Int32) (Syntax: 'T.P01')
  Instance Receiver: 
    null
");

            var m02 = compilation1.GetMember<MethodSymbol>("Test.M02");

            Assert.Equal("System.Int32 I1.P01 { get; set; }", ((CSharpSemanticModel)model).LookupSymbols(node.SpanStart, m02.TypeParameters[0], "P01").Single().ToTestDisplayString());
            Assert.Equal("System.Int32 I1.P01 { get; set; }", ((CSharpSemanticModel)model).LookupStaticMembers(node.SpanStart, m02.TypeParameters[0], "P01").Single().ToTestDisplayString());
            Assert.Contains("System.Int32 I1.P01 { get; set; }", ((CSharpSemanticModel)model).LookupSymbols(node.SpanStart, m02.TypeParameters[0]).ToTestDisplayStrings());
            Assert.Contains("System.Int32 I1.P01 { get; set; }", ((CSharpSemanticModel)model).LookupStaticMembers(node.SpanStart, m02.TypeParameters[0]).ToTestDisplayStrings());

            Assert.Equal("System.Int32 I1.P01 { get; set; }", model.LookupSymbols(node.SpanStart, m02.TypeParameters[0].GetPublicSymbol(), "P01").Single().ToTestDisplayString());
            Assert.Equal("System.Int32 I1.P01 { get; set; }", model.LookupStaticMembers(node.SpanStart, m02.TypeParameters[0].GetPublicSymbol(), "P01").Single().ToTestDisplayString());
            Assert.Contains("System.Int32 I1.P01 { get; set; }", model.LookupSymbols(node.SpanStart, m02.TypeParameters[0].GetPublicSymbol()).ToTestDisplayStrings());
            Assert.Contains("System.Int32 I1.P01 { get; set; }", model.LookupStaticMembers(node.SpanStart, m02.TypeParameters[0].GetPublicSymbol()).ToTestDisplayStrings());

            Assert.Contains("P01", model.LookupNames(node.SpanStart, m02.TypeParameters[0].GetPublicSymbol()));
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticPropertySet_03(bool isVirtual)
        {
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static int P01 { get; set; }
}

class Test
{
    static void M02<T, U>() where T : U where U : I1
    {
        T.P01 = 1;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>()",
@"
{
  // Code size       15 (0xf)
  .maxstack  1
  IL_0000:  nop
  IL_0001:  ldc.i4.1
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""void I1.P01.set""
  IL_000d:  nop
  IL_000e:  ret
}
");

            compilation1 = CreateCompilation(source1, options: TestOptions.ReleaseDll,
                                             parseOptions: TestOptions.RegularPreview,
                                             targetFramework: _supportingFramework);

            verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>()",
@"
{
  // Code size       13 (0xd)
  .maxstack  1
  IL_0000:  ldc.i4.1
  IL_0001:  constrained. ""T""
  IL_0007:  call       ""void I1.P01.set""
  IL_000c:  ret
}
");

            var tree = compilation1.SyntaxTrees.Single();
            var model = compilation1.GetSemanticModel(tree);
            var node = tree.GetRoot().DescendantNodes().OfType<AssignmentExpressionSyntax>().First().Left;

            Assert.Equal("T.P01", node.ToString());
            VerifyOperationTreeForNode(compilation1, model, node,
@"
IPropertyReferenceOperation: System.Int32 I1.P01 { get; set; } (ConstrainedToType: T) (Static) (OperationKind.PropertyReference, Type: System.Int32) (Syntax: 'T.P01')
  Instance Receiver: 
    null
");

            var m02 = compilation1.GetMember<MethodSymbol>("Test.M02");

            Assert.Equal("System.Int32 I1.P01 { get; set; }", ((CSharpSemanticModel)model).LookupSymbols(node.SpanStart, m02.TypeParameters[0], "P01").Single().ToTestDisplayString());
            Assert.Equal("System.Int32 I1.P01 { get; set; }", ((CSharpSemanticModel)model).LookupStaticMembers(node.SpanStart, m02.TypeParameters[0], "P01").Single().ToTestDisplayString());
            Assert.Contains("System.Int32 I1.P01 { get; set; }", ((CSharpSemanticModel)model).LookupSymbols(node.SpanStart, m02.TypeParameters[0]).ToTestDisplayStrings());
            Assert.Contains("System.Int32 I1.P01 { get; set; }", ((CSharpSemanticModel)model).LookupStaticMembers(node.SpanStart, m02.TypeParameters[0]).ToTestDisplayStrings());

            Assert.Equal("System.Int32 I1.P01 { get; set; }", model.LookupSymbols(node.SpanStart, m02.TypeParameters[0].GetPublicSymbol(), "P01").Single().ToTestDisplayString());
            Assert.Equal("System.Int32 I1.P01 { get; set; }", model.LookupStaticMembers(node.SpanStart, m02.TypeParameters[0].GetPublicSymbol(), "P01").Single().ToTestDisplayString());
            Assert.Contains("System.Int32 I1.P01 { get; set; }", model.LookupSymbols(node.SpanStart, m02.TypeParameters[0].GetPublicSymbol()).ToTestDisplayStrings());
            Assert.Contains("System.Int32 I1.P01 { get; set; }", model.LookupStaticMembers(node.SpanStart, m02.TypeParameters[0].GetPublicSymbol()).ToTestDisplayStrings());

            Assert.Contains("P01", model.LookupNames(node.SpanStart, m02.TypeParameters[0].GetPublicSymbol()));
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticPropertyCompound_03(bool isVirtual)
        {
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static int P01 { get; set; }
}

class Test
{
    static void M02<T, U>() where T : U where U : I1
    {
        T.P01 += 1;
    }

    static string M03<T, U>() where T : U where U : I1
    {
        return nameof(T.P01);
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>()",
@"
{
  // Code size       27 (0x1b)
  .maxstack  2
  IL_0000:  nop
  IL_0001:  constrained. ""T""
  IL_0007:  call       ""int I1.P01.get""
  IL_000c:  ldc.i4.1
  IL_000d:  add
  IL_000e:  constrained. ""T""
  IL_0014:  call       ""void I1.P01.set""
  IL_0019:  nop
  IL_001a:  ret
}
");

            verifier.VerifyIL("Test.M03<T, U>()",
@"
{
  // Code size       11 (0xb)
  .maxstack  1
  .locals init (string V_0)
  IL_0000:  nop
  IL_0001:  ldstr      ""P01""
  IL_0006:  stloc.0
  IL_0007:  br.s       IL_0009
  IL_0009:  ldloc.0
  IL_000a:  ret
}
");

            compilation1 = CreateCompilation(source1, options: TestOptions.ReleaseDll,
                                             parseOptions: TestOptions.RegularPreview,
                                             targetFramework: _supportingFramework);

            verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>()",
@"
{
  // Code size       25 (0x19)
  .maxstack  2
  IL_0000:  constrained. ""T""
  IL_0006:  call       ""int I1.P01.get""
  IL_000b:  ldc.i4.1
  IL_000c:  add
  IL_000d:  constrained. ""T""
  IL_0013:  call       ""void I1.P01.set""
  IL_0018:  ret
}
");

            verifier.VerifyIL("Test.M03<T, U>()",
@"
{
  // Code size        6 (0x6)
  .maxstack  1
  IL_0000:  ldstr      ""P01""
  IL_0005:  ret
}
");

            var tree = compilation1.SyntaxTrees.Single();
            var model = compilation1.GetSemanticModel(tree);
            var node = tree.GetRoot().DescendantNodes().OfType<AssignmentExpressionSyntax>().First().Left;

            Assert.Equal("T.P01", node.ToString());
            VerifyOperationTreeForNode(compilation1, model, node,
@"
IPropertyReferenceOperation: System.Int32 I1.P01 { get; set; } (ConstrainedToType: T) (Static) (OperationKind.PropertyReference, Type: System.Int32) (Syntax: 'T.P01')
  Instance Receiver: 
    null
");

            var m02 = compilation1.GetMember<MethodSymbol>("Test.M02");

            Assert.Equal("System.Int32 I1.P01 { get; set; }", ((CSharpSemanticModel)model).LookupSymbols(node.SpanStart, m02.TypeParameters[0], "P01").Single().ToTestDisplayString());
            Assert.Equal("System.Int32 I1.P01 { get; set; }", ((CSharpSemanticModel)model).LookupStaticMembers(node.SpanStart, m02.TypeParameters[0], "P01").Single().ToTestDisplayString());
            Assert.Contains("System.Int32 I1.P01 { get; set; }", ((CSharpSemanticModel)model).LookupSymbols(node.SpanStart, m02.TypeParameters[0]).ToTestDisplayStrings());
            Assert.Contains("System.Int32 I1.P01 { get; set; }", ((CSharpSemanticModel)model).LookupStaticMembers(node.SpanStart, m02.TypeParameters[0]).ToTestDisplayStrings());

            Assert.Equal("System.Int32 I1.P01 { get; set; }", model.LookupSymbols(node.SpanStart, m02.TypeParameters[0].GetPublicSymbol(), "P01").Single().ToTestDisplayString());
            Assert.Equal("System.Int32 I1.P01 { get; set; }", model.LookupStaticMembers(node.SpanStart, m02.TypeParameters[0].GetPublicSymbol(), "P01").Single().ToTestDisplayString());
            Assert.Contains("System.Int32 I1.P01 { get; set; }", model.LookupSymbols(node.SpanStart, m02.TypeParameters[0].GetPublicSymbol()).ToTestDisplayStrings());
            Assert.Contains("System.Int32 I1.P01 { get; set; }", model.LookupStaticMembers(node.SpanStart, m02.TypeParameters[0].GetPublicSymbol()).ToTestDisplayStrings());

            Assert.Contains("P01", model.LookupNames(node.SpanStart, m02.TypeParameters[0].GetPublicSymbol()));
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticPropertyGet_04(bool isVirtual)
        {
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static int P01 { get; set; }
}
";
            var source2 =
@"
class Test
{
    static void M02<T>() where T : I1
    {
        _ = T.P01;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (6,13): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //         _ = T.P01;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "T.P01").WithLocation(6, 13)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation3.VerifyDiagnostics(
                // (12,31): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static int P01 { get; set; }
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "get").WithLocation(12, 31),
                // (12,36): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static int P01 { get; set; }
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "set").WithLocation(12, 36)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticPropertySet_04(bool isVirtual)
        {
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static int P01 { get; set; }
}
";
            var source2 =
@"
class Test
{
    static void M02<T>() where T : I1
    {
        T.P01 = 1;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (6,9): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //         T.P01 = 1;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "T.P01").WithLocation(6, 9)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation3.VerifyDiagnostics(
                // (12,31): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static int P01 { get; set; }
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "get").WithLocation(12, 31),
                // (12,36): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static int P01 { get; set; }
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "set").WithLocation(12, 36)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticPropertyCompound_04(bool isVirtual)
        {
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static int P01 { get; set; }
}
";
            var source2 =
@"
class Test
{
    static void M02<T>() where T : I1
    {
        T.P01 += 1;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (6,9): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //         T.P01 += 1;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "T.P01").WithLocation(6, 9),
                // (6,9): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //         T.P01 += 1;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "T.P01").WithLocation(6, 9)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation3.VerifyDiagnostics(
                // (12,31): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static int P01 { get; set; }
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "get").WithLocation(12, 31),
                // (12,36): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static int P01 { get; set; }
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "set").WithLocation(12, 36)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticPropertyGet_06(bool isVirtual)
        {
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static int P01 { get; set; }
}
";
            var source2 =
@"
class Test
{
    static void M02<T>() where T : I1
    {
        _ = T.P01;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (6,13): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                //         _ = T.P01;
                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "T").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 13)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation3.VerifyDiagnostics(
                // (6,13): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                //         _ = T.P01;
                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "T").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 13),
                // (12,25): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual  static int P01 { get; set; }
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "P01").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(12, 25)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticPropertySet_06(bool isVirtual)
        {
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static int P01 { get; set; }
}
";
            var source2 =
@"
class Test
{
    static void M02<T>() where T : I1
    {
        T.P01 = 1;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (6,9): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                //         T.P01 = 1;
                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "T").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 9)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation3.VerifyDiagnostics(
                // (6,9): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                //         T.P01 = 1;
                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "T").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 9),
                // (12,25): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual  static int P01 { get; set; }
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "P01").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(12, 25)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticPropertyCompound_06(bool isVirtual)
        {
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static int P01 { get; set; }
}
";
            var source2 =
@"
class Test
{
    static void M02<T>() where T : I1
    {
        T.P01 += 1;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (6,9): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                //         T.P01 += 1;
                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "T").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 9)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation3.VerifyDiagnostics(
                // (6,9): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                //         T.P01 += 1;
                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "T").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 9),
                // (12,25): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual  static int P01 { get; set; }
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "P01").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(12, 25)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticEventAdd_01(bool isVirtual)
        {
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"#pragma warning disable CS0067 // The event is never used
interface I1
{
    " + modifier + @" static event System.Action P01;

    static void M02()
    {
        P01 += null;
        P04 += null;
    }

    void M03()
    {
        this.P01 += null;
        this.P04 += null;
    }

    static event System.Action P04;

    protected " + modifier + @" static event System.Action P05;
}

class Test
{
    static void MT1(I1 x)
    {
        I1.P01 += null;
        x.P01 += null;
        I1.P04 += null;
        x.P04 += null;
    }

    static void MT2<T>() where T : I1
    {
        T.P03 += null;
        T.P04 += null;
        T.P00 += null;
        T.P05 += null;

        _ = (System.Linq.Expressions.Expression<System.Action>)(() => T.P01 += null);
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (8,9): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         P01 += null;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "P01 += null").WithLocation(8, 9),
                // (14,9): error CS0176: Member 'I1.P01' cannot be accessed with an instance reference; qualify it with a type name instead
                //         this.P01 += null;
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "this.P01").WithArguments("I1.P01").WithLocation(14, 9),
                // (14,9): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         this.P01 += null;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "this.P01 += null").WithLocation(14, 9),
                // (15,9): error CS0176: Member 'I1.P04' cannot be accessed with an instance reference; qualify it with a type name instead
                //         this.P04 += null;
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "this.P04").WithArguments("I1.P04").WithLocation(15, 9),
                // (27,9): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         I1.P01 += null;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "I1.P01 += null").WithLocation(27, 9),
                // (28,9): error CS0176: Member 'I1.P01' cannot be accessed with an instance reference; qualify it with a type name instead
                //         x.P01 += null;
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "x.P01").WithArguments("I1.P01").WithLocation(28, 9),
                // (28,9): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         x.P01 += null;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "x.P01 += null").WithLocation(28, 9),
                // (30,9): error CS0176: Member 'I1.P04' cannot be accessed with an instance reference; qualify it with a type name instead
                //         x.P04 += null;
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "x.P04").WithArguments("I1.P04").WithLocation(30, 9),
                // (35,9): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         T.P03 += null;
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(35, 9),
                // (36,9): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         T.P04 += null;
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(36, 9),
                // (37,9): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         T.P00 += null;
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(37, 9),
                // (38,11): error CS0122: 'I1.P05' is inaccessible due to its protection level
                //         T.P05 += null;
                Diagnostic(ErrorCode.ERR_BadAccess, "P05").WithArguments("I1.P05").WithLocation(38, 11),
                // (40,71): error CS0832: An expression tree may not contain an assignment operator
                //         _ = (System.Linq.Expressions.Expression<System.Action>)(() => T.P01 += null);
                Diagnostic(ErrorCode.ERR_ExpressionTreeContainsAssignment, "T.P01 += null").WithLocation(40, 71)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticEventRemove_01(bool isVirtual)
        {
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"#pragma warning disable CS0067 // The event is never used
interface I1
{
    " + modifier + @" static event System.Action P01;

    static void M02()
    {
        P01 -= null;
        P04 -= null;
    }

    void M03()
    {
        this.P01 -= null;
        this.P04 -= null;
    }

    static event System.Action P04;

    protected " + modifier + @" static event System.Action P05;
}

class Test
{
    static void MT1(I1 x)
    {
        I1.P01 -= null;
        x.P01 -= null;
        I1.P04 -= null;
        x.P04 -= null;
    }

    static void MT2<T>() where T : I1
    {
        T.P03 -= null;
        T.P04 -= null;
        T.P00 -= null;
        T.P05 -= null;

        _ = (System.Linq.Expressions.Expression<System.Action>)(() => T.P01 -= null);
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (8,9): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         P01 -= null;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "P01 -= null").WithLocation(8, 9),
                // (14,9): error CS0176: Member 'I1.P01' cannot be accessed with an instance reference; qualify it with a type name instead
                //         this.P01 -= null;
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "this.P01").WithArguments("I1.P01").WithLocation(14, 9),
                // (14,9): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         this.P01 -= null;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "this.P01 -= null").WithLocation(14, 9),
                // (15,9): error CS0176: Member 'I1.P04' cannot be accessed with an instance reference; qualify it with a type name instead
                //         this.P04 -= null;
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "this.P04").WithArguments("I1.P04").WithLocation(15, 9),
                // (27,9): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         I1.P01 -= null;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "I1.P01 -= null").WithLocation(27, 9),
                // (28,9): error CS0176: Member 'I1.P01' cannot be accessed with an instance reference; qualify it with a type name instead
                //         x.P01 -= null;
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "x.P01").WithArguments("I1.P01").WithLocation(28, 9),
                // (28,9): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         x.P01 -= null;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "x.P01 -= null").WithLocation(28, 9),
                // (30,9): error CS0176: Member 'I1.P04' cannot be accessed with an instance reference; qualify it with a type name instead
                //         x.P04 -= null;
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "x.P04").WithArguments("I1.P04").WithLocation(30, 9),
                // (35,9): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         T.P03 -= null;
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(35, 9),
                // (36,9): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         T.P04 -= null;
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(36, 9),
                // (37,9): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         T.P00 -= null;
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(37, 9),
                // (38,11): error CS0122: 'I1.P05' is inaccessible due to its protection level
                //         T.P05 -= null;
                Diagnostic(ErrorCode.ERR_BadAccess, "P05").WithArguments("I1.P05").WithLocation(38, 11),
                // (40,71): error CS0832: An expression tree may not contain an assignment operator
                //         _ = (System.Linq.Expressions.Expression<System.Action>)(() => T.P01 -= null);
                Diagnostic(ErrorCode.ERR_ExpressionTreeContainsAssignment, "T.P01 -= null").WithLocation(40, 71)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticEvent_02(bool isVirtual)
        {
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"#pragma warning disable CS0067 // The event 'I1.P05' is never used
interface I1
{
    " + modifier + @" static event System.Action P01;

    static void M02()
    {
        _ = nameof(P01);
        _ = nameof(P04);
    }

    void M03()
    {
        _ = nameof(this.P01);
        _ = nameof(this.P04);
    }

    static event System.Action P04;

    protected " + modifier + @" static event System.Action P05;
}

class Test
{
    static void MT1(I1 x)
    {
        _ = nameof(I1.P01);
        _ = nameof(x.P01);
        _ = nameof(I1.P04);
        _ = nameof(x.P04);
    }

    static void MT2<T>() where T : I1
    {
        _ = nameof(T.P03);
        _ = nameof(T.P04);
        _ = nameof(T.P00);
        _ = nameof(T.P05);
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (35,20): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         _ = nameof(T.P03);
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(35, 20),
                // (36,20): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         _ = nameof(T.P04);
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(36, 20),
                // (37,20): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         _ = nameof(T.P00);
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(37, 20),
                // (38,22): error CS0122: 'I1.P05' is inaccessible due to its protection level
                //         _ = nameof(T.P05);
                Diagnostic(ErrorCode.ERR_BadAccess, "P05").WithArguments("I1.P05").WithLocation(38, 22)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticEvent_03(bool isVirtual)
        {
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static event System.Action E01;
}

class Test
{
    static void M02<T, U>() where T : U where U : I1
    {
        T.E01 += null;
        T.E01 -= null;
    }

    static string M03<T, U>() where T : U where U : I1
    {
        return nameof(T.E01);
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>()",
@"
{
  // Code size       28 (0x1c)
  .maxstack  1
  IL_0000:  nop
  IL_0001:  ldnull
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""void I1.E01.add""
  IL_000d:  nop
  IL_000e:  ldnull
  IL_000f:  constrained. ""T""
  IL_0015:  call       ""void I1.E01.remove""
  IL_001a:  nop
  IL_001b:  ret
}
");

            verifier.VerifyIL("Test.M03<T, U>()",
@"
{
  // Code size       11 (0xb)
  .maxstack  1
  .locals init (string V_0)
  IL_0000:  nop
  IL_0001:  ldstr      ""E01""
  IL_0006:  stloc.0
  IL_0007:  br.s       IL_0009
  IL_0009:  ldloc.0
  IL_000a:  ret
}
");

            compilation1 = CreateCompilation(source1, options: TestOptions.ReleaseDll,
                                             parseOptions: TestOptions.RegularPreview,
                                             targetFramework: _supportingFramework);

            verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>()",
@"
{
  // Code size       25 (0x19)
  .maxstack  1
  IL_0000:  ldnull
  IL_0001:  constrained. ""T""
  IL_0007:  call       ""void I1.E01.add""
  IL_000c:  ldnull
  IL_000d:  constrained. ""T""
  IL_0013:  call       ""void I1.E01.remove""
  IL_0018:  ret
}
");

            verifier.VerifyIL("Test.M03<T, U>()",
@"
{
  // Code size        6 (0x6)
  .maxstack  1
  IL_0000:  ldstr      ""E01""
  IL_0005:  ret
}
");

            var tree = compilation1.SyntaxTrees.Single();
            var model = compilation1.GetSemanticModel(tree);
            var node = tree.GetRoot().DescendantNodes().OfType<AssignmentExpressionSyntax>().First().Left;

            Assert.Equal("T.E01", node.ToString());
            VerifyOperationTreeForNode(compilation1, model, node,
@"
IEventReferenceOperation: event System.Action I1.E01 (ConstrainedToType: T) (Static) (OperationKind.EventReference, Type: System.Action) (Syntax: 'T.E01')
  Instance Receiver: 
    null
");
            node = tree.GetRoot().DescendantNodes().OfType<InvocationExpressionSyntax>().First().ArgumentList.Arguments[0].Expression;

            Assert.Equal("T.E01", node.ToString());
            VerifyOperationTreeForNode(compilation1, model, node,
@"
IEventReferenceOperation: event System.Action I1.E01 (ConstrainedToType: T) (Static) (OperationKind.EventReference, Type: System.Action) (Syntax: 'T.E01')
  Instance Receiver: 
    null
");

            var m02 = compilation1.GetMember<MethodSymbol>("Test.M02");

            Assert.Equal("event System.Action I1.E01", ((CSharpSemanticModel)model).LookupSymbols(node.SpanStart, m02.TypeParameters[0], "E01").Single().ToTestDisplayString());
            Assert.Equal("event System.Action I1.E01", ((CSharpSemanticModel)model).LookupStaticMembers(node.SpanStart, m02.TypeParameters[0], "E01").Single().ToTestDisplayString());
            Assert.Contains("event System.Action I1.E01", ((CSharpSemanticModel)model).LookupSymbols(node.SpanStart, m02.TypeParameters[0]).ToTestDisplayStrings());
            Assert.Contains("event System.Action I1.E01", ((CSharpSemanticModel)model).LookupStaticMembers(node.SpanStart, m02.TypeParameters[0]).ToTestDisplayStrings());

            Assert.Equal("event System.Action I1.E01", model.LookupSymbols(node.SpanStart, m02.TypeParameters[0].GetPublicSymbol(), "E01").Single().ToTestDisplayString());
            Assert.Equal("event System.Action I1.E01", model.LookupStaticMembers(node.SpanStart, m02.TypeParameters[0].GetPublicSymbol(), "E01").Single().ToTestDisplayString());
            Assert.Contains("event System.Action I1.E01", model.LookupSymbols(node.SpanStart, m02.TypeParameters[0].GetPublicSymbol()).ToTestDisplayStrings());
            Assert.Contains("event System.Action I1.E01", model.LookupStaticMembers(node.SpanStart, m02.TypeParameters[0].GetPublicSymbol()).ToTestDisplayStrings());

            Assert.Contains("E01", model.LookupNames(node.SpanStart, m02.TypeParameters[0].GetPublicSymbol()));
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticEventAdd_04(bool isVirtual)
        {
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"#pragma warning disable CS0067 // The event 'I1.P01' is never used
public interface I1
{
    " + modifier + @" static event System.Action P01;
}
";
            var source2 =
@"
class Test
{
    static void M02<T>() where T : I1
    {
        T.P01 += null;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (6,9): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //         T.P01 += null;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "T.P01 += null").WithLocation(6, 9)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation3.VerifyDiagnostics(
                // (12,41): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static event System.Action P01;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "P01").WithLocation(12, 41)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticEventRemove_04(bool isVirtual)
        {
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"#pragma warning disable CS0067 // The event 'I1.P01' is never used
public interface I1
{
    " + modifier + @" static event System.Action P01;
}
";
            var source2 =
@"
class Test
{
    static void M02<T>() where T : I1
    {
        T.P01 -= null;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (6,9): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //         T.P01 -= null;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "T.P01 -= null").WithLocation(6, 9)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation3.VerifyDiagnostics(
                // (12,41): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static event System.Action P01;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "P01").WithLocation(12, 41)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticEventAdd_06(bool isVirtual)
        {
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"#pragma warning disable CS0067 // The event 'I1.P01' is never used
public interface I1
{
    " + modifier + @" static event System.Action P01;
}
";
            var source2 =
@"
class Test
{
    static void M02<T>() where T : I1
    {
        T.P01 += null;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (6,9): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                //         T.P01 += null;
                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "T").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 9)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation3.VerifyDiagnostics(
                // (6,9): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                //         T.P01 += null;
                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "T").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 9),
                // (12,41): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual  static event System.Action P01;
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "P01").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(12, 41)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticEventRemove_06(bool isVirtual)
        {
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"#pragma warning disable CS0067 // The event 'I1.P01' is never used
public interface I1
{
    " + modifier + @" static event System.Action P01;
}
";
            var source2 =
@"
class Test
{
    static void M02<T>() where T : I1
    {
        T.P01 -= null;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (6,9): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                //         T.P01 -= null;
                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "T").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 9)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation3.VerifyDiagnostics(
                // (6,9): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                //         T.P01 -= null;
                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "T").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 9),
                // (12,41): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual  static event System.Action P01;
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "P01").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(12, 41)
                );
        }

        private (string modifier, string body) GetILModifierAndBody(bool isVirtual)
        {
            if (isVirtual)
            {
                return ("",
@"
{
  .maxstack  8
  IL_0000:  ldnull
  IL_0001:  throw
}
");
            }
            else
            {
                return ("abstract",
@"{
}
");
            }
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticIndexedProperty_03(bool isVirtual)
        {
            var (modifier, body) = GetILModifierAndBody(isVirtual);

            var ilSource = @"
.class interface public auto ansi abstract I1
{
    .custom instance void [mscorlib]System.Reflection.DefaultMemberAttribute::.ctor(string) = (
        01 00 04 49 74 65 6d 00 00
    )

    // Methods
    .method public hidebysig specialname newslot " + modifier + @" virtual 
        static int32 get_Item (
            int32 x
        ) cil managed 
    " + body + @"

    .method public hidebysig specialname newslot " + modifier + @" virtual 
        static void set_Item (
            int32 x,
            int32 'value'
        ) cil managed 
    " + body + @"

    // Properties
    .property int32 Item(
        int32 x
    )
    {
        .get int32 I1::get_Item(int32)
        .set void I1::set_Item(int32, int32)
    }

} // end of class I1
";

            var source1 =
@"
class Test
{
    static void M02<T>() where T : I1
    {
        T.Item[0] += 1;
    }

    static string M03<T>() where T : I1
    {
        return nameof(T.Item);
    }
}
";
            var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (6,9): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         T.Item[0] += 1;
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(6, 9),
                // (11,23): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         return nameof(T.Item);
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(11, 23)
                );

            var source2 =
@"
class Test
{
    static void M02<T>() where T : I1
    {
        T[0] += 1;
    }

    static void M03<T>() where T : I1
    {
        T.set_Item(0, T.get_Item(0) + 1);
    }
}
";
            var compilation2 = CreateCompilationWithIL(source2, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation2.VerifyDiagnostics(
                // (6,9): error CS0119: 'T' is a type, which is not valid in the given context
                //         T[0] += 1;
                Diagnostic(ErrorCode.ERR_BadSKunknown, "T").WithArguments("T", "type").WithLocation(6, 9),
                // (11,11): error CS0571: 'I1.this[int].set': cannot explicitly call operator or accessor
                //         T.set_Item(0, T.get_Item(0) + 1);
                Diagnostic(ErrorCode.ERR_CantCallSpecialMethod, "set_Item").WithArguments("I1.this[int].set").WithLocation(11, 11),
                // (11,25): error CS0571: 'I1.this[int].get': cannot explicitly call operator or accessor
                //         T.set_Item(0, T.get_Item(0) + 1);
                Diagnostic(ErrorCode.ERR_CantCallSpecialMethod, "get_Item").WithArguments("I1.this[int].get").WithLocation(11, 25)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticIndexedProperty_04(bool isVirtual)
        {
            var (modifier, body) = GetILModifierAndBody(isVirtual);

            var ilSource = @"
.class interface public auto ansi abstract I1
{
    // Methods
    .method public hidebysig specialname newslot " + modifier + @" virtual 
        static int32 get_Item (
            int32 x
        ) cil managed 
    " + body + @"

    .method public hidebysig specialname newslot " + modifier + @" virtual 
        static void set_Item (
            int32 x,
            int32 'value'
        ) cil managed 
    " + body + @"

    // Properties
    .property int32 Item(
        int32 x
    )
    {
        .get int32 I1::get_Item(int32)
        .set void I1::set_Item(int32, int32)
    }

} // end of class I1
";

            var source1 =
@"
class Test
{
    static void M02<T>() where T : I1
    {
        T.Item[0] += 1;
    }

    static string M03<T>() where T : I1
    {
        return nameof(T.Item);
    }
}
";
            var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (6,11): error CS1545: Property, indexer, or event 'I1.Item[int]' is not supported by the language; try directly calling accessor methods 'I1.get_Item(int)' or 'I1.set_Item(int, int)'
                //         T.Item[0] += 1;
                Diagnostic(ErrorCode.ERR_BindToBogusProp2, "Item").WithArguments("I1.Item[int]", "I1.get_Item(int)", "I1.set_Item(int, int)").WithLocation(6, 11),
                // (11,25): error CS1545: Property, indexer, or event 'I1.Item[int]' is not supported by the language; try directly calling accessor methods 'I1.get_Item(int)' or 'I1.set_Item(int, int)'
                //         return nameof(T.Item);
                Diagnostic(ErrorCode.ERR_BindToBogusProp2, "Item").WithArguments("I1.Item[int]", "I1.get_Item(int)", "I1.set_Item(int, int)").WithLocation(11, 25)
                );

            var source2 =
@"
class Test
{
    static void M02<T>() where T : I1
    {
        T.set_Item(0, T.get_Item(0) + 1);
    }
}
";
            var compilation2 = CreateCompilationWithIL(source2, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation2, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T>()",
@"
{
  // Code size       29 (0x1d)
  .maxstack  3
  IL_0000:  nop
  IL_0001:  ldc.i4.0
  IL_0002:  ldc.i4.0
  IL_0003:  constrained. ""T""
  IL_0009:  call       ""int I1.get_Item(int)""
  IL_000e:  ldc.i4.1
  IL_000f:  add
  IL_0010:  constrained. ""T""
  IL_0016:  call       ""void I1.set_Item(int, int)""
  IL_001b:  nop
  IL_001c:  ret
}
");
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticMethod_ConversionToDelegate_01(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
interface I1
{
    " + modifier + @" static void M01()" + body + @"

    static void M02()
    {
        _ = (System.Action)M01;
        _ = (System.Action)M04;
    }

    void M03()
    {
        _ = (System.Action)this.M01;
        _ = (System.Action)this.M04;
    }

    static void M04() {}

    protected " + modifier + @" static void M05()" + body + @"
}

class Test
{
    static void MT1(I1 x)
    {
        _ = (System.Action)I1.M01;
        _ = (System.Action)x.M01;
        _ = (System.Action)I1.M04;
        _ = (System.Action)x.M04;
    }

    static void MT2<T>() where T : I1
    {
        _ = (System.Action)T.M03;
        _ = (System.Action)T.M04;
        _ = (System.Action)T.M00;
        _ = (System.Action)T.M05;

        _ = (System.Linq.Expressions.Expression<System.Action>)(() => ((System.Action)T.M01).ToString());
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (8,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         _ = (System.Action)M01;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "(System.Action)M01").WithLocation(8, 13),
                // (14,28): error CS0176: Member 'I1.M01()' cannot be accessed with an instance reference; qualify it with a type name instead
                //         _ = (System.Action)this.M01;
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "this.M01").WithArguments("I1.M01()").WithLocation(14, 28),
                // (15,28): error CS0176: Member 'I1.M04()' cannot be accessed with an instance reference; qualify it with a type name instead
                //         _ = (System.Action)this.M04;
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "this.M04").WithArguments("I1.M04()").WithLocation(15, 28),
                // (27,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         _ = (System.Action)I1.M01;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "(System.Action)I1.M01").WithLocation(27, 13),
                // (28,28): error CS0176: Member 'I1.M01()' cannot be accessed with an instance reference; qualify it with a type name instead
                //         _ = (System.Action)x.M01;
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "x.M01").WithArguments("I1.M01()").WithLocation(28, 28),
                // (30,28): error CS0176: Member 'I1.M04()' cannot be accessed with an instance reference; qualify it with a type name instead
                //         _ = (System.Action)x.M04;
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "x.M04").WithArguments("I1.M04()").WithLocation(30, 28),
                // (35,28): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         _ = (System.Action)T.M03;
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(35, 28),
                // (36,28): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         _ = (System.Action)T.M04;
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(36, 28),
                // (37,28): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         _ = (System.Action)T.M00;
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(37, 28),
                // (38,30): error CS0122: 'I1.M05()' is inaccessible due to its protection level
                //         _ = (System.Action)T.M05;
                Diagnostic(ErrorCode.ERR_BadAccess, "M05").WithArguments("I1.M05()").WithLocation(38, 30),
                // (40,87): error CS8927: An expression tree may not contain an access of static virtual or abstract interface member
                //         _ = (System.Linq.Expressions.Expression<System.Action>)(() => ((System.Action)T.M01).ToString());
                Diagnostic(ErrorCode.ERR_ExpressionTreeContainsAbstractStaticMemberAccess, "T.M01").WithLocation(40, 87)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticMethod_ConversionToDelegate_03(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static void M01()" + body + @"
}

class Test
{
    static System.Action M02<T, U>() where T : U where U : I1
    {
        return T.M01;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>()",
@"
{
  // Code size       39 (0x27)
  .maxstack  2
  .locals init (System.Action V_0)
  IL_0000:  nop
  IL_0001:  ldsfld     ""System.Action Test.<M02>O__0_0<T, U>.<0>__M01""
  IL_0006:  dup
  IL_0007:  brtrue.s   IL_0022
  IL_0009:  pop
  IL_000a:  ldnull
  IL_000b:  constrained. ""T""
  IL_0011:  ldftn      ""void I1.M01()""
  IL_0017:  newobj     ""System.Action..ctor(object, System.IntPtr)""
  IL_001c:  dup
  IL_001d:  stsfld     ""System.Action Test.<M02>O__0_0<T, U>.<0>__M01""
  IL_0022:  stloc.0
  IL_0023:  br.s       IL_0025
  IL_0025:  ldloc.0
  IL_0026:  ret
}
");

            compilation1 = CreateCompilation(source1, options: TestOptions.ReleaseDll,
                                             parseOptions: TestOptions.RegularPreview,
                                             targetFramework: _supportingFramework);

            verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>()",
@"
{
  // Code size       34 (0x22)
  .maxstack  2
  IL_0000:  ldsfld     ""System.Action Test.<M02>O__0_0<T, U>.<0>__M01""
  IL_0005:  dup
  IL_0006:  brtrue.s   IL_0021
  IL_0008:  pop
  IL_0009:  ldnull
  IL_000a:  constrained. ""T""
  IL_0010:  ldftn      ""void I1.M01()""
  IL_0016:  newobj     ""System.Action..ctor(object, System.IntPtr)""
  IL_001b:  dup
  IL_001c:  stsfld     ""System.Action Test.<M02>O__0_0<T, U>.<0>__M01""
  IL_0021:  ret
}
");

            var tree = compilation1.SyntaxTrees.Single();
            var model = compilation1.GetSemanticModel(tree);
            var node = tree.GetRoot().DescendantNodes().OfType<MemberAccessExpressionSyntax>().First();

            Assert.Equal("T.M01", node.ToString());
            VerifyOperationTreeForNode(compilation1, model, node,
@"
IMethodReferenceOperation: void I1.M01() (ConstrainedToType: T) (IsVirtual) (Static) (OperationKind.MethodReference, Type: null) (Syntax: 'T.M01')
  Instance Receiver: 
    null
");
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticMethod_ConversionToDelegate_04(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static void M01()" + body + @"
}
";
            var source2 =
@"
class Test
{
    static void M02<T>() where T : I1
    {
        _ = (System.Action)T.M01;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (6,13): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //         _ = (System.Action)T.M01;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "(System.Action)T.M01").WithLocation(6, 13)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation3.VerifyDiagnostics(
                // (12,26): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static void M01();
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "M01").WithLocation(12, 26)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticMethod_ConversionToDelegate_06(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static void M01()" + body + @"
}
";
            var source2 =
@"
class Test
{
    static void M02<T>() where T : I1
    {
        _ = (System.Action)T.M01;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (6,28): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                //         _ = (System.Action)T.M01;
                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "T").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 28)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation3.VerifyDiagnostics(
                // (6,28): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                //         _ = (System.Action)T.M01;
                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "T").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 28),
                // (12,26): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual  static void M01() => throw null;
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M01").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(12, 26)
                );
        }

        private static bool Execute(bool isVirtual)
        {
            return ExecutionConditionUtil.IsMonoOrCoreClr;
        }

        [ConditionalTheory(typeof(CoreClrOnly))]
        [CombinatorialData]
        [WorkItem(60069, "https://github.com/dotnet/roslyn/issues/60069")]
        public void DelegateCaching_01(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
using System;

class TestStaticInterfaceMethods
{
    static Func<string> TestSimpleInterface<T>() where T : ISimple
    {
        return T.GetCookie;
    }

    static void Main()
    {
        Func<string> d1 = TestSimpleInterface<SimpleClass>();
        Func<string> d2 = TestSimpleInterface<SimpleStruct>();

        System.Console.WriteLine(d1());
        System.Console.WriteLine(d2());

        for (int i = 0; i < 5; i++)
        {
            if (d1 != (object)TestSimpleInterface<SimpleClass>())    
            {
                System.Console.WriteLine(""d1 is not cached!!!"");
            }

            if (d2 != (object)TestSimpleInterface<SimpleStruct>())    
            {
                System.Console.WriteLine(""d2 is not cached!!!"");
            }
        }
    }
}

interface ISimple
{
    static " + modifier + @" string GetCookie()" + body + @"
}

class SimpleClass : ISimple
{
    public static string GetCookie() => ""SimpleClass"";
}

struct SimpleStruct : ISimple
{
    public static string GetCookie() => ""SimpleStruct"";
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.ReleaseExe,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, verify: Verification.Skipped, expectedOutput: !Execute(isVirtual) ? null : @"
SimpleClass
SimpleStruct
").VerifyDiagnostics();
        }

        [ConditionalTheory(typeof(CoreClrOnly))]
        [CombinatorialData]
        [WorkItem(60069, "https://github.com/dotnet/roslyn/issues/60069")]
        public void DelegateCaching_02(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
using System;

class TestStaticInterfaceMethods
{
    static (Func<string>, Func<string>) TestSimpleInterface<T, U>() where T : ISimple where U : ISimple
    {
        return (T.GetCookie, U.GetCookie);
    }

    static void Main()
    {
        (Func<string> d1, Func<string> d2) = TestSimpleInterface<SimpleClass, SimpleStruct>();

        System.Console.WriteLine(d1());
        System.Console.WriteLine(d2());

        for (int i = 0; i < 5; i++)
        {
            (Func<string> d21, Func<string> d22) = TestSimpleInterface<SimpleClass, SimpleStruct>();
            if (d1 != (object)d21)    
            {
                System.Console.WriteLine(""d1 is not cached!!!"");
            }

            if (d2 != (object)d22)    
            {
                System.Console.WriteLine(""d2 is not cached!!!"");
            }
        }
    }
}

interface ISimple
{
    static " + modifier + @" string GetCookie()" + body + @"
}

class SimpleClass : ISimple
{
    public static string GetCookie() => ""SimpleClass"";
}

struct SimpleStruct : ISimple
{
    public static string GetCookie() => ""SimpleStruct"";
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.ReleaseExe,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, verify: Verification.Skipped, expectedOutput: !Execute(isVirtual) ? null : @"
SimpleClass
SimpleStruct
").VerifyDiagnostics();
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticMethod_DelegateCreation_01(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
interface I1
{
    " + modifier + @" static void M01()" + body + @"

    static void M02()
    {
        _ = new System.Action(M01);
        _ = new System.Action(M04);
    }

    void M03()
    {
        _ = new System.Action(this.M01);
        _ = new System.Action(this.M04);
    }

    static void M04() {}

    protected " + modifier + @" static void M05()" + body + @"
}

class Test
{
    static void MT1(I1 x)
    {
        _ = new System.Action(I1.M01);
        _ = new System.Action(x.M01);
        _ = new System.Action(I1.M04);
        _ = new System.Action(x.M04);
    }

    static void MT2<T>() where T : I1
    {
        _ = new System.Action(T.M03);
        _ = new System.Action(T.M04);
        _ = new System.Action(T.M00);
        _ = new System.Action(T.M05);

        _ = (System.Linq.Expressions.Expression<System.Action>)(() => new System.Action(T.M01).ToString());
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (8,31): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         _ = new System.Action(M01);
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "M01").WithLocation(8, 31),
                // (14,31): error CS0176: Member 'I1.M01()' cannot be accessed with an instance reference; qualify it with a type name instead
                //         _ = new System.Action(this.M01);
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "this.M01").WithArguments("I1.M01()").WithLocation(14, 31),
                // (15,31): error CS0176: Member 'I1.M04()' cannot be accessed with an instance reference; qualify it with a type name instead
                //         _ = new System.Action(this.M04);
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "this.M04").WithArguments("I1.M04()").WithLocation(15, 31),
                // (27,31): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         _ = new System.Action(I1.M01);
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "I1.M01").WithLocation(27, 31),
                // (28,31): error CS0176: Member 'I1.M01()' cannot be accessed with an instance reference; qualify it with a type name instead
                //         _ = new System.Action(x.M01);
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "x.M01").WithArguments("I1.M01()").WithLocation(28, 31),
                // (30,31): error CS0176: Member 'I1.M04()' cannot be accessed with an instance reference; qualify it with a type name instead
                //         _ = new System.Action(x.M04);
                Diagnostic(ErrorCode.ERR_ObjectProhibited, "x.M04").WithArguments("I1.M04()").WithLocation(30, 31),
                // (35,31): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         _ = new System.Action(T.M03);
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(35, 31),
                // (36,31): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         _ = new System.Action(T.M04);
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(36, 31),
                // (37,31): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         _ = new System.Action(T.M00);
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(37, 31),
                // (38,33): error CS0122: 'I1.M05()' is inaccessible due to its protection level
                //         _ = new System.Action(T.M05);
                Diagnostic(ErrorCode.ERR_BadAccess, "M05").WithArguments("I1.M05()").WithLocation(38, 33),
                // (40,89): error CS8927: An expression tree may not contain an access of static virtual or abstract interface member
                //         _ = (System.Linq.Expressions.Expression<System.Action>)(() => new System.Action(T.M01).ToString());
                Diagnostic(ErrorCode.ERR_ExpressionTreeContainsAbstractStaticMemberAccess, "T.M01").WithLocation(40, 89)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticMethod_DelegateCreation_03(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static void M01()" + body + @"
}

class Test
{
    static System.Action M02<T, U>() where T : U where U : I1
    {
        return new System.Action(T.M01);
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>()",
@"
{
  // Code size       24 (0x18)
  .maxstack  2
  .locals init (System.Action V_0)
  IL_0000:  nop
  IL_0001:  ldnull
  IL_0002:  constrained. ""T""
  IL_0008:  ldftn      ""void I1.M01()""
  IL_000e:  newobj     ""System.Action..ctor(object, System.IntPtr)""
  IL_0013:  stloc.0
  IL_0014:  br.s       IL_0016
  IL_0016:  ldloc.0
  IL_0017:  ret
}
");

            compilation1 = CreateCompilation(source1, options: TestOptions.ReleaseDll,
                                             parseOptions: TestOptions.RegularPreview,
                                             targetFramework: _supportingFramework);

            verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>()",
@"
{
  // Code size       19 (0x13)
  .maxstack  2
  IL_0000:  ldnull
  IL_0001:  constrained. ""T""
  IL_0007:  ldftn      ""void I1.M01()""
  IL_000d:  newobj     ""System.Action..ctor(object, System.IntPtr)""
  IL_0012:  ret
}
");

            var tree = compilation1.SyntaxTrees.Single();
            var model = compilation1.GetSemanticModel(tree);
            var node = tree.GetRoot().DescendantNodes().OfType<MemberAccessExpressionSyntax>().First();

            Assert.Equal("T.M01", node.ToString());
            VerifyOperationTreeForNode(compilation1, model, node,
@"
IMethodReferenceOperation: void I1.M01() (ConstrainedToType: T) (IsVirtual) (Static) (OperationKind.MethodReference, Type: null) (Syntax: 'T.M01')
  Instance Receiver: 
    null
");
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticMethod_DelegateCreation_04(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static void M01()" + body + @"
}
";
            var source2 =
@"
class Test
{
    static void M02<T>() where T : I1
    {
        _ = new System.Action(T.M01);
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (6,31): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //         _ = new System.Action(T.M01);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "T.M01").WithLocation(6, 31)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation3.VerifyDiagnostics(
                // (12,26): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static void M01();
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "M01").WithLocation(12, 26)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticMethod_DelegateCreation_06(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static void M01()" + body + @"
}
";
            var source2 =
@"
class Test
{
    static void M02<T>() where T : I1
    {
        _ = new System.Action(T.M01);
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (6,31): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                //         _ = new System.Action(T.M01);
                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "T").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 31)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation3.VerifyDiagnostics(
                // (6,31): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                //         _ = new System.Action(T.M01);
                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "T").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 31),
                // (12,26): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual  static void M01() => throw null;
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M01").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(12, 26)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticMethod_ConversionToFunctionPointer_01(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
unsafe interface I1
{
    " + modifier + @" static void M01()" + body + @"

    static void M02()
    {
        _ = (delegate*<void>)&M01;
        _ = (delegate*<void>)&M04;
    }

    void M03()
    {
        _ = (delegate*<void>)&this.M01;
        _ = (delegate*<void>)&this.M04;
    }

    static void M04() {}

    protected " + modifier + @" static void M05()" + body + @"
}

unsafe class Test
{
    static void MT1(I1 x)
    {
        _ = (delegate*<void>)&I1.M01;
        _ = (delegate*<void>)&x.M01;
        _ = (delegate*<void>)&I1.M04;
        _ = (delegate*<void>)&x.M04;
    }

    static void MT2<T>() where T : I1
    {
        _ = (delegate*<void>)&T.M03;
        _ = (delegate*<void>)&T.M04;
        _ = (delegate*<void>)&T.M00;
        _ = (delegate*<void>)&T.M05;

        _ = (System.Linq.Expressions.Expression<System.Action>)(() => ((System.IntPtr)((delegate*<void>)&T.M01)).ToString());
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll.WithAllowUnsafe(true),
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (8,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         _ = (delegate*<void>)&M01;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "(delegate*<void>)&M01").WithLocation(8, 13),
                // (14,13): error CS8757: No overload for 'M01' matches function pointer 'delegate*<void>'
                //         _ = (delegate*<void>)&this.M01;
                Diagnostic(ErrorCode.ERR_MethFuncPtrMismatch, "(delegate*<void>)&this.M01").WithArguments("M01", "delegate*<void>").WithLocation(14, 13),
                // (15,13): error CS8757: No overload for 'M04' matches function pointer 'delegate*<void>'
                //         _ = (delegate*<void>)&this.M04;
                Diagnostic(ErrorCode.ERR_MethFuncPtrMismatch, "(delegate*<void>)&this.M04").WithArguments("M04", "delegate*<void>").WithLocation(15, 13),
                // (27,13): error CS8926: A static virtual or abstract interface member can be accessed only on a type parameter.
                //         _ = (delegate*<void>)&I1.M01;
                Diagnostic(ErrorCode.ERR_BadAbstractStaticMemberAccess, "(delegate*<void>)&I1.M01").WithLocation(27, 13),
                // (28,13): error CS8757: No overload for 'M01' matches function pointer 'delegate*<void>'
                //         _ = (delegate*<void>)&x.M01;
                Diagnostic(ErrorCode.ERR_MethFuncPtrMismatch, "(delegate*<void>)&x.M01").WithArguments("M01", "delegate*<void>").WithLocation(28, 13),
                // (30,13): error CS8757: No overload for 'M04' matches function pointer 'delegate*<void>'
                //         _ = (delegate*<void>)&x.M04;
                Diagnostic(ErrorCode.ERR_MethFuncPtrMismatch, "(delegate*<void>)&x.M04").WithArguments("M04", "delegate*<void>").WithLocation(30, 13),
                // (35,31): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         _ = (delegate*<void>)&T.M03;
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(35, 31),
                // (36,31): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         _ = (delegate*<void>)&T.M04;
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(36, 31),
                // (37,31): error CS0704: Cannot do non-virtual member lookup in 'T' because it is a type parameter
                //         _ = (delegate*<void>)&T.M00;
                Diagnostic(ErrorCode.ERR_LookupInTypeVariable, "T").WithArguments("T").WithLocation(37, 31),
                // (38,33): error CS0122: 'I1.M05()' is inaccessible due to its protection level
                //         _ = (delegate*<void>)&T.M05;
                Diagnostic(ErrorCode.ERR_BadAccess, "M05").WithArguments("I1.M05()").WithLocation(38, 33),
                // (40,88): error CS1944: An expression tree may not contain an unsafe pointer operation
                //         _ = (System.Linq.Expressions.Expression<System.Action>)(() => ((System.IntPtr)((delegate*<void>)&T.M01)).ToString());
                Diagnostic(ErrorCode.ERR_ExpressionTreeContainsPointerOp, "(delegate*<void>)&T.M01").WithLocation(40, 88),
                // (40,106): error CS8810: '&' on method groups cannot be used in expression trees
                //         _ = (System.Linq.Expressions.Expression<System.Action>)(() => ((System.IntPtr)((delegate*<void>)&T.M01)).ToString());
                Diagnostic(ErrorCode.ERR_AddressOfMethodGroupInExpressionTree, "T.M01").WithLocation(40, 106)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticMethod_ConversionToFunctionPointer_03(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static void M01()" + body + @"
}

unsafe class Test
{
    static delegate*<void> M02<T, U>() where T : U where U : I1
    {
        return &T.M01;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll.WithAllowUnsafe(true),
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>()",
@"
{
  // Code size       18 (0x12)
  .maxstack  1
  .locals init (delegate*<void> V_0)
  IL_0000:  nop
  IL_0001:  constrained. ""T""
  IL_0007:  ldftn      ""void I1.M01()""
  IL_000d:  stloc.0
  IL_000e:  br.s       IL_0010
  IL_0010:  ldloc.0
  IL_0011:  ret
}
");

            compilation1 = CreateCompilation(source1, options: TestOptions.ReleaseDll.WithAllowUnsafe(true),
                                             parseOptions: TestOptions.RegularPreview,
                                             targetFramework: _supportingFramework);

            verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>()",
@"
{
  // Code size       13 (0xd)
  .maxstack  1
  IL_0000:  constrained. ""T""
  IL_0006:  ldftn      ""void I1.M01()""
  IL_000c:  ret
}
");

            var tree = compilation1.SyntaxTrees.Single();
            var model = compilation1.GetSemanticModel(tree);
            var node = tree.GetRoot().DescendantNodes().OfType<MemberAccessExpressionSyntax>().First();

            Assert.Equal("T.M01", node.ToString());
            VerifyOperationTreeForNode(compilation1, model, node,
@"
IMethodReferenceOperation: void I1.M01() (ConstrainedToType: T) (IsVirtual) (Static) (OperationKind.MethodReference, Type: null) (Syntax: 'T.M01')
  Instance Receiver: 
    null
");
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticMethod_ConversionFunctionPointer_04(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static void M01()" + body + @"
}
";
            var source2 =
@"
unsafe class Test
{
    static void M02<T>() where T : I1
    {
        _ = (delegate*<void>)&T.M01;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll.WithAllowUnsafe(true),
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (6,13): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //         _ = (delegate*<void>)&T.M01;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "(delegate*<void>)&T.M01").WithLocation(6, 13)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll.WithAllowUnsafe(true),
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation3.VerifyDiagnostics(
                // (12,26): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static void M01();
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "M01").WithLocation(12, 26)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractStaticMethod_ConversionToFunctionPointer_06(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static void M01()" + body + @"
}
";
            var source2 =
@"
unsafe class Test
{
    static void M02<T>() where T : I1
    {
        _ = (delegate*<void>)&T.M01;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll.WithAllowUnsafe(true),
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (6,31): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                //         _ = (delegate*<void>)&T.M01;
                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "T").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 31)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll.WithAllowUnsafe(true),
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation3.VerifyDiagnostics(
                // (6,31): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                //         _ = (delegate*<void>)&T.M01;
                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "T").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 31),
                // (12,26): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual  static void M01() => throw null;
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M01").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(12, 26)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticMethod_01(bool structure)
        {
            var typeKeyword = structure ? "struct" : "class";

            var source1 =
@"
public interface I1
{
    abstract static void M01();
}

" + typeKeyword + @"
    C1 : I1
{}

" + typeKeyword + @"
    C2 : I1
{
    public void M01() {}
}

" + typeKeyword + @"
    C3 : I1
{
    static void M01() {}
}

" + typeKeyword + @"
    C4 : I1
{
    void I1.M01() {}
}

" + typeKeyword + @"
    C5 : I1
{
    public static int M01() => throw null;
}

" + typeKeyword + @"
    C6 : I1
{
    static int I1.M01() => throw null;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (8,10): error CS0535: 'C1' does not implement interface member 'I1.M01()'
                //     C1 : I1
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C1", "I1.M01()").WithLocation(8, 10),
                // (12,10): error CS8928: 'C2' does not implement static interface member 'I1.M01()'. 'C2.M01()' cannot implement the interface member because it is not static.
                //     C2 : I1
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberNotStatic, "I1").WithArguments("C2", "I1.M01()", "C2.M01()").WithLocation(12, 10),
                // (18,10): error CS0737: 'C3' does not implement interface member 'I1.M01()'. 'C3.M01()' cannot implement an interface member because it is not public.
                //     C3 : I1
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberNotPublic, "I1").WithArguments("C3", "I1.M01()", "C3.M01()").WithLocation(18, 10),
                // (24,10): error CS0535: 'C4' does not implement interface member 'I1.M01()'
                //     C4 : I1
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C4", "I1.M01()").WithLocation(24, 10),
                // (26,13): error CS0539: 'C4.M01()' in explicit interface declaration is not found among members of the interface that can be implemented
                //     void I1.M01() {}
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "M01").WithArguments("C4.M01()").WithLocation(26, 13),
                // (30,10): error CS0738: 'C5' does not implement interface member 'I1.M01()'. 'C5.M01()' cannot implement 'I1.M01()' because it does not have the matching return type of 'void'.
                //     C5 : I1
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberWrongReturnType, "I1").WithArguments("C5", "I1.M01()", "C5.M01()", "void").WithLocation(30, 10),
                // (36,10): error CS0535: 'C6' does not implement interface member 'I1.M01()'
                //     C6 : I1
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C6", "I1.M01()").WithLocation(36, 10),
                // (38,19): error CS9334: 'C6.M01()' return type must be 'void' to match implemented member 'I1.M01()'
                //     static int I1.M01() => throw null;
                Diagnostic(ErrorCode.ERR_ExplicitInterfaceMemberReturnTypeMismatch, "M01").WithArguments("C6.M01()", "void", "I1.M01()").WithLocation(38, 19)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementVirtualStaticMethod_01(bool structure)
        {
            var typeKeyword = structure ? "struct" : "class";

            var source1 =
@"
public interface I1
{
    virtual static void M01(){}
}

" + typeKeyword + @"
    C1 : I1
{}

" + typeKeyword + @"
    C2 : I1
{
    public void M01() {}
}

" + typeKeyword + @"
    C3 : I1
{
    static void M01() {}
}

" + typeKeyword + @"
    C4 : I1
{
    void I1.M01() {}
}

" + typeKeyword + @"
    C5 : I1
{
    public static int M01() => throw null;
}

" + typeKeyword + @"
    C6 : I1
{
    static int I1.M01() => throw null;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (26,13): error CS0539: 'C4.M01()' in explicit interface declaration is not found among members of the interface that can be implemented
                //     void I1.M01() {}
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "M01").WithArguments("C4.M01()").WithLocation(26, 13),
                // (38,19): error CS9334: 'C6.M01()' return type must be 'void' to match implemented member 'I1.M01()'
                //     static int I1.M01() => throw null;
                Diagnostic(ErrorCode.ERR_ExplicitInterfaceMemberReturnTypeMismatch, "M01").WithArguments("C6.M01()", "void", "I1.M01()").WithLocation(38, 19)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticMethod_02(bool structure)
        {
            var typeKeyword = structure ? "struct" : "class";

            var source1 =
@"
public interface I1
{
    abstract void M01();
}

" + typeKeyword + @"
    C1 : I1
{}

" + typeKeyword + @"
    C2 : I1
{
    public static void M01() {}
}

" + typeKeyword + @"
    C3 : I1
{
    void M01() {}
}

" + typeKeyword + @"
    C4 : I1
{
    static void I1.M01() {}
}

" + typeKeyword + @"
    C5 : I1
{
    public int M01() => throw null;
}

" + typeKeyword + @"
    C6 : I1
{
    int I1.M01() => throw null;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (8,10): error CS0535: 'C1' does not implement interface member 'I1.M01()'
                //     C1 : I1
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C1", "I1.M01()").WithLocation(8, 10),
                // (12,10): error CS0736: 'C2' does not implement instance interface member 'I1.M01()'. 'C2.M01()' cannot implement the interface member because it is static.
                //     C2 : I1
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberStatic, "I1").WithArguments("C2", "I1.M01()", "C2.M01()").WithLocation(12, 10),
                // (18,10): error CS0737: 'C3' does not implement interface member 'I1.M01()'. 'C3.M01()' cannot implement an interface member because it is not public.
                //     C3 : I1
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberNotPublic, "I1").WithArguments("C3", "I1.M01()", "C3.M01()").WithLocation(18, 10),
                // (24,10): error CS0535: 'C4' does not implement interface member 'I1.M01()'
                //     C4 : I1
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C4", "I1.M01()").WithLocation(24, 10),
                // (26,20): error CS0539: 'C4.M01()' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static void I1.M01() {}
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "M01").WithArguments("C4.M01()").WithLocation(26, 20),
                // (30,10): error CS0738: 'C5' does not implement interface member 'I1.M01()'. 'C5.M01()' cannot implement 'I1.M01()' because it does not have the matching return type of 'void'.
                //     C5 : I1
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberWrongReturnType, "I1").WithArguments("C5", "I1.M01()", "C5.M01()", "void").WithLocation(30, 10),
                // (36,10): error CS0535: 'C6' does not implement interface member 'I1.M01()'
                //     C6 : I1
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C6", "I1.M01()").WithLocation(36, 10),
                // (38,12): error CS9334: 'C6.M01()' return type must be 'void' to match implemented member 'I1.M01()'
                //     int I1.M01() => throw null;
                Diagnostic(ErrorCode.ERR_ExplicitInterfaceMemberReturnTypeMismatch, "M01").WithArguments("C6.M01()", "void", "I1.M01()").WithLocation(38, 12)
                );
        }

        [Fact]
        public void ImplementAbstractStaticMethod_03()
        {
            var source1 =
@"
public interface I1
{
    abstract static void M01();
}

interface I2 : I1
{}

interface I3 : I1
{
    public virtual void M01() {}
}

interface I4 : I1
{
    static void M01() {}
}

interface I5 : I1
{
    void I1.M01() {}
}

interface I6 : I1
{
    static void I1.M01() {}
}

interface I7 : I1
{
    abstract static void M01();
}

interface I8 : I1
{
    abstract static void I1.M01();
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (12,25): warning CS0108: 'I3.M01()' hides inherited member 'I1.M01()'. Use the new keyword if hiding was intended.
                //     public virtual void M01() {}
                Diagnostic(ErrorCode.WRN_NewRequired, "M01").WithArguments("I3.M01()", "I1.M01()").WithLocation(12, 25),
                // (17,17): warning CS0108: 'I4.M01()' hides inherited member 'I1.M01()'. Use the new keyword if hiding was intended.
                //     static void M01() {}
                Diagnostic(ErrorCode.WRN_NewRequired, "M01").WithArguments("I4.M01()", "I1.M01()").WithLocation(17, 17),
                // (22,13): error CS0539: 'I5.M01()' in explicit interface declaration is not found among members of the interface that can be implemented
                //     void I1.M01() {}
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "M01").WithArguments("I5.M01()").WithLocation(22, 13),
                // (32,26): warning CS0108: 'I7.M01()' hides inherited member 'I1.M01()'. Use the new keyword if hiding was intended.
                //     abstract static void M01();
                Diagnostic(ErrorCode.WRN_NewRequired, "M01").WithArguments("I7.M01()", "I1.M01()").WithLocation(32, 26)
                );

            var m01 = compilation1.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<MethodSymbol>().Single();

            Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I2").FindImplementationForInterfaceMember(m01));
            Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I3").FindImplementationForInterfaceMember(m01));
            Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I4").FindImplementationForInterfaceMember(m01));
            Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I5").FindImplementationForInterfaceMember(m01));

            var i6 = compilation1.GlobalNamespace.GetTypeMember("I6");
            Assert.Same(i6.GetMembers().OfType<MethodSymbol>().Single(), i6.FindImplementationForInterfaceMember(m01));

            Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I7").FindImplementationForInterfaceMember(m01));
            Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I8").FindImplementationForInterfaceMember(m01));
        }

        [Fact]
        public void ImplementVirtualStaticMethod_03()
        {
            var source1 =
@"
public interface I1
{
    virtual  static void M01(){}
}

interface I2 : I1
{}

interface I3 : I1
{
    public virtual void M01() {}
}

interface I4 : I1
{
    static void M01() {}
}

interface I5 : I1
{
    void I1.M01() {}
}

interface I6 : I1
{
    static void I1.M01() {}
}

interface I7 : I1
{
    virtual  static void M01(){}
}

interface I8 : I1
{
    virtual  static void I1.M01(){}
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (12,25): warning CS0108: 'I3.M01()' hides inherited member 'I1.M01()'. Use the new keyword if hiding was intended.
                //     public virtual void M01() {}
                Diagnostic(ErrorCode.WRN_NewRequired, "M01").WithArguments("I3.M01()", "I1.M01()").WithLocation(12, 25),
                // (17,17): warning CS0108: 'I4.M01()' hides inherited member 'I1.M01()'. Use the new keyword if hiding was intended.
                //     static void M01() {}
                Diagnostic(ErrorCode.WRN_NewRequired, "M01").WithArguments("I4.M01()", "I1.M01()").WithLocation(17, 17),
                // (22,13): error CS0539: 'I5.M01()' in explicit interface declaration is not found among members of the interface that can be implemented
                //     void I1.M01() {}
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "M01").WithArguments("I5.M01()").WithLocation(22, 13),
                // (32,26): warning CS0108: 'I7.M01()' hides inherited member 'I1.M01()'. Use the new keyword if hiding was intended.
                //     virtual  static void M01();
                Diagnostic(ErrorCode.WRN_NewRequired, "M01").WithArguments("I7.M01()", "I1.M01()").WithLocation(32, 26),
                // (37,29): error CS0106: The modifier 'virtual' is not valid for this item
                //     virtual  static void I1.M01(){}
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M01").WithArguments("virtual").WithLocation(37, 29)
                );

            var m01 = compilation1.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<MethodSymbol>().Single();

            Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I2").FindImplementationForInterfaceMember(m01));
            Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I3").FindImplementationForInterfaceMember(m01));
            Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I4").FindImplementationForInterfaceMember(m01));
            Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I5").FindImplementationForInterfaceMember(m01));

            var i6 = compilation1.GlobalNamespace.GetTypeMember("I6");
            Assert.Same(i6.GetMembers().OfType<MethodSymbol>().Single(), i6.FindImplementationForInterfaceMember(m01));

            Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I7").FindImplementationForInterfaceMember(m01));

            var i8 = compilation1.GlobalNamespace.GetTypeMember("I8");
            Assert.Same(i8.GetMembers().OfType<MethodSymbol>().Single(), i8.FindImplementationForInterfaceMember(m01));
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticMethod_04(bool structure, bool isVirtual)
        {
            var typeKeyword = structure ? "struct" : "class";
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static void M01()" + body + @"
    " + modifier + @" static void M02()" + body + @"
}
";
            var source2 =
typeKeyword + @"
    Test: I1
{
    static void I1.M01() {}
    public static void M02() {}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (4,20): error CS8703: The modifier 'static' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     static void I1.M01() {}
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M01").WithArguments("static", "10.0", "11.0").WithLocation(4, 20),
                // (5,24): error CS8706: 'Test.M02()' cannot implement interface member 'I1.M02()' in type 'Test' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                //     public static void M02() {}
                Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, "M02").WithArguments("Test.M02()", "I1.M02()", "Test", "static abstract members in interfaces", "10.0", "11.0").WithLocation(5, 24)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation3.VerifyDiagnostics(
                // (4,20): error CS8703: The modifier 'static' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     static void I1.M01() {}
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M01").WithArguments("static", "10.0", "11.0").WithLocation(4, 20),
                // (10,26): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual  static void M01() => throw null;
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M01").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(10, 26),
                // (11,26): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual  static void M02() => throw null;
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M02").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(11, 26)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticMethod_05(bool structure, bool isVirtual)
        {
            var typeKeyword = structure ? "struct" : "class";
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static void M01()" + body + @"
}
";
            var source2 =
typeKeyword + @"
    Test1: I1
{
    public static void M01() {}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (4,24): error CS8929: 'Test1.M01()' cannot implement interface member 'I1.M01()' in type 'Test1' because the target runtime doesn't support static abstract members in interfaces.
                //     public static void M01() {}
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfacesForMember, "M01").WithArguments("Test1.M01()", "I1.M01()", "Test1").WithLocation(4, 24)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation3.VerifyDiagnostics(
                // (9,26): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static void M01();
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "M01").WithLocation(9, 26)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticMethod_06(bool structure, bool isVirtual)
        {
            var typeKeyword = structure ? "struct" : "class";
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static void M01()" + body + @"
}
";
            var source2 =
typeKeyword + @"
    Test1: I1
{
    static void I1.M01() {}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (4,20): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     static void I1.M01() {}
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "M01").WithLocation(4, 20)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation3.VerifyDiagnostics(
                // (4,20): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     static void I1.M01() {}
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "M01").WithLocation(4, 20),
                // (9,26): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static void M01();
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "M01").WithLocation(9, 26)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticMethod_07(bool structure, bool isVirtual)
        {
            // Basic implicit implementation scenario, MethodImpl is emitted

            var typeKeyword = structure ? "struct" : "class";
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static void M01()" + body + @"
}

" + typeKeyword + @"
    C : I1
{
    public static void M01() {}
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped,
                             emitOptions: EmitOptions.Default.WithEmitMetadataOnly(true).WithIncludePrivateMembers(false)).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var m01 = module.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<MethodSymbol>().Single();
                var c = module.GlobalNamespace.GetTypeMember("C");

                Assert.Equal(1, c.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());

                var cM01 = (MethodSymbol)c.FindImplementationForInterfaceMember(m01);

                Assert.True(cM01.IsStatic);
                Assert.False(cM01.IsAbstract);
                Assert.False(cM01.IsVirtual);
                Assert.False(cM01.IsMetadataVirtual());
                Assert.False(cM01.IsMetadataFinal);
                Assert.False(cM01.IsMetadataNewSlot());
                Assert.Equal(MethodKind.Ordinary, cM01.MethodKind);

                Assert.Equal("void C.M01()", cM01.ToTestDisplayString());

                if (module is PEModuleSymbol)
                {
                    Assert.Same(m01, cM01.ExplicitInterfaceImplementations.Single());
                }
                else
                {
                    Assert.Empty(cM01.ExplicitInterfaceImplementations);
                }
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticMethod_08(bool structure, bool isVirtual)
        {
            // Basic explicit implementation scenario

            var typeKeyword = structure ? "struct" : "class";
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static void M01()" + body + @"
}

" + typeKeyword + @"
    C : I1
{
    static void I1.M01() {}
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped,
                             emitOptions: EmitOptions.Default.WithEmitMetadataOnly(true).WithIncludePrivateMembers(false)).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var m01 = module.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<MethodSymbol>().Single();
                var c = module.GlobalNamespace.GetTypeMember("C");

                Assert.Equal(1, c.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());

                var cM01 = (MethodSymbol)c.FindImplementationForInterfaceMember(m01);

                Assert.True(cM01.IsStatic);
                Assert.False(cM01.IsAbstract);
                Assert.False(cM01.IsVirtual);
                Assert.False(cM01.IsMetadataVirtual());
                Assert.False(cM01.IsMetadataFinal);
                Assert.False(cM01.IsMetadataNewSlot());
                Assert.Equal(MethodKind.ExplicitInterfaceImplementation, cM01.MethodKind);

                Assert.Equal("void C.I1.M01()", cM01.ToTestDisplayString());
                Assert.Same(m01, cM01.ExplicitInterfaceImplementations.Single());
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticMethod_09(bool isVirtual)
        {
            // Explicit implementation from base is treated as an implementation
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static void M01()" + body + @"
}

public class C1
{
    public static void M01() {}
}

public class C2 : C1, I1
{
    static void I1.M01() {}
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C3 : C2, I1
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.Regular10, TestOptions.RegularPreview })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                     parseOptions: parseOptions,
                                                     targetFramework: _supportingFramework,
                                                     references: new[] { reference });
                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c3 = module.GlobalNamespace.GetTypeMember("C3");
                Assert.Empty(c3.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()));
                var m01 = c3.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();

                var cM01 = (MethodSymbol)c3.FindImplementationForInterfaceMember(m01);

                Assert.Equal("void C2.I1.M01()", cM01.ToTestDisplayString());
                Assert.Same(m01, cM01.ExplicitInterfaceImplementations.Single());
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticMethod_10(bool isVirtual)
        {
            // Implicit implementation is considered only for types implementing interface in source.
            // In metadata, only explicit implementations are considered
            var (modifier, body) = GetILModifierAndBody(isVirtual);

            var ilSource = @"
.class interface public auto ansi abstract I1
{
    .method public hidebysig static " + modifier + @" virtual 
        void M01 () cil managed 
    " + body + @"
} // end of class I1

.class public auto ansi beforefieldinit C1
    extends System.Object
    implements I1
{
    .method private hidebysig  
        static void I1.M01 () cil managed 
    {
        .override method void I1::M01()
        .maxstack 8

        IL_0000: ret
    } // end of method C1::I1.M01

    .method public hidebysig static 
        void M01 () cil managed 
    {
        IL_0000: ret
    } // end of method C1::M01

    .method public hidebysig specialname rtspecialname 
        instance void .ctor () cil managed 
    {
        IL_0000: ldarg.0
        IL_0001: call instance void System.Object::.ctor()
        IL_0006: ret
    } // end of method C1::.ctor
} // end of class C1

.class public auto ansi beforefieldinit C2
    extends C1
    implements I1
{
    .method public hidebysig static 
        void M01 () cil managed 
    {
        IL_0000: ret
    } // end of method C2::M01

    .method public hidebysig specialname rtspecialname 
        instance void .ctor () cil managed 
    {
        IL_0000: ldarg.0
        IL_0001: call instance void C1::.ctor()
        IL_0006: ret
    } // end of method C2::.ctor
} // end of class C2
";
            var source1 =
@"
public class C3 : C2
{
}

public class C4 : C1, I1
{
}

public class C5 : C2, I1
{
}
";

            var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var c1 = compilation1.GlobalNamespace.GetTypeMember("C1");
            var m01 = c1.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();

            var c1M01 = (MethodSymbol)c1.FindImplementationForInterfaceMember(m01);

            Assert.Equal("void C1.I1.M01()", c1M01.ToTestDisplayString());
            Assert.Same(m01, c1M01.ExplicitInterfaceImplementations.Single());

            var c2 = compilation1.GlobalNamespace.GetTypeMember("C2");
            Assert.Same(c1M01, c2.FindImplementationForInterfaceMember(m01));

            var c3 = compilation1.GlobalNamespace.GetTypeMember("C3");
            Assert.Same(c1M01, c3.FindImplementationForInterfaceMember(m01));

            var c4 = compilation1.GlobalNamespace.GetTypeMember("C4");
            Assert.Same(c1M01, c4.FindImplementationForInterfaceMember(m01));

            var c5 = compilation1.GlobalNamespace.GetTypeMember("C5");

            Assert.Equal("void C2.M01()", c5.FindImplementationForInterfaceMember(m01).ToTestDisplayString());

            compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (10,23): error CS8706: 'C2.M01()' cannot implement interface member 'I1.M01()' in type 'C5' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                // public class C5 : C2, I1
                Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, "I1").WithArguments("C2.M01()", "I1.M01()", "C5", "static abstract members in interfaces", "10.0", "11.0").WithLocation(10, 23)
                );
        }

        [Fact]
        public void ImplementAbstractStaticMethod_11()
        {
            // Non-abstract static virtual method. 

            var ilSource = @"
.class interface public auto ansi abstract I1
{
    .method public hidebysig virtual 
        static void M01 () cil managed 
    {
        IL_0000: ret
    } // end of method I1::M01
} // end of class I1
";

            var source1 =
@"
public class C1 : I1
{
}
";

            var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyEmitDiagnostics();

            var c1 = compilation1.GlobalNamespace.GetTypeMember("C1");
            var i1 = c1.Interfaces().Single();
            var m01 = i1.GetMembers().OfType<MethodSymbol>().Single();

            Assert.Same(m01, c1.FindImplementationForInterfaceMember(m01));
            Assert.Same(m01, i1.FindImplementationForInterfaceMember(m01));

            compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyEmitDiagnostics(
                // (2,19): error CS8706: 'I1.M01()' cannot implement interface member 'I1.M01()' in type 'C1' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                // public class C1 : I1
                Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, "I1").WithArguments("I1.M01()", "I1.M01()", "C1", "static abstract members in interfaces", "10.0", "11.0").WithLocation(2, 19)
                );

            var source2 =
@"
public class C1 : I1
{
   static void I1.M01() {}
}
";

            var compilation2 = CreateCompilationWithIL(source2, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation2.VerifyEmitDiagnostics();

            c1 = compilation2.GlobalNamespace.GetTypeMember("C1");
            m01 = c1.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();

            Assert.Equal("void C1.I1.M01()", c1.FindImplementationForInterfaceMember(m01).ToTestDisplayString());
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticMethod_12(bool isVirtual)
        {
            // Default interface implementation for a static method
            var (modifier, body) = GetILModifierAndBody(isVirtual);

            var ilSource = @"
.class interface public auto ansi abstract I1
{
    .method public hidebysig " + modifier + @" virtual 
        static void M01 () cil managed 
    " + body + @"
} // end of class I1
.class interface public auto ansi abstract I2
    implements I1
{
    // Methods
    .method private hidebysig 
        static void I1.M01 () cil managed 
    {
        .override method void I1::M01()
        IL_0000: ret
    } // end of method I2::I1.M01
} // end of class I2
";

            var source1 =
@"
public class C1 : I2
{
}
";

            var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyEmitDiagnostics();

            var c1 = compilation1.GlobalNamespace.GetTypeMember("C1");
            var i2 = c1.Interfaces().Single();
            var i1 = i2.Interfaces().Single();
            var m01 = i1.GetMembers().OfType<MethodSymbol>().Single();
            var i2M01 = i2.GetMembers().OfType<MethodSymbol>().Single();

            Assert.Same(i2M01, c1.FindImplementationForInterfaceMember(m01));
            Assert.Same(i2M01, i2.FindImplementationForInterfaceMember(m01));
            Assert.Same(m01, i2M01.ExplicitInterfaceImplementations.Single());
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticMethod_13(bool isVirtual)
        {
            // A forwarding method is added for an implicit implementation declared in base class. 
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static void M01()" + body + @"
}

class C1
{
    public static void M01() {}
}

class C2 : C1, I1
{
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var m01 = module.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<MethodSymbol>().Single();
                var c2 = module.GlobalNamespace.GetTypeMember("C2");

                var c2M01 = (MethodSymbol)c2.FindImplementationForInterfaceMember(m01);

                Assert.True(c2M01.IsStatic);
                Assert.False(c2M01.IsAbstract);
                Assert.False(c2M01.IsVirtual);
                Assert.False(c2M01.IsMetadataVirtual());
                Assert.False(c2M01.IsMetadataFinal);
                Assert.False(c2M01.IsMetadataNewSlot());

                if (module is PEModuleSymbol)
                {
                    Assert.Equal(MethodKind.ExplicitInterfaceImplementation, c2M01.MethodKind);
                    Assert.Equal("void C2.I1.M01()", c2M01.ToTestDisplayString());
                    Assert.Same(m01, c2M01.ExplicitInterfaceImplementations.Single());

                    var c1M01 = module.GlobalNamespace.GetMember<MethodSymbol>("C1.M01");

                    Assert.True(c1M01.IsStatic);
                    Assert.False(c1M01.IsAbstract);
                    Assert.False(c1M01.IsVirtual);
                    Assert.False(c1M01.IsMetadataVirtual());
                    Assert.False(c1M01.IsMetadataFinal);
                    Assert.False(c1M01.IsMetadataNewSlot());
                    Assert.Equal(MethodKind.Ordinary, c1M01.MethodKind);
                    Assert.Empty(c1M01.ExplicitInterfaceImplementations);
                }
                else
                {
                    Assert.Equal(MethodKind.Ordinary, c2M01.MethodKind);
                    Assert.Equal("void C1.M01()", c2M01.ToTestDisplayString());
                    Assert.Empty(c2M01.ExplicitInterfaceImplementations);
                }
            }

            verifier.VerifyIL("C2.I1.M01()",
@"
{
  // Code size        6 (0x6)
  .maxstack  0
  IL_0000:  call       ""void C1.M01()""
  IL_0005:  ret
}
");
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticMethod_14(bool isVirtual)
        {
            // A forwarding method is added for an implicit implementation with modopt mismatch. 
            var (modifier, body) = GetILModifierAndBody(isVirtual);

            var ilSource = @"
.class interface public auto ansi abstract I1
{
    .method public hidebysig " + modifier + @" virtual 
        static void modopt(I1) M01 () cil managed 
    " + body + @"
} // end of class I1
";

            var source1 =
@"
class C1 : I1
{
    public static void M01() {}
}

class C2 : I1
{
    static void I1.M01() {}
}
";

            var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var c1 = module.GlobalNamespace.GetTypeMember("C1");
                var m01 = c1.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();

                var c1M01 = (MethodSymbol)c1.FindImplementationForInterfaceMember(m01);

                Assert.True(c1M01.IsStatic);
                Assert.False(c1M01.IsAbstract);
                Assert.False(c1M01.IsVirtual);
                Assert.False(c1M01.IsMetadataVirtual());
                Assert.False(c1M01.IsMetadataFinal);
                Assert.False(c1M01.IsMetadataNewSlot());

                if (module is PEModuleSymbol)
                {
                    Assert.Equal(MethodKind.ExplicitInterfaceImplementation, c1M01.MethodKind);
                    Assert.Equal("void modopt(I1) C1.I1.M01()", c1M01.ToTestDisplayString());
                    Assert.Same(m01, c1M01.ExplicitInterfaceImplementations.Single());

                    c1M01 = module.GlobalNamespace.GetMember<MethodSymbol>("C1.M01");
                    Assert.Equal("void C1.M01()", c1M01.ToTestDisplayString());

                    Assert.True(c1M01.IsStatic);
                    Assert.False(c1M01.IsAbstract);
                    Assert.False(c1M01.IsVirtual);
                    Assert.False(c1M01.IsMetadataVirtual());
                    Assert.False(c1M01.IsMetadataFinal);
                    Assert.False(c1M01.IsMetadataNewSlot());
                    Assert.Equal(MethodKind.Ordinary, c1M01.MethodKind);

                    Assert.Empty(c1M01.ExplicitInterfaceImplementations);
                }
                else
                {
                    Assert.Equal(MethodKind.Ordinary, c1M01.MethodKind);
                    Assert.Equal("void C1.M01()", c1M01.ToTestDisplayString());
                    Assert.Empty(c1M01.ExplicitInterfaceImplementations);
                }

                var c2 = module.GlobalNamespace.GetTypeMember("C2");

                var c2M01 = (MethodSymbol)c2.FindImplementationForInterfaceMember(m01);

                Assert.True(c2M01.IsStatic);
                Assert.False(c2M01.IsAbstract);
                Assert.False(c2M01.IsVirtual);
                Assert.False(c2M01.IsMetadataVirtual());
                Assert.False(c2M01.IsMetadataFinal);
                Assert.False(c2M01.IsMetadataNewSlot());
                Assert.Equal(MethodKind.ExplicitInterfaceImplementation, c2M01.MethodKind);

                Assert.Equal("void modopt(I1) C2.I1.M01()", c2M01.ToTestDisplayString());
                Assert.Same(m01, c2M01.ExplicitInterfaceImplementations.Single());

                Assert.Same(c2M01, c2.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Single());
            }

            verifier.VerifyIL("C1.I1.M01()",
@"
{
  // Code size        6 (0x6)
  .maxstack  0
  IL_0000:  call       ""void C1.M01()""
  IL_0005:  ret
}
");
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticMethod_15(bool isVirtual)
        {
            // A forwarding method isn't created if base class implements interface exactly the same way. 
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static void M01()" + body + @"
    " + modifier + @" static void M02()" + body + @"
}

public class C1
{
    public static void M01() {}
}

public class C2 : C1, I1
{
    static void I1.M02() {}
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C3 : C2, I1
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.RegularPreview, TestOptions.Regular10 })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                         parseOptions: parseOptions,
                                                         targetFramework: _supportingFramework,
                                                         references: new[] { reference });
                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c3 = module.GlobalNamespace.GetTypeMember("C3");
                Assert.Empty(c3.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()));

                var m01 = c3.Interfaces().Single().GetMembers("M01").OfType<MethodSymbol>().Single();

                var c1M01 = c3.BaseType().BaseType().GetMember<MethodSymbol>("M01");
                Assert.Equal("void C1.M01()", c1M01.ToTestDisplayString());

                Assert.True(c1M01.IsStatic);
                Assert.False(c1M01.IsAbstract);
                Assert.False(c1M01.IsVirtual);
                Assert.False(c1M01.IsMetadataVirtual());
                Assert.False(c1M01.IsMetadataFinal);
                Assert.False(c1M01.IsMetadataNewSlot());

                Assert.Empty(c1M01.ExplicitInterfaceImplementations);

                if (c1M01.ContainingModule is PEModuleSymbol)
                {
                    var c2M01 = (MethodSymbol)c3.FindImplementationForInterfaceMember(m01);
                    Assert.Equal("void C2.I1.M01()", c2M01.ToTestDisplayString());
                    Assert.Same(m01, c2M01.ExplicitInterfaceImplementations.Single());
                }
                else
                {
                    Assert.Same(c1M01, c3.FindImplementationForInterfaceMember(m01));
                }

                var m02 = c3.Interfaces().Single().GetMembers("M02").OfType<MethodSymbol>().Single();

                var c2M02 = c3.BaseType().GetMember<MethodSymbol>("I1.M02");
                Assert.Equal("void C2.I1.M02()", c2M02.ToTestDisplayString());
                Assert.Same(c2M02, c3.FindImplementationForInterfaceMember(m02));
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticMethod_16(bool isVirtual)
        {
            // A new implicit implementation is properly considered.
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static void M01()" + body + @"
}

public class C1 : I1
{
    public static void M01() {}
}

public class C2 : C1
{
    new public static void M01() {}
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C3 : C2, I1
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                        parseOptions: TestOptions.RegularPreview,
                                                        targetFramework: _supportingFramework,
                                                        references: new[] { reference });
                var verifier = CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

                verifier.VerifyIL("C3.I1.M01()",
@"
{
  // Code size        6 (0x6)
  .maxstack  0
  IL_0000:  call       ""void C2.M01()""
  IL_0005:  ret
}
");
            }

            void validate(ModuleSymbol module)
            {
                var c3 = module.GlobalNamespace.GetTypeMember("C3");
                var m01 = c3.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();

                var c2M01 = c3.BaseType().GetMember<MethodSymbol>("M01");
                Assert.Equal("void C2.M01()", c2M01.ToTestDisplayString());

                Assert.True(c2M01.IsStatic);
                Assert.False(c2M01.IsAbstract);
                Assert.False(c2M01.IsVirtual);
                Assert.False(c2M01.IsMetadataVirtual());
                Assert.False(c2M01.IsMetadataFinal);
                Assert.False(c2M01.IsMetadataNewSlot());

                Assert.Empty(c2M01.ExplicitInterfaceImplementations);

                if (module is PEModuleSymbol)
                {
                    var c3M01 = (MethodSymbol)c3.FindImplementationForInterfaceMember(m01);
                    Assert.Equal("void C3.I1.M01()", c3M01.ToTestDisplayString());
                    Assert.Same(m01, c3M01.ExplicitInterfaceImplementations.Single());
                }
                else
                {
                    Assert.Same(c2M01, c3.FindImplementationForInterfaceMember(m01));
                }
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticMethod_17(bool genericFirst, bool isVirtual)
        {
            // An "ambiguity" in implicit implementation declared in generic base class 
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var generic =
@"
    public static void M01(T x) {}
";
            var nonGeneric =
@"
    public static void M01(int x) {}
";
            var source1 =
@"
public interface I1
{
    " + modifier + @" static void M01(int x)" + body + @"
}

public class C1<T> : I1
{
" + (genericFirst ? generic + nonGeneric : nonGeneric + generic) + @"
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { CreateCompilation("", targetFramework: _supportingFramework).ToMetadataReference() });

            Assert.Equal(2, compilation1.GlobalNamespace.GetTypeMember("C1").GetMembers().Where(m => m.Name.Contains("M01")).Count());
            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C2 : C1<int>, I1
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.Regular10, TestOptions.RegularPreview })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: parseOptions,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { reference });

                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c2 = module.GlobalNamespace.GetTypeMember("C2");
                var m01 = c2.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();

                Assert.True(m01.ContainingModule is RetargetingModuleSymbol or PEModuleSymbol);

                var c1M01 = (MethodSymbol)c2.FindImplementationForInterfaceMember(m01);
                Assert.Equal("void C1<T>.M01(System.Int32 x)", c1M01.OriginalDefinition.ToTestDisplayString());

                var baseI1M01 = c2.BaseType().FindImplementationForInterfaceMember(m01);
                Assert.Equal("void C1<T>.M01(System.Int32 x)", baseI1M01.OriginalDefinition.ToTestDisplayString());

                Assert.Equal(c1M01, baseI1M01);

                if (c1M01.OriginalDefinition.ContainingModule is PEModuleSymbol)
                {
                    Assert.Same(m01, c1M01.ExplicitInterfaceImplementations.Single());
                }
                else
                {
                    Assert.Empty(c1M01.ExplicitInterfaceImplementations);
                }
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticMethod_18(bool genericFirst, bool isVirtual)
        {
            // An "ambiguity" in implicit implementation declared in generic base class plus interface is generic too.
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var generic =
@"
    public static void M01(T x) {}
";
            var nonGeneric =
@"
    public static void M01(int x) {}
";
            var source1 =
@"
public interface I1<T>
{
    " + modifier + @" static void M01(T x)" + body + @"
}

public class C1<T> : I1<T>
{
" + (genericFirst ? generic + nonGeneric : nonGeneric + generic) + @"
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { CreateCompilation("", targetFramework: _supportingFramework).ToMetadataReference() });

            Assert.Equal(2, compilation1.GlobalNamespace.GetTypeMember("C1").GetMembers().Where(m => m.Name.Contains("M01")).Count());
            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C2 : C1<int>, I1<int>
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.Regular10, TestOptions.RegularPreview })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: parseOptions,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { reference });

                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c2 = module.GlobalNamespace.GetTypeMember("C2");
                var m01 = c2.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();

                Assert.True(m01.ContainingModule is RetargetingModuleSymbol or PEModuleSymbol);

                var c1M01 = (MethodSymbol)c2.FindImplementationForInterfaceMember(m01);
                Assert.Equal("void C1<T>.M01(T x)", c1M01.OriginalDefinition.ToTestDisplayString());

                var baseI1M01 = c2.BaseType().FindImplementationForInterfaceMember(m01);
                Assert.Equal("void C1<T>.M01(T x)", baseI1M01.OriginalDefinition.ToTestDisplayString());

                Assert.Equal(c1M01, baseI1M01);

                if (c1M01.OriginalDefinition.ContainingModule is PEModuleSymbol)
                {
                    Assert.Equal(m01, c1M01.ExplicitInterfaceImplementations.Single());
                }
                else
                {
                    Assert.Empty(c1M01.ExplicitInterfaceImplementations);
                }
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticMethod_19(bool genericFirst, bool isVirtual)
        {
            // Same as ImplementAbstractStaticMethod_17 only implementation is explicit in source.
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var generic =
@"
    public static void M01(T x) {}
";
            var nonGeneric =
@"
    static void I1.M01(int x) {}
";
            var source1 =
@"
public interface I1
{
    " + modifier + @" static void M01(int x)" + body + @"
}

public class C1<T> : I1
{
" + (genericFirst ? generic + nonGeneric : nonGeneric + generic) + @"
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { CreateCompilation("", targetFramework: _supportingFramework).ToMetadataReference() });

            Assert.Equal(2, compilation1.GlobalNamespace.GetTypeMember("C1").GetMembers().Where(m => m.Name.Contains("M01")).Count());
            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C2 : C1<int>, I1
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.Regular10, TestOptions.RegularPreview })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: parseOptions,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { reference });

                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c2 = module.GlobalNamespace.GetTypeMember("C2");
                var m01 = c2.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();

                Assert.True(m01.ContainingModule is RetargetingModuleSymbol or PEModuleSymbol);

                var c1M01 = (MethodSymbol)c2.FindImplementationForInterfaceMember(m01);
                Assert.Equal("void C1<T>.I1.M01(System.Int32 x)", c1M01.OriginalDefinition.ToTestDisplayString());
                Assert.Same(m01, c1M01.ExplicitInterfaceImplementations.Single());
                Assert.Same(c1M01, c2.BaseType().FindImplementationForInterfaceMember(m01));
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticMethod_20(bool genericFirst, bool isVirtual)
        {
            // Same as ImplementAbstractStaticMethod_18 only implementation is explicit in source.
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var generic =
@"
    static void I1<T>.M01(T x) {}
";
            var nonGeneric =
@"
    public static void M01(int x) {}
";
            var source1 =
@"
public interface I1<T>
{
    " + modifier + @" static void M01(T x)" + body + @"
}

public class C1<T> : I1<T>
{
" + (genericFirst ? generic + nonGeneric : nonGeneric + generic) + @"
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { CreateCompilation("", targetFramework: _supportingFramework).ToMetadataReference() });

            Assert.Equal(2, compilation1.GlobalNamespace.GetTypeMember("C1").GetMembers().Where(m => m.Name.Contains("M01")).Count());

            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C2 : C1<int>, I1<int>
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.Regular10, TestOptions.RegularPreview })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: parseOptions,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { reference });

                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c2 = module.GlobalNamespace.GetTypeMember("C2");
                var m01 = c2.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();

                Assert.True(m01.ContainingModule is RetargetingModuleSymbol or PEModuleSymbol);

                var c1M01 = (MethodSymbol)c2.FindImplementationForInterfaceMember(m01);
                Assert.Equal("void C1<T>.I1<T>.M01(T x)", c1M01.OriginalDefinition.ToTestDisplayString());
                Assert.Equal(m01, c1M01.ExplicitInterfaceImplementations.Single());
                Assert.Same(c1M01, c2.BaseType().FindImplementationForInterfaceMember(m01));
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticMethod_21(bool genericFirst, bool isVirtual)
        {
            // Same as ImplementAbstractStaticMethod_17 only implicit implementation is in an intermediate base.
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var generic =
@"
    public static void M01(T x) {}
";
            var nonGeneric =
@"
    public static void M01(int x) {}
";
            var source1 =
@"
public interface I1
{
    " + modifier + @" static void M01(int x)" + body + @"
}

public class C1<T>
{
" + (genericFirst ? generic + nonGeneric : nonGeneric + generic) + @"
}

public class C11<T> : C1<T>, I1
{
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { CreateCompilation("", targetFramework: _supportingFramework).ToMetadataReference() });

            Assert.Equal(2, compilation1.GlobalNamespace.GetTypeMember("C1").GetMembers().Where(m => m.Name.Contains("M01")).Count());
            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C2 : C11<int>, I1
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.Regular10, TestOptions.RegularPreview })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: parseOptions,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { reference });

                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c2 = module.GlobalNamespace.GetTypeMember("C2");
                var m01 = c2.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();

                Assert.True(m01.ContainingModule is RetargetingModuleSymbol or PEModuleSymbol);

                var c1M01 = (MethodSymbol)c2.FindImplementationForInterfaceMember(m01);
                var expectedDisplay = m01.ContainingModule is PEModuleSymbol ? "void C11<T>.I1.M01(System.Int32 x)" : "void C1<T>.M01(System.Int32 x)";
                Assert.Equal(expectedDisplay, c1M01.OriginalDefinition.ToTestDisplayString());

                var baseI1M01 = c2.BaseType().FindImplementationForInterfaceMember(m01);
                Assert.Equal(expectedDisplay, baseI1M01.OriginalDefinition.ToTestDisplayString());

                Assert.Equal(c1M01, baseI1M01);

                if (c1M01.OriginalDefinition.ContainingModule is PEModuleSymbol)
                {
                    Assert.Same(m01, c1M01.ExplicitInterfaceImplementations.Single());
                }
                else
                {
                    Assert.Empty(c1M01.ExplicitInterfaceImplementations);
                }
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticMethod_22(bool genericFirst, bool isVirtual)
        {
            // Same as ImplementAbstractStaticMethod_18 only implicit implementation is in an intermediate base.
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var generic =
@"
    public static void M01(T x) {}
";
            var nonGeneric =
@"
    public static void M01(int x) {}
";
            var source1 =
@"
public interface I1<T>
{
    " + modifier + @" static void M01(T x)" + body + @"
}

public class C1<T>
{
" + (genericFirst ? generic + nonGeneric : nonGeneric + generic) + @"
}

public class C11<T> : C1<T>, I1<T>
{
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { CreateCompilation("", targetFramework: _supportingFramework).ToMetadataReference() });

            Assert.Equal(2, compilation1.GlobalNamespace.GetTypeMember("C1").GetMembers().Where(m => m.Name.Contains("M01")).Count());
            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C2 : C11<int>, I1<int>
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.Regular10, TestOptions.RegularPreview })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: parseOptions,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { reference });

                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c2 = module.GlobalNamespace.GetTypeMember("C2");
                var m01 = c2.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();

                Assert.True(m01.ContainingModule is RetargetingModuleSymbol or PEModuleSymbol);

                var c1M01 = (MethodSymbol)c2.FindImplementationForInterfaceMember(m01);
                var expectedDisplay = m01.ContainingModule is PEModuleSymbol ? "void C11<T>.I1<T>.M01(T x)" : "void C1<T>.M01(T x)";
                Assert.Equal(expectedDisplay, c1M01.OriginalDefinition.ToTestDisplayString());

                var baseI1M01 = c2.BaseType().FindImplementationForInterfaceMember(m01);
                Assert.Equal(expectedDisplay, baseI1M01.OriginalDefinition.ToTestDisplayString());

                Assert.Equal(c1M01, baseI1M01);

                if (c1M01.OriginalDefinition.ContainingModule is PEModuleSymbol)
                {
                    Assert.Equal(m01, c1M01.ExplicitInterfaceImplementations.Single());
                }
                else
                {
                    Assert.Empty(c1M01.ExplicitInterfaceImplementations);
                }
            }
        }

        [Theory]
        [CombinatorialData]
        [WorkItem(61553, "https://github.com/dotnet/roslyn/issues/61553")]
        public void ImplementAbstractStaticMethod_23(bool genericFirst, bool isVirtual)
        {
            // An "ambiguity" in implicit implementation declared in generic base class 
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var generic =
@"
    public static void M01(T x)
    {
        System.Console.WriteLine(""T"");
    }
";
            var nonGeneric =
@"
    public static void M01(int x)
    {
        System.Console.WriteLine(""int"");
    }
";
            var source1 =
@"
public interface I1
{
    " + modifier + @" static void M01(int x)" + body + @"
}

public class C1<T>
{
" + (genericFirst ? generic + nonGeneric : nonGeneric + generic) + @"
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { CreateCompilation("", targetFramework: _supportingFramework).ToMetadataReference() });

            Assert.Equal(2, compilation1.GlobalNamespace.GetTypeMember("C1").GetMembers().Where(m => m.Name.Contains("M01")).Count());
            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C2 : C1<int>, I1
{
    static void Main()
    {
        Test<C2>();
    }

    static void Test<T>() where T : I1
    {
        T.M01(0);
    }
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                var compilation2 = CreateCompilation(source2, options: TestOptions.DebugExe,
                                             parseOptions: TestOptions.RegularPreview,
                                             targetFramework: _supportingFramework,
                                             references: new[] { reference });

                CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, expectedOutput: !(Execute(isVirtual) && ExecutionConditionUtil.IsMonoOrCoreClr) ? null : (genericFirst ? "T" : "int"), verify: Verification.Skipped).VerifyDiagnostics(
                    // (2,28): warning CS1956: Member 'C1<int>.M01(int)' implements interface member 'I1.M01(int)' in type 'C2'. There are multiple matches for the interface member at run-time. It is implementation dependent which method will be called.
                    // public class C2 : C1<int>, I1
                    Diagnostic(ErrorCode.WRN_MultipleRuntimeImplementationMatches, "I1").WithArguments("C1<int>.M01(int)", "I1.M01(int)", "C2").WithLocation(2, 28)
                    );
            }

            void validate(ModuleSymbol module)
            {
                var c2 = module.GlobalNamespace.GetTypeMember("C2");
                var m01 = c2.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();

                var baseI1M01 = c2.BaseType().FindImplementationForInterfaceMember(m01);
                Assert.Null(baseI1M01);

                Assert.True(m01.ContainingModule is RetargetingModuleSymbol or PEModuleSymbol);

                var c1M01 = (MethodSymbol)c2.FindImplementationForInterfaceMember(m01);

                if (module is PEModuleSymbol)
                {
                    Assert.Equal("void C2.I1.M01(System.Int32 x)", c1M01.ToTestDisplayString());
                    Assert.Same(m01, c1M01.ExplicitInterfaceImplementations.Single());
                }
                else if (genericFirst)
                {
                    Assert.Equal("void C1<T>.M01(T x)", c1M01.OriginalDefinition.ToTestDisplayString());
                }
                else
                {
                    Assert.Equal("void C1<T>.M01(System.Int32 x)", c1M01.OriginalDefinition.ToTestDisplayString());
                }

                foreach (var method in c2.BaseType().GetMembers().OfType<MethodSymbol>())
                {
                    Assert.Empty(method.ExplicitInterfaceImplementations);
                }
            }
        }

        [Theory]
        [CombinatorialData]
        [WorkItem(61553, "https://github.com/dotnet/roslyn/issues/61553")]
        public void ImplementAbstractStaticMethod_24(bool genericFirst, bool genericIsStatic, bool isVirtual)
        {
            // Static vs. instance doesn't cause an ambiguity in implicit implementation declared in generic base class 
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var generic =
@"
    public " + (genericIsStatic ? "static " : "") + @"void M01(T x)
    {
        System.Console.WriteLine(""T"");
    }
";
            var nonGeneric =
@"
    public " + (!genericIsStatic ? "static " : "") + @"void M01(int x)
    {
        System.Console.WriteLine(""int"");
    }
";
            var source1 =
@"
public interface I1
{
    " + modifier + @" static void M01(int x)" + body + @"
}

public class C1<T>
{
" + (genericFirst ? generic + nonGeneric : nonGeneric + generic) + @"
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { CreateCompilation("", targetFramework: _supportingFramework).ToMetadataReference() });

            Assert.Equal(2, compilation1.GlobalNamespace.GetTypeMember("C1").GetMembers().Where(m => m.Name.Contains("M01")).Count());
            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C2 : C1<int>, I1
{
    static void Main()
    {
        Test<C2>();
    }

    static void Test<T>() where T : I1
    {
        T.M01(0);
    }
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                var compilation2 = CreateCompilation(source2, options: TestOptions.DebugExe,
                                             parseOptions: TestOptions.RegularPreview,
                                             targetFramework: _supportingFramework,
                                             references: new[] { reference });

                CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, expectedOutput: !(Execute(isVirtual) && ExecutionConditionUtil.IsMonoOrCoreClr) ? null : (genericIsStatic ? "T" : "int"), verify: Verification.Skipped).VerifyDiagnostics();
            }

            void validate(ModuleSymbol module)
            {
                var c2 = module.GlobalNamespace.GetTypeMember("C2");
                var m01 = c2.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();

                var baseI1M01 = c2.BaseType().FindImplementationForInterfaceMember(m01);
                Assert.Null(baseI1M01);

                Assert.True(m01.ContainingModule is RetargetingModuleSymbol or PEModuleSymbol);

                var c1M01 = (MethodSymbol)c2.FindImplementationForInterfaceMember(m01);

                if (module is PEModuleSymbol)
                {
                    Assert.Equal("void C2.I1.M01(System.Int32 x)", c1M01.ToTestDisplayString());
                    Assert.Same(m01, c1M01.ExplicitInterfaceImplementations.Single());
                }
                else if (genericIsStatic)
                {
                    Assert.Equal("void C1<T>.M01(T x)", c1M01.OriginalDefinition.ToTestDisplayString());
                }
                else
                {
                    Assert.Equal("void C1<T>.M01(System.Int32 x)", c1M01.OriginalDefinition.ToTestDisplayString());
                }

                foreach (var method in c2.BaseType().GetMembers().OfType<MethodSymbol>())
                {
                    Assert.Empty(method.ExplicitInterfaceImplementations);
                }
            }
        }

        private static string UnaryOperatorName(string op, bool isChecked = false) => OperatorFacts.UnaryOperatorNameFromSyntaxKindIfAny(SyntaxFactory.ParseToken(op).Kind(), isChecked: isChecked);
        private static string BinaryOperatorName(string op, bool isChecked = false) =>
            op switch { ">>" => WellKnownMemberNames.RightShiftOperatorName, ">>>" => WellKnownMemberNames.UnsignedRightShiftOperatorName, _ => OperatorFacts.BinaryOperatorNameFromSyntaxKindIfAny(SyntaxFactory.ParseToken(op).Kind(), isChecked: isChecked) };

        internal static string GetUnaryOperatorName(string op, bool isChecked, out string checkedKeyword)
        {
            string opName = UnaryOperatorName(op, isChecked: false);
            checkedKeyword = "";

            if (isChecked)
            {
                string checkedName = UnaryOperatorName(op, isChecked: true);

                if (checkedName == opName)
                {
                    return null; // There is no checked form
                }
                else
                {
                    opName = checkedName;
                    checkedKeyword = "checked ";
                }
            }

            return opName;
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticUnaryOperator_01([CombinatorialValues("+", "-", "!", "~", "true", "false")] string op, bool structure, bool isChecked)
        {
            var typeKeyword = structure ? "struct" : "class";

            string opName = GetUnaryOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    abstract static T operator " + checkedKeyword + op + @"(T x);
}

" + typeKeyword + @"
    C1 : I1<C1>
{}

" + typeKeyword + @"
    C2 : I1<C2>
{
    public C2 operator " + checkedKeyword + op + @"(C2 x) => throw null;
}

" + typeKeyword + @"
    C3 : I1<C3>
{
    static C3 operator " + checkedKeyword + op + @"(C3 x) => throw null;
}

" + typeKeyword + @"
    C4 : I1<C4>
{
    C4 I1<C4>.operator " + checkedKeyword + op + @"(C4 x) => throw null;
}

" + typeKeyword + @"
    C5 : I1<C5>
{
    public static int operator " + checkedKeyword + op + @" (C5 x) => throw null;
}

" + typeKeyword + @"
    C6 : I1<C6>
{
    static int I1<C6>.operator " + checkedKeyword + op + @" (C6 x) => throw null;
}

" + typeKeyword + @"
    C7 : I1<C7>
{
    public static C7 " + opName + @"(C7 x) => throw null;
}

" + typeKeyword + @"
    C8 : I1<C8>
{
    static C8 I1<C8>." + opName + @"(C8 x) => throw null;
}

public interface I2<T> where T : I2<T>
{
    abstract static T " + opName + @"(T x);
}

" + typeKeyword + @"
    C9 : I2<C9>
{
    public static C9 operator " + checkedKeyword + op + @"(C9 x) => throw null;
}

" + typeKeyword + @"
    C10 : I2<C10>
{
    static C10 I2<C10>.operator " + checkedKeyword + op + @"(C10 x) => throw null;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_BadIncDecRetType or (int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_CheckedOperatorNeedsMatch or (int)ErrorCode.ERR_OpTFRetType)).Verify(
                // (8,10): error CS0535: 'C1' does not implement interface member 'I1<C1>.operator +(C1)'
                //     C1 : I1<C1>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C1>").WithArguments("C1", "I1<C1>.operator " + checkedKeyword + op + "(C1)").WithLocation(8, 10),
                // (12,10): error CS8928: 'C2' does not implement static interface member 'I1<C2>.operator +(C2)'. 'C2.operator +(C2)' cannot implement the interface member because it is not static.
                //     C2 : I1<C2>
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberNotStatic, "I1<C2>").WithArguments("C2", "I1<C2>.operator " + checkedKeyword + op + "(C2)", "C2.operator " + checkedKeyword + op + "(C2)").WithLocation(12, 10),
                // (14,24): error CS0558: User-defined operator 'C2.operator +(C2)' must be declared static and public
                //     public C2 operator +(C2 x) => throw null;
                Diagnostic(ErrorCode.ERR_OperatorsMustBeStaticAndPublic, op).WithArguments("C2.operator " + checkedKeyword + op + "(C2)").WithLocation(14, 24 + checkedKeyword.Length),
                // (18,10): error CS0737: 'C3' does not implement interface member 'I1<C3>.operator +(C3)'. 'C3.operator +(C3)' cannot implement an interface member because it is not public.
                //     C3 : I1<C3>
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberNotPublic, "I1<C3>").WithArguments("C3", "I1<C3>.operator " + checkedKeyword + op + "(C3)", "C3.operator " + checkedKeyword + op + "(C3)").WithLocation(18, 10),
                // (20,24): error CS0558: User-defined operator 'C3.operator +(C3)' must be declared static and public
                //     static C3 operator +(C3 x) => throw null;
                Diagnostic(ErrorCode.ERR_OperatorsMustBeStaticAndPublic, op).WithArguments("C3.operator " + checkedKeyword + op + "(C3)").WithLocation(20, 24 + checkedKeyword.Length),
                // (24,10): error CS0535: 'C4' does not implement interface member 'I1<C4>.operator +(C4)'
                //     C4 : I1<C4>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C4>").WithArguments("C4", "I1<C4>.operator " + checkedKeyword + op + "(C4)").WithLocation(24, 10),
                // (26,24): error CS8930: Explicit implementation of a user-defined operator 'C4.operator +(C4)' must be declared static
                //     C4 I1<C4>.operator +(C4 x) => throw null;
                Diagnostic(ErrorCode.ERR_ExplicitImplementationOfOperatorsMustBeStatic, op).WithArguments("C4.operator " + checkedKeyword + op + "(C4)").WithLocation(26, 24 + checkedKeyword.Length),
                // (26,24): error CS0539: 'C4.operator +(C4)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     C4 I1<C4>.operator +(C4 x) => throw null;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, op).WithArguments("C4.operator " + checkedKeyword + op + "(C4)").WithLocation(26, 24 + checkedKeyword.Length),
                // (30,10): error CS0738: 'C5' does not implement interface member 'I1<C5>.operator +(C5)'. 'C5.operator +(C5)' cannot implement 'I1<C5>.operator +(C5)' because it does not have the matching return type of 'C5'.
                //     C5 : I1<C5>
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberWrongReturnType, "I1<C5>").WithArguments("C5", "I1<C5>.operator " + checkedKeyword + op + "(C5)", "C5.operator " + checkedKeyword + op + "(C5)", "C5").WithLocation(30, 10),
                // (36,10): error CS0535: 'C6' does not implement interface member 'I1<C6>.operator +(C6)'
                //     C6 : I1<C6>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C6>").WithArguments("C6", "I1<C6>.operator " + checkedKeyword + op + "(C6)").WithLocation(36, 10),
                // (38,32): error CS9334: 'C6.operator +(C6)' return type must be 'C6' to match implemented member 'I1<C6>.operator +(C6)'
                //     static int I1<C6>.operator + (C6 x) => throw null;
                Diagnostic(ErrorCode.ERR_ExplicitInterfaceMemberReturnTypeMismatch, op).WithArguments("C6.operator " + checkedKeyword + op + "(C6)", "C6", "I1<C6>.operator " + checkedKeyword + op + "(C6)").WithLocation(38, 32 + checkedKeyword.Length),
                // (42,10): error CS0535: 'C7' does not implement interface member 'I1<C7>.operator +(C7)'
                //     C7 : I1<C7>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C7>").WithArguments("C7", "I1<C7>.operator " + checkedKeyword + op + "(C7)").WithLocation(42, 10),
                // (48,10): error CS0535: 'C8' does not implement interface member 'I1<C8>.operator +(C8)'
                //     C8 : I1<C8>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C8>").WithArguments("C8", "I1<C8>.operator " + checkedKeyword + op + "(C8)").WithLocation(48, 10),
                // (50,22): error CS0539: 'C8.op_UnaryPlus(C8)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static C8 I1<C8>.op_UnaryPlus(C8 x) => throw null;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, opName).WithArguments("C8." + opName + "(C8)").WithLocation(50, 22),
                // (59,10): error CS0535: 'C9' does not implement interface member 'I2<C9>.op_UnaryPlus(C9)'
                //     C9 : I2<C9>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I2<C9>").WithArguments("C9", "I2<C9>." + opName + "(C9)").WithLocation(59, 10),
                // (65,11): error CS0535: 'C10' does not implement interface member 'I2<C10>.op_UnaryPlus(C10)'
                //     C10 : I2<C10>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I2<C10>").WithArguments("C10", "I2<C10>." + opName + "(C10)").WithLocation(65, 11),
                // (67,33): error CS0539: 'C10.operator +(C10)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static C10 I2<C10>.operator +(C10 x) => throw null;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, op).WithArguments("C10.operator " + checkedKeyword + op + "(C10)").WithLocation(67, 33 + checkedKeyword.Length)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticIncrementOperator_01([CombinatorialValues("++", "--")] string op, bool structure, bool isChecked)
        {
            var typeKeyword = structure ? "struct" : "class";

            string opName = GetUnaryOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    abstract static T operator " + checkedKeyword + op + @"(T x);
}

" + typeKeyword + @"
    C1 : I1<C1>
{}

" + typeKeyword + @"
    C2 : I1<C2>
{
    public C2 operator " + checkedKeyword + op + @"(C2 x) => throw null;
}

" + typeKeyword + @"
    C3 : I1<C3>
{
    static C3 operator " + checkedKeyword + op + @"(C3 x) => throw null;
}

" + typeKeyword + @"
    C4 : I1<C4>
{
    C4 I1<C4>.operator " + checkedKeyword + op + @"(C4 x) => throw null;
}

" + typeKeyword + @"
    C5 : I1<C5>
{
    public static int operator " + checkedKeyword + op + @" (C5 x) => throw null;
}

" + typeKeyword + @"
    C6 : I1<C6>
{
    static int I1<C6>.operator " + checkedKeyword + op + @" (C6 x) => throw null;
}

" + typeKeyword + @"
    C7 : I1<C7>
{
    public static C7 " + opName + @"(C7 x) => throw null;
}

" + typeKeyword + @"
    C8 : I1<C8>
{
    static C8 I1<C8>." + opName + @"(C8 x) => throw null;
}

public interface I2<T> where T : I2<T>
{
    abstract static T " + opName + @"(T x);
}

" + typeKeyword + @"
    C9 : I2<C9>
{
    public static C9 operator " + checkedKeyword + op + @"(C9 x) => throw null;
}

" + typeKeyword + @"
    C10 : I2<C10>
{
    static C10 I2<C10>.operator " + checkedKeyword + op + @"(C10 x) => throw null;
}
";

            var compilation1 = CreateCompilation([source1, CompilerFeatureRequiredAttribute], options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_BadIncDecRetType or (int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_CheckedOperatorNeedsMatch or (int)ErrorCode.ERR_OpTFRetType)).Verify(
                // (8,10): error CS0535: 'C1' does not implement interface member 'I1<C1>.operator +(C1)'
                //     C1 : I1<C1>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C1>").WithArguments("C1", "I1<C1>.operator " + checkedKeyword + op + "(C1)").WithLocation(8, 10),
                // (12,10): error CS8928: 'C2' does not implement static interface member 'I1<C2>.operator +(C2)'. 'C2.operator +(C2)' cannot implement the interface member because it is not static.
                //     C2 : I1<C2>
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberNotStatic, "I1<C2>").WithArguments("C2", "I1<C2>.operator " + checkedKeyword + op + "(C2)", "C2.operator " + checkedKeyword + op + "(C2)").WithLocation(12, 10),
                // (14,32): error CS0558: User-defined operator 'C2.operator checked ++(C2)' must be declared static and public
                //     public C2 operator ++(C2 x) => throw null;
                Diagnostic(ErrorCode.ERR_OperatorsMustBeStaticAndPublic, op).WithArguments("C2.operator " + checkedKeyword + op + "(C2)").WithLocation(14, 24 + checkedKeyword.Length),
                // (18,10): error CS0737: 'C3' does not implement interface member 'I1<C3>.operator +(C3)'. 'C3.operator +(C3)' cannot implement an interface member because it is not public.
                //     C3 : I1<C3>
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberNotPublic, "I1<C3>").WithArguments("C3", "I1<C3>.operator " + checkedKeyword + op + "(C3)", "C3.operator " + checkedKeyword + op + "(C3)").WithLocation(18, 10),
                // (20,24): error CS0558: User-defined operator 'C3.operator +(C3)' must be declared static and public
                //     static C3 operator +(C3 x) => throw null;
                Diagnostic(ErrorCode.ERR_OperatorsMustBeStaticAndPublic, op).WithArguments("C3.operator " + checkedKeyword + op + "(C3)").WithLocation(20, 24 + checkedKeyword.Length),
                // (24,10): error CS0535: 'C4' does not implement interface member 'I1<C4>.operator +(C4)'
                //     C4 : I1<C4>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C4>").WithArguments("C4", "I1<C4>.operator " + checkedKeyword + op + "(C4)").WithLocation(24, 10),
                // (26,32): error CS8930: Explicit implementation of a user-defined operator 'C4.operator checked ++(C4)' must be declared static
                //     C4 I1<C4>.operator ++(C4 x) => throw null;
                Diagnostic(ErrorCode.ERR_ExplicitImplementationOfOperatorsMustBeStatic, op).WithArguments("C4.operator " + checkedKeyword + op + "(C4)").WithLocation(26, 24 + checkedKeyword.Length),
                // (26,24): error CS0539: 'C4.operator +(C4)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     C4 I1<C4>.operator +(C4 x) => throw null;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, op).WithArguments("C4.operator " + checkedKeyword + op + "(C4)").WithLocation(26, 24 + checkedKeyword.Length),
                // (30,10): error CS0738: 'C5' does not implement interface member 'I1<C5>.operator +(C5)'. 'C5.operator +(C5)' cannot implement 'I1<C5>.operator +(C5)' because it does not have the matching return type of 'C5'.
                //     C5 : I1<C5>
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberWrongReturnType, "I1<C5>").WithArguments("C5", "I1<C5>.operator " + checkedKeyword + op + "(C5)", "C5.operator " + checkedKeyword + op + "(C5)", "C5").WithLocation(30, 10),
                // (36,10): error CS0535: 'C6' does not implement interface member 'I1<C6>.operator +(C6)'
                //     C6 : I1<C6>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C6>").WithArguments("C6", "I1<C6>.operator " + checkedKeyword + op + "(C6)").WithLocation(36, 10),
                // (38,32): error CS9334: 'C6.operator +(C6)' return type must be 'C6' to match implemented member 'I1<C6>.operator +(C6)'
                //     static int I1<C6>.operator + (C6 x) => throw null;
                Diagnostic(ErrorCode.ERR_ExplicitInterfaceMemberReturnTypeMismatch, op).WithArguments("C6.operator " + checkedKeyword + op + "(C6)", "C6", "I1<C6>.operator " + checkedKeyword + op + "(C6)").WithLocation(38, 32 + checkedKeyword.Length),
                // (42,10): error CS0535: 'C7' does not implement interface member 'I1<C7>.operator +(C7)'
                //     C7 : I1<C7>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C7>").WithArguments("C7", "I1<C7>.operator " + checkedKeyword + op + "(C7)").WithLocation(42, 10),
                // (48,10): error CS0535: 'C8' does not implement interface member 'I1<C8>.operator +(C8)'
                //     C8 : I1<C8>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C8>").WithArguments("C8", "I1<C8>.operator " + checkedKeyword + op + "(C8)").WithLocation(48, 10),
                // (50,22): error CS0539: 'C8.op_UnaryPlus(C8)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static C8 I1<C8>.op_UnaryPlus(C8 x) => throw null;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, opName).WithArguments("C8." + opName + "(C8)").WithLocation(50, 22),
                // (59,10): error CS0535: 'C9' does not implement interface member 'I2<C9>.op_UnaryPlus(C9)'
                //     C9 : I2<C9>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I2<C9>").WithArguments("C9", "I2<C9>." + opName + "(C9)").WithLocation(59, 10),
                // (65,11): error CS0535: 'C10' does not implement interface member 'I2<C10>.op_UnaryPlus(C10)'
                //     C10 : I2<C10>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I2<C10>").WithArguments("C10", "I2<C10>." + opName + "(C10)").WithLocation(65, 11),
                // (67,33): error CS0539: 'C10.operator +(C10)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static C10 I2<C10>.operator +(C10 x) => throw null;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, op).WithArguments("C10.operator " + checkedKeyword + op + "(C10)").WithLocation(67, 33 + checkedKeyword.Length)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementVirtualStaticUnaryOperator_01([CombinatorialValues("+", "-", "!", "~", "true", "false")] string op, bool structure, bool isChecked)
        {
            var typeKeyword = structure ? "struct" : "class";

            string opName = GetUnaryOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    virtual static T operator " + checkedKeyword + op + @"(T x) => x;
}

" + typeKeyword + @"
    C1 : I1<C1>
{}

" + typeKeyword + @"
    C2 : I1<C2>
{
    public C2 operator " + checkedKeyword + op + @"(C2 x) => throw null;
}

" + typeKeyword + @"
    C3 : I1<C3>
{
    static C3 operator " + checkedKeyword + op + @"(C3 x) => throw null;
}

" + typeKeyword + @"
    C4 : I1<C4>
{
    C4 I1<C4>.operator " + checkedKeyword + op + @"(C4 x) => throw null;
}

" + typeKeyword + @"
    C5 : I1<C5>
{
    public static int operator " + checkedKeyword + op + @" (C5 x) => throw null;
}

" + typeKeyword + @"
    C6 : I1<C6>
{
    static int I1<C6>.operator " + checkedKeyword + op + @" (C6 x) => throw null;
}

" + typeKeyword + @"
    C7 : I1<C7>
{
    public static C7 " + opName + @"(C7 x) => throw null;
}

" + typeKeyword + @"
    C8 : I1<C8>
{
    static C8 I1<C8>." + opName + @"(C8 x) => throw null;
}

public interface I2<T> where T : I2<T>
{
    virtual static T " + opName + @"(T x) => x;
}

" + typeKeyword + @"
    C9 : I2<C9>
{
    public static C9 operator " + checkedKeyword + op + @"(C9 x) => throw null;
}

" + typeKeyword + @"
    C10 : I2<C10>
{
    static C10 I2<C10>.operator " + checkedKeyword + op + @"(C10 x) => throw null;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_BadIncDecRetType or (int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_CheckedOperatorNeedsMatch or (int)ErrorCode.ERR_OpTFRetType)).Verify(
                // (14,24): error CS0558: User-defined operator 'C2.operator +(C2)' must be declared static and public
                //     public C2 operator +(C2 x) => throw null;
                Diagnostic(ErrorCode.ERR_OperatorsMustBeStaticAndPublic, op).WithArguments("C2.operator " + checkedKeyword + op + "(C2)").WithLocation(14, 24 + checkedKeyword.Length),
                // (20,24): error CS0558: User-defined operator 'C3.operator +(C3)' must be declared static and public
                //     static C3 operator +(C3 x) => throw null;
                Diagnostic(ErrorCode.ERR_OperatorsMustBeStaticAndPublic, op).WithArguments("C3.operator " + checkedKeyword + op + "(C3)").WithLocation(20, 24 + checkedKeyword.Length),
                // (26,24): error CS8930: Explicit implementation of a user-defined operator 'C4.operator +(C4)' must be declared static
                //     C4 I1<C4>.operator +(C4 x) => throw null;
                Diagnostic(ErrorCode.ERR_ExplicitImplementationOfOperatorsMustBeStatic, op).WithArguments("C4.operator " + checkedKeyword + op + "(C4)").WithLocation(26, 24 + checkedKeyword.Length),
                // (26,24): error CS0539: 'C4.operator +(C4)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     C4 I1<C4>.operator +(C4 x) => throw null;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, op).WithArguments("C4.operator " + checkedKeyword + op + "(C4)").WithLocation(26, 24 + checkedKeyword.Length),
                // (38,32): error CS9334: 'C6.operator +(C6)' return type must be 'C6' to match implemented member 'I1<C6>.operator +(C6)'
                //     static int I1<C6>.operator + (C6 x) => throw null;
                Diagnostic(ErrorCode.ERR_ExplicitInterfaceMemberReturnTypeMismatch, op).WithArguments("C6.operator " + checkedKeyword + op + "(C6)", "C6", "I1<C6>.operator " + checkedKeyword + op + "(C6)").WithLocation(38, 32 + checkedKeyword.Length),
                // (50,22): error CS0539: 'C8.op_UnaryPlus(C8)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static C8 I1<C8>.op_UnaryPlus(C8 x) => throw null;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, opName).WithArguments("C8." + opName + "(C8)").WithLocation(50, 22),
                // (67,33): error CS0539: 'C10.operator +(C10)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static C10 I2<C10>.operator +(C10 x) => throw null;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, op).WithArguments("C10.operator " + checkedKeyword + op + "(C10)").WithLocation(67, 33 + checkedKeyword.Length)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementVirtualStaticIncrementOperator_01([CombinatorialValues("++", "--")] string op, bool structure, bool isChecked)
        {
            var typeKeyword = structure ? "struct" : "class";

            string opName = GetUnaryOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    virtual static T operator " + checkedKeyword + op + @"(T x) => x;
}

" + typeKeyword + @"
    C1 : I1<C1>
{}

" + typeKeyword + @"
    C2 : I1<C2>
{
    public C2 operator " + checkedKeyword + op + @"(C2 x) => throw null;
}

" + typeKeyword + @"
    C3 : I1<C3>
{
    static C3 operator " + checkedKeyword + op + @"(C3 x) => throw null;
}

" + typeKeyword + @"
    C4 : I1<C4>
{
    C4 I1<C4>.operator " + checkedKeyword + op + @"(C4 x) => throw null;
}

" + typeKeyword + @"
    C5 : I1<C5>
{
    public static int operator " + checkedKeyword + op + @" (C5 x) => throw null;
}

" + typeKeyword + @"
    C6 : I1<C6>
{
    static int I1<C6>.operator " + checkedKeyword + op + @" (C6 x) => throw null;
}

" + typeKeyword + @"
    C7 : I1<C7>
{
    public static C7 " + opName + @"(C7 x) => throw null;
}

" + typeKeyword + @"
    C8 : I1<C8>
{
    static C8 I1<C8>." + opName + @"(C8 x) => throw null;
}

public interface I2<T> where T : I2<T>
{
    virtual static T " + opName + @"(T x) => x;
}

" + typeKeyword + @"
    C9 : I2<C9>
{
    public static C9 operator " + checkedKeyword + op + @"(C9 x) => throw null;
}

" + typeKeyword + @"
    C10 : I2<C10>
{
    static C10 I2<C10>.operator " + checkedKeyword + op + @"(C10 x) => throw null;
}
";

            var compilation1 = CreateCompilation([source1, CompilerFeatureRequiredAttribute], options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_BadIncDecRetType or (int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_CheckedOperatorNeedsMatch or (int)ErrorCode.ERR_OpTFRetType)).Verify(
                // (14,24): error CS0558: User-defined operator 'C2.operator ++(C2)' must be declared static and public
                //     public C2 operator ++(C2 x) => throw null;
                Diagnostic(ErrorCode.ERR_OperatorsMustBeStaticAndPublic, op).WithArguments("C2.operator " + checkedKeyword + op + "(C2)").WithLocation(14, 24 + checkedKeyword.Length),
                // (20,24): error CS0558: User-defined operator 'C3.operator +(C3)' must be declared static and public
                //     static C3 operator +(C3 x) => throw null;
                Diagnostic(ErrorCode.ERR_OperatorsMustBeStaticAndPublic, op).WithArguments("C3.operator " + checkedKeyword + op + "(C3)").WithLocation(20, 24 + checkedKeyword.Length),
                // (26,24): error CS8930: Explicit implementation of a user-defined operator 'C4.operator ++(C4)' must be declared static
                //     C4 I1<C4>.operator ++(C4 x) => throw null;
                Diagnostic(ErrorCode.ERR_ExplicitImplementationOfOperatorsMustBeStatic, op).WithArguments("C4.operator " + checkedKeyword + op + "(C4)").WithLocation(26, 24 + checkedKeyword.Length),
                // (26,24): error CS0539: 'C4.operator +(C4)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     C4 I1<C4>.operator +(C4 x) => throw null;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, op).WithArguments("C4.operator " + checkedKeyword + op + "(C4)").WithLocation(26, 24 + checkedKeyword.Length),
                // (38,32): error CS9334: 'C6.operator +(C6)' return type must be 'C6' to match implemented member 'I1<C6>.operator +(C6)'
                //     static int I1<C6>.operator + (C6 x) => throw null;
                Diagnostic(ErrorCode.ERR_ExplicitInterfaceMemberReturnTypeMismatch, op).WithArguments("C6.operator " + checkedKeyword + op + "(C6)", "C6", "I1<C6>.operator " + checkedKeyword + op + "(C6)").WithLocation(38, 32 + checkedKeyword.Length),
                // (50,22): error CS0539: 'C8.op_UnaryPlus(C8)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static C8 I1<C8>.op_UnaryPlus(C8 x) => throw null;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, opName).WithArguments("C8." + opName + "(C8)").WithLocation(50, 22),
                // (67,33): error CS0539: 'C10.operator +(C10)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static C10 I2<C10>.operator +(C10 x) => throw null;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, op).WithArguments("C10.operator " + checkedKeyword + op + "(C10)").WithLocation(67, 33 + checkedKeyword.Length)
                );
        }

        internal static string GetBinaryOperatorName(string op, bool isChecked, out string checkedKeyword)
        {
            string opName = BinaryOperatorName(op, isChecked: false);
            checkedKeyword = "";

            if (isChecked)
            {
                string checkedName = BinaryOperatorName(op, isChecked: true);

                if (checkedName == opName)
                {
                    return null; // There is no checked form
                }
                else
                {
                    opName = checkedName;
                    checkedKeyword = "checked ";
                }
            }

            return opName;
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticBinaryOperator_01([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<<", ">>", ">>>", "<", ">", "<=", ">=", "==", "!=")] string op, bool structure, bool isChecked)
        {
            string opName = GetBinaryOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var typeKeyword = structure ? "struct" : "class";

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    abstract static T operator " + checkedKeyword + op + @"(T x, int y);
}

" + typeKeyword + @"
    C1 : I1<C1>
{}

" + typeKeyword + @"
    C2 : I1<C2>
{
    public C2 operator " + checkedKeyword + op + @"(C2 x, int y) => throw null;
}

" + typeKeyword + @"
    C3 : I1<C3>
{
    static C3 operator " + checkedKeyword + op + @"(C3 x, int y) => throw null;
}

" + typeKeyword + @"
    C4 : I1<C4>
{
    C4 I1<C4>.operator " + checkedKeyword + op + @"(C4 x, int y) => throw null;
}

" + typeKeyword + @"
    C5 : I1<C5>
{
    public static int operator " + checkedKeyword + op + @" (C5 x, int y) => throw null;
}

" + typeKeyword + @"
    C6 : I1<C6>
{
    static int I1<C6>.operator " + checkedKeyword + op + @" (C6 x, int y) => throw null;
}

" + typeKeyword + @"
    C7 : I1<C7>
{
    public static C7 " + opName + @"(C7 x, int y) => throw null;
}

" + typeKeyword + @"
    C8 : I1<C8>
{
    static C8 I1<C8>." + opName + @"(C8 x, int y) => throw null;
}

public interface I2<T> where T : I2<T>
{
    abstract static T " + opName + @"(T x, int y);
}

" + typeKeyword + @"
    C9 : I2<C9>
{
    public static C9 operator " + checkedKeyword + op + @"(C9 x, int y) => throw null;
}

" + typeKeyword + @"
    C10 : I2<C10>
{
    static C10 I2<C10>.operator " + checkedKeyword + op + @"(C10 x, int y) => throw null;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_CheckedOperatorNeedsMatch or (int)ErrorCode.WRN_EqualityOpWithoutEquals or (int)ErrorCode.WRN_EqualityOpWithoutGetHashCode)).Verify(
                // (8,10): error CS0535: 'C1' does not implement interface member 'I1<C1>.operator >>(C1, int)'
                //     C1 : I1<C1>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C1>").WithArguments("C1", "I1<C1>.operator " + checkedKeyword + op + "(C1, int)").WithLocation(8, 10),
                // (12,10): error CS8928: 'C2' does not implement static interface member 'I1<C2>.operator >>(C2, int)'. 'C2.operator >>(C2, int)' cannot implement the interface member because it is not static.
                //     C2 : I1<C2>
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberNotStatic, "I1<C2>").WithArguments("C2", "I1<C2>.operator " + checkedKeyword + op + "(C2, int)", "C2.operator " + checkedKeyword + op + "(C2, int)").WithLocation(12, 10),
                // (14,24): error CS0558: User-defined operator 'C2.operator >>(C2, int)' must be declared static and public
                //     public C2 operator >>(C2 x, int y) => throw null;
                Diagnostic(ErrorCode.ERR_OperatorsMustBeStaticAndPublic, op).WithArguments("C2.operator " + checkedKeyword + op + "(C2, int)").WithLocation(14, 24 + checkedKeyword.Length),
                // (18,10): error CS0737: 'C3' does not implement interface member 'I1<C3>.operator >>(C3, int)'. 'C3.operator >>(C3, int)' cannot implement an interface member because it is not public.
                //     C3 : I1<C3>
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberNotPublic, "I1<C3>").WithArguments("C3", "I1<C3>.operator " + checkedKeyword + op + "(C3, int)", "C3.operator " + checkedKeyword + op + "(C3, int)").WithLocation(18, 10),
                // (20,24): error CS0558: User-defined operator 'C3.operator >>(C3, int)' must be declared static and public
                //     static C3 operator >>(C3 x, int y) => throw null;
                Diagnostic(ErrorCode.ERR_OperatorsMustBeStaticAndPublic, op).WithArguments("C3.operator " + checkedKeyword + op + "(C3, int)").WithLocation(20, 24 + checkedKeyword.Length),
                // (24,10): error CS0535: 'C4' does not implement interface member 'I1<C4>.operator >>(C4, int)'
                //     C4 : I1<C4>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C4>").WithArguments("C4", "I1<C4>.operator " + checkedKeyword + op + "(C4, int)").WithLocation(24, 10),
                // (26,24): error CS8930: Explicit implementation of a user-defined operator 'C4.operator >>(C4, int)' must be declared static
                //     C4 I1<C4>.operator >>(C4 x, int y) => throw null;
                Diagnostic(ErrorCode.ERR_ExplicitImplementationOfOperatorsMustBeStatic, op).WithArguments("C4.operator " + checkedKeyword + op + "(C4, int)").WithLocation(26, 24 + checkedKeyword.Length),
                // (26,24): error CS0539: 'C4.operator >>(C4, int)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     C4 I1<C4>.operator >>(C4 x, int y) => throw null;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, op).WithArguments("C4.operator " + checkedKeyword + op + "(C4, int)").WithLocation(26, 24 + checkedKeyword.Length),
                // (30,10): error CS0738: 'C5' does not implement interface member 'I1<C5>.operator >>(C5, int)'. 'C5.operator >>(C5, int)' cannot implement 'I1<C5>.operator >>(C5, int)' because it does not have the matching return type of 'C5'.
                //     C5 : I1<C5>
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberWrongReturnType, "I1<C5>").WithArguments("C5", "I1<C5>.operator " + checkedKeyword + op + "(C5, int)", "C5.operator " + checkedKeyword + op + "(C5, int)", "C5").WithLocation(30, 10),
                // (36,10): error CS0535: 'C6' does not implement interface member 'I1<C6>.operator >>(C6, int)'
                //     C6 : I1<C6>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C6>").WithArguments("C6", "I1<C6>.operator " + checkedKeyword + op + "(C6, int)").WithLocation(36, 10),
                // (38,32): error CS9334: 'C6.operator >>(C6, int)' return type must be 'C6' to match implemented member 'I1<C6>.operator >>(C6, int)'
                //     static int I1<C6>.operator >> (C6 x, int y) => throw null;
                Diagnostic(ErrorCode.ERR_ExplicitInterfaceMemberReturnTypeMismatch, op).WithArguments("C6.operator " + checkedKeyword + op + "(C6, int)", "C6", "I1<C6>.operator " + checkedKeyword + op + "(C6, int)").WithLocation(38, 32 + checkedKeyword.Length),
                // (42,10): error CS0535: 'C7' does not implement interface member 'I1<C7>.operator >>(C7, int)'
                //     C7 : I1<C7>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C7>").WithArguments("C7", "I1<C7>.operator " + checkedKeyword + op + "(C7, int)").WithLocation(42, 10),
                // (48,10): error CS0535: 'C8' does not implement interface member 'I1<C8>.operator >>(C8, int)'
                //     C8 : I1<C8>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C8>").WithArguments("C8", "I1<C8>.operator " + checkedKeyword + op + "(C8, int)").WithLocation(48, 10),
                // (50,22): error CS0539: 'C8.op_RightShift(C8, int)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static C8 I1<C8>.op_RightShift(C8 x, int y) => throw null;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, opName).WithArguments("C8." + opName + "(C8, int)").WithLocation(50, 22),
                // (59,10): error CS0535: 'C9' does not implement interface member 'I2<C9>.op_RightShift(C9, int)'
                //     C9 : I2<C9>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I2<C9>").WithArguments("C9", "I2<C9>." + opName + "(C9, int)").WithLocation(59, 10),
                // (65,11): error CS0535: 'C10' does not implement interface member 'I2<C10>.op_RightShift(C10, int)'
                //     C10 : I2<C10>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I2<C10>").WithArguments("C10", "I2<C10>." + opName + "(C10, int)").WithLocation(65, 11),
                // (67,33): error CS0539: 'C10.operator >>(C10, int)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static C10 I2<C10>.operator >>(C10 x, int y) => throw null;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, op).WithArguments("C10.operator " + checkedKeyword + op + "(C10, int)").WithLocation(67, 33 + checkedKeyword.Length)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementVirtualStaticBinaryOperator_01([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<<", ">>", ">>>", "<", ">", "<=", ">=", "==", "!=")] string op, bool structure, bool isChecked)
        {
            string opName = GetBinaryOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var typeKeyword = structure ? "struct" : "class";

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    virtual static T operator " + checkedKeyword + op + @"(T x, int y) => x;
}

" + typeKeyword + @"
    C1 : I1<C1>
{}

" + typeKeyword + @"
    C2 : I1<C2>
{
    public C2 operator " + checkedKeyword + op + @"(C2 x, int y) => throw null;
}

" + typeKeyword + @"
    C3 : I1<C3>
{
    static C3 operator " + checkedKeyword + op + @"(C3 x, int y) => throw null;
}

" + typeKeyword + @"
    C4 : I1<C4>
{
    C4 I1<C4>.operator " + checkedKeyword + op + @"(C4 x, int y) => throw null;
}

" + typeKeyword + @"
    C5 : I1<C5>
{
    public static int operator " + checkedKeyword + op + @" (C5 x, int y) => throw null;
}

" + typeKeyword + @"
    C6 : I1<C6>
{
    static int I1<C6>.operator " + checkedKeyword + op + @" (C6 x, int y) => throw null;
}

" + typeKeyword + @"
    C7 : I1<C7>
{
    public static C7 " + opName + @"(C7 x, int y) => throw null;
}

" + typeKeyword + @"
    C8 : I1<C8>
{
    static C8 I1<C8>." + opName + @"(C8 x, int y) => throw null;
}

public interface I2<T> where T : I2<T>
{
    virtual static T " + opName + @"(T x, int y) => x;
}

" + typeKeyword + @"
    C9 : I2<C9>
{
    public static C9 operator " + checkedKeyword + op + @"(C9 x, int y) => throw null;
}

" + typeKeyword + @"
    C10 : I2<C10>
{
    static C10 I2<C10>.operator " + checkedKeyword + op + @"(C10 x, int y) => throw null;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_CheckedOperatorNeedsMatch or (int)ErrorCode.WRN_EqualityOpWithoutEquals or (int)ErrorCode.WRN_EqualityOpWithoutGetHashCode)).Verify(
                // (14,24): error CS0558: User-defined operator 'C2.operator >>(C2, int)' must be declared static and public
                //     public C2 operator >>(C2 x, int y) => throw null;
                Diagnostic(ErrorCode.ERR_OperatorsMustBeStaticAndPublic, op).WithArguments("C2.operator " + checkedKeyword + op + "(C2, int)").WithLocation(14, 24 + checkedKeyword.Length),
                // (20,24): error CS0558: User-defined operator 'C3.operator >>(C3, int)' must be declared static and public
                //     static C3 operator >>(C3 x, int y) => throw null;
                Diagnostic(ErrorCode.ERR_OperatorsMustBeStaticAndPublic, op).WithArguments("C3.operator " + checkedKeyword + op + "(C3, int)").WithLocation(20, 24 + checkedKeyword.Length),
                // (26,24): error CS8930: Explicit implementation of a user-defined operator 'C4.operator >>(C4, int)' must be declared static
                //     C4 I1<C4>.operator >>(C4 x, int y) => throw null;
                Diagnostic(ErrorCode.ERR_ExplicitImplementationOfOperatorsMustBeStatic, op).WithArguments("C4.operator " + checkedKeyword + op + "(C4, int)").WithLocation(26, 24 + checkedKeyword.Length),
                // (26,24): error CS0539: 'C4.operator >>(C4, int)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     C4 I1<C4>.operator >>(C4 x, int y) => throw null;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, op).WithArguments("C4.operator " + checkedKeyword + op + "(C4, int)").WithLocation(26, 24 + checkedKeyword.Length),
                // (38,32): error CS9334: 'C6.operator >>(C6, int)' return type must be 'C6' to match implemented member 'I1<C6>.operator >>(C6, int)'
                //     static int I1<C6>.operator >> (C6 x, int y) => throw null;
                Diagnostic(ErrorCode.ERR_ExplicitInterfaceMemberReturnTypeMismatch, op).WithArguments("C6.operator " + checkedKeyword + op + "(C6, int)", "C6", "I1<C6>.operator " + checkedKeyword + op + "(C6, int)").WithLocation(38, 32 + checkedKeyword.Length),
                // (50,22): error CS0539: 'C8.op_RightShift(C8, int)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static C8 I1<C8>.op_RightShift(C8 x, int y) => throw null;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, opName).WithArguments("C8." + opName + "(C8, int)").WithLocation(50, 22),
                // (67,33): error CS0539: 'C10.operator >>(C10, int)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static C10 I2<C10>.operator >>(C10 x, int y) => throw null;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, op).WithArguments("C10.operator " + checkedKeyword + op + "(C10, int)").WithLocation(67, 33 + checkedKeyword.Length)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticUnaryOperator_03([CombinatorialValues("+", "-", "!", "~", "true", "false")] string op, bool isChecked)
        {
            if (GetUnaryOperatorName(op, isChecked, out string checkedKeyword) is null)
            {
                return;
            }

            var source1 =
@"
public interface I1
{
    abstract static I1 operator " + checkedKeyword + op + @"(I1 x);
}

interface I2 : I1
{}

interface I3 : I1
{
    I1 operator " + checkedKeyword + op + @"(I1 x) => default;
}

interface I4 : I1
{
    static I1 operator " + checkedKeyword + op + @"(I1 x) => default;
}

interface I5 : I1
{
    I1 I1.operator " + checkedKeyword + op + @"(I1 x) => default;
}

interface I6 : I1
{
    static I1 I1.operator " + checkedKeyword + op + @"(I1 x) => default;
}

interface I7 : I1
{
    abstract static I1 operator " + checkedKeyword + op + @"(I1 x);
}

public interface I11<T> where T : I11<T>
{
    abstract static T operator " + checkedKeyword + op + @"(T x);
}

interface I8<T> : I11<T> where T : I8<T>
{
    T operator " + checkedKeyword + op + @"(T x) => default;
}

interface I9<T> : I11<T> where T : I9<T>
{
    static T operator " + checkedKeyword + op + @"(T x) => default;
}

interface I10<T> : I11<T> where T : I10<T>
{
    abstract static T operator " + checkedKeyword + op + @"(T x);
}

interface I12<T> : I11<T> where T : I12<T>
{
    static T I11<T>.operator " + checkedKeyword + op + @"(T x) => default;
}

interface I13<T> : I11<T> where T : I13<T>
{
    abstract static T I11<T>.operator " + checkedKeyword + op + @"(T x);
}

interface I14 : I1
{
    abstract static I1 I1.operator " + checkedKeyword + op + @"(I1 x);
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            ErrorCode badSignatureError = op.Length != 2 ? ErrorCode.ERR_BadUnaryOperatorSignature : ErrorCode.ERR_BadIncDecSignature;
            ErrorCode badAbstractSignatureError = op.Length != 2 ? ErrorCode.ERR_BadAbstractUnaryOperatorSignature : ErrorCode.ERR_BadAbstractIncDecSignature;

            compilation1.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_OpTFRetType or (int)ErrorCode.ERR_CheckedOperatorNeedsMatch)).Verify(
                // (12,17): error CS0558: User-defined operator 'I3.operator +(I1)' must be declared static and public
                //     I1 operator +(I1 x) => default;
                Diagnostic(ErrorCode.ERR_OperatorsMustBeStaticAndPublic, op).WithArguments("I3.operator " + checkedKeyword + op + "(I1)").WithLocation(12, 17 + checkedKeyword.Length),
                // (12,17): error CS0562: The parameter of a unary operator must be the containing type
                //     I1 operator +(I1 x) => default;
                Diagnostic(badSignatureError, op).WithLocation(12, 17 + checkedKeyword.Length),
                // (17,24): error CS0562: The parameter of a unary operator must be the containing type
                //     static I1 operator +(I1 x) => default;
                Diagnostic(badSignatureError, op).WithLocation(17, 24 + checkedKeyword.Length),
                // (22,20): error CS8930: Explicit implementation of a user-defined operator 'I5.operator +(I1)' must be declared static
                //     I1 I1.operator +(I1 x) => default;
                Diagnostic(ErrorCode.ERR_ExplicitImplementationOfOperatorsMustBeStatic, op).WithArguments("I5.operator " + checkedKeyword + op + "(I1)").WithLocation(22, 20 + checkedKeyword.Length),
                // (22,20): error CS0539: 'I5.operator +(I1)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     I1 I1.operator +(I1 x) => default;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, op).WithArguments("I5.operator " + checkedKeyword + op + "(I1)").WithLocation(22, 20 + checkedKeyword.Length),
                // (32,33): error CS8921: The parameter of a unary operator must be the containing type, or its type parameter constrained to it.
                //     abstract static I1 operator +(I1 x);
                Diagnostic(badAbstractSignatureError, op).WithLocation(32, 33 + checkedKeyword.Length),
                // (42,16): error CS0558: User-defined operator 'I8<T>.operator +(T)' must be declared static and public
                //     T operator +(T x) => default;
                Diagnostic(ErrorCode.ERR_OperatorsMustBeStaticAndPublic, op).WithArguments("I8<T>.operator " + checkedKeyword + op + "(T)").WithLocation(42, 16 + checkedKeyword.Length),
                // (42,16): error CS0562: The parameter of a unary operator must be the containing type
                //     T operator +(T x) => default;
                Diagnostic(badSignatureError, op).WithLocation(42, 16 + checkedKeyword.Length),
                // (47,23): error CS0562: The parameter of a unary operator must be the containing type
                //     static T operator +(T x) => default;
                Diagnostic(badSignatureError, op).WithLocation(47, 23 + checkedKeyword.Length)
                );

            var m01 = compilation1.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<MethodSymbol>().Single();

            Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I2").FindImplementationForInterfaceMember(m01));
            Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I3").FindImplementationForInterfaceMember(m01));
            Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I4").FindImplementationForInterfaceMember(m01));
            Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I5").FindImplementationForInterfaceMember(m01));

            var i6 = compilation1.GlobalNamespace.GetTypeMember("I6");
            Assert.Same(i6.GetMembers().OfType<MethodSymbol>().Single(), i6.FindImplementationForInterfaceMember(m01));

            Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I7").FindImplementationForInterfaceMember(m01));

            var i8 = compilation1.GlobalNamespace.GetTypeMember("I8");
            Assert.Null(i8.FindImplementationForInterfaceMember(i8.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single()));

            var i9 = compilation1.GlobalNamespace.GetTypeMember("I9");
            Assert.Null(i9.FindImplementationForInterfaceMember(i9.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single()));

            var i10 = compilation1.GlobalNamespace.GetTypeMember("I10");
            Assert.Null(i10.FindImplementationForInterfaceMember(i10.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single()));

            var i12 = compilation1.GlobalNamespace.GetTypeMember("I12");
            Assert.Same(i12.GetMembers().OfType<MethodSymbol>().Single(), i12.FindImplementationForInterfaceMember(i12.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single()));

            var i13 = compilation1.GlobalNamespace.GetTypeMember("I13");
            Assert.Null(i13.FindImplementationForInterfaceMember(i13.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single()));

            Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I14").FindImplementationForInterfaceMember(m01));
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticIncrementOperator_03([CombinatorialValues("++", "--")] string op, bool isChecked)
        {
            if (GetUnaryOperatorName(op, isChecked, out string checkedKeyword) is null)
            {
                return;
            }

            var source1 =
@"
public interface I1
{
    abstract static I1 operator " + checkedKeyword + op + @"(I1 x);
}

interface I2 : I1
{}

interface I3 : I1
{
    I1 operator " + checkedKeyword + op + @"(I1 x) => default;
}

interface I4 : I1
{
    static I1 operator " + checkedKeyword + op + @"(I1 x) => default;
}

interface I5 : I1
{
    I1 I1.operator " + checkedKeyword + op + @"(I1 x) => default;
}

interface I6 : I1
{
    static I1 I1.operator " + checkedKeyword + op + @"(I1 x) => default;
}

interface I7 : I1
{
    abstract static I1 operator " + checkedKeyword + op + @"(I1 x);
}

public interface I11<T> where T : I11<T>
{
    abstract static T operator " + checkedKeyword + op + @"(T x);
}

interface I8<T> : I11<T> where T : I8<T>
{
    T operator " + checkedKeyword + op + @"(T x) => default;
}

interface I9<T> : I11<T> where T : I9<T>
{
    static T operator " + checkedKeyword + op + @"(T x) => default;
}

interface I10<T> : I11<T> where T : I10<T>
{
    abstract static T operator " + checkedKeyword + op + @"(T x);
}

interface I12<T> : I11<T> where T : I12<T>
{
    static T I11<T>.operator " + checkedKeyword + op + @"(T x) => default;
}

interface I13<T> : I11<T> where T : I13<T>
{
    abstract static T I11<T>.operator " + checkedKeyword + op + @"(T x);
}

interface I14 : I1
{
    abstract static I1 I1.operator " + checkedKeyword + op + @"(I1 x);
}
";

            var compilation1 = CreateCompilation([source1, CompilerFeatureRequiredAttribute], options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            ErrorCode badSignatureError = op.Length != 2 ? ErrorCode.ERR_BadUnaryOperatorSignature : ErrorCode.ERR_BadIncDecSignature;
            ErrorCode badAbstractSignatureError = op.Length != 2 ? ErrorCode.ERR_BadAbstractUnaryOperatorSignature : ErrorCode.ERR_BadAbstractIncDecSignature;

            compilation1.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_OpTFRetType or (int)ErrorCode.ERR_CheckedOperatorNeedsMatch)).Verify(
                // (12,17): error CS0558: User-defined operator 'I3.operator ++(I1)' must be declared static and public
                //     I1 operator ++(I1 x) => default;
                Diagnostic(ErrorCode.ERR_OperatorsMustBeStaticAndPublic, op).WithArguments("I3.operator " + checkedKeyword + op + "(I1)").WithLocation(12, 17 + checkedKeyword.Length),
                // (12,17): error CS0559: The parameter type for ++ or -- operator must be the containing type
                //     I1 operator ++(I1 x) => default;
                Diagnostic(ErrorCode.ERR_BadIncDecSignature, op).WithLocation(12, 17 + checkedKeyword.Length),
                // (17,24): error CS0562: The parameter of a unary operator must be the containing type
                //     static I1 operator +(I1 x) => default;
                Diagnostic(badSignatureError, op).WithLocation(17, 24 + checkedKeyword.Length),
                // (22,20): error CS8930: Explicit implementation of a user-defined operator 'I5.operator ++(I1)' must be declared static
                //     I1 I1.operator ++(I1 x) => default;
                Diagnostic(ErrorCode.ERR_ExplicitImplementationOfOperatorsMustBeStatic, op).WithArguments("I5.operator " + checkedKeyword + op + "(I1)").WithLocation(22, 20 + checkedKeyword.Length),
                // (22,20): error CS0539: 'I5.operator +(I1)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     I1 I1.operator +(I1 x) => default;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, op).WithArguments("I5.operator " + checkedKeyword + op + "(I1)").WithLocation(22, 20 + checkedKeyword.Length),
                // (32,33): error CS8921: The parameter of a unary operator must be the containing type, or its type parameter constrained to it.
                //     abstract static I1 operator +(I1 x);
                Diagnostic(badAbstractSignatureError, op).WithLocation(32, 33 + checkedKeyword.Length),
                // (42,16): error CS0558: User-defined operator 'I8<T>.operator ++(T)' must be declared static and public
                //     T operator ++(T x) => default;
                Diagnostic(ErrorCode.ERR_OperatorsMustBeStaticAndPublic, op).WithArguments("I8<T>.operator " + checkedKeyword + op + "(T)").WithLocation(42, 16 + checkedKeyword.Length),
                // (42,16): error CS0559: The parameter type for ++ or -- operator must be the containing type
                //     T operator ++(T x) => default;
                Diagnostic(ErrorCode.ERR_BadIncDecSignature, op).WithLocation(42, 16 + checkedKeyword.Length),
                // (47,23): error CS0562: The parameter of a unary operator must be the containing type
                //     static T operator +(T x) => default;
                Diagnostic(badSignatureError, op).WithLocation(47, 23 + checkedKeyword.Length)
                );

            var m01 = compilation1.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<MethodSymbol>().Single();

            Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I2").FindImplementationForInterfaceMember(m01));
            Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I3").FindImplementationForInterfaceMember(m01));
            Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I4").FindImplementationForInterfaceMember(m01));
            Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I5").FindImplementationForInterfaceMember(m01));

            var i6 = compilation1.GlobalNamespace.GetTypeMember("I6");
            Assert.Same(i6.GetMembers().OfType<MethodSymbol>().Single(), i6.FindImplementationForInterfaceMember(m01));

            Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I7").FindImplementationForInterfaceMember(m01));

            var i8 = compilation1.GlobalNamespace.GetTypeMember("I8");
            Assert.Null(i8.FindImplementationForInterfaceMember(i8.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single()));

            var i9 = compilation1.GlobalNamespace.GetTypeMember("I9");
            Assert.Null(i9.FindImplementationForInterfaceMember(i9.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single()));

            var i10 = compilation1.GlobalNamespace.GetTypeMember("I10");
            Assert.Null(i10.FindImplementationForInterfaceMember(i10.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single()));

            var i12 = compilation1.GlobalNamespace.GetTypeMember("I12");
            Assert.Same(i12.GetMembers().OfType<MethodSymbol>().Single(), i12.FindImplementationForInterfaceMember(i12.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single()));

            var i13 = compilation1.GlobalNamespace.GetTypeMember("I13");
            Assert.Null(i13.FindImplementationForInterfaceMember(i13.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single()));

            Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I14").FindImplementationForInterfaceMember(m01));
        }

        [Theory]
        [CombinatorialData]
        public void ImplementVirtualStaticUnaryOperator_03([CombinatorialValues("+", "-", "!", "~", "true", "false")] string op, bool isChecked)
        {
            if (GetUnaryOperatorName(op, isChecked, out string checkedKeyword) is null)
            {
                return;
            }

            var source1 =
@"
public interface I1
{
    virtual  static I1 operator " + checkedKeyword + op + @"(I1 x) => x;
}

interface I2 : I1
{}

interface I3 : I1
{
    I1 operator " + checkedKeyword + op + @"(I1 x) => default;
}

interface I4 : I1
{
    static I1 operator " + checkedKeyword + op + @"(I1 x) => default;
}

interface I5 : I1
{
    I1 I1.operator " + checkedKeyword + op + @"(I1 x) => default;
}

interface I6 : I1
{
    static I1 I1.operator " + checkedKeyword + op + @"(I1 x) => default;
}

interface I7 : I1
{
    virtual  static I1 operator " + checkedKeyword + op + @"(I1 x) => x;
}

public interface I11<T> where T : I11<T>
{
    virtual  static T operator " + checkedKeyword + op + @"(T x) => x;
}

interface I8<T> : I11<T> where T : I8<T>
{
    T operator " + checkedKeyword + op + @"(T x) => default;
}

interface I9<T> : I11<T> where T : I9<T>
{
    static T operator " + checkedKeyword + op + @"(T x) => default;
}

interface I10<T> : I11<T> where T : I10<T>
{
    virtual  static T operator " + checkedKeyword + op + @"(T x) => x;
}

interface I12<T> : I11<T> where T : I12<T>
{
    static T I11<T>.operator " + checkedKeyword + op + @"(T x) => default;
}

interface I13<T> : I11<T> where T : I13<T>
{
    virtual  static T I11<T>.operator " + checkedKeyword + op + @"(T x) => x;
}

interface I14 : I1
{
    virtual  static I1 I1.operator " + checkedKeyword + op + @"(I1 x) => x;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            ErrorCode badSignatureError = op.Length != 2 ? ErrorCode.ERR_BadUnaryOperatorSignature : ErrorCode.ERR_BadIncDecSignature;
            ErrorCode badAbstractSignatureError = op.Length != 2 ? ErrorCode.ERR_BadAbstractUnaryOperatorSignature : ErrorCode.ERR_BadAbstractIncDecSignature;

            compilation1.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_OpTFRetType or (int)ErrorCode.ERR_CheckedOperatorNeedsMatch)).Verify(
                // (12,17): error CS0558: User-defined operator 'I3.operator +(I1)' must be declared static and public
                //     I1 operator +(I1 x) => default;
                Diagnostic(ErrorCode.ERR_OperatorsMustBeStaticAndPublic, op).WithArguments("I3.operator " + checkedKeyword + op + "(I1)").WithLocation(12, 17 + checkedKeyword.Length),
                // (12,17): error CS0562: The parameter of a unary operator must be the containing type
                //     I1 operator +(I1 x) => default;
                Diagnostic(badSignatureError, op).WithLocation(12, 17 + checkedKeyword.Length),
                // (17,24): error CS0562: The parameter of a unary operator must be the containing type
                //     static I1 operator +(I1 x) => default;
                Diagnostic(badSignatureError, op).WithLocation(17, 24 + checkedKeyword.Length),
                // (22,20): error CS8930: Explicit implementation of a user-defined operator 'I5.operator +(I1)' must be declared static
                //     I1 I1.operator +(I1 x) => default;
                Diagnostic(ErrorCode.ERR_ExplicitImplementationOfOperatorsMustBeStatic, op).WithArguments("I5.operator " + checkedKeyword + op + "(I1)").WithLocation(22, 20 + checkedKeyword.Length),
                // (22,20): error CS0539: 'I5.operator +(I1)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     I1 I1.operator +(I1 x) => default;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, op).WithArguments("I5.operator " + checkedKeyword + op + "(I1)").WithLocation(22, 20 + checkedKeyword.Length),
                // (32,33): error CS8921: The parameter of a unary operator must be the containing type, or its type parameter constrained to it.
                //     virtual  static I1 operator +(I1 x);
                Diagnostic(badAbstractSignatureError, op).WithLocation(32, 33 + checkedKeyword.Length),
                // (42,16): error CS0558: User-defined operator 'I8<T>.operator +(T)' must be declared static and public
                //     T operator +(T x) => default;
                Diagnostic(ErrorCode.ERR_OperatorsMustBeStaticAndPublic, op).WithArguments("I8<T>.operator " + checkedKeyword + op + "(T)").WithLocation(42, 16 + checkedKeyword.Length),
                // (42,16): error CS0562: The parameter of a unary operator must be the containing type
                //     T operator +(T x) => default;
                Diagnostic(badSignatureError, op).WithLocation(42, 16 + checkedKeyword.Length),
                // (47,23): error CS0562: The parameter of a unary operator must be the containing type
                //     static T operator +(T x) => default;
                Diagnostic(badSignatureError, op).WithLocation(47, 23 + checkedKeyword.Length),
                // (62,39): error CS0106: The modifier 'virtual' is not valid for this item
                //     virtual  static T I11<T>.operator +(T x);
                Diagnostic(ErrorCode.ERR_BadMemberFlag, op).WithArguments("virtual").WithLocation(62, 39 + checkedKeyword.Length),
                // (67,36): error CS0106: The modifier 'virtual' is not valid for this item
                //     virtual  static I1 I1.operator +(I1 x);
                Diagnostic(ErrorCode.ERR_BadMemberFlag, op).WithArguments("virtual").WithLocation(67, 36 + checkedKeyword.Length)
                );

            var m01 = compilation1.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<MethodSymbol>().Single();

            Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I2").FindImplementationForInterfaceMember(m01));
            Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I3").FindImplementationForInterfaceMember(m01));
            Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I4").FindImplementationForInterfaceMember(m01));
            Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I5").FindImplementationForInterfaceMember(m01));

            var i6 = compilation1.GlobalNamespace.GetTypeMember("I6");
            Assert.Same(i6.GetMembers().OfType<MethodSymbol>().Single(), i6.FindImplementationForInterfaceMember(m01));

            Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I7").FindImplementationForInterfaceMember(m01));

            foreach (var name in new[] { "I8", "I9", "I10" })
            {
                var iX = compilation1.GlobalNamespace.GetTypeMember(name);
                var iXM = iX.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();
                Assert.Same(iXM, iX.FindImplementationForInterfaceMember(iXM));
            }

            foreach (var name in new[] { "I12", "I13" })
            {
                var iX = compilation1.GlobalNamespace.GetTypeMember(name);
                var iXM = iX.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();
                Assert.Same(iX.GetMembers().OfType<MethodSymbol>().Single(), iX.FindImplementationForInterfaceMember(iXM));
            }

            var i14 = compilation1.GlobalNamespace.GetTypeMember("I14");
            Assert.Same(i14.GetMembers().OfType<MethodSymbol>().Single(), i14.FindImplementationForInterfaceMember(m01));
        }

        [Theory]
        [CombinatorialData]
        public void ImplementVirtualStaticIncrementOperator_03([CombinatorialValues("++", "--")] string op, bool isChecked)
        {
            if (GetUnaryOperatorName(op, isChecked, out string checkedKeyword) is null)
            {
                return;
            }

            var source1 =
@"
public interface I1
{
    virtual  static I1 operator " + checkedKeyword + op + @"(I1 x) => x;
}

interface I2 : I1
{}

interface I3 : I1
{
    I1 operator " + checkedKeyword + op + @"(I1 x) => default;
}

interface I4 : I1
{
    static I1 operator " + checkedKeyword + op + @"(I1 x) => default;
}

interface I5 : I1
{
    I1 I1.operator " + checkedKeyword + op + @"(I1 x) => default;
}

interface I6 : I1
{
    static I1 I1.operator " + checkedKeyword + op + @"(I1 x) => default;
}

interface I7 : I1
{
    virtual  static I1 operator " + checkedKeyword + op + @"(I1 x) => x;
}

public interface I11<T> where T : I11<T>
{
    virtual  static T operator " + checkedKeyword + op + @"(T x) => x;
}

interface I8<T> : I11<T> where T : I8<T>
{
    T operator " + checkedKeyword + op + @"(T x) => default;
}

interface I9<T> : I11<T> where T : I9<T>
{
    static T operator " + checkedKeyword + op + @"(T x) => default;
}

interface I10<T> : I11<T> where T : I10<T>
{
    virtual  static T operator " + checkedKeyword + op + @"(T x) => x;
}

interface I12<T> : I11<T> where T : I12<T>
{
    static T I11<T>.operator " + checkedKeyword + op + @"(T x) => default;
}

interface I13<T> : I11<T> where T : I13<T>
{
    virtual  static T I11<T>.operator " + checkedKeyword + op + @"(T x) => x;
}

interface I14 : I1
{
    virtual  static I1 I1.operator " + checkedKeyword + op + @"(I1 x) => x;
}
";

            var compilation1 = CreateCompilation([source1, CompilerFeatureRequiredAttribute], options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            ErrorCode badSignatureError = op.Length != 2 ? ErrorCode.ERR_BadUnaryOperatorSignature : ErrorCode.ERR_BadIncDecSignature;
            ErrorCode badAbstractSignatureError = op.Length != 2 ? ErrorCode.ERR_BadAbstractUnaryOperatorSignature : ErrorCode.ERR_BadAbstractIncDecSignature;

            compilation1.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_OpTFRetType or (int)ErrorCode.ERR_CheckedOperatorNeedsMatch)).Verify(
                // (12,17): error CS0558: User-defined operator 'I3.operator ++(I1)' must be declared static and public
                //     I1 operator ++(I1 x) => default;
                Diagnostic(ErrorCode.ERR_OperatorsMustBeStaticAndPublic, op).WithArguments("I3.operator " + checkedKeyword + op + "(I1)").WithLocation(12, 17 + checkedKeyword.Length),
                // (12,17): error CS0559: The parameter type for ++ or -- operator must be the containing type
                //     I1 operator ++(I1 x) => default;
                Diagnostic(ErrorCode.ERR_BadIncDecSignature, op).WithLocation(12, 17 + checkedKeyword.Length),
                // (17,24): error CS0562: The parameter of a unary operator must be the containing type
                //     static I1 operator +(I1 x) => default;
                Diagnostic(badSignatureError, op).WithLocation(17, 24 + checkedKeyword.Length),
                // (22,20): error CS8930: Explicit implementation of a user-defined operator 'I5.operator ++(I1)' must be declared static
                //     I1 I1.operator ++(I1 x) => default;
                Diagnostic(ErrorCode.ERR_ExplicitImplementationOfOperatorsMustBeStatic, op).WithArguments("I5.operator " + checkedKeyword + op + "(I1)").WithLocation(22, 20 + checkedKeyword.Length),
                // (22,20): error CS0539: 'I5.operator +(I1)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     I1 I1.operator +(I1 x) => default;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, op).WithArguments("I5.operator " + checkedKeyword + op + "(I1)").WithLocation(22, 20 + checkedKeyword.Length),
                // (32,33): error CS8921: The parameter of a unary operator must be the containing type, or its type parameter constrained to it.
                //     virtual  static I1 operator +(I1 x);
                Diagnostic(badAbstractSignatureError, op).WithLocation(32, 33 + checkedKeyword.Length),
                // (42,16): error CS0558: User-defined operator 'I8<T>.operator ++(T)' must be declared static and public
                //     T operator ++(T x) => default;
                Diagnostic(ErrorCode.ERR_OperatorsMustBeStaticAndPublic, op).WithArguments("I8<T>.operator " + checkedKeyword + op + "(T)").WithLocation(42, 16 + checkedKeyword.Length),
                // (42,16): error CS0559: The parameter type for ++ or -- operator must be the containing type
                //     T operator ++(T x) => default;
                Diagnostic(ErrorCode.ERR_BadIncDecSignature, op).WithLocation(42, 16 + checkedKeyword.Length),
                // (47,23): error CS0562: The parameter of a unary operator must be the containing type
                //     static T operator +(T x) => default;
                Diagnostic(badSignatureError, op).WithLocation(47, 23 + checkedKeyword.Length),
                // (62,39): error CS0106: The modifier 'virtual' is not valid for this item
                //     virtual  static T I11<T>.operator +(T x);
                Diagnostic(ErrorCode.ERR_BadMemberFlag, op).WithArguments("virtual").WithLocation(62, 39 + checkedKeyword.Length),
                // (67,36): error CS0106: The modifier 'virtual' is not valid for this item
                //     virtual  static I1 I1.operator +(I1 x);
                Diagnostic(ErrorCode.ERR_BadMemberFlag, op).WithArguments("virtual").WithLocation(67, 36 + checkedKeyword.Length)
                );

            var m01 = compilation1.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<MethodSymbol>().Single();

            Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I2").FindImplementationForInterfaceMember(m01));
            Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I3").FindImplementationForInterfaceMember(m01));
            Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I4").FindImplementationForInterfaceMember(m01));
            Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I5").FindImplementationForInterfaceMember(m01));

            var i6 = compilation1.GlobalNamespace.GetTypeMember("I6");
            Assert.Same(i6.GetMembers().OfType<MethodSymbol>().Single(), i6.FindImplementationForInterfaceMember(m01));

            Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I7").FindImplementationForInterfaceMember(m01));

            foreach (var name in new[] { "I8", "I9", "I10" })
            {
                var iX = compilation1.GlobalNamespace.GetTypeMember(name);
                var iXM = iX.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();
                Assert.Same(iXM, iX.FindImplementationForInterfaceMember(iXM));
            }

            foreach (var name in new[] { "I12", "I13" })
            {
                var iX = compilation1.GlobalNamespace.GetTypeMember(name);
                var iXM = iX.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();
                Assert.Same(iX.GetMembers().OfType<MethodSymbol>().Single(), iX.FindImplementationForInterfaceMember(iXM));
            }

            var i14 = compilation1.GlobalNamespace.GetTypeMember("I14");
            Assert.Same(i14.GetMembers().OfType<MethodSymbol>().Single(), i14.FindImplementationForInterfaceMember(m01));
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticBinaryOperator_03([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<<", ">>", ">>>", "<", ">", "<=", ">=", "==", "!=")] string op, bool isChecked)
        {
            if (GetBinaryOperatorName(op, isChecked, out string checkedKeyword) is null)
            {
                return;
            }

            var source1 =
@"
public interface I1
{
    abstract static I1 operator " + checkedKeyword + op + @"(I1 x, int y);
}

interface I2 : I1
{}

interface I3 : I1
{
    I1 operator " + checkedKeyword + op + @"(I1 x, int y) => default;
}

interface I4 : I1
{
    static I1 operator " + checkedKeyword + op + @"(I1 x, int y) => default;
}

interface I5 : I1
{
    I1 I1.operator " + checkedKeyword + op + @"(I1 x, int y) => default;
}

interface I6 : I1
{
    static I1 I1.operator " + checkedKeyword + op + @"(I1 x, int y) => default;
}

interface I7 : I1
{
    abstract static I1 operator " + checkedKeyword + op + @"(I1 x, int y);
}

public interface I11<T> where T : I11<T>
{
    abstract static T operator " + checkedKeyword + op + @"(T x, int y);
}

interface I8<T> : I11<T> where T : I8<T>
{
    T operator " + checkedKeyword + op + @"(T x, int y) => default;
}

interface I9<T> : I11<T> where T : I9<T>
{
    static T operator " + checkedKeyword + op + @"(T x, int y) => default;
}

interface I10<T> : I11<T> where T : I10<T>
{
    abstract static T operator " + checkedKeyword + op + @"(T x, int y);
}

interface I12<T> : I11<T> where T : I12<T>
{
    static T I11<T>.operator " + checkedKeyword + op + @"(T x, int y) => default;
}

interface I13<T> : I11<T> where T : I13<T>
{
    abstract static T I11<T>.operator " + checkedKeyword + op + @"(T x, int y);
}

interface I14 : I1
{
    abstract static I1 I1.operator " + checkedKeyword + op + @"(I1 x, int y);
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            bool isShift = op == "<<" || op == ">>" || op == ">>>";
            ErrorCode badSignatureError = isShift ? ErrorCode.ERR_BadShiftOperatorSignature : ErrorCode.ERR_BadBinaryOperatorSignature;
            ErrorCode badAbstractSignatureError = isShift ? ErrorCode.ERR_BadAbstractShiftOperatorSignature : ErrorCode.ERR_BadAbstractBinaryOperatorSignature;

            var expected = new[] {
                // (12,17): error CS0563: One of the parameters of a binary operator must be the containing type
                //     I1 operator |(I1 x, int y) => default;
                Diagnostic(badSignatureError, op).WithLocation(12, 17 + checkedKeyword.Length),
                // (17,24): error CS0563: One of the parameters of a binary operator must be the containing type
                //     static I1 operator |(I1 x, int y) => default;
                Diagnostic(badSignatureError, op).WithLocation(17, 24 + checkedKeyword.Length),
                // (22,20): error CS0539: 'I5.operator |(I1, int)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     I1 I1.operator |(I1 x, int y) => default;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, op).WithArguments("I5.operator " + checkedKeyword + op + "(I1, int)").WithLocation(22, 20 + checkedKeyword.Length),
                // (42,16): error CS0563: One of the parameters of a binary operator must be the containing type
                //     T operator |(T x, int y) => default;
                Diagnostic(badSignatureError, op).WithLocation(42, 16 + checkedKeyword.Length),
                // (47,23): error CS0563: One of the parameters of a binary operator must be the containing type
                //     static T operator |(T x, int y) => default;
                Diagnostic(badSignatureError, op).WithLocation(47, 23 + checkedKeyword.Length)
                };

            if (op is "==" or "!=")
            {
                expected = expected.Concat(
                    new[] {
                        // (4,33): error CS9046: One of the parameters of an equality, or inequality operator declared in interface 'I1' must be a type parameter on 'I1' constrained to 'I1'
                        //     abstract static I1 operator ==(I1 x, int y);
                        Diagnostic(ErrorCode.ERR_BadAbstractEqualityOperatorSignature, op).WithArguments("I1").WithLocation(4, 33),
                        // (12,17): error CS0567: Conversion, equality, or inequality operators declared in interfaces must be abstract or virtual
                        //     I1 operator ==(I1 x, int y) => default;
                        Diagnostic(ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators, op).WithLocation(12, 17 + checkedKeyword.Length),
                        // (17,24): error CS0567: Conversion, equality, or inequality operators declared in interfaces must be abstract or virtual
                        //     static I1 operator ==(I1 x, int y) => default;
                        Diagnostic(ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators, op).WithLocation(17, 24 + checkedKeyword.Length),
                        // (22,20): error CS8930: Explicit implementation of a user-defined operator 'I5.operator ==(I1, int)' must be declared static
                        //     I1 I1.operator ==(I1 x, int y) => default;
                        Diagnostic(ErrorCode.ERR_ExplicitImplementationOfOperatorsMustBeStatic, op).WithArguments("I5.operator " + op + "(I1, int)").WithLocation(22, 20),
                        // (32,33): error CS9046: One of the parameters of an equality, or inequality operator declared in interface 'I7' must be a type parameter on 'I7' constrained to 'I7'
                        //     abstract static I1 operator ==(I1 x, int y);
                        Diagnostic(ErrorCode.ERR_BadAbstractEqualityOperatorSignature, op).WithArguments("I7").WithLocation(32, 33),
                        // (42,16): error CS0567: Conversion, equality, or inequality operators declared in interfaces must be abstract or virtual
                        //     T operator ==(T x, int y) => default;
                        Diagnostic(ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators, op).WithLocation(42, 16 + checkedKeyword.Length),
                        // (47,23): error CS0567: Conversion, equality, or inequality operators declared in interfaces must be abstract or virtual
                        //     static T operator ==(T x, int y) => default;
                        Diagnostic(ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators, op).WithLocation(47, 23 + checkedKeyword.Length)
                        }
                    ).ToArray();
            }
            else
            {
                expected = expected.Concat(
                    new[] {
                        // (12,17): error CS0558: User-defined operator 'I3.operator |(I1, int)' must be declared static and public
                        //     I1 operator |(I1 x, int y) => default;
                        Diagnostic(ErrorCode.ERR_OperatorsMustBeStaticAndPublic, op).WithArguments("I3.operator " + checkedKeyword + op + "(I1, int)").WithLocation(12, 17 + checkedKeyword.Length),
                        // (22,20): error CS8930: Explicit implementation of a user-defined operator 'I5.operator |(I1, int)' must be declared static
                        //     I1 I1.operator |(I1 x, int y) => default;
                        Diagnostic(ErrorCode.ERR_ExplicitImplementationOfOperatorsMustBeStatic, op).WithArguments("I5.operator " + checkedKeyword + op + "(I1, int)").WithLocation(22, 20 + checkedKeyword.Length),
                        // (32,33): error CS8924: One of the parameters of a binary operator must be the containing type, or its type parameter constrained to it.
                        //     abstract static I1 operator |(I1 x, int y);
                        Diagnostic(badAbstractSignatureError, op).WithLocation(32, 33 + checkedKeyword.Length),
                        // (42,16): error CS0558: User-defined operator 'I8<T>.operator |(T, int)' must be declared static and public
                        //     T operator |(T x, int y) => default;
                        Diagnostic(ErrorCode.ERR_OperatorsMustBeStaticAndPublic, op).WithArguments("I8<T>.operator " + checkedKeyword + op + "(T, int)").WithLocation(42, 16 + checkedKeyword.Length)
                        }
                    ).ToArray();
            }

            compilation1.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_CheckedOperatorNeedsMatch)).Verify(expected);

            var m01 = compilation1.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<MethodSymbol>().Single();

            Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I2").FindImplementationForInterfaceMember(m01));
            Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I3").FindImplementationForInterfaceMember(m01));
            Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I4").FindImplementationForInterfaceMember(m01));
            Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I5").FindImplementationForInterfaceMember(m01));

            var i6 = compilation1.GlobalNamespace.GetTypeMember("I6");
            Assert.Same(i6.GetMembers().OfType<MethodSymbol>().Single(), i6.FindImplementationForInterfaceMember(m01));

            Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I7").FindImplementationForInterfaceMember(m01));

            var i8 = compilation1.GlobalNamespace.GetTypeMember("I8");
            Assert.Null(i8.FindImplementationForInterfaceMember(i8.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single()));

            var i9 = compilation1.GlobalNamespace.GetTypeMember("I9");
            Assert.Null(i9.FindImplementationForInterfaceMember(i9.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single()));

            var i10 = compilation1.GlobalNamespace.GetTypeMember("I10");
            Assert.Null(i10.FindImplementationForInterfaceMember(i10.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single()));

            var i12 = compilation1.GlobalNamespace.GetTypeMember("I12");
            Assert.Same(i12.GetMembers().OfType<MethodSymbol>().Single(), i12.FindImplementationForInterfaceMember(i12.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single()));

            var i13 = compilation1.GlobalNamespace.GetTypeMember("I13");
            Assert.Null(i13.FindImplementationForInterfaceMember(i13.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single()));

            Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I14").FindImplementationForInterfaceMember(m01));
        }

        [Theory]
        [CombinatorialData]
        public void ImplementVirtualStaticBinaryOperator_03([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<<", ">>", ">>>", "<", ">", "<=", ">=", "==", "!=")] string op, bool isChecked)
        {
            if (GetBinaryOperatorName(op, isChecked, out string checkedKeyword) is null)
            {
                return;
            }

            var source1 =
@"
public interface I1
{
    virtual  static I1 operator " + checkedKeyword + op + @"(I1 x, int y) => x;
}

interface I2 : I1
{}

interface I3 : I1
{
    I1 operator " + checkedKeyword + op + @"(I1 x, int y) => default;
}

interface I4 : I1
{
    static I1 operator " + checkedKeyword + op + @"(I1 x, int y) => default;
}

interface I5 : I1
{
    I1 I1.operator " + checkedKeyword + op + @"(I1 x, int y) => default;
}

interface I6 : I1
{
    static I1 I1.operator " + checkedKeyword + op + @"(I1 x, int y) => default;
}

interface I7 : I1
{
    virtual  static I1 operator " + checkedKeyword + op + @"(I1 x, int y) => x;
}

public interface I11<T> where T : I11<T>
{
    virtual  static T operator " + checkedKeyword + op + @"(T x, int y) => x;
}

interface I8<T> : I11<T> where T : I8<T>
{
    T operator " + checkedKeyword + op + @"(T x, int y) => default;
}

interface I9<T> : I11<T> where T : I9<T>
{
    static T operator " + checkedKeyword + op + @"(T x, int y) => default;
}

interface I10<T> : I11<T> where T : I10<T>
{
    virtual  static T operator " + checkedKeyword + op + @"(T x, int y) => x;
}

interface I12<T> : I11<T> where T : I12<T>
{
    static T I11<T>.operator " + checkedKeyword + op + @"(T x, int y) => default;
}

interface I13<T> : I11<T> where T : I13<T>
{
    virtual  static T I11<T>.operator " + checkedKeyword + op + @"(T x, int y) => x;
}

interface I14 : I1
{
    virtual  static I1 I1.operator " + checkedKeyword + op + @"(I1 x, int y) => x;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            bool isShift = op == "<<" || op == ">>" || op == ">>>";
            ErrorCode badSignatureError = isShift ? ErrorCode.ERR_BadShiftOperatorSignature : ErrorCode.ERR_BadBinaryOperatorSignature;
            ErrorCode badAbstractSignatureError = isShift ? ErrorCode.ERR_BadAbstractShiftOperatorSignature : ErrorCode.ERR_BadAbstractBinaryOperatorSignature;

            var expected = new[] {
                // (12,17): error CS0563: One of the parameters of a binary operator must be the containing type
                //     I1 operator |(I1 x, int y) => default;
                Diagnostic(badSignatureError, op).WithLocation(12, 17 + checkedKeyword.Length),
                // (17,24): error CS0563: One of the parameters of a binary operator must be the containing type
                //     static I1 operator |(I1 x, int y) => default;
                Diagnostic(badSignatureError, op).WithLocation(17, 24 + checkedKeyword.Length),
                // (22,20): error CS0539: 'I5.operator |(I1, int)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     I1 I1.operator |(I1 x, int y) => default;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, op).WithArguments("I5.operator " + checkedKeyword + op + "(I1, int)").WithLocation(22, 20 + checkedKeyword.Length),
                // (42,16): error CS0563: One of the parameters of a binary operator must be the containing type
                //     T operator |(T x, int y) => default;
                Diagnostic(badSignatureError, op).WithLocation(42, 16 + checkedKeyword.Length),
                // (47,23): error CS0563: One of the parameters of a binary operator must be the containing type
                //     static T operator |(T x, int y) => default;
                Diagnostic(badSignatureError, op).WithLocation(47, 23 + checkedKeyword.Length),
                // (62,39): error CS0106: The modifier 'virtual' is not valid for this item
                //     virtual  static T I11<T>.operator |(T x, int y);
                Diagnostic(ErrorCode.ERR_BadMemberFlag, op).WithArguments("virtual").WithLocation(62, 39 + checkedKeyword.Length),
                // (67,36): error CS0106: The modifier 'virtual' is not valid for this item
                //     virtual  static I1 I1.operator |(I1 x, int y);
                Diagnostic(ErrorCode.ERR_BadMemberFlag, op).WithArguments("virtual").WithLocation(67, 36 + checkedKeyword.Length)
                };

            if (op is "==" or "!=")
            {
                expected = expected.Concat(
                    new[] {
                        // (4,33): error CS9046: One of the parameters of an equality, or inequality operator declared in interface 'I1' must be a type parameter on 'I1' constrained to 'I1'
                        //     virtual  static I1 operator ==(I1 x, int y);
                        Diagnostic(ErrorCode.ERR_BadAbstractEqualityOperatorSignature, op).WithArguments("I1").WithLocation(4, 33),
                        // (12,17): error CS0567: Conversion, equality, or inequality operators declared in interfaces must be abstract or virtual
                        //     I1 operator ==(I1 x, int y) => default;
                        Diagnostic(ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators, op).WithLocation(12, 17 + checkedKeyword.Length),
                        // (17,24): error CS0567: Conversion, equality, or inequality operators declared in interfaces must be abstract or virtual
                        //     static I1 operator ==(I1 x, int y) => default;
                        Diagnostic(ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators, op).WithLocation(17, 24 + checkedKeyword.Length),
                        // (22,20): error CS8930: Explicit implementation of a user-defined operator 'I5.operator ==(I1, int)' must be declared static
                        //     I1 I1.operator ==(I1 x, int y) => default;
                        Diagnostic(ErrorCode.ERR_ExplicitImplementationOfOperatorsMustBeStatic, op).WithArguments("I5.operator " + op + "(I1, int)").WithLocation(22, 20),
                        // (32,33): error CS9046: One of the parameters of an equality, or inequality operator declared in interface 'I7' must be a type parameter on 'I7' constrained to 'I7'
                        //     virtual  static I1 operator ==(I1 x, int y);
                        Diagnostic(ErrorCode.ERR_BadAbstractEqualityOperatorSignature, op).WithArguments("I7").WithLocation(32, 33),
                        // (42,16): error CS0567: Conversion, equality, or inequality operators declared in interfaces must be abstract or virtual
                        //     T operator ==(T x, int y) => default;
                        Diagnostic(ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators, op).WithLocation(42, 16 + checkedKeyword.Length),
                        // (47,23): error CS0567: Conversion, equality, or inequality operators declared in interfaces must be abstract or virtual
                        //     static T operator ==(T x, int y) => default;
                        Diagnostic(ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators, op).WithLocation(47, 23 + checkedKeyword.Length)
                        }
                    ).ToArray();
            }
            else
            {
                expected = expected.Concat(
                    new[] {
                        // (12,17): error CS0558: User-defined operator 'I3.operator |(I1, int)' must be declared static and public
                        //     I1 operator |(I1 x, int y) => default;
                        Diagnostic(ErrorCode.ERR_OperatorsMustBeStaticAndPublic, op).WithArguments("I3.operator " + checkedKeyword + op + "(I1, int)").WithLocation(12, 17 + checkedKeyword.Length),
                        // (22,20): error CS8930: Explicit implementation of a user-defined operator 'I5.operator |(I1, int)' must be declared static
                        //     I1 I1.operator |(I1 x, int y) => default;
                        Diagnostic(ErrorCode.ERR_ExplicitImplementationOfOperatorsMustBeStatic, op).WithArguments("I5.operator " + checkedKeyword + op + "(I1, int)").WithLocation(22, 20 + checkedKeyword.Length),
                        // (32,33): error CS8924: One of the parameters of a binary operator must be the containing type, or its type parameter constrained to it.
                        //     virtual  static I1 operator |(I1 x, int y);
                        Diagnostic(badAbstractSignatureError, op).WithLocation(32, 33 + checkedKeyword.Length),
                        // (42,16): error CS0558: User-defined operator 'I8<T>.operator |(T, int)' must be declared static and public
                        //     T operator |(T x, int y) => default;
                        Diagnostic(ErrorCode.ERR_OperatorsMustBeStaticAndPublic, op).WithArguments("I8<T>.operator " + checkedKeyword + op + "(T, int)").WithLocation(42, 16 + checkedKeyword.Length)
                        }
                    ).ToArray();
            }

            compilation1.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_CheckedOperatorNeedsMatch)).Verify(expected);

            var m01 = compilation1.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<MethodSymbol>().Single();

            Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I2").FindImplementationForInterfaceMember(m01));
            Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I3").FindImplementationForInterfaceMember(m01));
            Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I4").FindImplementationForInterfaceMember(m01));
            Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I5").FindImplementationForInterfaceMember(m01));

            var i6 = compilation1.GlobalNamespace.GetTypeMember("I6");
            Assert.Same(i6.GetMembers().OfType<MethodSymbol>().Single(), i6.FindImplementationForInterfaceMember(m01));

            Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I7").FindImplementationForInterfaceMember(m01));

            foreach (var name in new[] { "I8", "I9", "I10" })
            {
                var iX = compilation1.GlobalNamespace.GetTypeMember(name);
                var iXM = iX.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();
                Assert.Same(iXM, iX.FindImplementationForInterfaceMember(iXM));
            }

            foreach (var name in new[] { "I12", "I13" })
            {
                var iX = compilation1.GlobalNamespace.GetTypeMember(name);
                var iXM = iX.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();
                Assert.Same(iX.GetMembers().OfType<MethodSymbol>().Single(), iX.FindImplementationForInterfaceMember(iXM));
            }

            var i14 = compilation1.GlobalNamespace.GetTypeMember("I14");
            Assert.Same(i14.GetMembers().OfType<MethodSymbol>().Single(), i14.FindImplementationForInterfaceMember(m01));
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticUnaryOperator_04([CombinatorialValues("+", "-", "!", "~", "++", "--", "true", "false")] string op, bool structure, bool isChecked, bool isVirtual)
        {
            if (GetUnaryOperatorName(op, isChecked, out string checkedKeyword) is null)
            {
                return;
            }

            var typeKeyword = structure ? "struct" : "class";
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static I1 operator " + checkedKeyword + op + @"(I1 x)" + body + @"
}

public interface I2<T> where T : I2<T>
{
    " + modifier + @" static T operator " + checkedKeyword + op + @"(T x)" + body + @"
}
";
            var source2 =
typeKeyword + @"
    Test1: I1
{
    static I1 I1.operator " + checkedKeyword + op + @"(I1 x) => default;
}
" + typeKeyword + @"
    Test2: I2<Test2>
{
    public static Test2 operator " + checkedKeyword + op + @"(Test2 x) => default;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.ToMetadataReference() });

            DiagnosticDescription[] expected2;

            if (isChecked)
            {
                expected2 = new[] {
                    // (4,15): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     static I1 I1.operator checked ++(I1 x) => default;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "I1.").WithArguments("static abstract members in interfaces", "11.0").WithLocation(4, 15),
                    // (4,27): error CS8936: Feature 'checked user-defined operators' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     static I1 I1.operator checked ++(I1 x) => default;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "checked").WithArguments("checked user-defined operators", "11.0").WithLocation(4, 27),
                    // (9,34): error CS8936: Feature 'checked user-defined operators' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     public static Test2 operator checked ++(Test2 x) => default;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "checked").WithArguments("checked user-defined operators", "11.0").WithLocation(9, 34),
                    // (9,42): error CS8706: 'Test2.operator checked ++(Test2)' cannot implement interface member 'I2<Test2>.operator checked ++(Test2)' in type 'Test2' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                    //     public static Test2 operator checked ++(Test2 x) => default;
                    Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, op).WithArguments("Test2.operator checked " + op + "(Test2)", "I2<Test2>.operator checked " + op + "(Test2)", "Test2", "static abstract members in interfaces", "10.0", "11.0").WithLocation(9, 42)
                    };
            }
            else
            {
                expected2 = new[] {
                    // (4,15): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     static I1 I1.operator true(I1 x) => default;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "I1.").WithArguments("static abstract members in interfaces", "11.0").WithLocation(4, 15),
                    // (9,34): error CS8706: 'Test2.operator true(Test2)' cannot implement interface member 'I2<Test2>.operator true(Test2)' in type 'Test2' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                    //     public static Test2 operator true(Test2 x) => default;
                    Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, op).WithArguments("Test2.operator " + op + "(Test2)", "I2<Test2>.operator " + op + "(Test2)", "Test2", "static abstract members in interfaces", "10.0", "11.0").WithLocation(9, 34)
                    };
            }

            compilation2.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_CheckedOperatorNeedsMatch or (int)ErrorCode.ERR_OpTFRetType)).Verify(expected2);

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            DiagnosticDescription[] expected3;

            if (isChecked)
            {
                expected3 = new[] {
                    // (4,15): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     static I1 I1.operator checked ++(I1 x) => default;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "I1.").WithArguments("static abstract members in interfaces", "11.0").WithLocation(4, 15),
                    // (4,27): error CS8936: Feature 'checked user-defined operators' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     static I1 I1.operator checked ++(I1 x) => default;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "checked").WithArguments("checked user-defined operators", "11.0").WithLocation(4, 27),
                    // (9,34): error CS8936: Feature 'checked user-defined operators' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     public static Test2 operator checked ++(Test2 x) => default;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "checked").WithArguments("checked user-defined operators", "11.0").WithLocation(9, 34),
                    // (14,33): error CS8936: Feature 'checked user-defined operators' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     virtual  static I1 operator checked ++(I1 x) => throw null;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "checked").WithArguments("checked user-defined operators", "11.0").WithLocation(14, 33),
                    // (14,41): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                    //     virtual  static I1 operator checked ++(I1 x) => throw null;
                    Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, op).WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(14, 41),
                    // (19,32): error CS8936: Feature 'checked user-defined operators' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     virtual  static T operator checked ++(T x) => throw null;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "checked").WithArguments("checked user-defined operators", "11.0").WithLocation(19, 32),
                    // (19,40): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                    //     virtual  static T operator checked ++(T x) => throw null;
                    Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, op).WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(19, 40)
                    };
            }
            else
            {
                expected3 = new[] {
                    // (4,15): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     static I1 I1.operator true(I1 x) => default;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "I1.").WithArguments("static abstract members in interfaces", "11.0").WithLocation(4, 15),
                    // (14,33): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                    //     virtual  static I1 operator true(I1 x) => throw null;
                    Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, op).WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(14, 33),
                    // (19,32): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                    //     virtual  static T operator true(T x) => throw null;
                    Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, op).WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(19, 32)
                    };
            }

            compilation3.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_CheckedOperatorNeedsMatch or (int)ErrorCode.ERR_OpTFRetType)).Verify(expected3);
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticBinaryOperator_04([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<<", ">>", ">>>", "<", ">", "<=", ">=", "==", "!=")] string op, bool structure, bool isChecked, bool isVirtual)
        {
            if (GetBinaryOperatorName(op, isChecked, out string checkedKeyword) is null)
            {
                return;
            }

            var typeKeyword = structure ? "struct" : "class";
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static I1 operator " + checkedKeyword + op + @"(I1 x, int y)" + body + @"
}

public interface I2<T> where T : I2<T>
{
    " + modifier + @" static T operator " + checkedKeyword + op + @"(T x, int y)" + body + @"
}
";
            var source2 =
typeKeyword + @"
    Test1: I1
{
    static I1 I1.operator " + checkedKeyword + op + @"(I1 x, int y) => default;
}
" + typeKeyword + @"
    Test2: I2<Test2>
{
    public static Test2 operator " + checkedKeyword + op + @"(Test2 x, int y) => default;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.ToMetadataReference() });

            if (!isChecked)
            {
                if (op != ">>>")
                {
                    compilation2.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.WRN_EqualityOpWithoutEquals or (int)ErrorCode.WRN_EqualityOpWithoutGetHashCode)).Verify(
                        // (4,15): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                        //     static I1 I1.operator >>(I1 x, int y) => default;
                        Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "I1.").WithArguments("static abstract members in interfaces", "11.0").WithLocation(4, 15),
                        // (9,34): error CS8706: 'Test2.operator >>(Test2, int)' cannot implement interface member 'I2<Test2>.operator >>(Test2, int)' in type 'Test2' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                        //     public static Test2 operator >>(Test2 x, int y) => default;
                        Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, op).WithArguments("Test2.operator " + op + "(Test2, int)", "I2<Test2>.operator " + op + "(Test2, int)", "Test2", "static abstract members in interfaces", "10.0", "11.0").WithLocation(9, 34)
                        );
                }
                else
                {
                    compilation2.VerifyDiagnostics(
                        // (4,15): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                        //     static I1 I1.operator >>>(I1 x, int y) => default;
                        Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "I1.").WithArguments("static abstract members in interfaces", "11.0").WithLocation(4, 15),
                        // (4,27): error CS8936: Feature 'unsigned right shift' is not available in C# 10.0. Please use language version 11.0 or greater.
                        //     static I1 I1.operator >>>(I1 x, int y) => default;
                        Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, ">>>").WithArguments("unsigned right shift", "11.0").WithLocation(4, 27),
                        // (9,34): error CS8936: Feature 'unsigned right shift' is not available in C# 10.0. Please use language version 11.0 or greater.
                        //     public static Test2 operator >>>(Test2 x, int y) => default;
                        Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, ">>>").WithArguments("unsigned right shift", "11.0").WithLocation(9, 34),
                        // (9,34): error CS8706: 'Test2.operator >>>(Test2, int)' cannot implement interface member 'I2<Test2>.operator >>>(Test2, int)' in type 'Test2' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                        //     public static Test2 operator >>>(Test2 x, int y) => default;
                        Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, ">>>").WithArguments("Test2.operator >>>(Test2, int)", "I2<Test2>.operator >>>(Test2, int)", "Test2", "static abstract members in interfaces", "10.0", "11.0").WithLocation(9, 34)
                        );
                }
            }
            else
            {
                compilation2.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_CheckedOperatorNeedsMatch or (int)ErrorCode.WRN_EqualityOpWithoutEquals or (int)ErrorCode.WRN_EqualityOpWithoutGetHashCode)).Verify(
                    // (4,15): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     static I1 I1.operator checked +(I1 x, int y) => default;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "I1.").WithArguments("static abstract members in interfaces", "11.0").WithLocation(4, 15),
                    // (4,27): error CS8936: Feature 'checked user-defined operators' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     static I1 I1.operator checked +(I1 x, int y) => default;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "checked").WithArguments("checked user-defined operators", "11.0").WithLocation(4, 27),
                    // (9,34): error CS8936: Feature 'checked user-defined operators' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     public static Test2 operator checked +(Test2 x, int y) => default;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "checked").WithArguments("checked user-defined operators", "11.0").WithLocation(9, 34),
                    // (9,42): error CS8706: 'Test2.operator checked +(Test2, int)' cannot implement interface member 'I2<Test2>.operator checked +(Test2, int)' in type 'Test2' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                    //     public static Test2 operator checked +(Test2 x, int y) => default;
                    Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, op).WithArguments("Test2.operator checked " + op + "(Test2, int)", "I2<Test2>.operator checked " + op + "(Test2, int)", "Test2", "static abstract members in interfaces", "10.0", "11.0").WithLocation(9, 42)
                    );
            }

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            if (!isChecked)
            {
                if (op != ">>>")
                {
                    compilation3.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.WRN_EqualityOpWithoutEquals or
                                                                            (int)ErrorCode.WRN_EqualityOpWithoutGetHashCode or (int)ErrorCode.ERR_BadAbstractEqualityOperatorSignature)).Verify(
                        // (4,15): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                        //     static I1 I1.operator +(I1 x, int y) => default;
                        Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "I1.").WithArguments("static abstract members in interfaces", "11.0").WithLocation(4, 15),
                        // (14,33): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                        //     virtual  static I1 operator +(I1 x, int y) => throw null;
                        Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, op).WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(14, 33),
                        // (19,32): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                        //     virtual  static T operator +(T x, int y) => throw null;
                        Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, op).WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(19, 32)
                        );
                }
                else
                {
                    compilation3.VerifyDiagnostics(
                        // (4,15): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                        //     static I1 I1.operator >>>(I1 x, int y) => default;
                        Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "I1.").WithArguments("static abstract members in interfaces", "11.0").WithLocation(4, 15),
                        // (4,27): error CS8936: Feature 'unsigned right shift' is not available in C# 10.0. Please use language version 11.0 or greater.
                        //     static I1 I1.operator >>>(I1 x, int y) => default;
                        Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, ">>>").WithArguments("unsigned right shift", "11.0").WithLocation(4, 27),
                        // (9,34): error CS8936: Feature 'unsigned right shift' is not available in C# 10.0. Please use language version 11.0 or greater.
                        //     public static Test2 operator >>>(Test2 x, int y) => default;
                        Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, ">>>").WithArguments("unsigned right shift", "11.0").WithLocation(9, 34),
                        // (14,33): error CS8936: Feature 'unsigned right shift' is not available in C# 10.0. Please use language version 11.0 or greater.
                        //     virtual  static I1 operator >>>(I1 x, int y) => throw null;
                        Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, ">>>").WithArguments("unsigned right shift", "11.0").WithLocation(14, 33),
                        // (14,33): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                        //     virtual  static I1 operator >>>(I1 x, int y) => throw null;
                        Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, ">>>").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(14, 33),
                        // (19,32): error CS8936: Feature 'unsigned right shift' is not available in C# 10.0. Please use language version 11.0 or greater.
                        //     virtual  static T operator >>>(T x, int y) => throw null;
                        Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, ">>>").WithArguments("unsigned right shift", "11.0").WithLocation(19, 32),
                        // (19,32): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                        //     virtual  static T operator >>>(T x, int y) => throw null;
                        Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, ">>>").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(19, 32)
                        );
                }
            }
            else
            {
                compilation3.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_CheckedOperatorNeedsMatch or (int)ErrorCode.WRN_EqualityOpWithoutEquals or (int)ErrorCode.WRN_EqualityOpWithoutGetHashCode)).Verify(
                    // (4,15): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     static I1 I1.operator checked +(I1 x, int y) => default;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "I1.").WithArguments("static abstract members in interfaces", "11.0").WithLocation(4, 15),
                    // (14,33): error CS8936: Feature 'checked user-defined operators' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     virtual  static I1 operator checked +(I1 x, int y) => throw null;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "checked").WithArguments("checked user-defined operators", "11.0").WithLocation(14, 33),
                    // (14,41): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                    //     virtual  static I1 operator checked +(I1 x, int y) => throw null;
                    Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, op).WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(14, 33 + checkedKeyword.Length),
                    // (4,27): error CS8936: Feature 'checked user-defined operators' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     static I1 I1.operator checked +(I1 x, int y) => default;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "checked").WithArguments("checked user-defined operators", "11.0").WithLocation(4, 27),
                    // (19,32): error CS8936: Feature 'checked user-defined operators' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     virtual  static T operator checked +(T x, int y) => throw null;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "checked").WithArguments("checked user-defined operators", "11.0").WithLocation(19, 32),
                    // (19,40): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                    //     virtual  static T operator checked +(T x, int y) => throw null;
                    Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, op).WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(19, 32 + checkedKeyword.Length),
                    // (9,34): error CS8936: Feature 'checked user-defined operators' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     public static Test2 operator checked +(Test2 x, int y) => default;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "checked").WithArguments("checked user-defined operators", "11.0").WithLocation(9, 34)
                    );
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticUnaryOperator_05([CombinatorialValues("+", "-", "!", "~", "++", "--", "true", "false")] string op, bool structure, bool isChecked, bool isVirtual)
        {
            if (GetUnaryOperatorName(op, isChecked, out string checkedKeyword) is null)
            {
                return;
            }

            var typeKeyword = structure ? "struct" : "class";
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1<T> where T : I1<T> 
{
    " + modifier + @" static T operator " + checkedKeyword + op + @"(T x)" + body + @"
}
";
            var source2 =
typeKeyword + @"
    Test1: I1<Test1>
{
    public static Test1 operator " + checkedKeyword + op + @"(Test1 x) => default;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_CheckedOperatorNeedsMatch or (int)ErrorCode.ERR_OpTFRetType)).Verify(
                // (4,34): error CS8929: 'Test1.operator +(Test1)' cannot implement interface member 'I1<Test1>.operator +(Test1)' in type 'Test1' because the target runtime doesn't support static abstract members in interfaces.
                //     public static Test1 operator +(Test1 x) => default;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfacesForMember, op).WithArguments("Test1.operator " + checkedKeyword + op + "(Test1)", "I1<Test1>.operator " + checkedKeyword + op + "(Test1)", "Test1").WithLocation(4, 34 + checkedKeyword.Length)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation3.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_CheckedOperatorNeedsMatch or (int)ErrorCode.ERR_OpTFRetType)).Verify(
                // (9,32): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static T operator +(T x);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, op).WithLocation(9, 32 + checkedKeyword.Length)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticBinaryOperator_05([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<<", ">>", ">>>", "<", ">", "<=", ">=", "==", "!=")] string op, bool structure, bool isChecked, bool isVirtual)
        {
            if (GetBinaryOperatorName(op, isChecked, out string checkedKeyword) is null)
            {
                return;
            }

            var typeKeyword = structure ? "struct" : "class";
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1<T> where T : I1<T> 
{
    " + modifier + @" static T operator " + checkedKeyword + op + @"(T x, int y)" + body + @"
}
";
            var source2 =
typeKeyword + @"
    Test1: I1<Test1>
{
    public static Test1 operator " + checkedKeyword + op + @"(Test1 x, int y) => default;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_CheckedOperatorNeedsMatch or (int)ErrorCode.WRN_EqualityOpWithoutEquals or (int)ErrorCode.WRN_EqualityOpWithoutGetHashCode)).Verify(
                // (4,34): error CS8929: 'Test1.operator >>(Test1, int)' cannot implement interface member 'I1<Test1>.operator >>(Test1, int)' in type 'Test1' because the target runtime doesn't support static abstract members in interfaces.
                //     public static Test1 operator >>(Test1 x, int y) => default;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfacesForMember, op).WithArguments("Test1.operator " + checkedKeyword + op + "(Test1, int)", "I1<Test1>.operator " + checkedKeyword + op + "(Test1, int)", "Test1").WithLocation(4, 34 + checkedKeyword.Length)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation3.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_CheckedOperatorNeedsMatch or (int)ErrorCode.WRN_EqualityOpWithoutEquals or (int)ErrorCode.WRN_EqualityOpWithoutGetHashCode)).Verify(
                // (9,32): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static T operator >>(T x, int y);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, op).WithLocation(9, 32 + checkedKeyword.Length)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticUnaryOperator_06([CombinatorialValues("+", "-", "!", "~", "++", "--", "true", "false")] string op, bool structure, bool isChecked, bool isVirtual)
        {
            if (GetUnaryOperatorName(op, isChecked, out string checkedKeyword) is null)
            {
                return;
            }

            var typeKeyword = structure ? "struct" : "class";
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static I1 operator " + checkedKeyword + op + @"(I1 x)" + body + @"
}
";
            var source2 =
typeKeyword + @"
    Test1: I1
{
    static I1 I1.operator " + checkedKeyword + op + @"(I1 x) => default;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (4,27): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     static I1 I1.operator +(I1 x) => default;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, op).WithLocation(4, 27 + checkedKeyword.Length)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation3.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_OpTFRetType or (int)ErrorCode.ERR_CheckedOperatorNeedsMatch)).Verify(
                // (4,27): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     static I1 I1.operator +(I1 x) => default;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, op).WithLocation(4, 27 + checkedKeyword.Length),
                // (9,33): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static I1 operator +(I1 x);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, op).WithLocation(9, 33 + checkedKeyword.Length)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticBinaryOperator_06([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<<", ">>", ">>>", "<", ">", "<=", ">=", "==", "!=")] string op, bool structure, bool isChecked, bool isVirtual)
        {
            if (GetBinaryOperatorName(op, isChecked, out string checkedKeyword) is null)
            {
                return;
            }

            var typeKeyword = structure ? "struct" : "class";
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static I1 operator " + checkedKeyword + op + @"(I1 x, int y)" + body + @"
}
";
            var source2 =
typeKeyword + @"
    Test1: I1
{
    static I1 I1.operator " + checkedKeyword + op + @"(I1 x, int y) => default;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (4,27): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     static I1 I1.operator +(I1 x, int y) => default;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, op).WithLocation(4, 27 + checkedKeyword.Length)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation3.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_CheckedOperatorNeedsMatch or (int)ErrorCode.ERR_BadAbstractEqualityOperatorSignature)).Verify(
                // (4,27): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     static I1 I1.operator +(I1 x, int y) => default;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, op).WithLocation(4, 27 + checkedKeyword.Length),
                // (9,33): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static I1 operator +(I1 x, int y);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, op).WithLocation(9, 33 + checkedKeyword.Length)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticUnaryOperator_07([CombinatorialValues("+", "-", "!", "~", "++", "--")] string op, bool structure, bool isChecked, bool isVirtual)
        {
            // Basic implicit implementation scenario, MethodImpl is emitted

            string opName = GetUnaryOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var typeKeyword = structure ? "struct" : "class";
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public partial interface I1<T> where T : I1<T>
{
    " + modifier + @" static T operator " + checkedKeyword + op + @"(T x)" + body + @"
}

partial " + typeKeyword + @"
    C : I1<C>
{
    public static C operator " + checkedKeyword + op + @"(C x) => default;
}
";
            if (isChecked)
            {
                source1 +=
@"
public partial interface I1<T> where T : I1<T>
{
    " + modifier + @" static T operator " + op + @"(T x)" + body + @"
}

partial " + typeKeyword + @"
    C : I1<C>
{
    public static C operator " + op + @"(C x) => default;
}
";
            }

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped,
                             emitOptions: EmitOptions.Default.WithEmitMetadataOnly(true).WithIncludePrivateMembers(false)).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var c = module.GlobalNamespace.GetTypeMember("C");
                var i1 = c.Interfaces().Single();
                var m01 = i1.GetMembers(opName).OfType<MethodSymbol>().Single();

                Assert.Equal(isChecked ? 2 : 1, c.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());

                var cM01 = (MethodSymbol)c.FindImplementationForInterfaceMember(m01);

                Assert.True(cM01.IsStatic);
                Assert.False(cM01.IsAbstract);
                Assert.False(cM01.IsVirtual);
                Assert.False(cM01.IsMetadataVirtual());
                Assert.False(cM01.IsMetadataFinal);
                Assert.False(cM01.IsMetadataNewSlot());
                Assert.Equal(MethodKind.UserDefinedOperator, cM01.MethodKind);
                Assert.False(cM01.HasRuntimeSpecialName);
                Assert.True(cM01.HasSpecialName);

                Assert.Equal("C C." + opName + "(C x)", cM01.ToTestDisplayString());

                if (module is PEModuleSymbol)
                {
                    Assert.Equal(m01, cM01.ExplicitInterfaceImplementations.Single());
                }
                else
                {
                    Assert.Empty(cM01.ExplicitInterfaceImplementations);
                }
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticUnaryTrueFalseOperator_07([CombinatorialValues("true", "false")] string op, bool structure, bool isVirtual)
        {
            // Basic implicit implementation scenario, MethodImpl is emitted

            var typeKeyword = structure ? "struct" : "class";
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public partial interface I1<T> where T : I1<T>
{
    " + modifier + @" static bool operator " + op + @"(T x)" + body + @"
}

partial " + typeKeyword + @"
    C : I1<C>
{
    public static bool operator " + op + @"(C x) => default;
}
";
            string matchingOp = op == "true" ? "false" : "true";

            source1 +=
@"
public partial interface I1<T> where T : I1<T>
{
    " + modifier + @" static bool operator " + matchingOp + @"(T x)" + body + @"
}

partial " + typeKeyword + @"
    C
{
    public static bool operator " + matchingOp + @"(C x) => default;
}
";

            var opName = UnaryOperatorName(op);
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped,
                             emitOptions: EmitOptions.Default.WithEmitMetadataOnly(true).WithIncludePrivateMembers(false)).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var c = module.GlobalNamespace.GetTypeMember("C");
                var i1 = c.Interfaces().Single();
                var m01 = i1.GetMembers(opName).OfType<MethodSymbol>().Single();

                Assert.Equal(2, c.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());

                var cM01 = (MethodSymbol)c.FindImplementationForInterfaceMember(m01);

                Assert.True(cM01.IsStatic);
                Assert.False(cM01.IsAbstract);
                Assert.False(cM01.IsVirtual);
                Assert.False(cM01.IsMetadataVirtual());
                Assert.False(cM01.IsMetadataFinal);
                Assert.False(cM01.IsMetadataNewSlot());
                Assert.Equal(MethodKind.UserDefinedOperator, cM01.MethodKind);
                Assert.False(cM01.HasRuntimeSpecialName);
                Assert.True(cM01.HasSpecialName);

                Assert.Equal("System.Boolean C." + opName + "(C x)", cM01.ToTestDisplayString());

                if (module is PEModuleSymbol)
                {
                    Assert.Equal(m01, cM01.ExplicitInterfaceImplementations.Single());
                }
                else
                {
                    Assert.Empty(cM01.ExplicitInterfaceImplementations);
                }
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticBinaryOperator_07([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<<", ">>", ">>>", "<", ">", "<=", ">=", "==", "!=")] string op, bool structure, bool isChecked, bool isVirtual)
        {
            // Basic implicit implementation scenario, MethodImpl is emitted

            string opName = GetBinaryOperatorName(op, isChecked, out string checkedKeyword);
            var (modifier, body) = GetModifierAndBody(isVirtual);

            if (opName is null)
            {
                return;
            }

            var typeKeyword = structure ? "struct" : "class";

            var source1 =
@"
public partial interface I1<T> where T : I1<T>
{
    " + modifier + @" static T operator " + checkedKeyword + op + @"(T x, int y)" + body + @"
}

#pragma warning disable CS0660, CS0661 // 'C1' defines operator == or operator != but does not override Object.Equals(object o)/Object.GetHashCode()

partial " + typeKeyword + @"
    C : I1<C>
{
    public static C operator " + checkedKeyword + op + @"(C x, int y) => default;
}
";
            string matchingOp = isChecked ? op : MatchingBinaryOperator(op);

            if (matchingOp is object)
            {
                source1 +=
@"
public partial interface I1<T> where T : I1<T>
{
    " + modifier + @" static T operator " + matchingOp + @"(T x, int y)" + body + @"
}

partial " + typeKeyword + @"
    C
{
    public static C operator " + matchingOp + @"(C x, int y) => default;
}
";
            }

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped,
                             emitOptions: EmitOptions.Default.WithEmitMetadataOnly(true).WithIncludePrivateMembers(false)).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var c = module.GlobalNamespace.GetTypeMember("C");
                var i1 = c.Interfaces().Single();
                var m01 = i1.GetMembers(opName).OfType<MethodSymbol>().Single();

                Assert.Equal(matchingOp is null ? 1 : 2, c.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());

                var cM01 = (MethodSymbol)c.FindImplementationForInterfaceMember(m01);

                Assert.True(cM01.IsStatic);
                Assert.False(cM01.IsAbstract);
                Assert.False(cM01.IsVirtual);
                Assert.False(cM01.IsMetadataVirtual());
                Assert.False(cM01.IsMetadataFinal);
                Assert.False(cM01.IsMetadataNewSlot());
                Assert.Equal(MethodKind.UserDefinedOperator, cM01.MethodKind);
                Assert.False(cM01.HasRuntimeSpecialName);
                Assert.True(cM01.HasSpecialName);

                Assert.Equal("C C." + opName + "(C x, System.Int32 y)", cM01.ToTestDisplayString());

                if (module is PEModuleSymbol)
                {
                    Assert.Equal(m01, cM01.ExplicitInterfaceImplementations.Single());
                }
                else
                {
                    Assert.Empty(cM01.ExplicitInterfaceImplementations);
                }
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticUnaryOperator_08([CombinatorialValues("+", "-", "!", "~", "++", "--")] string op, bool structure, bool isChecked, bool isVirtual)
        {
            // Basic explicit implementation scenario

            string opName = GetUnaryOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var typeKeyword = structure ? "struct" : "class";
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public partial interface I1
{
    " + modifier + @" static I1 operator " + checkedKeyword + op + @"(I1 x)" + body + @"
}

partial " + typeKeyword + @"
    C : I1
{
    static I1 I1.operator " + checkedKeyword + op + @"(I1 x) => default;
}
";
            if (isChecked)
            {
                source1 +=
@"
public partial interface I1
{
    " + modifier + @" static I1 operator " + op + @"(I1 x)" + body + @"
}

partial " + typeKeyword + @"
    C : I1
{
    static I1 I1.operator " + op + @"(I1 x) => default;
}
";
            }

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var tree = compilation1.SyntaxTrees.Single();
            var model = compilation1.GetSemanticModel(tree);
            var node = tree.GetRoot().DescendantNodes().OfType<LiteralExpressionSyntax>().Where(l => l.ToString() == "default").First();

            Assert.Equal("default", node.ToString());
            Assert.Equal("I1", model.GetTypeInfo(node).ConvertedType.ToTestDisplayString());

            var declaredSymbol = model.GetDeclaredSymbol(node.FirstAncestorOrSelf<OperatorDeclarationSyntax>());
            Assert.Equal("I1 C.I1." + opName + "(I1 x)", declaredSymbol.ToTestDisplayString());
            Assert.DoesNotContain(opName, declaredSymbol.ContainingType.MemberNames);

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped,
                             emitOptions: EmitOptions.Default.WithEmitMetadataOnly(true).WithIncludePrivateMembers(false)).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var m01 = module.GlobalNamespace.GetTypeMember("I1").GetMembers(opName).OfType<MethodSymbol>().Single();
                var c = module.GlobalNamespace.GetTypeMember("C");

                Assert.Equal(isChecked ? 2 : 1, c.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());

                var cM01 = (MethodSymbol)c.FindImplementationForInterfaceMember(m01);

                Assert.True(cM01.IsStatic);
                Assert.False(cM01.IsAbstract);
                Assert.False(cM01.IsVirtual);
                Assert.False(cM01.IsMetadataVirtual());
                Assert.False(cM01.IsMetadataFinal);
                Assert.False(cM01.IsMetadataNewSlot());
                Assert.Equal(MethodKind.ExplicitInterfaceImplementation, cM01.MethodKind);
                Assert.False(cM01.HasRuntimeSpecialName);
                Assert.False(cM01.HasSpecialName);

                Assert.Equal("I1 C.I1." + opName + "(I1 x)", cM01.ToTestDisplayString());
                Assert.Same(m01, cM01.ExplicitInterfaceImplementations.Single());
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticUnaryTrueFalseOperator_08([CombinatorialValues("true", "false")] string op, bool structure, bool isVirtual)
        {
            // Basic explicit implementation scenario

            var typeKeyword = structure ? "struct" : "class";
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public partial interface I1
{
    " + modifier + @" static bool operator " + op + @"(I1 x)" + body + @"
}

partial " + typeKeyword + @"
    C : I1
{
    static bool I1.operator " + op + @"(I1 x) => default;
}
";
            string matchingOp = op == "true" ? "false" : "true";

            source1 +=
@"
public partial interface I1
{
    " + modifier + @" static bool operator " + matchingOp + @"(I1 x)" + body + @"
}

partial " + typeKeyword + @"
    C
{
    static bool I1.operator " + matchingOp + @"(I1 x) => default;
}
";

            var opName = UnaryOperatorName(op);
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var tree = compilation1.SyntaxTrees.Single();
            var model = compilation1.GetSemanticModel(tree);
            var node = tree.GetRoot().DescendantNodes().OfType<LiteralExpressionSyntax>().Where(l => l.ToString() == "default").First();

            Assert.Equal("default", node.ToString());
            Assert.Equal("System.Boolean", model.GetTypeInfo(node).ConvertedType.ToTestDisplayString());

            var declaredSymbol = model.GetDeclaredSymbol(node.FirstAncestorOrSelf<OperatorDeclarationSyntax>());
            Assert.Equal("System.Boolean C.I1." + opName + "(I1 x)", declaredSymbol.ToTestDisplayString());
            Assert.DoesNotContain(opName, declaredSymbol.ContainingType.MemberNames);

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped,
                             emitOptions: EmitOptions.Default.WithEmitMetadataOnly(true).WithIncludePrivateMembers(false)).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var m01 = module.GlobalNamespace.GetTypeMember("I1").GetMembers(opName).OfType<MethodSymbol>().Single();
                var c = module.GlobalNamespace.GetTypeMember("C");

                Assert.Equal(2, c.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());

                var cM01 = (MethodSymbol)c.FindImplementationForInterfaceMember(m01);

                Assert.True(cM01.IsStatic);
                Assert.False(cM01.IsAbstract);
                Assert.False(cM01.IsVirtual);
                Assert.False(cM01.IsMetadataVirtual());
                Assert.False(cM01.IsMetadataFinal);
                Assert.False(cM01.IsMetadataNewSlot());
                Assert.Equal(MethodKind.ExplicitInterfaceImplementation, cM01.MethodKind);
                Assert.False(cM01.HasRuntimeSpecialName);
                Assert.False(cM01.HasSpecialName);

                Assert.Equal("System.Boolean C.I1." + opName + "(I1 x)", cM01.ToTestDisplayString());
                Assert.Same(m01, cM01.ExplicitInterfaceImplementations.Single());
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticBinaryOperator_08([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<<", ">>", ">>>", "<", ">", "<=", ">=")] string op, bool structure, bool isChecked, bool isVirtual)
        {
            // Basic explicit implementation scenario

            string opName = GetBinaryOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var typeKeyword = structure ? "struct" : "class";
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public partial interface I1
{
    " + modifier + @" static I1 operator " + checkedKeyword + op + @"(I1 x, int y)" + body + @"
}

partial " + typeKeyword + @"
    C : I1
{
    static I1 I1.operator " + checkedKeyword + op + @"(I1 x, int y) => default;
}
";
            string matchingOp = isChecked ? op : MatchingBinaryOperator(op);

            if (matchingOp is object)
            {
                source1 +=
@"
public partial interface I1
{
    " + modifier + @" static I1 operator " + matchingOp + @"(I1 x, int y)" + body + @"
}

partial " + typeKeyword + @"
    C
{
    static I1 I1.operator " + matchingOp + @"(I1 x, int y) => default;
}
";
            }

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var tree = compilation1.SyntaxTrees.Single();
            var model = compilation1.GetSemanticModel(tree);
            var node = tree.GetRoot().DescendantNodes().OfType<LiteralExpressionSyntax>().Where(l => l.ToString() == "default").First();

            Assert.Equal("default", node.ToString());
            Assert.Equal("I1", model.GetTypeInfo(node).ConvertedType.ToTestDisplayString());

            var declaredSymbol = model.GetDeclaredSymbol(node.FirstAncestorOrSelf<OperatorDeclarationSyntax>());
            Assert.Equal("I1 C.I1." + opName + "(I1 x, System.Int32 y)", declaredSymbol.ToTestDisplayString());
            Assert.DoesNotContain(opName, declaredSymbol.ContainingType.MemberNames);

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped,
                             emitOptions: EmitOptions.Default.WithEmitMetadataOnly(true).WithIncludePrivateMembers(false)).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var m01 = module.GlobalNamespace.GetTypeMember("I1").GetMembers(opName).OfType<MethodSymbol>().Single();
                var c = module.GlobalNamespace.GetTypeMember("C");

                Assert.Equal(matchingOp is null ? 1 : 2, c.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());

                var cM01 = (MethodSymbol)c.FindImplementationForInterfaceMember(m01);

                Assert.True(cM01.IsStatic);
                Assert.False(cM01.IsAbstract);
                Assert.False(cM01.IsVirtual);
                Assert.False(cM01.IsMetadataVirtual());
                Assert.False(cM01.IsMetadataFinal);
                Assert.False(cM01.IsMetadataNewSlot());
                Assert.Equal(MethodKind.ExplicitInterfaceImplementation, cM01.MethodKind);
                Assert.False(cM01.HasRuntimeSpecialName);
                Assert.False(cM01.HasSpecialName);

                Assert.Equal("I1 C.I1." + opName + "(I1 x, System.Int32 y)", cM01.ToTestDisplayString());
                Assert.Same(m01, cM01.ExplicitInterfaceImplementations.Single());
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticEqualityOperator_08([CombinatorialValues("==", "!=")] string op, bool structure, bool isVirtual)
        {
            // Basic explicit implementation scenario

            string opName = GetBinaryOperatorName(op, isChecked: false, checkedKeyword: out _);

            if (opName is null)
            {
                return;
            }

            var typeKeyword = structure ? "struct" : "class";
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public partial interface I1<T> where T : I1<T>
{
    " + modifier + @" static T operator " + op + @"(T x, int y)" + body + @"
}

partial " + typeKeyword + @"
    C : I1<C>
{
    static C I1<C>.operator " + op + @"(C x, int y) => default;
}
";
            string matchingOp = MatchingBinaryOperator(op);

            source1 +=
@"
public partial interface I1<T>
{
    " + modifier + @" static T operator " + matchingOp + @"(T x, int y)" + body + @"
}

partial " + typeKeyword + @"
    C
{
    static C I1<C>.operator " + matchingOp + @"(C x, int y) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var tree = compilation1.SyntaxTrees.Single();
            var model = compilation1.GetSemanticModel(tree);
            var node = tree.GetRoot().DescendantNodes().OfType<LiteralExpressionSyntax>().Where(l => l.ToString() == "default").First();

            Assert.Equal("default", node.ToString());
            Assert.Equal("C", model.GetTypeInfo(node).ConvertedType.ToTestDisplayString());

            var declaredSymbol = model.GetDeclaredSymbol(node.FirstAncestorOrSelf<OperatorDeclarationSyntax>());
            Assert.Equal("C C.I1<C>." + opName + "(C x, System.Int32 y)", declaredSymbol.ToTestDisplayString());
            Assert.DoesNotContain(opName, declaredSymbol.ContainingType.MemberNames);

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped,
                             emitOptions: EmitOptions.Default.WithEmitMetadataOnly(true).WithIncludePrivateMembers(false)).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var c = module.GlobalNamespace.GetTypeMember("C");
                var m01 = c.Interfaces().Single().GetMembers(opName).OfType<MethodSymbol>().Single();

                Assert.Equal(matchingOp is null ? 1 : 2, c.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());

                var cM01 = (MethodSymbol)c.FindImplementationForInterfaceMember(m01);

                Assert.True(cM01.IsStatic);
                Assert.False(cM01.IsAbstract);
                Assert.False(cM01.IsVirtual);
                Assert.False(cM01.IsMetadataVirtual());
                Assert.False(cM01.IsMetadataFinal);
                Assert.False(cM01.IsMetadataNewSlot());
                Assert.Equal(MethodKind.ExplicitInterfaceImplementation, cM01.MethodKind);
                Assert.False(cM01.HasRuntimeSpecialName);
                Assert.False(cM01.HasSpecialName);

                Assert.Equal("C C.I1<C>." + opName + "(C x, System.Int32 y)", cM01.ToTestDisplayString());
                Assert.Equal(m01, cM01.ExplicitInterfaceImplementations.Single());
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticUnaryOperator_09([CombinatorialValues("+", "-", "!", "~", "++", "--")] string op, bool isChecked, bool isVirtual)
        {
            // Explicit implementation from base is treated as an implementation

            string opName = GetUnaryOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public partial interface I1
{
    " + modifier + @" static I1 operator " + checkedKeyword + op + @"(I1 x)" + body + @"
}

public partial class C2 : I1
{
    static I1 I1.operator " + checkedKeyword + op + @"(I1 x) => default;
}
";
            if (isChecked)
            {
                source1 +=
@"
public partial interface I1
{
    " + modifier + @" static I1 operator " + op + @"(I1 x)" + body + @"
}

public partial class C2 : I1
{
    static I1 I1.operator " + op + @"(I1 x) => default;
}
";
            }

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C3 : C2, I1
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.Regular10, TestOptions.RegularPreview })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                     parseOptions: parseOptions,
                                                     targetFramework: _supportingFramework,
                                                     references: new[] { reference });
                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c3 = module.GlobalNamespace.GetTypeMember("C3");
                Assert.Empty(c3.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()));
                var m01 = c3.Interfaces().Single().GetMembers(opName).OfType<MethodSymbol>().Single();

                var cM01 = (MethodSymbol)c3.FindImplementationForInterfaceMember(m01);

                Assert.Equal("I1 C2.I1." + opName + "(I1 x)", cM01.ToTestDisplayString());
                Assert.Same(m01, cM01.ExplicitInterfaceImplementations.Single());
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticUnaryTrueFalseOperator_09([CombinatorialValues("true", "false")] string op, bool isVirtual)
        {
            // Explicit implementation from base is treated as an implementation
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public partial interface I1
{
    " + modifier + @" static bool operator " + op + @"(I1 x)" + body + @"
}

public partial class C2 : I1
{
    static bool I1.operator " + op + @"(I1 x) => default;
}
";
            string matchingOp = op == "true" ? "false" : "true";

            source1 +=
@"
public partial interface I1
{
    " + modifier + @" static bool operator " + matchingOp + @"(I1 x)" + body + @"
}

public partial class C2
{
    static bool I1.operator " + matchingOp + @"(I1 x) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C3 : C2, I1
{
}
";

            var opName = UnaryOperatorName(op);

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.Regular10, TestOptions.RegularPreview })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                     parseOptions: parseOptions,
                                                     targetFramework: _supportingFramework,
                                                     references: new[] { reference });
                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c3 = module.GlobalNamespace.GetTypeMember("C3");
                Assert.Empty(c3.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()));
                var m01 = c3.Interfaces().Single().GetMembers(opName).OfType<MethodSymbol>().Single();

                var cM01 = (MethodSymbol)c3.FindImplementationForInterfaceMember(m01);

                Assert.Equal("System.Boolean C2.I1." + opName + "(I1 x)", cM01.ToTestDisplayString());
                Assert.Same(m01, cM01.ExplicitInterfaceImplementations.Single());
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticBinaryOperator_09([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<<", ">>", ">>>", "<", ">", "<=", ">=")] string op, bool isChecked, bool isVirtual)
        {
            // Explicit implementation from base is treated as an implementation

            string opName = GetBinaryOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public partial interface I1
{
    " + modifier + @" static I1 operator " + checkedKeyword + op + @"(I1 x, int y)" + body + @"
}

public partial class C2 : I1
{
    static I1 I1.operator " + checkedKeyword + op + @"(I1 x, int y) => default;
}
";
            string matchingOp = isChecked ? op : MatchingBinaryOperator(op);

            if (matchingOp is object)
            {
                source1 +=
@"
public partial interface I1
{
    " + modifier + @" static I1 operator " + matchingOp + @"(I1 x, int y)" + body + @"
}

public partial class C2
{
    static I1 I1.operator " + matchingOp + @"(I1 x, int y) => default;
}
";
            }

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C3 : C2, I1
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.Regular10, TestOptions.RegularPreview })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                     parseOptions: parseOptions,
                                                     targetFramework: _supportingFramework,
                                                     references: new[] { reference });
                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c3 = module.GlobalNamespace.GetTypeMember("C3");
                Assert.Empty(c3.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()));
                var m01 = c3.Interfaces().Single().GetMembers(opName).OfType<MethodSymbol>().Single();

                var cM01 = (MethodSymbol)c3.FindImplementationForInterfaceMember(m01);

                Assert.Equal("I1 C2.I1." + opName + "(I1 x, System.Int32 y)", cM01.ToTestDisplayString());
                Assert.Same(m01, cM01.ExplicitInterfaceImplementations.Single());
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticEqualityOperator_09([CombinatorialValues("==", "!=")] string op, bool isVirtual)
        {
            // Explicit implementation from base is treated as an implementation

            string opName = GetBinaryOperatorName(op, isChecked: false, checkedKeyword: out _);

            if (opName is null)
            {
                return;
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public partial interface I1<T> where T : I1<T>
{
    " + modifier + @" static T operator " + op + @"(T x, int y)" + body + @"
}

public partial class C2<T> : I1<T> where T : I1<T>
{
    static T I1<T>.operator " + op + @"(T x, int y) => default;
}
";
            string matchingOp = MatchingBinaryOperator(op);

            source1 +=
@"
public partial interface I1<T>
{
    " + modifier + @" static T operator " + matchingOp + @"(T x, int y)" + body + @"
}

public partial class C2<T>
{
    static T I1<T>.operator " + matchingOp + @"(T x, int y) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C3 : C2<C3>, I1<C3>
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.Regular10, TestOptions.RegularPreview })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                     parseOptions: parseOptions,
                                                     targetFramework: _supportingFramework,
                                                     references: new[] { reference });
                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c3 = module.GlobalNamespace.GetTypeMember("C3");
                Assert.Empty(c3.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()));
                var m01 = c3.Interfaces().Single().GetMembers(opName).OfType<MethodSymbol>().Single();

                var cM01 = (MethodSymbol)c3.FindImplementationForInterfaceMember(m01);

                Assert.Equal("C3 C2<C3>.I1<C3>." + opName + "(C3 x, System.Int32 y)", cM01.ToTestDisplayString());
                Assert.Equal(m01, cM01.ExplicitInterfaceImplementations.Single());
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticUnaryOperator_10([CombinatorialValues("+", "-", "!", "~", "++", "--", "true", "false")] string op, bool isChecked, bool isVirtual)
        {
            // Implicit implementation is considered only for types implementing interface in source.
            // In metadata, only explicit implementations are considered

            string opName = GetUnaryOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var (modifier, body) = GetILModifierAndBody(isVirtual);

            var ilSource = @"
.class interface public auto ansi abstract I1
{
    .method public hidebysig specialname " + modifier + @" virtual static 
        class I1 " + opName + @" (
            class I1 x
        ) cil managed 
    " + body + @"
}

.class public auto ansi beforefieldinit C1
    extends System.Object
    implements I1
{
    .method private hidebysig
        static class I1 I1." + opName + @" (class I1 x) cil managed 
    {
        .override method class I1 I1::" + opName + @"(class I1)

        IL_0000: ldnull
        IL_0001: ret
    }

    .method public hidebysig static
        specialname class I1 " + opName + @" (class I1 x) cil managed 
    {
        IL_0000: ldnull
        IL_0001: ret
    }

    .method public hidebysig specialname rtspecialname 
        instance void .ctor () cil managed 
    {
        IL_0000: ldarg.0
        IL_0001: call instance void System.Object::.ctor()
        IL_0006: ret
    }
}

.class public auto ansi beforefieldinit C2
    extends C1
    implements I1
{
    .method public hidebysig static
        specialname class I1 " + opName + @" (class I1 x) cil managed 
    {
        IL_0000: ldnull
        IL_0001: ret
    }

    .method public hidebysig specialname rtspecialname 
        instance void .ctor () cil managed 
    {
        IL_0000: ldarg.0
        IL_0001: call instance void C1::.ctor()
        IL_0006: ret
    } // end of method C2::.ctor
} // end of class C2
";
            var source1 =
@"
public class C3 : C2
{
}

public class C4 : C1, I1
{
}

public class C5 : C2, I1
{
}
";

            var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var c1 = compilation1.GlobalNamespace.GetTypeMember("C1");
            var m01 = c1.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();

            Assert.Equal(MethodKind.UserDefinedOperator, m01.MethodKind);
            Assert.Equal(MethodKind.UserDefinedOperator, c1.GetMember<MethodSymbol>(opName).MethodKind);

            var c1M01 = (MethodSymbol)c1.FindImplementationForInterfaceMember(m01);

            Assert.Equal("I1 C1.I1." + opName + "(I1 x)", c1M01.ToTestDisplayString());
            Assert.Equal(MethodKind.ExplicitInterfaceImplementation, c1M01.MethodKind);
            Assert.Same(m01, c1M01.ExplicitInterfaceImplementations.Single());

            var c2 = compilation1.GlobalNamespace.GetTypeMember("C2");
            Assert.Same(c1M01, c2.FindImplementationForInterfaceMember(m01));

            var c3 = compilation1.GlobalNamespace.GetTypeMember("C3");
            Assert.Same(c1M01, c3.FindImplementationForInterfaceMember(m01));

            var c4 = compilation1.GlobalNamespace.GetTypeMember("C4");
            Assert.Same(c1M01, c4.FindImplementationForInterfaceMember(m01));

            var c5 = compilation1.GlobalNamespace.GetTypeMember("C5");

            var c2M01 = (MethodSymbol)c5.FindImplementationForInterfaceMember(m01);
            Assert.Equal("I1 C2." + opName + "(I1 x)", c2M01.ToTestDisplayString());
            Assert.Equal(MethodKind.UserDefinedOperator, c2M01.MethodKind);

            compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (10,23): error CS8706: 'C2.operator true(I1)' cannot implement interface member 'I1.operator true(I1)' in type 'C5' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                // public class C5 : C2, I1
                Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, "I1").WithArguments("C2.operator " + checkedKeyword + op + "(I1)", "I1.operator " + checkedKeyword + op + "(I1)", "C5", "static abstract members in interfaces", "10.0", "11.0").WithLocation(10, 23)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticBinaryOperator_10([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<<", ">>", ">>>", "<", ">", "<=", ">=", "==", "!=")] string op, bool isChecked, bool isVirtual)
        {
            // Implicit implementation is considered only for types implementing interface in source.
            // In metadata, only explicit implementations are considered

            string opName = GetBinaryOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var (modifier, body) = GetILModifierAndBody(isVirtual);

            var ilSource = @"
.class interface public auto ansi abstract I1
{
    .method public hidebysig specialname " + modifier + @" virtual static 
        class I1 " + opName + @" (
            class I1 x,
            int32 y
        ) cil managed 
    " + body + @"
}

.class public auto ansi beforefieldinit C1
    extends System.Object
    implements I1
{
    .method private hidebysig
        static class I1 I1." + opName + @" (class I1 x, int32 y) cil managed 
    {
        .override method class I1 I1::" + opName + @"(class I1, int32)

        IL_0000: ldnull
        IL_0001: ret
    }

    .method public hidebysig static
        specialname class I1 " + opName + @" (class I1 x, int32 y) cil managed 
    {
        IL_0000: ldnull
        IL_0001: ret
    }

    .method public hidebysig specialname rtspecialname 
        instance void .ctor () cil managed 
    {
        IL_0000: ldarg.0
        IL_0001: call instance void System.Object::.ctor()
        IL_0006: ret
    }
}

.class public auto ansi beforefieldinit C2
    extends C1
    implements I1
{
    .method public hidebysig static
        specialname class I1 " + opName + @" (class I1 x, int32 y) cil managed 
    {
        IL_0000: ldnull
        IL_0001: ret
    }

    .method public hidebysig specialname rtspecialname 
        instance void .ctor () cil managed 
    {
        IL_0000: ldarg.0
        IL_0001: call instance void C1::.ctor()
        IL_0006: ret
    } // end of method C2::.ctor
} // end of class C2
";
            var source1 =
@"
public class C3 : C2
{
}

public class C4 : C1, I1
{
}

public class C5 : C2, I1
{
}
";

            var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var c1 = compilation1.GlobalNamespace.GetTypeMember("C1");
            var m01 = c1.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();

            Assert.Equal(MethodKind.UserDefinedOperator, m01.MethodKind);
            Assert.Equal(MethodKind.UserDefinedOperator, c1.GetMember<MethodSymbol>(opName).MethodKind);

            var c1M01 = (MethodSymbol)c1.FindImplementationForInterfaceMember(m01);

            Assert.Equal("I1 C1.I1." + opName + "(I1 x, System.Int32 y)", c1M01.ToTestDisplayString());
            Assert.Equal(MethodKind.ExplicitInterfaceImplementation, c1M01.MethodKind);
            Assert.Same(m01, c1M01.ExplicitInterfaceImplementations.Single());

            var c2 = compilation1.GlobalNamespace.GetTypeMember("C2");
            Assert.Same(c1M01, c2.FindImplementationForInterfaceMember(m01));

            var c3 = compilation1.GlobalNamespace.GetTypeMember("C3");
            Assert.Same(c1M01, c3.FindImplementationForInterfaceMember(m01));

            var c4 = compilation1.GlobalNamespace.GetTypeMember("C4");
            Assert.Same(c1M01, c4.FindImplementationForInterfaceMember(m01));

            var c5 = compilation1.GlobalNamespace.GetTypeMember("C5");

            var c2M01 = (MethodSymbol)c5.FindImplementationForInterfaceMember(m01);
            Assert.Equal("I1 C2." + opName + "(I1 x, System.Int32 y)", c2M01.ToTestDisplayString());
            Assert.Equal(MethodKind.UserDefinedOperator, c2M01.MethodKind);

            compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (10,23): error CS8706: 'C2.operator >>>(I1, int)' cannot implement interface member 'I1.operator >>>(I1, int)' in type 'C5' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                // public class C5 : C2, I1
                Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, "I1").WithArguments("C2.operator " + checkedKeyword + op + "(I1, int)", "I1.operator " + checkedKeyword + op + "(I1, int)", "C5", "static abstract members in interfaces", "10.0", "11.0").WithLocation(10, 23)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticUnaryOperator_11([CombinatorialValues("+", "-", "!", "~", "++", "--", "true", "false")] string op, bool isChecked)
        {
            // Non-abstract static virtual method. 

            string opName = GetUnaryOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var ilSource = @"
.class interface public auto ansi abstract I1
{
    .method public hidebysig specialname virtual
        static class I1 " + opName + @" (
            class I1 x
        ) cil managed 
    {
        IL_0000: ldnull
        IL_0001: ret
    }
}
";

            var source1 =
@"
public class C1 : I1
{
}
";

            var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyEmitDiagnostics();

            var c1 = compilation1.GlobalNamespace.GetTypeMember("C1");
            var i1 = c1.Interfaces().Single();
            var m01 = i1.GetMembers().OfType<MethodSymbol>().Single();

            Assert.Equal(MethodKind.UserDefinedOperator, m01.MethodKind);
            Assert.Same(m01, c1.FindImplementationForInterfaceMember(m01));
            Assert.Same(m01, i1.FindImplementationForInterfaceMember(m01));

            compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyEmitDiagnostics(
                // (2,19): error CS8706: 'I1.operator true(I1)' cannot implement interface member 'I1.operator true(I1)' in type 'C1' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                // public class C1 : I1
                Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, "I1").WithArguments("I1.operator " + checkedKeyword + op + @"(I1)", "I1.operator " + checkedKeyword + op + @"(I1)", "C1", "static abstract members in interfaces", "10.0", "11.0").WithLocation(2, 19)
                );

            var source2 =
@"
public class C1 : I1
{
    static I1 I1.operator " + checkedKeyword + op + @"(I1 x) => default;
}
";

            var compilation2 = CreateCompilationWithIL(source2, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation2.VerifyEmitDiagnostics();

            c1 = compilation2.GlobalNamespace.GetTypeMember("C1");
            m01 = c1.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();

            Assert.Equal("I1 I1." + opName + "(I1 x)", m01.ToTestDisplayString());
            Assert.Equal("I1 C1.I1." + opName + "(I1 x)", c1.FindImplementationForInterfaceMember(m01).ToTestDisplayString());
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticBinaryOperator_11([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<<", ">>", ">>>", "<", ">", "<=", ">=", "==", "!=")] string op, bool isChecked)
        {
            // Non-abstract static virtual method. 

            string opName = GetBinaryOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var ilSource = @"
.class interface public auto ansi abstract I1
{
    .method public hidebysig specialname virtual
        static class I1 " + opName + @" (
            class I1 x,
            int32 y
        ) cil managed 
    {
        IL_0000: ldnull
        IL_0001: ret
    }
}
";

            var source1 =
@"
public class C1 : I1
{
}
";

            var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyEmitDiagnostics();

            var c1 = compilation1.GlobalNamespace.GetTypeMember("C1");
            var i1 = c1.Interfaces().Single();
            var m01 = i1.GetMembers().OfType<MethodSymbol>().Single();

            Assert.Equal(MethodKind.UserDefinedOperator, m01.MethodKind);
            Assert.Same(m01, c1.FindImplementationForInterfaceMember(m01));
            Assert.Same(m01, i1.FindImplementationForInterfaceMember(m01));

            compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyEmitDiagnostics(
                // (2,19): error CS8706: 'I1.operator >>>(I1, int)' cannot implement interface member 'I1.operator >>>(I1, int)' in type 'C1' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                // public class C1 : I1
                Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, "I1").WithArguments("I1.operator " + checkedKeyword + op + @"(I1, int)", "I1.operator " + checkedKeyword + op + @"(I1, int)", "C1", "static abstract members in interfaces", "10.0", "11.0").WithLocation(2, 19)
                );

            var source2 =
@"
public class C1 : I1
{
    static I1 I1.operator " + checkedKeyword + op + @"(I1 x, int y) => default;
}
";

            var compilation2 = CreateCompilationWithIL(source2, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation2.VerifyEmitDiagnostics();

            c1 = compilation2.GlobalNamespace.GetTypeMember("C1");
            m01 = c1.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();

            Assert.Equal("I1 I1." + opName + "(I1 x, System.Int32 y)", m01.ToTestDisplayString());
            Assert.Equal("I1 C1.I1." + opName + "(I1 x, System.Int32 y)", c1.FindImplementationForInterfaceMember(m01).ToTestDisplayString());
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticUnaryOperator_12([CombinatorialValues("+", "-", "!", "~", "++", "--", "true", "false")] string op, bool isChecked, bool isVirtual)
        {
            // Default interface implementation for a static method

            string opName = GetUnaryOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var (modifier, body) = GetILModifierAndBody(isVirtual);

            var ilSource = @"
.class interface public auto ansi abstract I1
{
    .method public hidebysig specialname " + modifier + @" virtual static 
        class I1 " + opName + @" (
            class I1 x
        ) cil managed 
    " + body + @"
}
.class interface public auto ansi abstract I2
    implements I1
{
    .method private hidebysig
        static class I1 I1." + opName + @" (class I1 x) cil managed 
    {
        .override method class I1 I1::" + opName + @"(class I1)

        IL_0000: ldnull
        IL_0001: ret
    }
}
";

            var source1 =
@"
public class C1 : I2
{
}
";

            var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyEmitDiagnostics();

            var c1 = compilation1.GlobalNamespace.GetTypeMember("C1");
            var i2 = c1.Interfaces().Single();
            var i1 = i2.Interfaces().Single();
            var m01 = i1.GetMembers().OfType<MethodSymbol>().Single();
            var i2M01 = i2.GetMembers().OfType<MethodSymbol>().Single();

            Assert.Equal(MethodKind.UserDefinedOperator, m01.MethodKind);
            Assert.Same(i2M01, c1.FindImplementationForInterfaceMember(m01));
            Assert.Same(i2M01, i2.FindImplementationForInterfaceMember(m01));

            Assert.Same(m01, i2M01.ExplicitInterfaceImplementations.Single());
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticBinaryOperator_12([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<<", ">>", ">>>", "<", ">", "<=", ">=", "==", "!=")] string op, bool isChecked, bool isVirtual)
        {
            // Default interface implementation for a static method

            string opName = GetBinaryOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var (modifier, body) = GetILModifierAndBody(isVirtual);

            var ilSource = @"
.class interface public auto ansi abstract I1
{
    .method public hidebysig specialname " + modifier + @" virtual static 
        class I1 " + opName + @" (
            class I1 x,
            int32 y
        ) cil managed 
    " + body + @"
}
.class interface public auto ansi abstract I2
    implements I1
{
    .method private hidebysig
        static class I1 I1." + opName + @" (class I1 x, int32 y) cil managed 
    {
        .override method class I1 I1::" + opName + @"(class I1, int32)

        IL_0000: ldnull
        IL_0001: ret
    }
}
";

            var source1 =
@"
public class C1 : I2
{
}
";

            var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyEmitDiagnostics();

            var c1 = compilation1.GlobalNamespace.GetTypeMember("C1");
            var i2 = c1.Interfaces().Single();
            var i1 = i2.Interfaces().Single();
            var m01 = i1.GetMembers().OfType<MethodSymbol>().Single();
            var i2M01 = i2.GetMembers().OfType<MethodSymbol>().Single();

            Assert.Equal(MethodKind.UserDefinedOperator, m01.MethodKind);
            Assert.Same(i2M01, c1.FindImplementationForInterfaceMember(m01));
            Assert.Same(i2M01, i2.FindImplementationForInterfaceMember(m01));

            Assert.Same(m01, i2M01.ExplicitInterfaceImplementations.Single());
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticBinaryOperator_13([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<", ">", "<=", ">=", "==", "!=")] string op, bool isChecked, bool isVirtual)
        {
            // A forwarding method is added for an implicit implementation declared in base class. 

            string opName = GetBinaryOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public partial interface I1<T> where T : I1<T>
{
    " + modifier + @" static T operator " + checkedKeyword + op + @"(T x, C1 y)" + body + @"
}

#pragma warning disable CS0660, CS0661 // 'C1' defines operator == or operator != but does not override Object.Equals(object o)/Object.GetHashCode()

public partial class C1
{
    public static C2 operator " + checkedKeyword + op + @"(C2 x, C1 y) => default;
}

public class C2 : C1, I1<C2>
{
}
";
            string matchingOp = isChecked ? op : MatchingBinaryOperator(op);

            if (matchingOp is object)
            {
                source1 +=
@"
public partial interface I1<T>
{
    " + modifier + @" static T operator " + matchingOp + @"(T x, C1 y)" + body + @"
}

public partial class C1
{
    public static C2 operator " + matchingOp + @"(C2 x, C1 y) => default;
}
";
            }

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var c2 = module.GlobalNamespace.GetTypeMember("C2");
                var i1 = c2.Interfaces().Single();
                var m01 = i1.GetMembers(opName).OfType<MethodSymbol>().Single();

                var c2M01 = (MethodSymbol)c2.FindImplementationForInterfaceMember(m01);

                Assert.True(c2M01.IsStatic);
                Assert.False(c2M01.IsAbstract);
                Assert.False(c2M01.IsVirtual);
                Assert.False(c2M01.IsMetadataVirtual());
                Assert.False(c2M01.IsMetadataFinal);
                Assert.False(c2M01.IsMetadataNewSlot());

                if (module is PEModuleSymbol)
                {
                    Assert.Equal(MethodKind.ExplicitInterfaceImplementation, c2M01.MethodKind);
                    Assert.False(c2M01.HasRuntimeSpecialName);
                    Assert.False(c2M01.HasSpecialName);

                    Assert.Equal("C2 C2.I1<C2>." + opName + "(C2 x, C1 y)", c2M01.ToTestDisplayString());
                    Assert.Equal(m01, c2M01.ExplicitInterfaceImplementations.Single());

                    var c1M01 = module.GlobalNamespace.GetMember<MethodSymbol>("C1." + opName);

                    Assert.True(c1M01.IsStatic);
                    Assert.False(c1M01.IsAbstract);
                    Assert.False(c1M01.IsVirtual);
                    Assert.False(c1M01.IsMetadataVirtual());
                    Assert.False(c1M01.IsMetadataFinal);
                    Assert.False(c1M01.IsMetadataNewSlot());
                    Assert.Equal(MethodKind.UserDefinedOperator, c1M01.MethodKind);
                    Assert.False(c1M01.HasRuntimeSpecialName);
                    Assert.True(c1M01.HasSpecialName);
                    Assert.Empty(c1M01.ExplicitInterfaceImplementations);
                }
                else
                {
                    Assert.Equal(MethodKind.UserDefinedOperator, c2M01.MethodKind);
                    Assert.False(c2M01.HasRuntimeSpecialName);
                    Assert.True(c2M01.HasSpecialName);

                    Assert.Equal("C2 C1." + opName + "(C2 x, C1 y)", c2M01.ToTestDisplayString());
                    Assert.Empty(c2M01.ExplicitInterfaceImplementations);
                }
            }

            verifier.VerifyIL("C2.I1<C2>." + opName + "(C2, C1)",
@"
{
  // Code size        8 (0x8)
  .maxstack  2
  IL_0000:  ldarg.0
  IL_0001:  ldarg.1
  IL_0002:  call       ""C2 C1." + opName + @"(C2, C1)""
  IL_0007:  ret
}
");
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticUnaryOperator_14([CombinatorialValues("+", "-", "!", "~", "++", "--")] string op, bool isChecked, bool isVirtual)
        {
            // A forwarding method is added for an implicit implementation with modopt mismatch. 

            string opName = GetUnaryOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var (modifier, body) = GetILModifierAndBody(isVirtual);

            var ilSource = @"
.class interface public auto ansi abstract I1`1<(class I1`1<!T>) T>
{
    // Methods
    .method public hidebysig specialname " + modifier + @" virtual static 
        !T modopt(I1`1) " + opName + @" (
            !T x
        ) cil managed 
    " + body + @"
} 
";

            var source1 =
@"
partial class C1 : I1<C1>
{
    public static C1 operator " + checkedKeyword + op + @"(C1 x) => default;
}

class C2 : I1<C2>
{
    static C2 I1<C2>.operator " + checkedKeyword + op + @"(C2 x) => default;
}
";
            if (isChecked)
            {
                source1 +=
@"
partial class C1 : I1<C1>
{
    public static C1 operator " + op + @"(C1 x) => default;
}
";
            }

            var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var c1 = module.GlobalNamespace.GetTypeMember("C1");
                var m01 = c1.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();

                var c1M01 = (MethodSymbol)c1.FindImplementationForInterfaceMember(m01);

                Assert.True(c1M01.IsStatic);
                Assert.False(c1M01.IsAbstract);
                Assert.False(c1M01.IsVirtual);
                Assert.False(c1M01.IsMetadataVirtual());
                Assert.False(c1M01.IsMetadataFinal);
                Assert.False(c1M01.IsMetadataNewSlot());

                if (module is PEModuleSymbol)
                {
                    Assert.Equal(MethodKind.ExplicitInterfaceImplementation, c1M01.MethodKind);
                    Assert.Equal("C1 modopt(I1<>) C1.I1<C1>." + opName + "(C1 x)", c1M01.ToTestDisplayString());
                    Assert.Equal(m01, c1M01.ExplicitInterfaceImplementations.Single());

                    c1M01 = module.GlobalNamespace.GetMember<MethodSymbol>("C1." + opName);
                    Assert.Equal("C1 C1." + opName + "(C1 x)", c1M01.ToTestDisplayString());

                    Assert.True(c1M01.IsStatic);
                    Assert.False(c1M01.IsAbstract);
                    Assert.False(c1M01.IsVirtual);
                    Assert.False(c1M01.IsMetadataVirtual());
                    Assert.False(c1M01.IsMetadataFinal);
                    Assert.False(c1M01.IsMetadataNewSlot());
                    Assert.Equal(MethodKind.UserDefinedOperator, c1M01.MethodKind);

                    Assert.Empty(c1M01.ExplicitInterfaceImplementations);
                }
                else
                {
                    Assert.Equal(MethodKind.UserDefinedOperator, c1M01.MethodKind);
                    Assert.Equal("C1 C1." + opName + "(C1 x)", c1M01.ToTestDisplayString());
                    Assert.Empty(c1M01.ExplicitInterfaceImplementations);
                }

                var c2 = module.GlobalNamespace.GetTypeMember("C2");
                m01 = c2.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();
                var c2M01 = (MethodSymbol)c2.FindImplementationForInterfaceMember(m01);

                Assert.True(c2M01.IsStatic);
                Assert.False(c2M01.IsAbstract);
                Assert.False(c2M01.IsVirtual);
                Assert.False(c2M01.IsMetadataVirtual());
                Assert.False(c2M01.IsMetadataFinal);
                Assert.False(c2M01.IsMetadataNewSlot());
                Assert.Equal(MethodKind.ExplicitInterfaceImplementation, c2M01.MethodKind);

                Assert.Equal("C2 modopt(I1<>) C2.I1<C2>." + opName + "(C2 x)", c2M01.ToTestDisplayString());
                Assert.Equal(m01, c2M01.ExplicitInterfaceImplementations.Single());

                Assert.Same(c2M01, c2.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Single());
            }

            verifier.VerifyIL("C1.I1<C1>." + opName + "(C1)",
@"
{
  // Code size        7 (0x7)
  .maxstack  1
  IL_0000:  ldarg.0
  IL_0001:  call       ""C1 C1." + opName + @"(C1)""
  IL_0006:  ret
}
");
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticUnaryTrueFalseOperator_14([CombinatorialValues("true", "false")] string op, bool isVirtual)
        {
            // A forwarding method is added for an implicit implementation with modopt mismatch. 

            var opName = UnaryOperatorName(op);
            var (modifier, body) = GetILModifierAndBody(isVirtual);

            var ilSource = @"
.class interface public auto ansi abstract I1`1<(class I1`1<!T>) T>
{
    // Methods
    .method public hidebysig specialname " + modifier + @" virtual static 
        bool modopt(I1`1) " + opName + @" (
            !T x
        ) cil managed 
    " + body + @"
} 
";

            var source1 =
@"
class C1 : I1<C1>
{
    public static bool operator " + op + @"(C1 x) => default;
    public static bool operator " + (op == "true" ? "false" : "true") + @"(C1 x) => default;
}

class C2 : I1<C2>
{
    static bool I1<C2>.operator " + op + @"(C2 x) => default;
}
";

            var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var c1 = module.GlobalNamespace.GetTypeMember("C1");
                var m01 = c1.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();

                var c1M01 = (MethodSymbol)c1.FindImplementationForInterfaceMember(m01);

                Assert.True(c1M01.IsStatic);
                Assert.False(c1M01.IsAbstract);
                Assert.False(c1M01.IsVirtual);
                Assert.False(c1M01.IsMetadataVirtual());
                Assert.False(c1M01.IsMetadataFinal);
                Assert.False(c1M01.IsMetadataNewSlot());

                if (module is PEModuleSymbol)
                {
                    Assert.Equal(MethodKind.ExplicitInterfaceImplementation, c1M01.MethodKind);
                    Assert.Equal("System.Boolean modopt(I1<>) C1.I1<C1>." + opName + "(C1 x)", c1M01.ToTestDisplayString());
                    Assert.Equal(m01, c1M01.ExplicitInterfaceImplementations.Single());

                    c1M01 = module.GlobalNamespace.GetMember<MethodSymbol>("C1." + opName);
                    Assert.Equal("System.Boolean C1." + opName + "(C1 x)", c1M01.ToTestDisplayString());

                    Assert.True(c1M01.IsStatic);
                    Assert.False(c1M01.IsAbstract);
                    Assert.False(c1M01.IsVirtual);
                    Assert.False(c1M01.IsMetadataVirtual());
                    Assert.False(c1M01.IsMetadataFinal);
                    Assert.False(c1M01.IsMetadataNewSlot());
                    Assert.Equal(MethodKind.UserDefinedOperator, c1M01.MethodKind);

                    Assert.Empty(c1M01.ExplicitInterfaceImplementations);
                }
                else
                {
                    Assert.Equal(MethodKind.UserDefinedOperator, c1M01.MethodKind);
                    Assert.Equal("System.Boolean C1." + opName + "(C1 x)", c1M01.ToTestDisplayString());
                    Assert.Empty(c1M01.ExplicitInterfaceImplementations);
                }

                var c2 = module.GlobalNamespace.GetTypeMember("C2");
                m01 = c2.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();
                var c2M01 = (MethodSymbol)c2.FindImplementationForInterfaceMember(m01);

                Assert.True(c2M01.IsStatic);
                Assert.False(c2M01.IsAbstract);
                Assert.False(c2M01.IsVirtual);
                Assert.False(c2M01.IsMetadataVirtual());
                Assert.False(c2M01.IsMetadataFinal);
                Assert.False(c2M01.IsMetadataNewSlot());
                Assert.Equal(MethodKind.ExplicitInterfaceImplementation, c2M01.MethodKind);

                Assert.Equal("System.Boolean modopt(I1<>) C2.I1<C2>." + opName + "(C2 x)", c2M01.ToTestDisplayString());
                Assert.Equal(m01, c2M01.ExplicitInterfaceImplementations.Single());

                Assert.Same(c2M01, c2.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Single());
            }

            verifier.VerifyIL("C1.I1<C1>." + opName + "(C1)",
@"
{
  // Code size        7 (0x7)
  .maxstack  1
  IL_0000:  ldarg.0
  IL_0001:  call       ""bool C1." + opName + @"(C1)""
  IL_0006:  ret
}
");
        }

        internal static string MatchingBinaryOperator(string op)
        {
            return op switch { "<" => ">", ">" => "<", "<=" => ">=", ">=" => "<=", "==" => "!=", "!=" => "==", _ => null };
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticBinaryOperator_14([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<<", ">>", ">>>", "<", ">", "<=", ">=", "==", "!=")] string op, bool isChecked, bool isVirtual)
        {
            // A forwarding method is added for an implicit implementation with modopt mismatch. 

            string opName = GetBinaryOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var (modifier, body) = GetILModifierAndBody(isVirtual);

            var ilSource = @"
.class interface public auto ansi abstract I1`1<(class I1`1<!T>) T>
{
    // Methods
    .method public hidebysig specialname " + modifier + @" virtual static 
        !T modopt(I1`1) " + opName + @" (
            !T x,
            int32 y
        ) cil managed 
    " + body + @"
} 
";
            string matchingOp = isChecked ? op : MatchingBinaryOperator(op);
            string additionalMethods = "";

            if (matchingOp is object)
            {
                additionalMethods =
@"
    public static C1 operator " + matchingOp + @"(C1 x, int y) => default;
";
            }

            var source1 =
@"
#pragma warning disable CS0660, CS0661 // 'C1' defines operator == or operator != but does not override Object.Equals(object o)/Object.GetHashCode()

class C1 : I1<C1>
{
    public static C1 operator " + checkedKeyword + op + @"(C1 x, int y) => default;
" + additionalMethods + @"
}

class C2 : I1<C2>
{
    static C2 I1<C2>.operator " + checkedKeyword + op + @"(C2 x, int y) => default;
}
";

            var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var c1 = module.GlobalNamespace.GetTypeMember("C1");
                var m01 = c1.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();

                var c1M01 = (MethodSymbol)c1.FindImplementationForInterfaceMember(m01);

                Assert.True(c1M01.IsStatic);
                Assert.False(c1M01.IsAbstract);
                Assert.False(c1M01.IsVirtual);
                Assert.False(c1M01.IsMetadataVirtual());
                Assert.False(c1M01.IsMetadataFinal);
                Assert.False(c1M01.IsMetadataNewSlot());

                if (module is PEModuleSymbol)
                {
                    Assert.Equal(MethodKind.ExplicitInterfaceImplementation, c1M01.MethodKind);
                    Assert.Equal("C1 modopt(I1<>) C1.I1<C1>." + opName + "(C1 x, System.Int32 y)", c1M01.ToTestDisplayString());
                    Assert.Equal(m01, c1M01.ExplicitInterfaceImplementations.Single());

                    c1M01 = module.GlobalNamespace.GetMember<MethodSymbol>("C1." + opName);
                    Assert.Equal("C1 C1." + opName + "(C1 x, System.Int32 y)", c1M01.ToTestDisplayString());

                    Assert.True(c1M01.IsStatic);
                    Assert.False(c1M01.IsAbstract);
                    Assert.False(c1M01.IsVirtual);
                    Assert.False(c1M01.IsMetadataVirtual());
                    Assert.False(c1M01.IsMetadataFinal);
                    Assert.False(c1M01.IsMetadataNewSlot());
                    Assert.Equal(MethodKind.UserDefinedOperator, c1M01.MethodKind);

                    Assert.Empty(c1M01.ExplicitInterfaceImplementations);
                }
                else
                {
                    Assert.Equal(MethodKind.UserDefinedOperator, c1M01.MethodKind);
                    Assert.Equal("C1 C1." + opName + "(C1 x, System.Int32 y)", c1M01.ToTestDisplayString());
                    Assert.Empty(c1M01.ExplicitInterfaceImplementations);
                }
                var c2 = module.GlobalNamespace.GetTypeMember("C2");
                m01 = c2.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();
                var c2M01 = (MethodSymbol)c2.FindImplementationForInterfaceMember(m01);

                Assert.True(c2M01.IsStatic);
                Assert.False(c2M01.IsAbstract);
                Assert.False(c2M01.IsVirtual);
                Assert.False(c2M01.IsMetadataVirtual());
                Assert.False(c2M01.IsMetadataFinal);
                Assert.False(c2M01.IsMetadataNewSlot());
                Assert.Equal(MethodKind.ExplicitInterfaceImplementation, c2M01.MethodKind);

                Assert.Equal("C2 modopt(I1<>) C2.I1<C2>." + opName + "(C2 x, System.Int32 y)", c2M01.ToTestDisplayString());
                Assert.Equal(m01, c2M01.ExplicitInterfaceImplementations.Single());

                Assert.Same(c2M01, c2.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Single());
            }

            verifier.VerifyIL("C1.I1<C1>." + opName + "(C1, int)",
@"
{
  // Code size        8 (0x8)
  .maxstack  2
  IL_0000:  ldarg.0
  IL_0001:  ldarg.1
  IL_0002:  call       ""C1 C1." + opName + @"(C1, int)""
  IL_0007:  ret
}
");
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticUnaryOperator_15([CombinatorialValues("+", "-", "!", "~", "++", "--")] string op, bool isChecked, bool isVirtual)
        {
            // A forwarding method isn't created if base class implements interface exactly the same way. 

            string opName = GetUnaryOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public partial interface I1
{
    " + modifier + @" static I1 operator " + checkedKeyword + op + @"(I1 x)" + body + @"
}

public partial class C2 : I1
{
    static I1 I1.operator " + checkedKeyword + op + @"(I1 x) => default;
}
";
            if (isChecked)
            {
                source1 +=
@"
public partial interface I1
{
    " + modifier + @" static I1 operator " + op + @"(I1 x)" + body + @"
}

public partial class C2 : I1
{
    static I1 I1.operator " + op + @"(I1 x) => default;
}
";
            }

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C3 : C2, I1
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.RegularPreview, TestOptions.Regular10 })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                         parseOptions: parseOptions,
                                                         targetFramework: _supportingFramework,
                                                         references: new[] { reference });
                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c3 = module.GlobalNamespace.GetTypeMember("C3");
                Assert.Empty(c3.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()));

                var m02 = c3.Interfaces().Single().GetMembers(opName).OfType<MethodSymbol>().Single();

                var c2M02 = c3.BaseType().GetMembers("I1." + opName).OfType<MethodSymbol>().Single();
                Assert.Equal("I1 C2.I1." + opName + "(I1 x)", c2M02.ToTestDisplayString());
                Assert.Same(c2M02, c3.FindImplementationForInterfaceMember(m02));
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticUnaryTrueFalseOperator_15(bool isVirtual)
        {
            // A forwarding method isn't created if base class implements interface exactly the same way. 
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static bool operator true(I1 x)" + body + @"
    " + modifier + @" static bool operator false(I1 x)" + body + @"
}

public partial class C2 : I1
{
    static bool I1.operator true(I1 x) => default;
    static bool I1.operator false(I1 x) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C3 : C2, I1
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.RegularPreview, TestOptions.Regular10 })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                         parseOptions: parseOptions,
                                                         targetFramework: _supportingFramework,
                                                         references: new[] { reference });
                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c3 = module.GlobalNamespace.GetTypeMember("C3");
                Assert.Empty(c3.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()));

                var m01 = c3.Interfaces().Single().GetMembers("op_True").OfType<MethodSymbol>().Single();
                var m02 = c3.Interfaces().Single().GetMembers("op_False").OfType<MethodSymbol>().Single();

                var c2M01 = c3.BaseType().GetMembers("I1.op_True").OfType<MethodSymbol>().Single();
                Assert.Equal("System.Boolean C2.I1.op_True(I1 x)", c2M01.ToTestDisplayString());
                Assert.Same(c2M01, c3.FindImplementationForInterfaceMember(m01));

                var c2M02 = c3.BaseType().GetMembers("I1.op_False").OfType<MethodSymbol>().Single();
                Assert.Equal("System.Boolean C2.I1.op_False(I1 x)", c2M02.ToTestDisplayString());
                Assert.Same(c2M02, c3.FindImplementationForInterfaceMember(m02));
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticBinaryOperator_15([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<", ">", "<=", ">=", "==", "!=")] string op, bool isChecked, bool isVirtual)
        {
            // A forwarding method isn't created if base class implements interface exactly the same way. 

            string opName = GetBinaryOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public partial interface I1<T> where T : I1<T>
{
    " + modifier + @" static T operator " + checkedKeyword + op + @"(T x, C1 y)" + body + @"
    " + modifier + @" static T operator " + checkedKeyword + op + @"(T x, C2 y)" + body + @"
}

#pragma warning disable CS0660, CS0661 // 'C1' defines operator == or operator != but does not override Object.Equals(object o)/Object.GetHashCode()

public partial class C1
{
    public static C2 operator " + checkedKeyword + op + @"(C2 x, C1 y) => default;
}

public partial class C2 : C1, I1<C2>
{
    static C2 I1<C2>.operator " + checkedKeyword + op + @"(C2 x, C2 y) => default;
}
";

            string matchingOp = isChecked ? op : MatchingBinaryOperator(op);

            if (matchingOp is object)
            {
                source1 +=
@"
public partial interface I1<T>
{
    " + modifier + @" static T operator " + matchingOp + @"(T x, C1 y)" + body + @"
    " + modifier + @" static T operator " + matchingOp + @"(T x, C2 y)" + body + @"
}

public partial class C1
{
    public static C2 operator " + matchingOp + @"(C2 x, C1 y) => default;
}

public partial class C2
{
    static C2 I1<C2>.operator " + matchingOp + @"(C2 x, C2 y) => default;
}
";
            }

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C3 : C2, I1<C2>
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.RegularPreview, TestOptions.Regular10 })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                         parseOptions: parseOptions,
                                                         targetFramework: _supportingFramework,
                                                         references: new[] { reference });
                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c3 = module.GlobalNamespace.GetTypeMember("C3");
                Assert.Empty(c3.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()));

                var m01 = c3.Interfaces().Single().GetMembers(opName).OfType<MethodSymbol>().First();

                var c1M01 = c3.BaseType().BaseType().GetMember<MethodSymbol>(opName);
                Assert.Equal("C2 C1." + opName + "(C2 x, C1 y)", c1M01.ToTestDisplayString());

                Assert.True(c1M01.IsStatic);
                Assert.False(c1M01.IsAbstract);
                Assert.False(c1M01.IsVirtual);
                Assert.False(c1M01.IsMetadataVirtual());
                Assert.False(c1M01.IsMetadataFinal);
                Assert.False(c1M01.IsMetadataNewSlot());

                Assert.Empty(c1M01.ExplicitInterfaceImplementations);

                if (c1M01.ContainingModule is PEModuleSymbol)
                {
                    var c2M01 = (MethodSymbol)c3.FindImplementationForInterfaceMember(m01);
                    Assert.Equal("C2 C2.I1<C2>." + opName + "(C2 x, C1 y)", c2M01.ToTestDisplayString());
                    Assert.Equal(m01, c2M01.ExplicitInterfaceImplementations.Single());
                }
                else
                {
                    Assert.Same(c1M01, c3.FindImplementationForInterfaceMember(m01));
                }

                var m02 = c3.Interfaces().Single().GetMembers(opName).OfType<MethodSymbol>().ElementAt(1);

                var c2M02 = c3.BaseType().GetMembers("I1<C2>." + opName).OfType<MethodSymbol>().First();
                Assert.Equal("C2 C2.I1<C2>." + opName + "(C2 x, C2 y)", c2M02.ToTestDisplayString());
                Assert.Same(c2M02, c3.FindImplementationForInterfaceMember(m02));
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticBinaryOperator_16([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<", ">", "<=", ">=", "==", "!=")] string op, bool isChecked, bool isVirtual)
        {
            // A new implicit implementation is properly considered.

            string opName = GetBinaryOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public partial interface I1<T> where T : I1<T>
{
    " + modifier + @" static T operator " + checkedKeyword + op + @"(T x, C1 y)" + body + @"
}

#pragma warning disable CS0660, CS0661 // 'C1' defines operator == or operator != but does not override Object.Equals(object o)/Object.GetHashCode()

public partial class C1 : I1<C2>
{
    public static C2 operator " + checkedKeyword + op + @"(C2 x, C1 y) => default;
}

public partial class C2 : C1
{
    public static C2 operator " + checkedKeyword + op + @"(C2 x, C1 y) => default;
}
";
            string matchingOp = isChecked ? op : MatchingBinaryOperator(op);

            if (matchingOp is object)
            {
                source1 +=
@"
public partial interface I1<T>
{
    " + modifier + @" static T operator " + matchingOp + @"(T x, C1 y)" + body + @"
}

public partial class C1 : I1<C2>
{
    public static C2 operator " + matchingOp + @"(C2 x, C1 y) => default;
}

public partial class C2 : C1
{
    public static C2 operator " + matchingOp + @"(C2 x, C1 y) => default;
}
";
            }

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C3 : C2, I1<C2>
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { reference });
                var verifier = CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

                verifier.VerifyIL("C3.I1<C2>." + opName + "(C2, C1)",
@"
{
  // Code size        8 (0x8)
  .maxstack  2
  IL_0000:  ldarg.0
  IL_0001:  ldarg.1
  IL_0002:  call       ""C2 C2." + opName + @"(C2, C1)""
  IL_0007:  ret
}
");
            }

            void validate(ModuleSymbol module)
            {
                var c3 = module.GlobalNamespace.GetTypeMember("C3");
                var m01 = c3.Interfaces().Single().GetMembers(opName).OfType<MethodSymbol>().Single();

                var c2M01 = c3.BaseType().GetMember<MethodSymbol>(opName);
                Assert.Equal("C2 C2." + opName + "(C2 x, C1 y)", c2M01.ToTestDisplayString());

                Assert.True(c2M01.IsStatic);
                Assert.False(c2M01.IsAbstract);
                Assert.False(c2M01.IsVirtual);
                Assert.False(c2M01.IsMetadataVirtual());
                Assert.False(c2M01.IsMetadataFinal);
                Assert.False(c2M01.IsMetadataNewSlot());

                Assert.Empty(c2M01.ExplicitInterfaceImplementations);

                if (module is PEModuleSymbol)
                {
                    var c3M01 = (MethodSymbol)c3.FindImplementationForInterfaceMember(m01);
                    Assert.Equal("C2 C3.I1<C2>." + opName + "(C2 x, C1 y)", c3M01.ToTestDisplayString());
                    Assert.Equal(m01, c3M01.ExplicitInterfaceImplementations.Single());
                }
                else
                {
                    Assert.Same(c2M01, c3.FindImplementationForInterfaceMember(m01));
                }
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticBinaryOperator_18([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<", ">", "<=", ">=", "==", "!=")] string op, bool genericFirst, bool isChecked, bool isVirtual)
        {
            // An "ambiguity" in implicit implementation declared in generic base class plus interface is generic too.

            string opName = GetBinaryOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);

            var generic =
@"
    public static C1<T, U> operator " + checkedKeyword + op + @"(C1<T, U> x, U y) => default;
";
            var nonGeneric =
@"
    public static C1<T, U> operator " + checkedKeyword + op + @"(C1<T, U> x, int y) => default;
";
            var source1 =
@"
public partial interface I1<T, U> where T : I1<T, U>
{
    " + modifier + @" static T operator " + checkedKeyword + op + @"(T x, U y)" + body + @"
}

#pragma warning disable CS0660, CS0661 // 'C1' defines operator == or operator != but does not override Object.Equals(object o)/Object.GetHashCode()

public partial class C1<T, U> : I1<C1<T, U>, U>
{
" + (genericFirst ? generic + nonGeneric : nonGeneric + generic) + @"
}
";

            string matchingOp = isChecked ? op : MatchingBinaryOperator(op);

            if (matchingOp is object)
            {
                source1 +=
@"
public partial interface I1<T, U>
{
    " + modifier + @" static T operator " + matchingOp + @"(T x, U y)" + body + @"
}

public partial class C1<T, U>
{
    public static C1<T, U> operator " + matchingOp + @"(C1<T, U> x, U y) => default;
    public static C1<T, U> operator " + matchingOp + @"(C1<T, U> x, int y) => default;
}
";
            }

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { CreateCompilation("", targetFramework: _supportingFramework).ToMetadataReference() });

            compilation1.VerifyDiagnostics();
            Assert.Equal(2, compilation1.GlobalNamespace.GetTypeMember("C1").GetMembers().Where(m => m.Name.Contains(opName)).Count());

            var source2 =
@"
public class C2 : C1<int, int>, I1<C1<int, int>, int>
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.Regular10, TestOptions.RegularPreview })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: parseOptions,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { reference });

                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c2 = module.GlobalNamespace.GetTypeMember("C2");
                var m01 = c2.Interfaces().Single().GetMembers(opName).OfType<MethodSymbol>().Single();

                Assert.True(m01.ContainingModule is RetargetingModuleSymbol or PEModuleSymbol);

                var c1M01 = (MethodSymbol)c2.FindImplementationForInterfaceMember(m01);
                Assert.Equal("C1<T, U> C1<T, U>." + opName + "(C1<T, U> x, U y)", c1M01.OriginalDefinition.ToTestDisplayString());

                var baseI1M01 = c2.BaseType().FindImplementationForInterfaceMember(m01);
                Assert.Equal("C1<T, U> C1<T, U>." + opName + "(C1<T, U> x, U y)", baseI1M01.OriginalDefinition.ToTestDisplayString());

                Assert.Equal(c1M01, baseI1M01);

                if (c1M01.OriginalDefinition.ContainingModule is PEModuleSymbol)
                {
                    Assert.Equal(m01, c1M01.ExplicitInterfaceImplementations.Single());
                }
                else
                {
                    Assert.Empty(c1M01.ExplicitInterfaceImplementations);
                }
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticBinaryOperator_20([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<", ">", "<=", ">=", "==", "!=")] string op, bool genericFirst, bool isChecked, bool isVirtual)
        {
            // Same as ImplementAbstractStaticBinaryOperator_18 only implementation is explicit in source.
            string opName = GetBinaryOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);

            var generic =
@"
    static C1<T, U> I1<C1<T, U>, U>.operator " + checkedKeyword + op + @"(C1<T, U> x, U y) => default;
";
            var nonGeneric =
@"
    public static C1<T, U> operator " + checkedKeyword + op + @"(C1<T, U> x, int y) => default;
";
            var source1 =
@"
public partial interface I1<T, U> where T : I1<T, U>
{
    " + modifier + @" static T operator " + checkedKeyword + op + @"(T x, U y)" + body + @"
}

#pragma warning disable CS0660, CS0661 // 'C1' defines operator == or operator != but does not override Object.Equals(object o)/Object.GetHashCode()

public partial class C1<T, U> : I1<C1<T, U>, U>
{
" + (genericFirst ? generic + nonGeneric : nonGeneric + generic) + @"
}
";
            string matchingOp = isChecked ? op : MatchingBinaryOperator(op);

            if (matchingOp is object)
            {
                source1 +=
@"
public partial interface I1<T, U> where T : I1<T, U>
{
    " + modifier + @" static T operator " + matchingOp + @"(T x, U y)" + body + @"
}

public partial class C1<T, U> : I1<C1<T, U>, U>
{
    public static C1<T, U> operator " + matchingOp + @"(C1<T, U> x, int y) => default;
    static C1<T, U> I1<C1<T, U>, U>.operator " + matchingOp + @"(C1<T, U> x, U y) => default;
}
";
            }

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { CreateCompilation("", targetFramework: _supportingFramework).ToMetadataReference() });

            compilation1.VerifyDiagnostics();
            Assert.Equal(2, compilation1.GlobalNamespace.GetTypeMember("C1").GetMembers().Where(m => m.Name.Contains(opName)).Count());

            var source2 =
@"
public class C2 : C1<int, int>, I1<C1<int, int>, int>
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.Regular10, TestOptions.RegularPreview })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: parseOptions,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { reference });

                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c2 = module.GlobalNamespace.GetTypeMember("C2");
                var m01 = c2.Interfaces().Single().GetMembers(opName).OfType<MethodSymbol>().Single();

                Assert.True(m01.ContainingModule is RetargetingModuleSymbol or PEModuleSymbol);

                var c1M01 = (MethodSymbol)c2.FindImplementationForInterfaceMember(m01);
                Assert.Equal("C1<T, U> C1<T, U>.I1<C1<T, U>, U>." + opName + "(C1<T, U> x, U y)", c1M01.OriginalDefinition.ToTestDisplayString());

                Assert.Equal(m01, c1M01.ExplicitInterfaceImplementations.Single());
                Assert.Same(c1M01, c2.BaseType().FindImplementationForInterfaceMember(m01));
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticBinaryOperator_22([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<", ">", "<=", ">=", "==", "!=")] string op, bool genericFirst, bool isChecked, bool isVirtual)
        {
            // Same as ImplementAbstractStaticMethod_18 only implicit implementation is in an intermediate base.
            string opName = GetBinaryOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);

            var generic =
@"
    public static C11<T, U> operator " + checkedKeyword + op + @"(C11<T, U> x, C1<T, U> y) => default;
";
            var nonGeneric =
@"
    public static C11<T, U> operator " + checkedKeyword + op + @"(C11<T, int> x, C1<T, U> y) => default;
";
            var source1 =
@"
public partial interface I1<T, U> where T : I1<T, U>
{
    " + modifier + @" static T operator " + checkedKeyword + op + @"(T x, U y)" + body + @"
}

#pragma warning disable CS0660, CS0661 // 'C1' defines operator == or operator != but does not override Object.Equals(object o)/Object.GetHashCode()

public partial class C1<T, U>
{
" + (genericFirst ? generic + nonGeneric : nonGeneric + generic) + @"
}

public class C11<T, U> : C1<T, U>, I1<C11<T, U>, C1<T, U>>
{
}
";
            string matchingOp = isChecked ? op : MatchingBinaryOperator(op);

            if (matchingOp is object)
            {
                source1 +=
@"
public partial interface I1<T, U>
{
    " + modifier + @" static T operator " + matchingOp + @"(T x, U y)" + body + @"
}

public partial class C1<T, U>
{
    public static C11<T, U> operator " + matchingOp + @"(C11<T, U> x, C1<T, U> y) => default;
    public static C11<T, U> operator " + matchingOp + @"(C11<T, int> x, C1<T, U> y) => default;
}
";
            }

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { CreateCompilation("", targetFramework: _supportingFramework).ToMetadataReference() });

            compilation1.VerifyDiagnostics();
            Assert.Equal(2, compilation1.GlobalNamespace.GetTypeMember("C1").GetMembers().Where(m => m.Name.Contains(opName)).Count());

            var source2 =
@"
public class C2 : C11<int, int>, I1<C11<int, int>, C1<int, int>>
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.Regular10, TestOptions.RegularPreview })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: parseOptions,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { reference });

                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c2 = module.GlobalNamespace.GetTypeMember("C2");
                var m01 = c2.Interfaces().Single().GetMembers(opName).OfType<MethodSymbol>().Single();

                Assert.True(m01.ContainingModule is RetargetingModuleSymbol or PEModuleSymbol);

                var c1M01 = (MethodSymbol)c2.FindImplementationForInterfaceMember(m01);
                var expectedDisplay = m01.ContainingModule is PEModuleSymbol ? "C11<T, U> C11<T, U>.I1<C11<T, U>, C1<T, U>>." + opName + "(C11<T, U> x, C1<T, U> y)" : "C11<T, U> C1<T, U>." + opName + "(C11<T, U> x, C1<T, U> y)";
                Assert.Equal(expectedDisplay, c1M01.OriginalDefinition.ToTestDisplayString());

                var baseI1M01 = c2.BaseType().FindImplementationForInterfaceMember(m01);
                Assert.Equal(expectedDisplay, baseI1M01.OriginalDefinition.ToTestDisplayString());

                Assert.Equal(c1M01, baseI1M01);

                if (c1M01.OriginalDefinition.ContainingModule is PEModuleSymbol)
                {
                    Assert.Equal(m01, c1M01.ExplicitInterfaceImplementations.Single());
                }
                else
                {
                    Assert.Empty(c1M01.ExplicitInterfaceImplementations);
                }
            }
        }

        [Theory]
        [CombinatorialData]
        public void ExplicitImplementationModifiersUnaryOperator_01([CombinatorialValues("+", "-", "!", "~", "++", "--", "true", "false")] string op)
        {
            var source1 =
@"
public interface I1
{
    abstract static I1 operator " + op + @"(I1 x);
}

class
    C1 : I1
{
    static I1 I1.operator " + op + @"(I1 x) => default;
}

class
    C2 : I1
{
    private static I1 I1.operator " + op + @"(I1 x) => default;
}

class
    C3 : I1
{
    protected static I1 I1.operator " + op + @"(I1 x) => default;
}

class
    C4 : I1
{
    internal static I1 I1.operator " + op + @"(I1 x) => default;
}

class
    C5 : I1
{
    protected internal static I1 I1.operator " + op + @"(I1 x) => default;
}

class
    C6 : I1
{
    private protected static I1 I1.operator " + op + @"(I1 x) => default;
}

class
    C7 : I1
{
    public static I1 I1.operator " + op + @"(I1 x) => default;
}

class
    C8 : I1
{
    static partial I1 I1.operator " + op + @"(I1 x) => default;
}

class
    C9 : I1
{
    async static I1 I1.operator " + op + @"(I1 x) => default;
}

class
    C10 : I1
{
    unsafe static I1 I1.operator " + op + @"(I1 x) => default;
}

class
    C11 : I1
{
    static readonly I1 I1.operator " + op + @"(I1 x) => default;
}

class
    C12 : I1
{
    extern static I1 I1.operator " + op + @"(I1 x);
}

class
    C13 : I1
{
    abstract static I1 I1.operator " + op + @"(I1 x) => default;
}

class
    C14 : I1
{
    virtual static I1 I1.operator " + op + @"(I1 x) => default;
}

class
    C15 : I1
{
    sealed static I1 I1.operator " + op + @"(I1 x) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll.WithAllowUnsafe(true),
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var c1 = compilation1.GlobalNamespace.GetTypeMember("C1");

            Assert.Equal(Accessibility.Private, c1.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Single().DeclaredAccessibility);

            compilation1.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.WRN_ExternMethodNoImplementation or (int)ErrorCode.ERR_OpTFRetType or (int)ErrorCode.ERR_OperatorNeedsMatch)).Verify(
                // (16,35): error CS0106: The modifier 'private' is not valid for this item
                //     private static I1 I1.operator !(I1 x) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, op).WithArguments("private").WithLocation(16, 35),
                // (22,37): error CS0106: The modifier 'protected' is not valid for this item
                //     protected static I1 I1.operator !(I1 x) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, op).WithArguments("protected").WithLocation(22, 37),
                // (28,36): error CS0106: The modifier 'internal' is not valid for this item
                //     internal static I1 I1.operator !(I1 x) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, op).WithArguments("internal").WithLocation(28, 36),
                // (34,46): error CS0106: The modifier 'protected internal' is not valid for this item
                //     protected internal static I1 I1.operator !(I1 x) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, op).WithArguments("protected internal").WithLocation(34, 46),
                // (40,45): error CS0106: The modifier 'private protected' is not valid for this item
                //     private protected static I1 I1.operator !(I1 x) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, op).WithArguments("private protected").WithLocation(40, 45),
                // (46,34): error CS0106: The modifier 'public' is not valid for this item
                //     public static I1 I1.operator !(I1 x) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, op).WithArguments("public").WithLocation(46, 34),
                // (52,12): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', or a method return type.
                //     static partial I1 I1.operator !(I1 x) => default;
                Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(52, 12),
                // (58,33): error CS0106: The modifier 'async' is not valid for this item
                //     async static I1 I1.operator !(I1 x) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, op).WithArguments("async").WithLocation(58, 33),
                // (70,36): error CS0106: The modifier 'readonly' is not valid for this item
                //     static readonly I1 I1.operator !(I1 x) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, op).WithArguments("readonly").WithLocation(70, 36),
                // (82,36): error CS0106: The modifier 'abstract' is not valid for this item
                //     abstract static I1 I1.operator !(I1 x) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, op).WithArguments("abstract").WithLocation(82, 36),
                // (88,35): error CS0106: The modifier 'virtual' is not valid for this item
                //     virtual static I1 I1.operator !(I1 x) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, op).WithArguments("virtual").WithLocation(88, 35),
                // (94,34): error CS0106: The modifier 'sealed' is not valid for this item
                //     sealed static I1 I1.operator !(I1 x) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, op).WithArguments("sealed").WithLocation(94, 34)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ExplicitImplementationModifiersBinaryOperator_01([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<<", ">>", ">>>", "<", ">", "<=", ">=", "==", "!=")] string op)
        {
            var source1 =
@"
public interface I1
{
    abstract static I1 operator " + op + @"(I1 x, int y);
}

struct
    C1 : I1
{
    static I1 I1.operator " + op + @"(I1 x, int y) => default;
}

struct
    C2 : I1
{
    private static I1 I1.operator " + op + @"(I1 x, int y) => default;
}

struct
    C3 : I1
{
    protected static I1 I1.operator " + op + @"(I1 x, int y) => default;
}

struct
    C4 : I1
{
    internal static I1 I1.operator " + op + @"(I1 x, int y) => default;
}

struct
    C5 : I1
{
    protected internal static I1 I1.operator " + op + @"(I1 x, int y) => default;
}

struct
    C6 : I1
{
    private protected static I1 I1.operator " + op + @"(I1 x, int y) => default;
}

struct
    C7 : I1
{
    public static I1 I1.operator " + op + @"(I1 x, int y) => default;
}

struct
    C8 : I1
{
    static partial I1 I1.operator " + op + @"(I1 x, int y) => default;
}

struct
    C9 : I1
{
    async static I1 I1.operator " + op + @"(I1 x, int y) => default;
}

struct
    C10 : I1
{
    unsafe static I1 I1.operator " + op + @"(I1 x, int y) => default;
}

struct
    C11 : I1
{
    static readonly I1 I1.operator " + op + @"(I1 x, int y) => default;
}

struct
    C12 : I1
{
    extern static I1 I1.operator " + op + @"(I1 x, int y);
}

struct
    C13 : I1
{
    abstract static I1 I1.operator " + op + @"(I1 x, int y) => default;
}

struct
    C14 : I1
{
    virtual static I1 I1.operator " + op + @"(I1 x, int y) => default;
}

struct
    C15 : I1
{
    sealed static I1 I1.operator " + op + @"(I1 x, int y) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll.WithAllowUnsafe(true),
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var c1 = compilation1.GlobalNamespace.GetTypeMember("C1");

            Assert.Equal(Accessibility.Private, c1.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Single().DeclaredAccessibility);

            compilation1.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.WRN_ExternMethodNoImplementation or (int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_BadAbstractEqualityOperatorSignature)).Verify(
                // (16,35): error CS0106: The modifier 'private' is not valid for this item
                //     private static I1 I1.operator ^(I1 x, int y) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, op).WithArguments("private").WithLocation(16, 35),
                // (22,37): error CS0106: The modifier 'protected' is not valid for this item
                //     protected static I1 I1.operator ^(I1 x, int y) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, op).WithArguments("protected").WithLocation(22, 37),
                // (28,36): error CS0106: The modifier 'internal' is not valid for this item
                //     internal static I1 I1.operator ^(I1 x, int y) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, op).WithArguments("internal").WithLocation(28, 36),
                // (34,46): error CS0106: The modifier 'protected internal' is not valid for this item
                //     protected internal static I1 I1.operator ^(I1 x, int y) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, op).WithArguments("protected internal").WithLocation(34, 46),
                // (40,45): error CS0106: The modifier 'private protected' is not valid for this item
                //     private protected static I1 I1.operator ^(I1 x, int y) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, op).WithArguments("private protected").WithLocation(40, 45),
                // (46,34): error CS0106: The modifier 'public' is not valid for this item
                //     public static I1 I1.operator ^(I1 x, int y) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, op).WithArguments("public").WithLocation(46, 34),
                // (52,12): error CS0267: The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', or a method return type.
                //     static partial I1 I1.operator ^(I1 x, int y) => default;
                Diagnostic(ErrorCode.ERR_PartialMisplaced, "partial").WithLocation(52, 12),
                // (58,33): error CS0106: The modifier 'async' is not valid for this item
                //     async static I1 I1.operator ^(I1 x, int y) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, op).WithArguments("async").WithLocation(58, 33),
                // (70,36): error CS0106: The modifier 'readonly' is not valid for this item
                //     static readonly I1 I1.operator ^(I1 x, int y) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, op).WithArguments("readonly").WithLocation(70, 36),
                // (82,36): error CS0106: The modifier 'abstract' is not valid for this item
                //     abstract static I1 I1.operator ^(I1 x, int y) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, op).WithArguments("abstract").WithLocation(82, 36),
                // (88,35): error CS0106: The modifier 'virtual' is not valid for this item
                //     virtual static I1 I1.operator ^(I1 x, int y) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, op).WithArguments("virtual").WithLocation(88, 35),
                // (94,34): error CS0106: The modifier 'sealed' is not valid for this item
                //     sealed static I1 I1.operator ^(I1 x, int y) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, op).WithArguments("sealed").WithLocation(94, 34)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ExplicitInterfaceSpecifierErrorsUnaryOperator_01([CombinatorialValues("+", "-", "!", "~", "++", "--", "true", "false")] string op)
        {
            var source1 =
@"
public interface I1<T> where T : struct
{
    abstract static I1<T> operator " + op + @"(I1<T> x);
}

class C1
{
    static I1<int> I1<int>.operator " + op + @"(I1<int> x) => default;
}

class C2 : I1<C2>
{
    static I1<C2> I1<C2>.operator " + op + @"(I1<C2> x) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_OpTFRetType or (int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_BadAbstractEqualityOperatorSignature)).Verify(
                // (9,20): error CS0540: 'C1.I1<int>.operator -(I1<int>)': containing type does not implement interface 'I1<int>'
                //     static I1<int> I1<int>.operator -(I1<int> x) => default;
                Diagnostic(ErrorCode.ERR_ClassDoesntImplementInterface, "I1<int>").WithArguments("C1.I1<int>.operator " + op + "(I1<int>)", "I1<int>").WithLocation(9, 20),
                // (12,7): error CS0453: The type 'C2' must be a non-nullable value type in order to use it as parameter 'T' in the generic type or method 'I1<T>'
                // class C2 : I1<C2>
                Diagnostic(ErrorCode.ERR_ValConstraintNotSatisfied, "C2").WithArguments("I1<T>", "T", "C2").WithLocation(12, 7),
                // (14,19): error CS0453: The type 'C2' must be a non-nullable value type in order to use it as parameter 'T' in the generic type or method 'I1<T>'
                //     static I1<C2> I1<C2>.operator -(I1<C2> x) => default;
                Diagnostic(ErrorCode.ERR_ValConstraintNotSatisfied, "I1<C2>").WithArguments("I1<T>", "T", "C2").WithLocation(14, 19),
                // (14,35): error CS0453: The type 'C2' must be a non-nullable value type in order to use it as parameter 'T' in the generic type or method 'I1<T>'
                //     static I1<C2> I1<C2>.operator -(I1<C2> x) => default;
                Diagnostic(ErrorCode.ERR_ValConstraintNotSatisfied, op).WithArguments("I1<T>", "T", "C2").WithLocation(14, 35),
                // (14,44): error CS0453: The type 'C2' must be a non-nullable value type in order to use it as parameter 'T' in the generic type or method 'I1<T>'
                //     static I1<C2> I1<C2>.operator -(I1<C2> x) => default;
                Diagnostic(ErrorCode.ERR_ValConstraintNotSatisfied, "x").WithArguments("I1<T>", "T", "C2").WithLocation(14, 44 + op.Length - 1)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ExplicitInterfaceSpecifierErrorsBinaryOperator_01([CombinatorialValues("+", "-", "*", "/", "%", "&", "|", "^", "<<", ">>", ">>>", "<", ">", "<=", ">=", "==", "!=")] string op)
        {
            var source1 =
@"
public interface I1<T> where T : class
{
    abstract static I1<T> operator " + op + @"(I1<T> x, int y);
}

struct C1
{
    static I1<string> I1<string>.operator " + op + @"(I1<string> x, int y) => default;
}

struct C2 : I1<C2>
{
    static I1<C2> I1<C2>.operator " + op + @"(I1<C2> x, int y) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.ERR_BadAbstractEqualityOperatorSignature)).Verify(
                // (9,23): error CS0540: 'C1.I1<string>.operator %(I1<string>, int)': containing type does not implement interface 'I1<string>'
                //     static I1<string> I1<string>.operator %(I1<string> x, int y) => default;
                Diagnostic(ErrorCode.ERR_ClassDoesntImplementInterface, "I1<string>").WithArguments("C1.I1<string>.operator " + op + "(I1<string>, int)", "I1<string>").WithLocation(9, 23),
                // (12,8): error CS0452: The type 'C2' must be a reference type in order to use it as parameter 'T' in the generic type or method 'I1<T>'
                // struct C2 : I1<C2>
                Diagnostic(ErrorCode.ERR_RefConstraintNotSatisfied, "C2").WithArguments("I1<T>", "T", "C2").WithLocation(12, 8),
                // (14,19): error CS0452: The type 'C2' must be a reference type in order to use it as parameter 'T' in the generic type or method 'I1<T>'
                //     static I1<C2> I1<C2>.operator %(I1<C2> x, int y) => default;
                Diagnostic(ErrorCode.ERR_RefConstraintNotSatisfied, "I1<C2>").WithArguments("I1<T>", "T", "C2").WithLocation(14, 19),
                // (14,35): error CS0452: The type 'C2' must be a reference type in order to use it as parameter 'T' in the generic type or method 'I1<T>'
                //     static I1<C2> I1<C2>.operator %(I1<C2> x, int y) => default;
                Diagnostic(ErrorCode.ERR_RefConstraintNotSatisfied, op).WithArguments("I1<T>", "T", "C2").WithLocation(14, 35),
                // (14,44): error CS0452: The type 'C2' must be a reference type in order to use it as parameter 'T' in the generic type or method 'I1<T>'
                //     static I1<C2> I1<C2>.operator %(I1<C2> x, int y) => default;
                Diagnostic(ErrorCode.ERR_RefConstraintNotSatisfied, "x").WithArguments("I1<T>", "T", "C2").WithLocation(14, 44 + op.Length - 1)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticProperty_01(bool structure)
        {
            var typeKeyword = structure ? "struct" : "class";

            var source1 =
@"
public interface I1
{
    abstract static int M01 { get; set; }
}

" + typeKeyword + @"
    C1 : I1
{}

" + typeKeyword + @"
    C2 : I1
{
    public int M01 { get; set; }
}

" + typeKeyword + @"
    C3 : I1
{
    static int M01 { get; set; }
}

" + typeKeyword + @"
    C4 : I1
{
    int I1.M01 { get; set; }
}

" + typeKeyword + @"
    C5 : I1
{
    public static long M01 { get; set; }
}

" + typeKeyword + @"
    C6 : I1
{
    static long I1.M01 { get; set; }
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (8,10): error CS0535: 'C1' does not implement interface member 'I1.M01'
                //     C1 : I1
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C1", "I1.M01").WithLocation(8, 10),
                // (12,10): error CS8928: 'C2' does not implement static interface member 'I1.M01'. 'C2.M01' cannot implement the interface member because it is not static.
                //     C2 : I1
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberNotStatic, "I1").WithArguments("C2", "I1.M01", "C2.M01").WithLocation(12, 10),
                // (18,10): error CS0737: 'C3' does not implement interface member 'I1.M01'. 'C3.M01' cannot implement an interface member because it is not public.
                //     C3 : I1
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberNotPublic, "I1").WithArguments("C3", "I1.M01", "C3.M01").WithLocation(18, 10),
                // (24,10): error CS0535: 'C4' does not implement interface member 'I1.M01'
                //     C4 : I1
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C4", "I1.M01").WithLocation(24, 10),
                // (26,12): error CS0539: 'C4.M01' in explicit interface declaration is not found among members of the interface that can be implemented
                //     int I1.M01 { get; set; }
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "M01").WithArguments("C4.M01").WithLocation(26, 12),
                // (30,10): error CS0738: 'C5' does not implement interface member 'I1.M01'. 'C5.M01' cannot implement 'I1.M01' because it does not have the matching return type of 'int'.
                //     C5 : I1
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberWrongReturnType, "I1").WithArguments("C5", "I1.M01", "C5.M01", "int").WithLocation(30, 10),
                // (36,10): error CS0535: 'C6' does not implement interface member 'I1.M01'
                //     C6 : I1
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C6", "I1.M01").WithLocation(36, 10),
                // (38,20): error CS9333: 'C6.M01' type must be 'int' to match implemented member 'I1.M01'
                //     static long I1.M01 { get; set; }
                Diagnostic(ErrorCode.ERR_ExplicitInterfaceMemberTypeMismatch, "M01").WithArguments("C6.M01", "int", "I1.M01").WithLocation(38, 20)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementVirtualStaticProperty_01(bool structure)
        {
            var typeKeyword = structure ? "struct" : "class";

            var source1 =
@"
public interface I1
{
    virtual static int M01 { get; set; }
}

" + typeKeyword + @"
    C1 : I1
{}

" + typeKeyword + @"
    C2 : I1
{
    public int M01 { get; set; }
}

" + typeKeyword + @"
    C3 : I1
{
    static int M01 { get; set; }
}

" + typeKeyword + @"
    C4 : I1
{
    int I1.M01 { get; set; }
}

" + typeKeyword + @"
    C5 : I1
{
    public static long M01 { get; set; }
}

" + typeKeyword + @"
    C6 : I1
{
    static long I1.M01 { get; set; }
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (26,12): error CS0539: 'C4.M01' in explicit interface declaration is not found among members of the interface that can be implemented
                //     int I1.M01 { get; set; }
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "M01").WithArguments("C4.M01").WithLocation(26, 12),
                // (38,20): error CS9333: 'C6.M01' type must be 'int' to match implemented member 'I1.M01'
                //     static long I1.M01 { get; set; }
                Diagnostic(ErrorCode.ERR_ExplicitInterfaceMemberTypeMismatch, "M01").WithArguments("C6.M01", "int", "I1.M01").WithLocation(38, 20)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticProperty_02(bool structure)
        {
            var typeKeyword = structure ? "struct" : "class";

            var source1 =
@"
public interface I1
{
    abstract int M01 { get; set; }
}

" + typeKeyword + @"
    C1 : I1
{}

" + typeKeyword + @"
    C2 : I1
{
    public static int M01 { get; set; }
}

" + typeKeyword + @"
    C3 : I1
{
    int M01 { get; set; }
}

" + typeKeyword + @"
    C4 : I1
{
    static int I1.M01 { get; set; }
}

" + typeKeyword + @"
    C5 : I1
{
    public long M01 { get; set; }
}

" + typeKeyword + @"
    C6 : I1
{
    long I1.M01 { get; set; }
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (8,10): error CS0535: 'C1' does not implement interface member 'I1.M01'
                //     C1 : I1
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C1", "I1.M01").WithLocation(8, 10),
                // (12,10): error CS0736: 'C2' does not implement instance interface member 'I1.M01'. 'C2.M01' cannot implement the interface member because it is static.
                //     C2 : I1
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberStatic, "I1").WithArguments("C2", "I1.M01", "C2.M01").WithLocation(12, 10),
                // (18,10): error CS0737: 'C3' does not implement interface member 'I1.M01'. 'C3.M01' cannot implement an interface member because it is not public.
                //     C3 : I1
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberNotPublic, "I1").WithArguments("C3", "I1.M01", "C3.M01").WithLocation(18, 10),
                // (24,10): error CS0535: 'C4' does not implement interface member 'I1.M01'
                //     C4 : I1
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C4", "I1.M01").WithLocation(24, 10),
                // (26,19): error CS0539: 'C4.M01' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static int I1.M01 { get; set; }
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "M01").WithArguments("C4.M01").WithLocation(26, 19),
                // (30,10): error CS0738: 'C5' does not implement interface member 'I1.M01'. 'C5.M01' cannot implement 'I1.M01' because it does not have the matching return type of 'int'.
                //     C5 : I1
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberWrongReturnType, "I1").WithArguments("C5", "I1.M01", "C5.M01", "int").WithLocation(30, 10),
                // (36,10): error CS0535: 'C6' does not implement interface member 'I1.M01'
                //     C6 : I1
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C6", "I1.M01").WithLocation(36, 10),
                // (38,13): error CS9333: 'C6.M01' type must be 'int' to match implemented member 'I1.M01'
                //     long I1.M01 { get; set; }
                Diagnostic(ErrorCode.ERR_ExplicitInterfaceMemberTypeMismatch, "M01").WithArguments("C6.M01", "int", "I1.M01").WithLocation(38, 13)
                );
        }

        [Fact]
        public void ImplementAbstractStaticProperty_03()
        {
            var source1 =
@"
public interface I1
{
    abstract static int M01 { get; set; }
}

interface I2 : I1
{}

interface I3 : I1
{
    public virtual int M01 { get => 0; set{} }
}

interface I4 : I1
{
    static int M01 { get; set; }
}

interface I5 : I1
{
    int I1.M01 { get => 0; set{} }
}

interface I6 : I1
{
    static int I1.M01 { get => 0; set{} }
}

interface I7 : I1
{
    abstract static int M01 { get; set; }
}

interface I8 : I1
{
    abstract static int I1.M01 { get; set; }
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (12,24): warning CS0108: 'I3.M01' hides inherited member 'I1.M01'. Use the new keyword if hiding was intended.
                //     public virtual int M01 { get => 0; set{} }
                Diagnostic(ErrorCode.WRN_NewRequired, "M01").WithArguments("I3.M01", "I1.M01").WithLocation(12, 24),
                // (17,16): warning CS0108: 'I4.M01' hides inherited member 'I1.M01'. Use the new keyword if hiding was intended.
                //     static int M01 { get; set; }
                Diagnostic(ErrorCode.WRN_NewRequired, "M01").WithArguments("I4.M01", "I1.M01").WithLocation(17, 16),
                // (22,12): error CS0539: 'I5.M01' in explicit interface declaration is not found among members of the interface that can be implemented
                //     int I1.M01 { get => 0; set{} }
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "M01").WithArguments("I5.M01").WithLocation(22, 12),
                // (32,25): warning CS0108: 'I7.M01' hides inherited member 'I1.M01'. Use the new keyword if hiding was intended.
                //     abstract static int M01 { get; set; }
                Diagnostic(ErrorCode.WRN_NewRequired, "M01").WithArguments("I7.M01", "I1.M01").WithLocation(32, 25)
                );

            foreach (var m01 in compilation1.GlobalNamespace.GetTypeMember("I1").GetMembers())
            {
                Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I2").FindImplementationForInterfaceMember(m01));
                Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I3").FindImplementationForInterfaceMember(m01));
                Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I4").FindImplementationForInterfaceMember(m01));
                Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I5").FindImplementationForInterfaceMember(m01));
                Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I7").FindImplementationForInterfaceMember(m01));
                Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I8").FindImplementationForInterfaceMember(m01));
            }

            var m = compilation1.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<PropertySymbol>().Single();
            var i6 = compilation1.GlobalNamespace.GetTypeMember("I6");
            var i6m = i6.GetMembers().OfType<PropertySymbol>().Single();
            Assert.Same(i6m, i6.FindImplementationForInterfaceMember(m));
            Assert.Same(i6m.GetMethod, ((PropertySymbol)i6.FindImplementationForInterfaceMember(m)).GetMethod);
            Assert.Same(i6m.SetMethod, ((PropertySymbol)i6.FindImplementationForInterfaceMember(m)).SetMethod);
        }

        [Fact]
        public void ImplementVirtualStaticProperty_03()
        {
            var source1 =
@"
public interface I1
{
    virtual  static int M01 { get; set; }
}

interface I2 : I1
{}

interface I3 : I1
{
    public virtual int M01 { get => 0; set{} }
}

interface I4 : I1
{
    static int M01 { get; set; }
}

interface I5 : I1
{
    int I1.M01 { get => 0; set{} }
}

interface I6 : I1
{
    static int I1.M01 { get => 0; set{} }
}

interface I7 : I1
{
    virtual  static int M01 { get; set; }
}

interface I8 : I1
{
    virtual  static int I1.M01 { get; set; }
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (12,24): warning CS0108: 'I3.M01' hides inherited member 'I1.M01'. Use the new keyword if hiding was intended.
                //     public virtual int M01 { get => 0; set{} }
                Diagnostic(ErrorCode.WRN_NewRequired, "M01").WithArguments("I3.M01", "I1.M01").WithLocation(12, 24),
                // (17,16): warning CS0108: 'I4.M01' hides inherited member 'I1.M01'. Use the new keyword if hiding was intended.
                //     static int M01 { get; set; }
                Diagnostic(ErrorCode.WRN_NewRequired, "M01").WithArguments("I4.M01", "I1.M01").WithLocation(17, 16),
                // (22,12): error CS0539: 'I5.M01' in explicit interface declaration is not found among members of the interface that can be implemented
                //     int I1.M01 { get => 0; set{} }
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "M01").WithArguments("I5.M01").WithLocation(22, 12),
                // (32,25): warning CS0108: 'I7.M01' hides inherited member 'I1.M01'. Use the new keyword if hiding was intended.
                //     virtual  static int M01 { get; set; }
                Diagnostic(ErrorCode.WRN_NewRequired, "M01").WithArguments("I7.M01", "I1.M01").WithLocation(32, 25),
                // (37,28): error CS0106: The modifier 'virtual' is not valid for this item
                //     virtual  static int I1.M01 { get; set; }
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M01").WithArguments("virtual").WithLocation(37, 28)
                );

            foreach (var m01 in compilation1.GlobalNamespace.GetTypeMember("I1").GetMembers())
            {
                if (m01.Kind == SymbolKind.Field)
                {
                    continue;
                }

                Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I2").FindImplementationForInterfaceMember(m01));
                Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I3").FindImplementationForInterfaceMember(m01));
                Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I4").FindImplementationForInterfaceMember(m01));
                Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I5").FindImplementationForInterfaceMember(m01));
                Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I7").FindImplementationForInterfaceMember(m01));
            }

            var m = compilation1.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<PropertySymbol>().Single();

            foreach (var name in new[] { "I6", "I8" })
            {
                var i6 = compilation1.GlobalNamespace.GetTypeMember(name);
                var i6m = i6.GetMembers().OfType<PropertySymbol>().Single();
                Assert.Same(i6m, i6.FindImplementationForInterfaceMember(m));
                Assert.Same(i6m.GetMethod, ((PropertySymbol)i6.FindImplementationForInterfaceMember(m)).GetMethod);
                Assert.Same(i6m.SetMethod, ((PropertySymbol)i6.FindImplementationForInterfaceMember(m)).SetMethod);
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticProperty_04(bool structure, bool isVirtual)
        {
            var typeKeyword = structure ? "struct" : "class";
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static int M01 { get; set; }
    " + modifier + @" static int M02 { get; set; }
}
";
            var source2 =
typeKeyword + @"
    Test: I1
{
    static int I1.M01 { get; set; }
    public static int M02 { get; set; }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (4,19): error CS8703: The modifier 'static' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     static int I1.M01 { get; set; }
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M01").WithArguments("static", "10.0", "11.0").WithLocation(4, 19),
                // (5,23): error CS8706: 'Test.M02' cannot implement interface member 'I1.M02' in type 'Test' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                //     public static int M02 { get; set; }
                Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, "M02").WithArguments("Test.M02", "I1.M02", "Test", "static abstract members in interfaces", "10.0", "11.0").WithLocation(5, 23),
                // (5,29): error CS8706: 'Test.M02.get' cannot implement interface member 'I1.M02.get' in type 'Test' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                //     public static int M02 { get; set; }
                Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, "get").WithArguments("Test.M02.get", "I1.M02.get", "Test", "static abstract members in interfaces", "10.0", "11.0").WithLocation(5, 29),
                // (5,34): error CS8706: 'Test.M02.set' cannot implement interface member 'I1.M02.set' in type 'Test' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                //     public static int M02 { get; set; }
                Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, "set").WithArguments("Test.M02.set", "I1.M02.set", "Test", "static abstract members in interfaces", "10.0", "11.0").WithLocation(5, 34)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation3.VerifyDiagnostics(
                // (4,19): error CS8703: The modifier 'static' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     static int I1.M01 { get; set; }
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M01").WithArguments("static", "10.0", "11.0").WithLocation(4, 19),
                // (10,25): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual  static int M01 { get; set; }
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M01").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(10, 25),
                // (11,25): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual  static int M02 { get; set; }
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M02").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(11, 25)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticProperty_05(bool structure, bool isVirtual)
        {
            var typeKeyword = structure ? "struct" : "class";
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static int M01 { get; set; }
}
";
            var source2 =
typeKeyword + @"
    Test1: I1
{
    public static int M01 { get; set; }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (4,23): error CS8929: 'Test1.M01' cannot implement interface member 'I1.M01' in type 'Test1' because the target runtime doesn't support static abstract members in interfaces.
                //     public static int M01 { get; set; }
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfacesForMember, "M01").WithArguments("Test1.M01", "I1.M01", "Test1").WithLocation(4, 23),
                // (4,29): error CS8929: 'Test1.M01.get' cannot implement interface member 'I1.M01.get' in type 'Test1' because the target runtime doesn't support static abstract members in interfaces.
                //     public static int M01 { get; set; }
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfacesForMember, "get").WithArguments("Test1.M01.get", "I1.M01.get", "Test1").WithLocation(4, 29),
                // (4,34): error CS8929: 'Test1.M01.set' cannot implement interface member 'I1.M01.set' in type 'Test1' because the target runtime doesn't support static abstract members in interfaces.
                //     public static int M01 { get; set; }
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfacesForMember, "set").WithArguments("Test1.M01.set", "I1.M01.set", "Test1").WithLocation(4, 34)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation3.VerifyDiagnostics(
                // (9,31): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static int M01 { get; set; }
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "get").WithLocation(9, 31),
                // (9,36): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static int M01 { get; set; }
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "set").WithLocation(9, 36)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticProperty_06(bool structure, bool isVirtual)
        {
            var typeKeyword = structure ? "struct" : "class";
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static int M01 { get; set; }
}
";
            var source2 =
typeKeyword + @"
    Test1: I1
{
    static int I1.M01 { get; set; }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (4,19): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     static int I1.M01 { get; set; }
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "M01").WithLocation(4, 19)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation3.VerifyDiagnostics(
                // (4,19): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     static int I1.M01 { get; set; }
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "M01").WithLocation(4, 19),
                // (9,31): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static int M01 { get; set; }
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "get").WithLocation(9, 31),
                // (9,36): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static int M01 { get; set; }
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "set").WithLocation(9, 36)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticProperty_07(bool structure, bool isVirtual)
        {
            // Basic implicit implementation scenario, MethodImpl is emitted

            var typeKeyword = structure ? "struct" : "class";
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static int M01 { get; set; }
}

" + typeKeyword + @"
    C : I1
{
    public static int M01 { get => 0; set {} }
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped,
                             emitOptions: EmitOptions.Default.WithEmitMetadataOnly(true).WithIncludePrivateMembers(false)).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var m01 = module.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<PropertySymbol>().Single();
                var m01Get = m01.GetMethod;
                var m01Set = m01.SetMethod;
                var c = module.GlobalNamespace.GetTypeMember("C");

                Assert.Equal(1, c.GetMembers().OfType<PropertySymbol>().Count());
                Assert.Equal(2, c.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());

                var cM01 = (PropertySymbol)c.FindImplementationForInterfaceMember(m01);

                Assert.True(cM01.IsStatic);
                Assert.False(cM01.IsAbstract);
                Assert.False(cM01.IsVirtual);

                Assert.Equal("System.Int32 C.M01 { get; set; }", cM01.ToTestDisplayString());

                var cM01Get = cM01.GetMethod;
                Assert.Same(cM01Get, c.FindImplementationForInterfaceMember(m01Get));

                Assert.True(cM01Get.IsStatic);
                Assert.False(cM01Get.IsAbstract);
                Assert.False(cM01Get.IsVirtual);
                Assert.False(cM01Get.IsMetadataVirtual());
                Assert.False(cM01Get.IsMetadataFinal);
                Assert.False(cM01Get.IsMetadataNewSlot());
                Assert.Equal(MethodKind.PropertyGet, cM01Get.MethodKind);
                Assert.False(cM01Get.HasRuntimeSpecialName);
                Assert.True(cM01Get.HasSpecialName);

                Assert.Equal("System.Int32 C.M01.get", cM01Get.ToTestDisplayString());

                var cM01Set = cM01.SetMethod;
                Assert.Same(cM01Set, c.FindImplementationForInterfaceMember(m01Set));

                Assert.True(cM01Set.IsStatic);
                Assert.False(cM01Set.IsAbstract);
                Assert.False(cM01Set.IsVirtual);
                Assert.False(cM01Set.IsMetadataVirtual());
                Assert.False(cM01Set.IsMetadataFinal);
                Assert.False(cM01Set.IsMetadataNewSlot());
                Assert.Equal(MethodKind.PropertySet, cM01Set.MethodKind);
                Assert.False(cM01Set.HasRuntimeSpecialName);
                Assert.True(cM01Set.HasSpecialName);

                Assert.Equal("void C.M01.set", cM01Set.ToTestDisplayString());

                if (module is PEModuleSymbol)
                {
                    Assert.Same(m01, cM01.ExplicitInterfaceImplementations.Single());
                    Assert.Same(m01Get, cM01Get.ExplicitInterfaceImplementations.Single());
                    Assert.Same(m01Set, cM01Set.ExplicitInterfaceImplementations.Single());
                }
                else
                {
                    Assert.Empty(cM01.ExplicitInterfaceImplementations);
                    Assert.Empty(cM01Get.ExplicitInterfaceImplementations);
                    Assert.Empty(cM01Set.ExplicitInterfaceImplementations);
                }
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticReadonlyProperty_07(bool structure, bool isVirtual)
        {
            // Basic implicit implementation scenario, MethodImpl is emitted

            var typeKeyword = structure ? "struct" : "class";
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static int M01 { get; }
}

" + typeKeyword + @"
    C : I1
{
    public static int M01 { get; set; }
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped,
                             emitOptions: EmitOptions.Default.WithEmitMetadataOnly(true).WithIncludePrivateMembers(false)).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var m01 = module.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<PropertySymbol>().Single();
                var m01Get = m01.GetMethod;
                Assert.Null(m01.SetMethod);

                var c = module.GlobalNamespace.GetTypeMember("C");

                Assert.Equal(1, c.GetMembers().OfType<PropertySymbol>().Count());
                Assert.Equal(2, c.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());

                var cM01 = (PropertySymbol)c.FindImplementationForInterfaceMember(m01);

                Assert.True(cM01.IsStatic);
                Assert.False(cM01.IsAbstract);
                Assert.False(cM01.IsVirtual);

                Assert.Equal("System.Int32 C.M01 { get; set; }", cM01.ToTestDisplayString());

                var cM01Get = cM01.GetMethod;
                Assert.Same(cM01Get, c.FindImplementationForInterfaceMember(m01Get));

                Assert.True(cM01Get.IsStatic);
                Assert.False(cM01Get.IsAbstract);
                Assert.False(cM01Get.IsVirtual);
                Assert.False(cM01Get.IsMetadataVirtual());
                Assert.False(cM01Get.IsMetadataFinal);
                Assert.False(cM01Get.IsMetadataNewSlot());
                Assert.Equal(MethodKind.PropertyGet, cM01Get.MethodKind);

                Assert.Equal("System.Int32 C.M01.get", cM01Get.ToTestDisplayString());

                var cM01Set = cM01.SetMethod;

                Assert.True(cM01Set.IsStatic);
                Assert.False(cM01Set.IsAbstract);
                Assert.False(cM01Set.IsVirtual);
                Assert.False(cM01Set.IsMetadataVirtual());
                Assert.False(cM01Set.IsMetadataFinal);
                Assert.False(cM01Set.IsMetadataNewSlot());
                Assert.Equal(MethodKind.PropertySet, cM01Set.MethodKind);

                Assert.Equal("void C.M01.set", cM01Set.ToTestDisplayString());

                if (module is PEModuleSymbol)
                {
                    Assert.Same(m01, cM01.ExplicitInterfaceImplementations.Single());
                    Assert.Same(m01Get, cM01Get.ExplicitInterfaceImplementations.Single());
                }
                else
                {
                    Assert.Empty(cM01.ExplicitInterfaceImplementations);
                    Assert.Empty(cM01Get.ExplicitInterfaceImplementations);
                }

                Assert.Empty(cM01Set.ExplicitInterfaceImplementations);
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticProperty_08(bool structure, bool isVirtual)
        {
            // Basic explicit implementation scenario

            var typeKeyword = structure ? "struct" : "class";
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static int M01 { get; set; }
}

" + typeKeyword + @"
    C : I1
{
    static int I1.M01 { get => 0; set {} }
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped,
                             emitOptions: EmitOptions.Default.WithEmitMetadataOnly(true).WithIncludePrivateMembers(false)).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var m01 = module.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<PropertySymbol>().Single();
                var m01Get = m01.GetMethod;
                var m01Set = m01.SetMethod;
                var c = module.GlobalNamespace.GetTypeMember("C");

                Assert.Equal(1, c.GetMembers().OfType<PropertySymbol>().Count());
                Assert.Equal(2, c.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());

                var cM01 = (PropertySymbol)c.FindImplementationForInterfaceMember(m01);

                Assert.True(cM01.IsStatic);
                Assert.False(cM01.IsAbstract);
                Assert.False(cM01.IsVirtual);

                Assert.Equal("System.Int32 C.I1.M01 { get; set; }", cM01.ToTestDisplayString());

                var cM01Get = cM01.GetMethod;
                Assert.Same(cM01Get, c.FindImplementationForInterfaceMember(m01Get));

                Assert.True(cM01Get.IsStatic);
                Assert.False(cM01Get.IsAbstract);
                Assert.False(cM01Get.IsVirtual);
                Assert.False(cM01Get.IsMetadataVirtual());
                Assert.False(cM01Get.IsMetadataFinal);
                Assert.False(cM01Get.IsMetadataNewSlot());
                Assert.Equal(MethodKind.PropertyGet, cM01Get.MethodKind);
                Assert.False(cM01Get.HasRuntimeSpecialName);
                Assert.True(cM01Get.HasSpecialName);

                Assert.Equal("System.Int32 C.I1.M01.get", cM01Get.ToTestDisplayString());

                var cM01Set = cM01.SetMethod;
                Assert.Same(cM01Set, c.FindImplementationForInterfaceMember(m01Set));

                Assert.True(cM01Set.IsStatic);
                Assert.False(cM01Set.IsAbstract);
                Assert.False(cM01Set.IsVirtual);
                Assert.False(cM01Set.IsMetadataVirtual());
                Assert.False(cM01Set.IsMetadataFinal);
                Assert.False(cM01Set.IsMetadataNewSlot());
                Assert.Equal(MethodKind.PropertySet, cM01Set.MethodKind);
                Assert.False(cM01Set.HasRuntimeSpecialName);
                Assert.True(cM01Set.HasSpecialName);

                Assert.Equal("void C.I1.M01.set", cM01Set.ToTestDisplayString());

                Assert.Same(m01, cM01.ExplicitInterfaceImplementations.Single());
                Assert.Same(m01Get, cM01Get.ExplicitInterfaceImplementations.Single());
                Assert.Same(m01Set, cM01Set.ExplicitInterfaceImplementations.Single());
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticProperty_09(bool isVirtual)
        {
            // Explicit implementation from base is treated as an implementation
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static int M01 { get; set; }
}

public class C1
{
    public static void M01() {}
}

public class C2 : C1, I1
{
    static int I1.M01 { get; set; }
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C3 : C2, I1
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.Regular10, TestOptions.RegularPreview })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                     parseOptions: parseOptions,
                                                     targetFramework: _supportingFramework,
                                                     references: new[] { reference });
                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c3 = module.GlobalNamespace.GetTypeMember("C3");
                Assert.Empty(c3.GetMembers().OfType<PropertySymbol>());
                Assert.Empty(c3.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()));
                var m01 = c3.Interfaces().Single().GetMembers().OfType<PropertySymbol>().Single();

                var cM01 = (PropertySymbol)c3.FindImplementationForInterfaceMember(m01);

                Assert.Equal("System.Int32 C2.I1.M01 { get; set; }", cM01.ToTestDisplayString());

                Assert.Same(cM01.GetMethod, c3.FindImplementationForInterfaceMember(m01.GetMethod));
                Assert.Same(cM01.SetMethod, c3.FindImplementationForInterfaceMember(m01.SetMethod));

                Assert.Same(m01, cM01.ExplicitInterfaceImplementations.Single());
                Assert.Same(m01.GetMethod, cM01.GetMethod.ExplicitInterfaceImplementations.Single());
                Assert.Same(m01.SetMethod, cM01.SetMethod.ExplicitInterfaceImplementations.Single());
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticProperty_10(bool isVirtual)
        {
            // Implicit implementation is considered only for types implementing interface in source.
            // In metadata, only explicit implementations are considered
            var (modifier, body) = GetILModifierAndBody(isVirtual);

            var ilSource = @"
.class interface public auto ansi abstract I1
{
    .method public hidebysig specialname " + modifier + @" virtual static 
        int32 get_M01 () cil managed 
    " + body + @"

    .method public hidebysig specialname " + modifier + @" virtual static 
        void set_M01 (
            int32 'value'
        ) cil managed 
    " + body + @"

    .property int32 M01()
    {
        .get int32 I1::get_M01()
        .set void I1::set_M01(int32)
    }
}

.class public auto ansi beforefieldinit C1
    extends System.Object
    implements I1
{
    .method private hidebysig specialname static
        int32 I1.get_M01 () cil managed 
    {
        .override method int32 I1::get_M01()
        IL_0000: ldc.i4.0
        IL_0001: ret
    }

    .method private hidebysig specialname static
        void I1.set_M01 (
            int32 'value'
        ) cil managed 
    {
        .override method void I1::set_M01(int32)
        IL_0000: ret
    }

    .property instance int32 I1.M01()
    {
        .get int32 C1::I1.get_M01()
        .set void C1::I1.set_M01(int32)
    }

    .method public hidebysig specialname static 
        int32 get_M01 () cil managed 
    {
        IL_0000: ldc.i4.0
        IL_0001: ret
    }

    .method public hidebysig specialname static 
        void set_M01 (
            int32 'value'
        ) cil managed 
    {
        IL_0000: ret
    }

    .property int32 M01()
    {
        .get int32 C1::get_M01()
        .set void C1::set_M01(int32)
    }

    .method public hidebysig specialname rtspecialname 
        instance void .ctor () cil managed 
    {
        IL_0000: ldarg.0
        IL_0001: call instance void System.Object::.ctor()
        IL_0006: ret
    }
}

.class public auto ansi beforefieldinit C2
    extends C1
    implements I1
{
    .method public hidebysig specialname static 
        int32 get_M01 () cil managed 
    {
        IL_0000: ldc.i4.0
        IL_0001: ret
    }

    .method public hidebysig specialname static 
        void set_M01 (
            int32 'value'
        ) cil managed 
    {
        IL_0000: ret
    }

    .property int32 M01()
    {
        .get int32 C2::get_M01()
        .set void C2::set_M01(int32)
    }

    .method public hidebysig specialname rtspecialname 
        instance void .ctor () cil managed 
    {
        IL_0000: ldarg.0
        IL_0001: call instance void C1::.ctor()
        IL_0006: ret
    }
}
";
            var source1 =
@"
public class C3 : C2
{
}

public class C4 : C1, I1
{
}

public class C5 : C2, I1
{
}
";

            var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var c1 = compilation1.GlobalNamespace.GetTypeMember("C1");
            var m01 = c1.Interfaces().Single().GetMembers().OfType<PropertySymbol>().Single();

            var c1M01 = (PropertySymbol)c1.FindImplementationForInterfaceMember(m01);

            Assert.Equal("System.Int32 C1.I1.M01 { get; set; }", c1M01.ToTestDisplayString());

            Assert.Same(c1M01.GetMethod, c1.FindImplementationForInterfaceMember(m01.GetMethod));
            Assert.Same(c1M01.SetMethod, c1.FindImplementationForInterfaceMember(m01.SetMethod));
            Assert.Same(m01, c1M01.ExplicitInterfaceImplementations.Single());
            Assert.Same(m01.GetMethod, c1M01.GetMethod.ExplicitInterfaceImplementations.Single());
            Assert.Same(m01.SetMethod, c1M01.SetMethod.ExplicitInterfaceImplementations.Single());

            var c2 = compilation1.GlobalNamespace.GetTypeMember("C2");
            Assert.Same(c1M01, c2.FindImplementationForInterfaceMember(m01));
            Assert.Same(c1M01.GetMethod, c2.FindImplementationForInterfaceMember(m01.GetMethod));
            Assert.Same(c1M01.SetMethod, c2.FindImplementationForInterfaceMember(m01.SetMethod));

            var c3 = compilation1.GlobalNamespace.GetTypeMember("C3");
            Assert.Same(c1M01, c3.FindImplementationForInterfaceMember(m01));
            Assert.Same(c1M01.GetMethod, c3.FindImplementationForInterfaceMember(m01.GetMethod));
            Assert.Same(c1M01.SetMethod, c3.FindImplementationForInterfaceMember(m01.SetMethod));

            var c4 = compilation1.GlobalNamespace.GetTypeMember("C4");
            Assert.Same(c1M01, c4.FindImplementationForInterfaceMember(m01));
            Assert.Same(c1M01.GetMethod, c4.FindImplementationForInterfaceMember(m01.GetMethod));
            Assert.Same(c1M01.SetMethod, c4.FindImplementationForInterfaceMember(m01.SetMethod));

            var c5 = compilation1.GlobalNamespace.GetTypeMember("C5");

            var c2M01 = (PropertySymbol)c5.FindImplementationForInterfaceMember(m01);
            Assert.Equal("System.Int32 C2.M01 { get; set; }", c2M01.ToTestDisplayString());
            Assert.Same(c2M01.GetMethod, c5.FindImplementationForInterfaceMember(m01.GetMethod));
            Assert.Same(c2M01.SetMethod, c5.FindImplementationForInterfaceMember(m01.SetMethod));

            compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (10,23): error CS8706: 'C2.M01.get' cannot implement interface member 'I1.M01.get' in type 'C5' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                // public class C5 : C2, I1
                Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, "I1").WithArguments("C2.M01.get", "I1.M01.get", "C5", "static abstract members in interfaces", "10.0", "11.0").WithLocation(10, 23),
                // (10,23): error CS8706: 'C2.M01.set' cannot implement interface member 'I1.M01.set' in type 'C5' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                // public class C5 : C2, I1
                Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, "I1").WithArguments("C2.M01.set", "I1.M01.set", "C5", "static abstract members in interfaces", "10.0", "11.0").WithLocation(10, 23),
                // (10,23): error CS8706: 'C2.M01' cannot implement interface member 'I1.M01' in type 'C5' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                // public class C5 : C2, I1
                Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, "I1").WithArguments("C2.M01", "I1.M01", "C5", "static abstract members in interfaces", "10.0", "11.0").WithLocation(10, 23)
                );
        }

        [Fact]
        public void ImplementAbstractStaticProperty_11()
        {
            // Non-abstract static virtual method. 
            scenario1();
            scenario2();
            scenario3();

            void scenario1()
            {
                var ilSource = @"
.class interface public auto ansi abstract I1
{
    .method private hidebysig specialname static virtual
        int32 get_M01 () cil managed 
    {
        IL_0000: ldc.i4.0
        IL_0001: ret
    }

    .method private hidebysig specialname static virtual
        void set_M01 (
            int32 'value'
        ) cil managed 
    {
        IL_0000: ret
    }

    .property int32 M01()
    {
        .get int32 I1::get_M01()
        .set void I1::set_M01(int32)
    }
}
";

                var source1 =
@"
public class C1 : I1
{
}
";

                var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation1.VerifyEmitDiagnostics();

                var c1 = compilation1.GlobalNamespace.GetTypeMember("C1");
                var i1 = c1.Interfaces().Single();
                var m01 = i1.GetMembers().OfType<PropertySymbol>().Single();

                Assert.Same(m01, c1.FindImplementationForInterfaceMember(m01));
                Assert.Same(m01, i1.FindImplementationForInterfaceMember(m01));
                Assert.Same(m01.GetMethod, c1.FindImplementationForInterfaceMember(m01.GetMethod));
                Assert.Same(m01.GetMethod, i1.FindImplementationForInterfaceMember(m01.GetMethod));
                Assert.Same(m01.SetMethod, c1.FindImplementationForInterfaceMember(m01.SetMethod));
                Assert.Same(m01.SetMethod, i1.FindImplementationForInterfaceMember(m01.SetMethod));

                compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.Regular10,
                                                     targetFramework: _supportingFramework);

                compilation1.VerifyEmitDiagnostics(
                    // (2,19): error CS8706: 'I1.M01.get' cannot implement interface member 'I1.M01.get' in type 'C1' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                    // public class C1 : I1
                    Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, "I1").WithArguments("I1.M01.get", "I1.M01.get", "C1", "static abstract members in interfaces", "10.0", "11.0").WithLocation(2, 19),
                    // (2,19): error CS8706: 'I1.M01.set' cannot implement interface member 'I1.M01.set' in type 'C1' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                    // public class C1 : I1
                    Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, "I1").WithArguments("I1.M01.set", "I1.M01.set", "C1", "static abstract members in interfaces", "10.0", "11.0").WithLocation(2, 19)
                    );

                var source2 =
@"
public class C1 : I1
{
   static int I1.M01 { get; set; }
}
";

                var compilation2 = CreateCompilationWithIL(source2, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation2.VerifyEmitDiagnostics(
                    // (4,18): error CS0122: 'I1.M01' is inaccessible due to its protection level
                    //    static int I1.M01 { get; set; }
                    Diagnostic(ErrorCode.ERR_BadAccess, "M01").WithArguments("I1.M01").WithLocation(4, 18)
                    );

                c1 = compilation2.GlobalNamespace.GetTypeMember("C1");
                i1 = c1.Interfaces().Single();
                m01 = i1.GetMembers().OfType<PropertySymbol>().Single();
                var c1m01 = c1.GetMembers().OfType<PropertySymbol>().Single();

                Assert.Same(c1m01, c1.FindImplementationForInterfaceMember(m01));
                Assert.Same(m01, i1.FindImplementationForInterfaceMember(m01));
                Assert.Same(c1m01.GetMethod, c1.FindImplementationForInterfaceMember(m01.GetMethod));
                Assert.Same(m01.GetMethod, i1.FindImplementationForInterfaceMember(m01.GetMethod));
                Assert.Same(c1m01.SetMethod, c1.FindImplementationForInterfaceMember(m01.SetMethod));
                Assert.Same(m01.SetMethod, i1.FindImplementationForInterfaceMember(m01.SetMethod));

                var source3 =
@"
public class C1 : I1
{
   public static int M01 { get; set; }
}
";

                var compilation3 = CreateCompilationWithIL(source3, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation3.VerifyDiagnostics(
                    // (4,28): error CS9044: 'C1' does not implement interface member 'I1.M01.get'. 'C1.M01.get' cannot implicitly implement an inaccessible member.
                    //    public static int M01 { get; set; }
                    Diagnostic(ErrorCode.ERR_ImplicitImplementationOfInaccessibleInterfaceMember, "get").WithArguments("C1", "I1.M01.get", "C1.M01.get").WithLocation(4, 28),
                    // (4,33): error CS9044: 'C1' does not implement interface member 'I1.M01.set'. 'C1.M01.set' cannot implicitly implement an inaccessible member.
                    //    public static int M01 { get; set; }
                    Diagnostic(ErrorCode.ERR_ImplicitImplementationOfInaccessibleInterfaceMember, "set").WithArguments("C1", "I1.M01.set", "C1.M01.set").WithLocation(4, 33)
                    );

                validate3(compilation3.SourceModule);

                void validate3(ModuleSymbol module)
                {
                    var c = module.GlobalNamespace.GetTypeMember("C1");
                    Assert.Equal(1, c.GetMembers().OfType<PropertySymbol>().Count());
                    Assert.Equal(2, c.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());

                    var m01 = c.Interfaces().Single().GetMembers().OfType<PropertySymbol>().Single();
                    var c1m01 = c.GetMembers().OfType<PropertySymbol>().Single();
                    Assert.Same(c1m01, c.FindImplementationForInterfaceMember(m01));
                    Assert.Same(c1m01.GetMethod, c.FindImplementationForInterfaceMember(m01.GetMethod));
                    Assert.Same(c1m01.SetMethod, c.FindImplementationForInterfaceMember(m01.SetMethod));
                }
            }

            void scenario2()
            {
                var ilSource = @"
.class interface public auto ansi abstract I1
{
    .method public hidebysig specialname abstract virtual static 
        int32 get_M01 () cil managed 
    {
    }

    .method private hidebysig specialname static virtual
        void set_M01 (
            int32 'value'
        ) cil managed 
    {
        IL_0000: ret
    }

    .property int32 M01()
    {
        .get int32 I1::get_M01()
        .set void I1::set_M01(int32)
    }
}
";

                var source1 =
@"
public class C1 : I1
{
}
";

                var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation1.VerifyDiagnostics(
                    // (2,19): error CS0535: 'C1' does not implement interface member 'I1.M01'
                    // public class C1 : I1
                    Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C1", "I1.M01").WithLocation(2, 19)
                    );

                var c1 = compilation1.GlobalNamespace.GetTypeMember("C1");
                var i1 = c1.Interfaces().Single();
                var m01 = i1.GetMembers().OfType<PropertySymbol>().Single();

                Assert.Null(c1.FindImplementationForInterfaceMember(m01));
                Assert.Null(i1.FindImplementationForInterfaceMember(m01));
                Assert.Null(c1.FindImplementationForInterfaceMember(m01.GetMethod));
                Assert.Null(i1.FindImplementationForInterfaceMember(m01.GetMethod));
                Assert.Same(m01.SetMethod, c1.FindImplementationForInterfaceMember(m01.SetMethod));
                Assert.Same(m01.SetMethod, i1.FindImplementationForInterfaceMember(m01.SetMethod));

                var source2 =
@"
public class C1 : I1
{
   static int I1.M01 { get; }
}
";

                var compilation2 = CreateCompilationWithIL(source2, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation2.VerifyEmitDiagnostics(
                    // (4,18): error CS0122: 'I1.M01.set' is inaccessible due to its protection level
                    //    static int I1.M01 { get; }
                    Diagnostic(ErrorCode.ERR_BadAccess, "M01").WithArguments("I1.M01.set").WithLocation(4, 18),
                    // (4,18): error CS0551: Explicit interface implementation 'C1.I1.M01' is missing accessor 'I1.M01.set'
                    //    static int I1.M01 { get; }
                    Diagnostic(ErrorCode.ERR_ExplicitPropertyMissingAccessor, "M01").WithArguments("C1.I1.M01", "I1.M01.set").WithLocation(4, 18)
                    );

                validate2(compilation2.SourceModule);

                void validate2(ModuleSymbol module)
                {
                    var c = module.GlobalNamespace.GetTypeMember("C1");
                    var m01 = c.Interfaces().Single().GetMembers().OfType<PropertySymbol>().Single();
                    var m01Get = m01.GetMethod;
                    var m01Set = m01.SetMethod;

                    Assert.Equal(1, c.GetMembers().OfType<PropertySymbol>().Count());
                    Assert.Equal(1, c.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());

                    var cM01 = (PropertySymbol)c.FindImplementationForInterfaceMember(m01);

                    Assert.True(cM01.IsStatic);
                    Assert.False(cM01.IsAbstract);
                    Assert.False(cM01.IsVirtual);

                    Assert.Equal("System.Int32 C1.I1.M01 { get; }", cM01.ToTestDisplayString());

                    var cM01Get = cM01.GetMethod;
                    Assert.Same(cM01Get, c.FindImplementationForInterfaceMember(m01Get));

                    Assert.True(cM01Get.IsStatic);
                    Assert.False(cM01Get.IsAbstract);
                    Assert.False(cM01Get.IsVirtual);
                    Assert.False(cM01Get.IsMetadataVirtual());
                    Assert.False(cM01Get.IsMetadataFinal);
                    Assert.False(cM01Get.IsMetadataNewSlot());
                    Assert.Equal(MethodKind.PropertyGet, cM01Get.MethodKind);

                    Assert.Equal("System.Int32 C1.I1.M01.get", cM01Get.ToTestDisplayString());

                    Assert.Null(cM01.SetMethod);
                    Assert.Same(m01Set, c.FindImplementationForInterfaceMember(m01Set));

                    Assert.Same(m01, cM01.ExplicitInterfaceImplementations.Single());
                    Assert.Same(m01Get, cM01Get.ExplicitInterfaceImplementations.Single());
                }

                var source3 =
@"
public class C1 : I1
{
   public static int M01 { get; set; }
}
";

                var compilation3 = CreateCompilationWithIL(source3, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation3.VerifyDiagnostics(
                    // (4,33): error CS9044: 'C1' does not implement interface member 'I1.M01.set'. 'C1.M01.set' cannot implicitly implement an inaccessible member.
                    //    public static int M01 { get; set; }
                    Diagnostic(ErrorCode.ERR_ImplicitImplementationOfInaccessibleInterfaceMember, "set").WithArguments("C1", "I1.M01.set", "C1.M01.set").WithLocation(4, 33)
                    );

                validate3(compilation3.SourceModule);

                void validate3(ModuleSymbol module)
                {
                    var c = module.GlobalNamespace.GetTypeMember("C1");

                    var m01 = c.Interfaces().Single().GetMembers().OfType<PropertySymbol>().Single();
                    var m01Get = m01.GetMethod;

                    Assert.Equal(1, c.GetMembers().OfType<PropertySymbol>().Count());
                    Assert.Equal(2, c.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());

                    var cM01 = (PropertySymbol)c.FindImplementationForInterfaceMember(m01);

                    Assert.True(cM01.IsStatic);
                    Assert.False(cM01.IsAbstract);
                    Assert.False(cM01.IsVirtual);

                    Assert.Equal("System.Int32 C1.M01 { get; set; }", cM01.ToTestDisplayString());

                    var cM01Get = cM01.GetMethod;
                    Assert.Same(cM01Get, c.FindImplementationForInterfaceMember(m01Get));

                    Assert.True(cM01Get.IsStatic);
                    Assert.False(cM01Get.IsAbstract);
                    Assert.False(cM01Get.IsVirtual);
                    Assert.False(cM01Get.IsMetadataVirtual());
                    Assert.False(cM01Get.IsMetadataFinal);
                    Assert.False(cM01Get.IsMetadataNewSlot());
                    Assert.Equal(MethodKind.PropertyGet, cM01Get.MethodKind);

                    Assert.Equal("System.Int32 C1.M01.get", cM01Get.ToTestDisplayString());

                    var cM01Set = cM01.SetMethod;

                    Assert.True(cM01Set.IsStatic);
                    Assert.False(cM01Set.IsAbstract);
                    Assert.False(cM01Set.IsVirtual);
                    Assert.False(cM01Set.IsMetadataVirtual());
                    Assert.False(cM01Set.IsMetadataFinal);
                    Assert.False(cM01Set.IsMetadataNewSlot());
                    Assert.Equal(MethodKind.PropertySet, cM01Set.MethodKind);

                    Assert.Equal("void C1.M01.set", cM01Set.ToTestDisplayString());

                    var m01Set = m01.SetMethod;
                    Assert.Same(cM01Set, c.FindImplementationForInterfaceMember(m01Set));

                    if (module is PEModuleSymbol)
                    {
                        Assert.Same(m01, cM01.ExplicitInterfaceImplementations.Single());
                        Assert.Same(m01Get, cM01Get.ExplicitInterfaceImplementations.Single());
                        Assert.Same(m01Set, cM01Set.ExplicitInterfaceImplementations.Single());
                    }
                    else
                    {
                        Assert.Empty(cM01.ExplicitInterfaceImplementations);
                        Assert.Empty(cM01Get.ExplicitInterfaceImplementations);
                        Assert.Empty(cM01Set.ExplicitInterfaceImplementations);
                    }
                }

                var source4 =
@"
public class C1 : I1
{
   static int I1.M01 { get; set; }
}
";

                var compilation4 = CreateCompilationWithIL(source4, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation4.VerifyDiagnostics(
                    // (4,18): error CS0122: 'I1.M01.set' is inaccessible due to its protection level
                    //    static int I1.M01 { get; set; }
                    Diagnostic(ErrorCode.ERR_BadAccess, "M01").WithArguments("I1.M01.set").WithLocation(4, 18)
                    );

                c1 = compilation4.GlobalNamespace.GetTypeMember("C1");
                i1 = c1.Interfaces().Single();
                m01 = i1.GetMembers().OfType<PropertySymbol>().Single();
                var c1M01 = c1.GetMembers().OfType<PropertySymbol>().Single();

                Assert.Same(c1M01, c1.FindImplementationForInterfaceMember(m01));
                Assert.Same(c1M01.GetMethod, c1.FindImplementationForInterfaceMember(m01.GetMethod));
                Assert.Same(c1M01.SetMethod, c1.FindImplementationForInterfaceMember(m01.SetMethod));
                Assert.Same(m01, c1M01.ExplicitInterfaceImplementations.Single());
                Assert.Same(m01.GetMethod, c1M01.GetMethod.ExplicitInterfaceImplementations.Single());
                Assert.Same(m01.SetMethod, c1M01.SetMethod.ExplicitInterfaceImplementations.Single());

                var source5 =
@"
public class C1 : I1
{
   public static int M01 { get; }
}
";

                var compilation5 = CreateCompilationWithIL(source5, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                CompileAndVerify(compilation5, sourceSymbolValidator: validate5, symbolValidator: validate5, verify: Verification.Skipped).VerifyDiagnostics();

                void validate5(ModuleSymbol module)
                {
                    var c = module.GlobalNamespace.GetTypeMember("C1");

                    var m01 = c.Interfaces().Single().GetMembers().OfType<PropertySymbol>().Single();
                    var m01Get = m01.GetMethod;

                    Assert.Equal(1, c.GetMembers().OfType<PropertySymbol>().Count());
                    Assert.Equal(1, c.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());

                    var cM01 = (PropertySymbol)c.FindImplementationForInterfaceMember(m01);

                    Assert.True(cM01.IsStatic);
                    Assert.False(cM01.IsAbstract);
                    Assert.False(cM01.IsVirtual);

                    Assert.Equal("System.Int32 C1.M01 { get; }", cM01.ToTestDisplayString());

                    var cM01Get = cM01.GetMethod;
                    Assert.Same(cM01Get, c.FindImplementationForInterfaceMember(m01Get));

                    Assert.True(cM01Get.IsStatic);
                    Assert.False(cM01Get.IsAbstract);
                    Assert.False(cM01Get.IsVirtual);
                    Assert.False(cM01Get.IsMetadataVirtual());
                    Assert.False(cM01Get.IsMetadataFinal);
                    Assert.False(cM01Get.IsMetadataNewSlot());
                    Assert.Equal(MethodKind.PropertyGet, cM01Get.MethodKind);

                    Assert.Equal("System.Int32 C1.M01.get", cM01Get.ToTestDisplayString());

                    var m01Set = m01.SetMethod;
                    Assert.Same(m01Set, c.FindImplementationForInterfaceMember(m01Set));

                    if (module is PEModuleSymbol)
                    {
                        Assert.Same(m01Get, cM01Get.ExplicitInterfaceImplementations.Single());
                    }
                    else
                    {
                        Assert.Empty(cM01Get.ExplicitInterfaceImplementations);
                    }

                    Assert.Empty(cM01.ExplicitInterfaceImplementations);
                }

                var source6 =
@"
public class C1 : I1
{
   public static int M01 { set{} }
}
";

                var compilation6 = CreateCompilationWithIL(source6, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation6.VerifyDiagnostics(
                    // (2,19): error CS0535: 'C1' does not implement interface member 'I1.M01.get'
                    // public class C1 : I1
                    Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C1", "I1.M01.get").WithLocation(2, 19),
                    // (4,28): error CS9044: 'C1' does not implement interface member 'I1.M01.set'. 'C1.M01.set' cannot implicitly implement an inaccessible member.
                    //    public static int M01 { set{} }
                    Diagnostic(ErrorCode.ERR_ImplicitImplementationOfInaccessibleInterfaceMember, "set").WithArguments("C1", "I1.M01.set", "C1.M01.set").WithLocation(4, 28)
                    );

                c1 = compilation6.GlobalNamespace.GetTypeMember("C1");
                i1 = c1.Interfaces().Single();
                m01 = i1.GetMembers().OfType<PropertySymbol>().Single();
                c1M01 = c1.GetMembers().OfType<PropertySymbol>().Single();

                Assert.Same(c1M01, c1.FindImplementationForInterfaceMember(m01));
                Assert.Null(c1.FindImplementationForInterfaceMember(m01.GetMethod));
                Assert.Same(c1M01.SetMethod, c1.FindImplementationForInterfaceMember(m01.SetMethod));

                var source7 =
@"
public class C1 : I1
{
   static int I1.M01 { set{} }
}
";

                var compilation7 = CreateCompilationWithIL(source7, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation7.VerifyDiagnostics(
                    // (2,19): error CS0535: 'C1' does not implement interface member 'I1.M01.get'
                    // public class C1 : I1
                    Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C1", "I1.M01.get").WithLocation(2, 19),
                    // (4,18): error CS0122: 'I1.M01.set' is inaccessible due to its protection level
                    //    static int I1.M01 { set{} }
                    Diagnostic(ErrorCode.ERR_BadAccess, "M01").WithArguments("I1.M01.set").WithLocation(4, 18),
                    // (4,18): error CS0551: Explicit interface implementation 'C1.I1.M01' is missing accessor 'I1.M01.get'
                    //    static int I1.M01 { set{} }
                    Diagnostic(ErrorCode.ERR_ExplicitPropertyMissingAccessor, "M01").WithArguments("C1.I1.M01", "I1.M01.get").WithLocation(4, 18)
                    );

                c1 = compilation7.GlobalNamespace.GetTypeMember("C1");
                i1 = c1.Interfaces().Single();
                m01 = i1.GetMembers().OfType<PropertySymbol>().Single();
                c1M01 = c1.GetMembers().OfType<PropertySymbol>().Single();

                Assert.Same(c1M01, c1.FindImplementationForInterfaceMember(m01));
                Assert.Null(c1.FindImplementationForInterfaceMember(m01.GetMethod));
                Assert.Same(c1M01.SetMethod, c1.FindImplementationForInterfaceMember(m01.SetMethod));
                Assert.Same(m01, c1M01.ExplicitInterfaceImplementations.Single());
                Assert.Same(m01.SetMethod, c1M01.SetMethod.ExplicitInterfaceImplementations.Single());
            }

            void scenario3()
            {
                var ilSource = @"
.class interface public auto ansi abstract I1
{
    .method private hidebysig specialname static virtual
        int32 get_M01 () cil managed 
    {
        IL_0000: ldc.i4.0
        IL_0001: ret
    }

    .method public hidebysig specialname abstract virtual static 
        void set_M01 (
            int32 'value'
        ) cil managed 
    {
    }

    .property int32 M01()
    {
        .get int32 I1::get_M01()
        .set void I1::set_M01(int32)
    }
}
";

                var source1 =
@"
public class C1 : I1
{
}
";

                var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation1.VerifyDiagnostics(
                    // (2,19): error CS0535: 'C1' does not implement interface member 'I1.M01'
                    // public class C1 : I1
                    Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C1", "I1.M01").WithLocation(2, 19)
                    );

                var c1 = compilation1.GlobalNamespace.GetTypeMember("C1");
                var i1 = c1.Interfaces().Single();
                var m01 = i1.GetMembers().OfType<PropertySymbol>().Single();

                Assert.Null(c1.FindImplementationForInterfaceMember(m01));
                Assert.Null(i1.FindImplementationForInterfaceMember(m01));
                Assert.Same(m01.GetMethod, c1.FindImplementationForInterfaceMember(m01.GetMethod));
                Assert.Same(m01.GetMethod, i1.FindImplementationForInterfaceMember(m01.GetMethod));
                Assert.Null(c1.FindImplementationForInterfaceMember(m01.SetMethod));
                Assert.Null(i1.FindImplementationForInterfaceMember(m01.SetMethod));

                var source2 =
@"
public class C1 : I1
{
   static int I1.M01 { set{} }
}
";

                var compilation2 = CreateCompilationWithIL(source2, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation2.VerifyEmitDiagnostics(
                    // (4,18): error CS0122: 'I1.M01.get' is inaccessible due to its protection level
                    //    static int I1.M01 { set{} }
                    Diagnostic(ErrorCode.ERR_BadAccess, "M01").WithArguments("I1.M01.get").WithLocation(4, 18),
                    // (4,18): error CS0551: Explicit interface implementation 'C1.I1.M01' is missing accessor 'I1.M01.get'
                    //    static int I1.M01 { set{} }
                    Diagnostic(ErrorCode.ERR_ExplicitPropertyMissingAccessor, "M01").WithArguments("C1.I1.M01", "I1.M01.get").WithLocation(4, 18)
                    );

                validate2(compilation2.SourceModule);

                void validate2(ModuleSymbol module)
                {
                    var c = module.GlobalNamespace.GetTypeMember("C1");
                    var m01 = c.Interfaces().Single().GetMembers().OfType<PropertySymbol>().Single();
                    var m01Get = m01.GetMethod;
                    var m01Set = m01.SetMethod;

                    Assert.Equal(1, c.GetMembers().OfType<PropertySymbol>().Count());
                    Assert.Equal(1, c.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());

                    var cM01 = (PropertySymbol)c.FindImplementationForInterfaceMember(m01);

                    Assert.True(cM01.IsStatic);
                    Assert.False(cM01.IsAbstract);
                    Assert.False(cM01.IsVirtual);

                    Assert.Equal("System.Int32 C1.I1.M01 { set; }", cM01.ToTestDisplayString());

                    var cM01Set = cM01.SetMethod;
                    Assert.Same(cM01Set, c.FindImplementationForInterfaceMember(m01Set));

                    Assert.True(cM01Set.IsStatic);
                    Assert.False(cM01Set.IsAbstract);
                    Assert.False(cM01Set.IsVirtual);
                    Assert.False(cM01Set.IsMetadataVirtual());
                    Assert.False(cM01Set.IsMetadataFinal);
                    Assert.False(cM01Set.IsMetadataNewSlot());
                    Assert.Equal(MethodKind.PropertySet, cM01Set.MethodKind);

                    Assert.Equal("void C1.I1.M01.set", cM01Set.ToTestDisplayString());

                    Assert.Null(cM01.GetMethod);
                    Assert.Same(m01Get, c.FindImplementationForInterfaceMember(m01Get));

                    Assert.Same(m01, cM01.ExplicitInterfaceImplementations.Single());
                    Assert.Same(m01Set, cM01Set.ExplicitInterfaceImplementations.Single());
                }

                var source3 =
@"
public class C1 : I1
{
   public static int M01 { get; set; }
}
";

                var compilation3 = CreateCompilationWithIL(source3, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation3.VerifyDiagnostics(
                    // (4,28): error CS9044: 'C1' does not implement interface member 'I1.M01.get'. 'C1.M01.get' cannot implicitly implement an inaccessible member.
                    //    public static int M01 { get; set; }
                    Diagnostic(ErrorCode.ERR_ImplicitImplementationOfInaccessibleInterfaceMember, "get").WithArguments("C1", "I1.M01.get", "C1.M01.get").WithLocation(4, 28)
                    );

                validate3(compilation3.SourceModule);

                void validate3(ModuleSymbol module)
                {
                    var c = module.GlobalNamespace.GetTypeMember("C1");

                    var m01 = c.Interfaces().Single().GetMembers().OfType<PropertySymbol>().Single();
                    var m01Set = m01.SetMethod;

                    Assert.Equal(1, c.GetMembers().OfType<PropertySymbol>().Count());
                    Assert.Equal(2, c.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());

                    var cM01 = (PropertySymbol)c.FindImplementationForInterfaceMember(m01);

                    Assert.True(cM01.IsStatic);
                    Assert.False(cM01.IsAbstract);
                    Assert.False(cM01.IsVirtual);

                    Assert.Equal("System.Int32 C1.M01 { get; set; }", cM01.ToTestDisplayString());

                    var cM01Set = cM01.SetMethod;
                    Assert.Same(cM01Set, c.FindImplementationForInterfaceMember(m01Set));

                    Assert.True(cM01Set.IsStatic);
                    Assert.False(cM01Set.IsAbstract);
                    Assert.False(cM01Set.IsVirtual);
                    Assert.False(cM01Set.IsMetadataVirtual());
                    Assert.False(cM01Set.IsMetadataFinal);
                    Assert.False(cM01Set.IsMetadataNewSlot());
                    Assert.Equal(MethodKind.PropertySet, cM01Set.MethodKind);

                    Assert.Equal("void C1.M01.set", cM01Set.ToTestDisplayString());

                    var cM01Get = cM01.GetMethod;

                    Assert.True(cM01Get.IsStatic);
                    Assert.False(cM01Get.IsAbstract);
                    Assert.False(cM01Get.IsVirtual);
                    Assert.False(cM01Get.IsMetadataVirtual());
                    Assert.False(cM01Get.IsMetadataFinal);
                    Assert.False(cM01Get.IsMetadataNewSlot());
                    Assert.Equal(MethodKind.PropertyGet, cM01Get.MethodKind);

                    Assert.Equal("System.Int32 C1.M01.get", cM01Get.ToTestDisplayString());

                    var m01Get = m01.GetMethod;
                    Assert.Same(cM01Get, c.FindImplementationForInterfaceMember(m01Get));

                    if (module is PEModuleSymbol)
                    {
                        Assert.Same(m01, cM01.ExplicitInterfaceImplementations.Single());
                        Assert.Same(m01Set, cM01Set.ExplicitInterfaceImplementations.Single());
                        Assert.Same(m01Get, cM01Get.ExplicitInterfaceImplementations.Single());
                    }
                    else
                    {
                        Assert.Empty(cM01.ExplicitInterfaceImplementations);
                        Assert.Empty(cM01Set.ExplicitInterfaceImplementations);
                        Assert.Empty(cM01Get.ExplicitInterfaceImplementations);
                    }
                }

                var source4 =
@"
public class C1 : I1
{
   static int I1.M01 { get; set; }
}
";

                var compilation4 = CreateCompilationWithIL(source4, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation4.VerifyDiagnostics(
                    // (4,18): error CS0122: 'I1.M01.get' is inaccessible due to its protection level
                    //    static int I1.M01 { get; set; }
                    Diagnostic(ErrorCode.ERR_BadAccess, "M01").WithArguments("I1.M01.get").WithLocation(4, 18)
                   );

                c1 = compilation4.GlobalNamespace.GetTypeMember("C1");
                i1 = c1.Interfaces().Single();
                m01 = i1.GetMembers().OfType<PropertySymbol>().Single();
                var c1M01 = c1.GetMembers().OfType<PropertySymbol>().Single();

                Assert.Same(c1M01, c1.FindImplementationForInterfaceMember(m01));
                Assert.Same(c1M01.SetMethod, c1.FindImplementationForInterfaceMember(m01.SetMethod));
                Assert.Same(c1M01.GetMethod, c1.FindImplementationForInterfaceMember(m01.GetMethod));
                Assert.Same(m01, c1M01.ExplicitInterfaceImplementations.Single());
                Assert.Same(m01.GetMethod, c1M01.GetMethod.ExplicitInterfaceImplementations.Single());
                Assert.Same(m01.SetMethod, c1M01.SetMethod.ExplicitInterfaceImplementations.Single());

                var source5 =
@"
public class C1 : I1
{
   public static int M01 { set{} }
}
";

                var compilation5 = CreateCompilationWithIL(source5, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                CompileAndVerify(compilation5, sourceSymbolValidator: validate5, symbolValidator: validate5, verify: Verification.Skipped).VerifyDiagnostics();

                void validate5(ModuleSymbol module)
                {
                    var c = module.GlobalNamespace.GetTypeMember("C1");

                    var m01 = c.Interfaces().Single().GetMembers().OfType<PropertySymbol>().Single();
                    var m01Set = m01.SetMethod;

                    Assert.Equal(1, c.GetMembers().OfType<PropertySymbol>().Count());
                    Assert.Equal(1, c.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());

                    var cM01 = (PropertySymbol)c.FindImplementationForInterfaceMember(m01);

                    Assert.True(cM01.IsStatic);
                    Assert.False(cM01.IsAbstract);
                    Assert.False(cM01.IsVirtual);

                    Assert.Equal("System.Int32 C1.M01 { set; }", cM01.ToTestDisplayString());

                    var cM01Set = cM01.SetMethod;
                    Assert.Same(cM01Set, c.FindImplementationForInterfaceMember(m01Set));

                    Assert.True(cM01Set.IsStatic);
                    Assert.False(cM01Set.IsAbstract);
                    Assert.False(cM01Set.IsVirtual);
                    Assert.False(cM01Set.IsMetadataVirtual());
                    Assert.False(cM01Set.IsMetadataFinal);
                    Assert.False(cM01Set.IsMetadataNewSlot());
                    Assert.Equal(MethodKind.PropertySet, cM01Set.MethodKind);

                    Assert.Equal("void C1.M01.set", cM01Set.ToTestDisplayString());

                    var m01Get = m01.GetMethod;
                    Assert.Same(m01Get, c.FindImplementationForInterfaceMember(m01Get));

                    if (module is PEModuleSymbol)
                    {
                        Assert.Same(m01Set, cM01Set.ExplicitInterfaceImplementations.Single());
                    }
                    else
                    {
                        Assert.Empty(cM01Set.ExplicitInterfaceImplementations);
                    }

                    Assert.Empty(cM01.ExplicitInterfaceImplementations);
                }

                var source6 =
@"
public class C1 : I1
{
   public static int M01 { get; }
}
";

                var compilation6 = CreateCompilationWithIL(source6, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation6.VerifyDiagnostics(
                    // (2,19): error CS0535: 'C1' does not implement interface member 'I1.M01.set'
                    // public class C1 : I1
                    Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C1", "I1.M01.set").WithLocation(2, 19),
                    // (4,28): error CS9044: 'C1' does not implement interface member 'I1.M01.get'. 'C1.M01.get' cannot implicitly implement an inaccessible member.
                    //    public static int M01 { get; }
                    Diagnostic(ErrorCode.ERR_ImplicitImplementationOfInaccessibleInterfaceMember, "get").WithArguments("C1", "I1.M01.get", "C1.M01.get").WithLocation(4, 28)
                    );

                c1 = compilation6.GlobalNamespace.GetTypeMember("C1");
                i1 = c1.Interfaces().Single();
                m01 = i1.GetMembers().OfType<PropertySymbol>().Single();
                c1M01 = c1.GetMembers().OfType<PropertySymbol>().Single();

                Assert.Same(c1M01, c1.FindImplementationForInterfaceMember(m01));
                Assert.Same(c1M01.GetMethod, c1.FindImplementationForInterfaceMember(m01.GetMethod));
                Assert.Null(c1.FindImplementationForInterfaceMember(m01.SetMethod));

                var source7 =
@"
public class C1 : I1
{
   static int I1.M01 { get; }
}
";

                var compilation7 = CreateCompilationWithIL(source7, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation7.VerifyDiagnostics(
                    // (2,19): error CS0535: 'C1' does not implement interface member 'I1.M01.set'
                    // public class C1 : I1
                    Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C1", "I1.M01.set").WithLocation(2, 19),
                    // (4,18): error CS0122: 'I1.M01.get' is inaccessible due to its protection level
                    //    static int I1.M01 { get; }
                    Diagnostic(ErrorCode.ERR_BadAccess, "M01").WithArguments("I1.M01.get").WithLocation(4, 18),
                    // (4,18): error CS0551: Explicit interface implementation 'C1.I1.M01' is missing accessor 'I1.M01.set'
                    //    static int I1.M01 { get; }
                    Diagnostic(ErrorCode.ERR_ExplicitPropertyMissingAccessor, "M01").WithArguments("C1.I1.M01", "I1.M01.set").WithLocation(4, 18)
                    );

                c1 = compilation7.GlobalNamespace.GetTypeMember("C1");
                i1 = c1.Interfaces().Single();
                m01 = i1.GetMembers().OfType<PropertySymbol>().Single();
                c1M01 = c1.GetMembers().OfType<PropertySymbol>().Single();

                Assert.Same(c1M01, c1.FindImplementationForInterfaceMember(m01));
                Assert.Same(c1M01.GetMethod, c1.FindImplementationForInterfaceMember(m01.GetMethod));
                Assert.Null(c1.FindImplementationForInterfaceMember(m01.SetMethod));
                Assert.Same(m01, c1M01.ExplicitInterfaceImplementations.Single());
                Assert.Same(m01.GetMethod, c1M01.GetMethod.ExplicitInterfaceImplementations.Single());
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticProperty_12(bool isVirtual)
        {
            // Default interface implementation for a static method
            var (modifier, body) = GetILModifierAndBody(isVirtual);

            var ilSource = @"
.class interface public auto ansi abstract I1
{
    .method public hidebysig specialname " + modifier + @" virtual static 
        int32 get_M01 () cil managed 
    " + body + @"

    .method public hidebysig specialname " + modifier + @" virtual static 
        void set_M01 (
            int32 'value'
        ) cil managed 
    " + body + @"

    .property int32 M01()
    {
        .get int32 I1::get_M01()
        .set void I1::set_M01(int32)
    }
}

.class interface public auto ansi abstract I2
    implements I1
{
    .method private hidebysig specialname static
        int32 I1.get_M01 () cil managed 
    {
        .override method int32 I1::get_M01()
        IL_0000: ldc.i4.0
        IL_0001: ret
    }

    .method private hidebysig specialname static
        void I1.set_M01 (
            int32 'value'
        ) cil managed 
    {
        .override method void I1::set_M01(int32)
        IL_0000: ret
    }

    .property instance int32 I1.M01()
    {
        .get int32 I2::I1.get_M01()
        .set void I2::I1.set_M01(int32)
    }
}
";

            var source1 =
@"
public class C1 : I2
{
}
";

            var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyEmitDiagnostics();

            var c1 = compilation1.GlobalNamespace.GetTypeMember("C1");
            var i2 = c1.Interfaces().Single();
            var i1 = i2.Interfaces().Single();
            var m01 = i1.GetMembers().OfType<PropertySymbol>().Single();
            var i2M01 = i2.GetMembers().OfType<PropertySymbol>().Single();

            Assert.Same(i2M01, c1.FindImplementationForInterfaceMember(m01));
            Assert.Same(i2M01, i2.FindImplementationForInterfaceMember(m01));
            Assert.Same(i2M01.GetMethod, c1.FindImplementationForInterfaceMember(m01.GetMethod));
            Assert.Same(i2M01.GetMethod, i2.FindImplementationForInterfaceMember(m01.GetMethod));
            Assert.Same(i2M01.SetMethod, c1.FindImplementationForInterfaceMember(m01.SetMethod));
            Assert.Same(i2M01.SetMethod, i2.FindImplementationForInterfaceMember(m01.SetMethod));

            Assert.Same(m01, i2M01.ExplicitInterfaceImplementations.Single());
            Assert.Same(m01.GetMethod, i2M01.GetMethod.ExplicitInterfaceImplementations.Single());
            Assert.Same(m01.SetMethod, i2M01.SetMethod.ExplicitInterfaceImplementations.Single());
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticProperty_13(bool isVirtual)
        {
            // A forwarding method is added for an implicit implementation declared in base class. 
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static int M01 { get; set; }
}

class C1
{
    public static int M01 { get; set; }
}

class C2 : C1, I1
{
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var m01 = module.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<PropertySymbol>().Single();
                var c2 = module.GlobalNamespace.GetTypeMember("C2");

                var c2M01 = (PropertySymbol)c2.FindImplementationForInterfaceMember(m01);
                var c2M01Get = (MethodSymbol)c2.FindImplementationForInterfaceMember(m01.GetMethod);
                var c2M01Set = (MethodSymbol)c2.FindImplementationForInterfaceMember(m01.SetMethod);

                Assert.True(c2M01Get.IsStatic);
                Assert.False(c2M01Get.IsAbstract);
                Assert.False(c2M01Get.IsVirtual);
                Assert.False(c2M01Get.IsMetadataVirtual());
                Assert.False(c2M01Get.IsMetadataFinal);
                Assert.False(c2M01Get.IsMetadataNewSlot());

                Assert.True(c2M01Set.IsStatic);
                Assert.False(c2M01Set.IsAbstract);
                Assert.False(c2M01Set.IsVirtual);
                Assert.False(c2M01Set.IsMetadataVirtual());
                Assert.False(c2M01Set.IsMetadataFinal);
                Assert.False(c2M01Set.IsMetadataNewSlot());

                if (module is PEModuleSymbol)
                {
                    Assert.Equal(MethodKind.ExplicitInterfaceImplementation, c2M01Get.MethodKind);
                    Assert.False(c2M01Get.HasRuntimeSpecialName);
                    Assert.False(c2M01Get.HasSpecialName);
                    Assert.Equal("System.Int32 C2.I1.get_M01()", c2M01Get.ToTestDisplayString());
                    Assert.Same(m01.GetMethod, c2M01Get.ExplicitInterfaceImplementations.Single());

                    Assert.Equal(MethodKind.ExplicitInterfaceImplementation, c2M01Set.MethodKind);
                    Assert.False(c2M01Set.HasRuntimeSpecialName);
                    Assert.False(c2M01Set.HasSpecialName);
                    Assert.Equal("void C2.I1.set_M01(System.Int32 value)", c2M01Set.ToTestDisplayString());
                    Assert.Same(m01.SetMethod, c2M01Set.ExplicitInterfaceImplementations.Single());

                    // Forwarding methods for accessors aren't tied to a property
                    Assert.Null(c2M01);

                    var c1M01 = module.GlobalNamespace.GetMember<PropertySymbol>("C1.M01");
                    var c1M01Get = c1M01.GetMethod;
                    var c1M01Set = c1M01.SetMethod;

                    Assert.True(c1M01.IsStatic);
                    Assert.False(c1M01.IsAbstract);
                    Assert.False(c1M01.IsVirtual);
                    Assert.Empty(c1M01.ExplicitInterfaceImplementations);

                    Assert.True(c1M01Get.IsStatic);
                    Assert.False(c1M01Get.IsAbstract);
                    Assert.False(c1M01Get.IsVirtual);
                    Assert.False(c1M01Get.IsMetadataVirtual());
                    Assert.False(c1M01Get.IsMetadataFinal);
                    Assert.False(c1M01Get.IsMetadataNewSlot());
                    Assert.Equal(MethodKind.PropertyGet, c1M01Get.MethodKind);
                    Assert.False(c1M01Get.HasRuntimeSpecialName);
                    Assert.True(c1M01Get.HasSpecialName);
                    Assert.Empty(c1M01Get.ExplicitInterfaceImplementations);

                    Assert.True(c1M01Set.IsStatic);
                    Assert.False(c1M01Set.IsAbstract);
                    Assert.False(c1M01Set.IsVirtual);
                    Assert.False(c1M01Set.IsMetadataVirtual());
                    Assert.False(c1M01Set.IsMetadataFinal);
                    Assert.False(c1M01Set.IsMetadataNewSlot());
                    Assert.Equal(MethodKind.PropertySet, c1M01Set.MethodKind);
                    Assert.False(c1M01Set.HasRuntimeSpecialName);
                    Assert.True(c1M01Set.HasSpecialName);
                    Assert.Empty(c1M01Set.ExplicitInterfaceImplementations);
                }
                else
                {
                    Assert.True(c2M01.IsStatic);
                    Assert.False(c2M01.IsAbstract);
                    Assert.False(c2M01.IsVirtual);

                    Assert.Equal("System.Int32 C1.M01 { get; set; }", c2M01.ToTestDisplayString());
                    Assert.Empty(c2M01.ExplicitInterfaceImplementations);

                    Assert.Equal(MethodKind.PropertyGet, c2M01Get.MethodKind);
                    Assert.False(c2M01Get.HasRuntimeSpecialName);
                    Assert.True(c2M01Get.HasSpecialName);
                    Assert.Same(c2M01.GetMethod, c2M01Get);
                    Assert.Empty(c2M01Get.ExplicitInterfaceImplementations);

                    Assert.Equal(MethodKind.PropertySet, c2M01Set.MethodKind);
                    Assert.False(c2M01Set.HasRuntimeSpecialName);
                    Assert.True(c2M01Set.HasSpecialName);
                    Assert.Same(c2M01.SetMethod, c2M01Set);
                    Assert.Empty(c2M01Set.ExplicitInterfaceImplementations);
                }
            }

            verifier.VerifyIL("C2.I1.get_M01",
@"
{
  // Code size        6 (0x6)
  .maxstack  1
  IL_0000:  call       ""int C1.M01.get""
  IL_0005:  ret
}
");

            verifier.VerifyIL("C2.I1.set_M01",
@"
{
  // Code size        7 (0x7)
  .maxstack  1
  IL_0000:  ldarg.0
  IL_0001:  call       ""void C1.M01.set""
  IL_0006:  ret
}
");
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticProperty_14(bool isVirtual)
        {
            // A forwarding method is added for an implicit implementation with modopt mismatch. 
            var (modifier, body) = GetILModifierAndBody(isVirtual);

            var ilSource = @"
.class interface public auto ansi abstract I1
{
    .method public hidebysig specialname " + modifier + @" virtual static 
        int32 get_M01 () cil managed 
    " + body + @"

    .method public hidebysig specialname " + modifier + @" virtual static 
        void modopt(I1) set_M01 (
            int32 modopt(I1) 'value'
        ) cil managed 
    " + body + @"

    .property int32 M01()
    {
        .get int32 I1::get_M01()
        .set void modopt(I1) I1::set_M01(int32 modopt(I1))
    }
}

.class interface public auto ansi abstract I2
{
    .method public hidebysig specialname abstract virtual static 
        int32 modopt(I2) get_M01 () cil managed 
    {
    }

    .method public hidebysig specialname abstract virtual static 
        void set_M01 (
            int32 modopt(I2) 'value'
        ) cil managed 
    {
    }

    .property int32 modopt(I2) M01()
    {
        .get int32 modopt(I2) I2::get_M01()
        .set void I2::set_M01(int32 modopt(I2))
    }
}
";

            var source1 =
@"
class C1 : I1
{
    public static int M01 { get; set; }
}

class C2 : I1
{
    static int I1.M01 { get; set; }
}

class C3 : I2
{
    static int I2.M01 { get; set; }
}
";

            var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var c1 = module.GlobalNamespace.GetTypeMember("C1");
                var m01 = c1.Interfaces().Single().GetMembers().OfType<PropertySymbol>().Single();

                var c1M01 = (PropertySymbol)c1.FindImplementationForInterfaceMember(m01);
                var c1M01Get = c1M01.GetMethod;
                var c1M01Set = c1M01.SetMethod;

                Assert.Equal("System.Int32 C1.M01 { get; set; }", c1M01.ToTestDisplayString());
                Assert.Empty(c1M01.ExplicitInterfaceImplementations);
                Assert.True(c1M01.IsStatic);
                Assert.False(c1M01.IsAbstract);
                Assert.False(c1M01.IsVirtual);

                Assert.Equal(MethodKind.PropertyGet, c1M01Get.MethodKind);
                Assert.Equal("System.Int32 C1.M01.get", c1M01Get.ToTestDisplayString());
                Assert.True(c1M01Get.IsStatic);
                Assert.False(c1M01Get.IsAbstract);
                Assert.False(c1M01Get.IsVirtual);
                Assert.False(c1M01Get.IsMetadataVirtual());
                Assert.False(c1M01Get.IsMetadataFinal);
                Assert.False(c1M01Get.IsMetadataNewSlot());
                Assert.Same(c1M01Get, c1.FindImplementationForInterfaceMember(m01.GetMethod));

                Assert.Equal(MethodKind.PropertySet, c1M01Set.MethodKind);
                Assert.Equal("void C1.M01.set", c1M01Set.ToTestDisplayString());
                Assert.Empty(c1M01Set.ExplicitInterfaceImplementations);
                Assert.True(c1M01Set.IsStatic);
                Assert.False(c1M01Set.IsAbstract);
                Assert.False(c1M01Set.IsVirtual);
                Assert.False(c1M01Set.IsMetadataVirtual());
                Assert.False(c1M01Set.IsMetadataFinal);
                Assert.False(c1M01Set.IsMetadataNewSlot());

                if (module is PEModuleSymbol)
                {
                    Assert.Same(m01.GetMethod, c1M01Get.ExplicitInterfaceImplementations.Single());

                    c1M01Set = (MethodSymbol)c1.FindImplementationForInterfaceMember(m01.SetMethod);
                    Assert.Equal(MethodKind.ExplicitInterfaceImplementation, c1M01Set.MethodKind);
                    Assert.Equal("void modopt(I1) C1.I1.set_M01(System.Int32 modopt(I1) value)", c1M01Set.ToTestDisplayString());
                    Assert.Same(m01.SetMethod, c1M01Set.ExplicitInterfaceImplementations.Single());

                    Assert.True(c1M01Set.IsStatic);
                    Assert.False(c1M01Set.IsAbstract);
                    Assert.False(c1M01Set.IsVirtual);
                    Assert.False(c1M01Set.IsMetadataVirtual());
                    Assert.False(c1M01Set.IsMetadataFinal);
                    Assert.False(c1M01Set.IsMetadataNewSlot());
                }
                else
                {
                    Assert.Empty(c1M01Get.ExplicitInterfaceImplementations);
                    Assert.Same(c1M01Set, c1.FindImplementationForInterfaceMember(m01.SetMethod));
                }

                var c2 = module.GlobalNamespace.GetTypeMember("C2");

                var c2M01 = (PropertySymbol)c2.FindImplementationForInterfaceMember(m01);
                var c2M01Get = c2M01.GetMethod;
                var c2M01Set = c2M01.SetMethod;

                Assert.Equal("System.Int32 C2.I1.M01 { get; set; }", c2M01.ToTestDisplayString());

                Assert.True(c2M01.IsStatic);
                Assert.False(c2M01.IsAbstract);
                Assert.False(c2M01.IsVirtual);
                Assert.Same(m01, c2M01.ExplicitInterfaceImplementations.Single());

                Assert.True(c2M01Get.IsStatic);
                Assert.False(c2M01Get.IsAbstract);
                Assert.False(c2M01Get.IsVirtual);
                Assert.False(c2M01Get.IsMetadataVirtual());
                Assert.False(c2M01Get.IsMetadataFinal);
                Assert.False(c2M01Get.IsMetadataNewSlot());
                Assert.Equal(MethodKind.PropertyGet, c2M01Get.MethodKind);
                Assert.Equal("System.Int32 C2.I1.M01.get", c2M01Get.ToTestDisplayString());
                Assert.Same(m01.GetMethod, c2M01Get.ExplicitInterfaceImplementations.Single());
                Assert.Same(c2M01Get, c2.FindImplementationForInterfaceMember(m01.GetMethod));

                Assert.True(c2M01Set.IsStatic);
                Assert.False(c2M01Set.IsAbstract);
                Assert.False(c2M01Set.IsVirtual);
                Assert.False(c2M01Set.IsMetadataVirtual());
                Assert.False(c2M01Set.IsMetadataFinal);
                Assert.False(c2M01Set.IsMetadataNewSlot());
                Assert.Equal(MethodKind.PropertySet, c2M01Set.MethodKind);
                Assert.Equal("void modopt(I1) C2.I1.M01.set", c2M01Set.ToTestDisplayString());
                Assert.Equal("System.Int32 modopt(I1) value", c2M01Set.Parameters.Single().ToTestDisplayString());
                Assert.Same(m01.SetMethod, c2M01Set.ExplicitInterfaceImplementations.Single());
                Assert.Same(c2M01Set, c2.FindImplementationForInterfaceMember(m01.SetMethod));

                Assert.Same(c2M01, c2.GetMembers().OfType<PropertySymbol>().Single());
                Assert.Equal(2, c2.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());

                var c3 = module.GlobalNamespace.GetTypeMember("C3");
                m01 = c3.Interfaces().Single().GetMembers().OfType<PropertySymbol>().Single();

                var c3M01 = (PropertySymbol)c3.FindImplementationForInterfaceMember(m01);
                var c3M01Get = c3M01.GetMethod;
                var c3M01Set = c3M01.SetMethod;

                Assert.Equal("System.Int32 modopt(I2) C3.I2.M01 { get; set; }", c3M01.ToTestDisplayString());

                Assert.True(c3M01.IsStatic);
                Assert.False(c3M01.IsAbstract);
                Assert.False(c3M01.IsVirtual);
                Assert.Same(m01, c3M01.ExplicitInterfaceImplementations.Single());

                Assert.True(c3M01Get.IsStatic);
                Assert.False(c3M01Get.IsAbstract);
                Assert.False(c3M01Get.IsVirtual);
                Assert.False(c3M01Get.IsMetadataVirtual());
                Assert.False(c3M01Get.IsMetadataFinal);
                Assert.False(c3M01Get.IsMetadataNewSlot());
                Assert.Equal(MethodKind.PropertyGet, c3M01Get.MethodKind);
                Assert.Equal("System.Int32 modopt(I2) C3.I2.M01.get", c3M01Get.ToTestDisplayString());
                Assert.Same(m01.GetMethod, c3M01Get.ExplicitInterfaceImplementations.Single());
                Assert.Same(c3M01Get, c3.FindImplementationForInterfaceMember(m01.GetMethod));

                Assert.True(c3M01Set.IsStatic);
                Assert.False(c3M01Set.IsAbstract);
                Assert.False(c3M01Set.IsVirtual);
                Assert.False(c3M01Set.IsMetadataVirtual());
                Assert.False(c3M01Set.IsMetadataFinal);
                Assert.False(c3M01Set.IsMetadataNewSlot());
                Assert.Equal(MethodKind.PropertySet, c3M01Set.MethodKind);
                Assert.Equal("void C3.I2.M01.set", c3M01Set.ToTestDisplayString());
                Assert.Equal("System.Int32 modopt(I2) value", c3M01Set.Parameters.Single().ToTestDisplayString());
                Assert.Same(m01.SetMethod, c3M01Set.ExplicitInterfaceImplementations.Single());
                Assert.Same(c3M01Set, c3.FindImplementationForInterfaceMember(m01.SetMethod));

                Assert.Same(c3M01, c3.GetMembers().OfType<PropertySymbol>().Single());
                Assert.Equal(2, c3.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());
            }

            verifier.VerifyIL("C1.I1.set_M01",
@"
{
  // Code size        7 (0x7)
  .maxstack  1
  IL_0000:  ldarg.0
  IL_0001:  call       ""void C1.M01.set""
  IL_0006:  ret
}
");
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStatiProperty_15(bool isVirtual)
        {
            // A forwarding method isn't created if base class implements interface exactly the same way. 
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static int M01 { get; set; }
    " + modifier + @" static int M02 { get; set; }
}

public class C1
{
    public static int M01 { get; set; }
}

public class C2 : C1, I1
{
    static int I1.M02 { get; set; }
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C3 : C2, I1
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.RegularPreview, TestOptions.Regular10 })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                         parseOptions: parseOptions,
                                                         targetFramework: _supportingFramework,
                                                         references: new[] { reference });
                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c3 = module.GlobalNamespace.GetTypeMember("C3");
                Assert.Empty(c3.GetMembers().OfType<PropertySymbol>());
                Assert.Empty(c3.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()));

                var m01 = c3.Interfaces().Single().GetMembers("M01").OfType<PropertySymbol>().Single();

                var c1M01 = c3.BaseType().BaseType().GetMember<PropertySymbol>("M01");
                Assert.Equal("System.Int32 C1.M01 { get; set; }", c1M01.ToTestDisplayString());

                Assert.True(c1M01.IsStatic);
                Assert.False(c1M01.IsAbstract);
                Assert.False(c1M01.IsVirtual);

                Assert.Empty(c1M01.ExplicitInterfaceImplementations);

                var c1M01Get = c1M01.GetMethod;
                Assert.True(c1M01Get.IsStatic);
                Assert.False(c1M01Get.IsAbstract);
                Assert.False(c1M01Get.IsVirtual);
                Assert.False(c1M01Get.IsMetadataVirtual());
                Assert.False(c1M01Get.IsMetadataFinal);
                Assert.False(c1M01Get.IsMetadataNewSlot());

                Assert.Empty(c1M01Get.ExplicitInterfaceImplementations);

                var c1M01Set = c1M01.SetMethod;
                Assert.True(c1M01Set.IsStatic);
                Assert.False(c1M01Set.IsAbstract);
                Assert.False(c1M01Set.IsVirtual);
                Assert.False(c1M01Set.IsMetadataVirtual());
                Assert.False(c1M01Set.IsMetadataFinal);
                Assert.False(c1M01Set.IsMetadataNewSlot());

                Assert.Empty(c1M01Set.ExplicitInterfaceImplementations);

                if (c1M01.ContainingModule is PEModuleSymbol)
                {
                    var c2M01Get = c3.FindImplementationForInterfaceMember(m01.GetMethod);
                    Assert.Equal("System.Int32 C2.I1.get_M01()", c2M01Get.ToTestDisplayString());

                    var c2M01Set = c3.FindImplementationForInterfaceMember(m01.SetMethod);
                    Assert.Equal("void C2.I1.set_M01(System.Int32 value)", c2M01Set.ToTestDisplayString());

                    // Forwarding methods for accessors aren't tied to a property
                    Assert.Null(c3.FindImplementationForInterfaceMember(m01));
                }
                else
                {
                    Assert.Same(c1M01, c3.FindImplementationForInterfaceMember(m01));
                    Assert.Same(c1M01.GetMethod, c3.FindImplementationForInterfaceMember(m01.GetMethod));
                    Assert.Same(c1M01.SetMethod, c3.FindImplementationForInterfaceMember(m01.SetMethod));
                }

                var m02 = c3.Interfaces().Single().GetMembers("M02").OfType<PropertySymbol>().Single();

                var c2M02 = c3.BaseType().GetMember<PropertySymbol>("I1.M02");
                Assert.Equal("System.Int32 C2.I1.M02 { get; set; }", c2M02.ToTestDisplayString());
                Assert.Same(c2M02, c3.FindImplementationForInterfaceMember(m02));
                Assert.Same(c2M02.GetMethod, c3.FindImplementationForInterfaceMember(m02.GetMethod));
                Assert.Same(c2M02.SetMethod, c3.FindImplementationForInterfaceMember(m02.SetMethod));
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticProperty_16(bool isVirtual)
        {
            // A new implicit implementation is properly considered.
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1
{
    " + modifier + @" static int M01 { get; set; }
}

public class C1 : I1
{
    public static int M01 { get; set; }
}

public class C2 : C1
{
    new public static int M01 { get; set; }
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C3 : C2, I1
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                        parseOptions: TestOptions.RegularPreview,
                                                        targetFramework: _supportingFramework,
                                                        references: new[] { reference });
                var verifier = CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

                verifier.VerifyIL("C3.I1.get_M01",
@"
{
  // Code size        6 (0x6)
  .maxstack  1
  IL_0000:  call       ""int C2.M01.get""
  IL_0005:  ret
}
");

                verifier.VerifyIL("C3.I1.set_M01",
@"
{
  // Code size        7 (0x7)
  .maxstack  1
  IL_0000:  ldarg.0
  IL_0001:  call       ""void C2.M01.set""
  IL_0006:  ret
}
");
            }

            void validate(ModuleSymbol module)
            {
                var c3 = module.GlobalNamespace.GetTypeMember("C3");
                var m01 = c3.Interfaces().Single().GetMembers().OfType<PropertySymbol>().Single();

                var c2M01 = c3.BaseType().GetMember<PropertySymbol>("M01");
                var c2M01Get = c2M01.GetMethod;
                var c2M01Set = c2M01.SetMethod;
                Assert.Equal("System.Int32 C2.M01 { get; set; }", c2M01.ToTestDisplayString());

                Assert.True(c2M01.IsStatic);
                Assert.False(c2M01.IsAbstract);
                Assert.False(c2M01.IsVirtual);
                Assert.Empty(c2M01.ExplicitInterfaceImplementations);

                Assert.True(c2M01Get.IsStatic);
                Assert.False(c2M01Get.IsAbstract);
                Assert.False(c2M01Get.IsVirtual);
                Assert.False(c2M01Get.IsMetadataVirtual());
                Assert.False(c2M01Get.IsMetadataFinal);
                Assert.False(c2M01Get.IsMetadataNewSlot());
                Assert.Empty(c2M01Get.ExplicitInterfaceImplementations);

                Assert.True(c2M01Set.IsStatic);
                Assert.False(c2M01Set.IsAbstract);
                Assert.False(c2M01Set.IsVirtual);
                Assert.False(c2M01Set.IsMetadataVirtual());
                Assert.False(c2M01Set.IsMetadataFinal);
                Assert.False(c2M01Set.IsMetadataNewSlot());
                Assert.Empty(c2M01Set.ExplicitInterfaceImplementations);

                if (module is PEModuleSymbol)
                {
                    var c3M01 = (PropertySymbol)c3.FindImplementationForInterfaceMember(m01);
                    // Forwarding methods for accessors aren't tied to a property
                    Assert.Null(c3M01);

                    var c3M01Get = (MethodSymbol)c3.FindImplementationForInterfaceMember(m01.GetMethod);
                    Assert.Equal("System.Int32 C3.I1.get_M01()", c3M01Get.ToTestDisplayString());
                    Assert.Same(m01.GetMethod, c3M01Get.ExplicitInterfaceImplementations.Single());

                    var c3M01Set = (MethodSymbol)c3.FindImplementationForInterfaceMember(m01.SetMethod);
                    Assert.Equal("void C3.I1.set_M01(System.Int32 value)", c3M01Set.ToTestDisplayString());
                    Assert.Same(m01.SetMethod, c3M01Set.ExplicitInterfaceImplementations.Single());
                }
                else
                {
                    Assert.Same(c2M01, c3.FindImplementationForInterfaceMember(m01));
                    Assert.Same(c2M01Get, c3.FindImplementationForInterfaceMember(m01.GetMethod));
                    Assert.Same(c2M01Set, c3.FindImplementationForInterfaceMember(m01.SetMethod));
                }
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticProperty_19(bool genericFirst, bool isVirtual)
        {
            // An "ambiguity" in implicit/explicit implementation declared in generic base class.
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var generic =
@"
    public static T M01 { get; set; }
";
            var nonGeneric =
@"
    static int I1.M01 { get; set; }
";
            var source1 =
@"
public interface I1
{
    " + modifier + @" static int M01 { get; set; }
}

public class C1<T> : I1
{
" + (genericFirst ? generic + nonGeneric : nonGeneric + generic) + @"
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { CreateCompilation("", targetFramework: _supportingFramework).ToMetadataReference() });

            Assert.Equal(2, compilation1.GlobalNamespace.GetTypeMember("C1").GetMembers().OfType<PropertySymbol>().Where(m => m.Name.Contains("M01")).Count());
            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C2 : C1<int>, I1
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.Regular10, TestOptions.RegularPreview })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: parseOptions,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { reference });

                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c2 = module.GlobalNamespace.GetTypeMember("C2");
                var m01 = c2.Interfaces().Single().GetMembers().OfType<PropertySymbol>().Single();

                Assert.True(m01.ContainingModule is RetargetingModuleSymbol or PEModuleSymbol);

                var c1M01 = (PropertySymbol)c2.FindImplementationForInterfaceMember(m01);
                Assert.Equal("System.Int32 C1<T>.I1.M01 { get; set; }", c1M01.OriginalDefinition.ToTestDisplayString());
                Assert.Same(m01, c1M01.ExplicitInterfaceImplementations.Single());
                Assert.Same(c1M01, c2.BaseType().FindImplementationForInterfaceMember(m01));
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticProperty_20(bool genericFirst, bool isVirtual)
        {
            // Same as ImplementAbstractStaticProperty_19 only interface is generic too.
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var generic =
@"
    static T I1<T>.M01 { get; set; }
";
            var nonGeneric =
@"
    public static int M01 { get; set; }
";
            var source1 =
@"
public interface I1<T>
{
    " + modifier + @" static T M01 { get; set; }
}

public class C1<T> : I1<T>
{
" + (genericFirst ? generic + nonGeneric : nonGeneric + generic) + @"
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { CreateCompilation("", targetFramework: _supportingFramework).ToMetadataReference() });

            Assert.Equal(2, compilation1.GlobalNamespace.GetTypeMember("C1").GetMembers().OfType<PropertySymbol>().Where(m => m.Name.Contains("M01")).Count());

            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C2 : C1<int>, I1<int>
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.Regular10, TestOptions.RegularPreview })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: parseOptions,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { reference });

                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c2 = module.GlobalNamespace.GetTypeMember("C2");
                var m01 = c2.Interfaces().Single().GetMembers().OfType<PropertySymbol>().Single();

                Assert.True(m01.ContainingModule is RetargetingModuleSymbol or PEModuleSymbol);

                var c1M01 = (PropertySymbol)c2.FindImplementationForInterfaceMember(m01);
                Assert.Equal("T C1<T>.I1<T>.M01 { get; set; }", c1M01.OriginalDefinition.ToTestDisplayString());
                Assert.Equal(m01, c1M01.ExplicitInterfaceImplementations.Single());
                Assert.Same(c1M01, c2.BaseType().FindImplementationForInterfaceMember(m01));
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticEvent_01(bool structure)
        {
            var typeKeyword = structure ? "struct" : "class";

            var source1 =
@"#pragma warning disable CS0067 // WRN_UnreferencedEvent
public interface I1
{
    abstract static event System.Action M01;
}

" + typeKeyword + @"
    C1 : I1
{}

" + typeKeyword + @"
    C2 : I1
{
    public event System.Action M01;
}

" + typeKeyword + @"
    C3 : I1
{
    static event System.Action M01;
}

" + typeKeyword + @"
    C4 : I1
{
    event System.Action I1.M01 { add{} remove{}}
}

" + typeKeyword + @"
    C5 : I1
{
    public static event System.Action<int> M01;
}

" + typeKeyword + @"
    C6 : I1
{
    static event System.Action<int> I1.M01 { add{} remove{}}
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (8,10): error CS0535: 'C1' does not implement interface member 'I1.M01'
                //     C1 : I1
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C1", "I1.M01").WithLocation(8, 10),
                // (12,10): error CS8928: 'C2' does not implement static interface member 'I1.M01'. 'C2.M01' cannot implement the interface member because it is not static.
                //     C2 : I1
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberNotStatic, "I1").WithArguments("C2", "I1.M01", "C2.M01").WithLocation(12, 10),
                // (18,10): error CS0737: 'C3' does not implement interface member 'I1.M01'. 'C3.M01' cannot implement an interface member because it is not public.
                //     C3 : I1
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberNotPublic, "I1").WithArguments("C3", "I1.M01", "C3.M01").WithLocation(18, 10),
                // (24,10): error CS0535: 'C4' does not implement interface member 'I1.M01'
                //     C4 : I1
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C4", "I1.M01").WithLocation(24, 10),
                // (26,28): error CS0539: 'C4.M01' in explicit interface declaration is not found among members of the interface that can be implemented
                //     event System.Action I1.M01 { add{} remove{}}
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "M01").WithArguments("C4.M01").WithLocation(26, 28),
                // (30,10): error CS0738: 'C5' does not implement interface member 'I1.M01'. 'C5.M01' cannot implement 'I1.M01' because it does not have the matching return type of 'Action'.
                //     C5 : I1
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberWrongReturnType, "I1").WithArguments("C5", "I1.M01", "C5.M01", "System.Action").WithLocation(30, 10),
                // (36,10): error CS0535: 'C6' does not implement interface member 'I1.M01'
                //     C6 : I1
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C6", "I1.M01").WithLocation(36, 10),
                // (38,40): error CS9333: 'C6.M01' type must be 'System.Action' to match implemented member 'I1.M01'
                //     static event System.Action<int> I1.M01 { add{} remove{}}
                Diagnostic(ErrorCode.ERR_ExplicitInterfaceMemberTypeMismatch, "M01").WithArguments("C6.M01", "System.Action", "I1.M01").WithLocation(38, 40)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementVirtualStaticEvent_01(bool structure)
        {
            var typeKeyword = structure ? "struct" : "class";

            var source1 =
@"#pragma warning disable CS0067 // WRN_UnreferencedEvent
public interface I1
{
    virtual static event System.Action M01;
}

" + typeKeyword + @"
    C1 : I1
{}

" + typeKeyword + @"
    C2 : I1
{
    public event System.Action M01;
}

" + typeKeyword + @"
    C3 : I1
{
    static event System.Action M01;
}

" + typeKeyword + @"
    C4 : I1
{
    event System.Action I1.M01 { add{} remove{}}
}

" + typeKeyword + @"
    C5 : I1
{
    public static event System.Action<int> M01;
}

" + typeKeyword + @"
    C6 : I1
{
    static event System.Action<int> I1.M01 { add{} remove{}}
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (26,28): error CS0539: 'C4.M01' in explicit interface declaration is not found among members of the interface that can be implemented
                //     event System.Action I1.M01 { add{} remove{}}
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "M01").WithArguments("C4.M01").WithLocation(26, 28),
                // (38,40): error CS9333: 'C6.M01' type must be 'System.Action' to match implemented member 'I1.M01'
                //     static event System.Action<int> I1.M01 { add{} remove{}}
                Diagnostic(ErrorCode.ERR_ExplicitInterfaceMemberTypeMismatch, "M01").WithArguments("C6.M01", "System.Action", "I1.M01").WithLocation(38, 40)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticEvent_02(bool structure)
        {
            var typeKeyword = structure ? "struct" : "class";

            var source1 =
@"#pragma warning disable CS0067 // WRN_UnreferencedEvent
public interface I1
{
    abstract event System.Action M01;
}

" + typeKeyword + @"
    C1 : I1
{}

" + typeKeyword + @"
    C2 : I1
{
    public static event System.Action M01;
}

" + typeKeyword + @"
    C3 : I1
{
    event System.Action M01;
}

" + typeKeyword + @"
    C4 : I1
{
    static event System.Action I1.M01 { add{} remove{} }
}

" + typeKeyword + @"
    C5 : I1
{
    public event System.Action<int> M01;
}

" + typeKeyword + @"
    C6 : I1
{
    event System.Action<int> I1.M01 { add{} remove{} }
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (8,10): error CS0535: 'C1' does not implement interface member 'I1.M01'
                //     C1 : I1
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C1", "I1.M01").WithLocation(8, 10),
                // (12,10): error CS0736: 'C2' does not implement instance interface member 'I1.M01'. 'C2.M01' cannot implement the interface member because it is static.
                //     C2 : I1
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberStatic, "I1").WithArguments("C2", "I1.M01", "C2.M01").WithLocation(12, 10),
                // (18,10): error CS0737: 'C3' does not implement interface member 'I1.M01'. 'C3.M01' cannot implement an interface member because it is not public.
                //     C3 : I1
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberNotPublic, "I1").WithArguments("C3", "I1.M01", "C3.M01").WithLocation(18, 10),
                // (24,10): error CS0535: 'C4' does not implement interface member 'I1.M01'
                //     C4 : I1
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C4", "I1.M01").WithLocation(24, 10),
                // (26,35): error CS0539: 'C4.M01' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static event System.Action I1.M01 { add{} remove{} }
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "M01").WithArguments("C4.M01").WithLocation(26, 35),
                // (30,10): error CS0738: 'C5' does not implement interface member 'I1.M01'. 'C5.M01' cannot implement 'I1.M01' because it does not have the matching return type of 'Action'.
                //     C5 : I1
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberWrongReturnType, "I1").WithArguments("C5", "I1.M01", "C5.M01", "System.Action").WithLocation(30, 10),
                // (36,10): error CS0535: 'C6' does not implement interface member 'I1.M01'
                //     C6 : I1
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C6", "I1.M01").WithLocation(36, 10),
                // (38,33): error CS9333: 'C6.M01' type must be 'System.Action' to match implemented member 'I1.M01'
                //     event System.Action<int> I1.M01 { add{} remove{} }
                Diagnostic(ErrorCode.ERR_ExplicitInterfaceMemberTypeMismatch, "M01").WithArguments("C6.M01", "System.Action", "I1.M01").WithLocation(38, 33)
                );
        }

        [Fact]
        public void ImplementAbstractStaticEvent_03()
        {
            var source1 =
@"#pragma warning disable CS0067 // WRN_UnreferencedEvent
public interface I1
{
    abstract static event System.Action M01;
}

interface I2 : I1
{}

interface I3 : I1
{
    public virtual event System.Action M01 { add{} remove{} }
}

interface I4 : I1
{
    static event System.Action M01;
}

interface I5 : I1
{
    event System.Action I1.M01 { add{} remove{} }
}

interface I6 : I1
{
    static event System.Action I1.M01 { add{} remove{} }
}

interface I7 : I1
{
    abstract static event System.Action M01;
}

interface I8 : I1
{
    abstract static event System.Action I1.M01;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (12,40): warning CS0108: 'I3.M01' hides inherited member 'I1.M01'. Use the new keyword if hiding was intended.
                //     public virtual event System.Action M01 { add{} remove{} }
                Diagnostic(ErrorCode.WRN_NewRequired, "M01").WithArguments("I3.M01", "I1.M01").WithLocation(12, 40),
                // (17,32): warning CS0108: 'I4.M01' hides inherited member 'I1.M01'. Use the new keyword if hiding was intended.
                //     static event System.Action M01;
                Diagnostic(ErrorCode.WRN_NewRequired, "M01").WithArguments("I4.M01", "I1.M01").WithLocation(17, 32),
                // (22,28): error CS0539: 'I5.M01' in explicit interface declaration is not found among members of the interface that can be implemented
                //     event System.Action I1.M01 { add{} remove{} }
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "M01").WithArguments("I5.M01").WithLocation(22, 28),
                // (32,41): warning CS0108: 'I7.M01' hides inherited member 'I1.M01'. Use the new keyword if hiding was intended.
                //     abstract static event System.Action M01;
                Diagnostic(ErrorCode.WRN_NewRequired, "M01").WithArguments("I7.M01", "I1.M01").WithLocation(32, 41)
                );

            foreach (var m01 in compilation1.GlobalNamespace.GetTypeMember("I1").GetMembers())
            {
                Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I2").FindImplementationForInterfaceMember(m01));
                Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I3").FindImplementationForInterfaceMember(m01));
                Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I4").FindImplementationForInterfaceMember(m01));
                Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I5").FindImplementationForInterfaceMember(m01));

                Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I7").FindImplementationForInterfaceMember(m01));
                Assert.Null(compilation1.GlobalNamespace.GetTypeMember("I8").FindImplementationForInterfaceMember(m01));
            }

            var m = compilation1.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<EventSymbol>().Single();
            var i6 = compilation1.GlobalNamespace.GetTypeMember("I6");
            var i6m = i6.GetMembers().OfType<EventSymbol>().Single();
            Assert.Same(i6m, i6.FindImplementationForInterfaceMember(m));
            Assert.Same(i6m.AddMethod, ((EventSymbol)i6.FindImplementationForInterfaceMember(m)).AddMethod);
            Assert.Same(i6m.RemoveMethod, ((EventSymbol)i6.FindImplementationForInterfaceMember(m)).RemoveMethod);
        }

        [Fact]
        public void ImplementVirtualStaticEvent_03()
        {
            var source1 =
@"#pragma warning disable CS0067 // WRN_UnreferencedEvent
public interface I1
{
    virtual  static event System.Action M01;
}

interface I2 : I1
{}

interface I3 : I1
{
    public virtual event System.Action M01 { add{} remove{} }
}

interface I4 : I1
{
    static event System.Action M01;
}

interface I5 : I1
{
    event System.Action I1.M01 { add{} remove{} }
}

interface I6 : I1
{
    static event System.Action I1.M01 { add{} remove{} }
}

interface I7 : I1
{
    virtual  static event System.Action M01;
}

interface I8 : I1
{
    virtual  static event System.Action I1.M01;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (12,40): warning CS0108: 'I3.M01' hides inherited member 'I1.M01'. Use the new keyword if hiding was intended.
                //     public virtual event System.Action M01 { add{} remove{} }
                Diagnostic(ErrorCode.WRN_NewRequired, "M01").WithArguments("I3.M01", "I1.M01").WithLocation(12, 40),
                // (17,32): warning CS0108: 'I4.M01' hides inherited member 'I1.M01'. Use the new keyword if hiding was intended.
                //     static event System.Action M01;
                Diagnostic(ErrorCode.WRN_NewRequired, "M01").WithArguments("I4.M01", "I1.M01").WithLocation(17, 32),
                // (22,28): error CS0539: 'I5.M01' in explicit interface declaration is not found among members of the interface that can be implemented
                //     event System.Action I1.M01 { add{} remove{} }
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "M01").WithArguments("I5.M01").WithLocation(22, 28),
                // (32,41): warning CS0108: 'I7.M01' hides inherited member 'I1.M01'. Use the new keyword if hiding was intended.
                //     virtual  static event System.Action M01;
                Diagnostic(ErrorCode.WRN_NewRequired, "M01").WithArguments("I7.M01", "I1.M01").WithLocation(32, 41),
                // (37,44): error CS0106: The modifier 'virtual' is not valid for this item
                //     virtual  static event System.Action I1.M01;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "M01").WithArguments("virtual").WithLocation(37, 44),
                // (37,44): error CS0071: An explicit interface implementation of an event must use event accessor syntax
                //     virtual  static event System.Action I1.M01;
                Diagnostic(ErrorCode.ERR_ExplicitEventFieldImpl, "M01").WithLocation(37, 44)
                );

            foreach (var m01 in compilation1.GlobalNamespace.GetTypeMember("I1").GetMembers())
            {
                Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I2").FindImplementationForInterfaceMember(m01));
                Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I3").FindImplementationForInterfaceMember(m01));
                Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I4").FindImplementationForInterfaceMember(m01));
                Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I5").FindImplementationForInterfaceMember(m01));
                Assert.Same(m01, compilation1.GlobalNamespace.GetTypeMember("I7").FindImplementationForInterfaceMember(m01));
            }

            var m = compilation1.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<EventSymbol>().Single();

            foreach (var name in new[] { "I6", "I8" })
            {
                var i6 = compilation1.GlobalNamespace.GetTypeMember(name);
                var i6m = i6.GetMembers().OfType<EventSymbol>().Single();
                Assert.Same(i6m, i6.FindImplementationForInterfaceMember(m));
                Assert.Same(i6m.AddMethod, ((EventSymbol)i6.FindImplementationForInterfaceMember(m)).AddMethod);
                Assert.Same(i6m.RemoveMethod, ((EventSymbol)i6.FindImplementationForInterfaceMember(m)).RemoveMethod);
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticEvent_04(bool structure, bool isVirtual)
        {
            var typeKeyword = structure ? "struct" : "class";
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"#pragma warning disable CS0067 // WRN_UnreferencedEvent
public interface I1
{
    " + modifier + @" static event System.Action M01;
    " + modifier + @" static event System.Action M02;
}
";
            var source2 =
typeKeyword + @"
    Test: I1
{
    static event System.Action I1.M01 { add{} remove => throw null; }
    public static event System.Action M02;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (4,35): error CS8703: The modifier 'static' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     static event System.Action I1.M01 { add{} remove => throw null; }
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M01").WithArguments("static", "10.0", "11.0").WithLocation(4, 35),
                // (5,39): error CS8706: 'Test.M02.add' cannot implement interface member 'I1.M02.add' in type 'Test' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                //     public static event System.Action M02;
                Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, "M02").WithArguments("Test.M02.add", "I1.M02.add", "Test", "static abstract members in interfaces", "10.0", "11.0").WithLocation(5, 39),
                // (5,39): error CS8706: 'Test.M02.remove' cannot implement interface member 'I1.M02.remove' in type 'Test' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                //     public static event System.Action M02;
                Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, "M02").WithArguments("Test.M02.remove", "I1.M02.remove", "Test", "static abstract members in interfaces", "10.0", "11.0").WithLocation(5, 39),
                // (5,39): error CS8706: 'Test.M02' cannot implement interface member 'I1.M02' in type 'Test' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                //     public static event System.Action M02;
                Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, "M02").WithArguments("Test.M02", "I1.M02", "Test", "static abstract members in interfaces", "10.0", "11.0").WithLocation(5, 39),
                // (5,39): warning CS0067: The event 'Test.M02' is never used
                //     public static event System.Action M02;
                Diagnostic(ErrorCode.WRN_UnreferencedEvent, "M02").WithArguments("Test.M02").WithLocation(5, 39)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation3.VerifyDiagnostics(
                // (4,35): error CS8703: The modifier 'static' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     static event System.Action I1.M01 { add{} remove => throw null; }
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M01").WithArguments("static", "10.0", "11.0").WithLocation(4, 35),
                // (5,39): warning CS0067: The event 'Test.M02' is never used
                //     public static event System.Action M02;
                Diagnostic(ErrorCode.WRN_UnreferencedEvent, "M02").WithArguments("Test.M02").WithLocation(5, 39),
                // (10,41): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual  static event System.Action M01;
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M01").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(10, 41),
                // (11,41): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual  static event System.Action M02;
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "M02").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(11, 41)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticEvent_05(bool structure, bool isVirtual)
        {
            var typeKeyword = structure ? "struct" : "class";
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"#pragma warning disable CS0067 // WRN_UnreferencedEvent
public interface I1
{
    " + modifier + @" static event System.Action M01;
}
";
            var source2 =
typeKeyword + @"
    Test1: I1
{
    public static event System.Action M01 { add{} remove{} }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (4,39): error CS8929: 'Test1.M01' cannot implement interface member 'I1.M01' in type 'Test1' because the target runtime doesn't support static abstract members in interfaces.
                //     public static event System.Action M01 { add{} remove{} }
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfacesForMember, "M01").WithArguments("Test1.M01", "I1.M01", "Test1").WithLocation(4, 39),
                // (4,45): error CS8929: 'Test1.M01.add' cannot implement interface member 'I1.M01.add' in type 'Test1' because the target runtime doesn't support static abstract members in interfaces.
                //     public static event System.Action M01 { add{} remove{} }
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfacesForMember, "add").WithArguments("Test1.M01.add", "I1.M01.add", "Test1").WithLocation(4, 45),
                // (4,51): error CS8929: 'Test1.M01.remove' cannot implement interface member 'I1.M01.remove' in type 'Test1' because the target runtime doesn't support static abstract members in interfaces.
                //     public static event System.Action M01 { add{} remove{} }
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfacesForMember, "remove").WithArguments("Test1.M01.remove", "I1.M01.remove", "Test1").WithLocation(4, 51)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation3.VerifyDiagnostics(
                // (9,41): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static event System.Action M01;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "M01").WithLocation(9, 41)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticEvent_06(bool structure, bool isVirtual)
        {
            var typeKeyword = structure ? "struct" : "class";
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"#pragma warning disable CS0067 // WRN_UnreferencedEvent
public interface I1
{
    " + modifier + @" static event System.Action M01;
}
";
            var source2 =
typeKeyword + @"
    Test1: I1
{
    static event System.Action I1.M01 { add => throw null; remove => throw null; }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (4,35): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     static event System.Action I1.M01 { add => throw null; remove => throw null; }
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "M01").WithLocation(4, 35)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation3.VerifyDiagnostics(
                // (4,35): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     static event System.Action I1.M01 { add => throw null; remove => throw null; }
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "M01").WithLocation(4, 35),
                // (9,41): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static event System.Action M01;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "M01").WithLocation(9, 41)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticEvent_07(bool structure, bool isVirtual)
        {
            // Basic implicit implementation scenario, MethodImpl is emitted

            var typeKeyword = structure ? "struct" : "class";
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"#pragma warning disable CS0067 // WRN_UnreferencedEvent
public interface I1
{
    " + modifier + @" static event System.Action M01;
}

" + typeKeyword + @"
    C : I1
{
    public static event System.Action M01 { add => throw null; remove {} }
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped,
                             emitOptions: EmitOptions.Default.WithEmitMetadataOnly(true).WithIncludePrivateMembers(false)).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var m01 = module.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<EventSymbol>().Single();
                var m01Add = m01.AddMethod;
                var m01Remove = m01.RemoveMethod;
                var c = module.GlobalNamespace.GetTypeMember("C");

                Assert.Equal(1, c.GetMembers().OfType<EventSymbol>().Count());
                Assert.Equal(2, c.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());

                var cM01 = (EventSymbol)c.FindImplementationForInterfaceMember(m01);

                Assert.True(cM01.IsStatic);
                Assert.False(cM01.IsAbstract);
                Assert.False(cM01.IsVirtual);

                Assert.Equal("event System.Action C.M01", cM01.ToTestDisplayString());

                var cM01Add = cM01.AddMethod;
                Assert.Same(cM01Add, c.FindImplementationForInterfaceMember(m01Add));

                Assert.True(cM01Add.IsStatic);
                Assert.False(cM01Add.IsAbstract);
                Assert.False(cM01Add.IsVirtual);
                Assert.False(cM01Add.IsMetadataVirtual());
                Assert.False(cM01Add.IsMetadataFinal);
                Assert.False(cM01Add.IsMetadataNewSlot());
                Assert.Equal(MethodKind.EventAdd, cM01Add.MethodKind);
                Assert.False(cM01Add.HasRuntimeSpecialName);
                Assert.True(cM01Add.HasSpecialName);

                Assert.Equal("void C.M01.add", cM01Add.ToTestDisplayString());

                var cM01Remove = cM01.RemoveMethod;
                Assert.Same(cM01Remove, c.FindImplementationForInterfaceMember(m01Remove));

                Assert.True(cM01Remove.IsStatic);
                Assert.False(cM01Remove.IsAbstract);
                Assert.False(cM01Remove.IsVirtual);
                Assert.False(cM01Remove.IsMetadataVirtual());
                Assert.False(cM01Remove.IsMetadataFinal);
                Assert.False(cM01Remove.IsMetadataNewSlot());
                Assert.Equal(MethodKind.EventRemove, cM01Remove.MethodKind);
                Assert.False(cM01Remove.HasRuntimeSpecialName);
                Assert.True(cM01Remove.HasSpecialName);

                Assert.Equal("void C.M01.remove", cM01Remove.ToTestDisplayString());

                if (module is PEModuleSymbol)
                {
                    Assert.Same(m01, cM01.ExplicitInterfaceImplementations.Single());
                    Assert.Same(m01Add, cM01Add.ExplicitInterfaceImplementations.Single());
                    Assert.Same(m01Remove, cM01Remove.ExplicitInterfaceImplementations.Single());
                }
                else
                {
                    Assert.Empty(cM01.ExplicitInterfaceImplementations);
                    Assert.Empty(cM01Add.ExplicitInterfaceImplementations);
                    Assert.Empty(cM01Remove.ExplicitInterfaceImplementations);
                }
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticEvent_08(bool structure, bool isVirtual)
        {
            // Basic explicit implementation scenario

            var typeKeyword = structure ? "struct" : "class";
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"#pragma warning disable CS0067 // WRN_UnreferencedEvent
public interface I1
{
    " + modifier + @" static event System.Action M01;
}

" + typeKeyword + @"
    C : I1
{
    static event System.Action I1.M01 { add => throw null; remove {} }
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped,
                             emitOptions: EmitOptions.Default.WithEmitMetadataOnly(true).WithIncludePrivateMembers(false)).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var m01 = module.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<EventSymbol>().Single();
                var m01Add = m01.AddMethod;
                var m01Remove = m01.RemoveMethod;
                var c = module.GlobalNamespace.GetTypeMember("C");

                Assert.Equal(1, c.GetMembers().OfType<EventSymbol>().Count());
                Assert.Equal(2, c.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());

                var cM01 = (EventSymbol)c.FindImplementationForInterfaceMember(m01);

                Assert.True(cM01.IsStatic);
                Assert.False(cM01.IsAbstract);
                Assert.False(cM01.IsVirtual);

                Assert.Equal("event System.Action C.I1.M01", cM01.ToTestDisplayString());

                var cM01Add = cM01.AddMethod;
                Assert.Same(cM01Add, c.FindImplementationForInterfaceMember(m01Add));

                Assert.True(cM01Add.IsStatic);
                Assert.False(cM01Add.IsAbstract);
                Assert.False(cM01Add.IsVirtual);
                Assert.False(cM01Add.IsMetadataVirtual());
                Assert.False(cM01Add.IsMetadataFinal);
                Assert.False(cM01Add.IsMetadataNewSlot());
                Assert.Equal(MethodKind.EventAdd, cM01Add.MethodKind);
                Assert.False(cM01Add.HasRuntimeSpecialName);
                Assert.True(cM01Add.HasSpecialName);

                Assert.Equal("void C.I1.M01.add", cM01Add.ToTestDisplayString());

                var cM01Remove = cM01.RemoveMethod;
                Assert.Same(cM01Remove, c.FindImplementationForInterfaceMember(m01Remove));

                Assert.True(cM01Remove.IsStatic);
                Assert.False(cM01Remove.IsAbstract);
                Assert.False(cM01Remove.IsVirtual);
                Assert.False(cM01Remove.IsMetadataVirtual());
                Assert.False(cM01Remove.IsMetadataFinal);
                Assert.False(cM01Remove.IsMetadataNewSlot());
                Assert.Equal(MethodKind.EventRemove, cM01Remove.MethodKind);
                Assert.False(cM01Remove.HasRuntimeSpecialName);
                Assert.True(cM01Remove.HasSpecialName);

                Assert.Equal("void C.I1.M01.remove", cM01Remove.ToTestDisplayString());

                Assert.Same(m01, cM01.ExplicitInterfaceImplementations.Single());
                Assert.Same(m01Add, cM01Add.ExplicitInterfaceImplementations.Single());
                Assert.Same(m01Remove, cM01Remove.ExplicitInterfaceImplementations.Single());
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticEvent_09(bool isVirtual)
        {
            // Explicit implementation from base is treated as an implementation
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"#pragma warning disable CS0067 // WRN_UnreferencedEvent
public interface I1
{
    " + modifier + @" static event System.Action M01;
}

public class C1
{
    public static event System.Action M01 { add => throw null; remove {} }
}

public class C2 : C1, I1
{
    static event System.Action I1.M01 { add => throw null; remove {} }
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C3 : C2, I1
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.Regular10, TestOptions.RegularPreview })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                     parseOptions: parseOptions,
                                                     targetFramework: _supportingFramework,
                                                     references: new[] { reference });
                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c3 = module.GlobalNamespace.GetTypeMember("C3");
                Assert.Empty(c3.GetMembers().OfType<EventSymbol>());
                Assert.Empty(c3.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()));
                var m01 = c3.Interfaces().Single().GetMembers().OfType<EventSymbol>().Single();

                var cM01 = (EventSymbol)c3.FindImplementationForInterfaceMember(m01);

                Assert.Equal("event System.Action C2.I1.M01", cM01.ToTestDisplayString());

                Assert.Same(cM01.AddMethod, c3.FindImplementationForInterfaceMember(m01.AddMethod));
                Assert.Same(cM01.RemoveMethod, c3.FindImplementationForInterfaceMember(m01.RemoveMethod));

                Assert.Same(m01, cM01.ExplicitInterfaceImplementations.Single());
                Assert.Same(m01.AddMethod, cM01.AddMethod.ExplicitInterfaceImplementations.Single());
                Assert.Same(m01.RemoveMethod, cM01.RemoveMethod.ExplicitInterfaceImplementations.Single());
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticEvent_10(bool isVirtual)
        {
            // Implicit implementation is considered only for types implementing interface in source.
            // In metadata, only explicit implementations are considered
            var (modifier, body) = GetILModifierAndBody(isVirtual);

            var ilSource = @"
.class interface public auto ansi abstract I1
{
    .method public hidebysig specialname " + modifier + @" virtual static 
        void add_M01 (
            class [mscorlib]System.Action 'value'
        ) cil managed 
    " + body + @"

    .method public hidebysig specialname " + modifier + @" virtual static 
        void remove_M01 (
            class [mscorlib]System.Action 'value'
        ) cil managed 
    " + body + @"

    .event [mscorlib]System.Action M01
    {
        .addon void I1::add_M01(class [mscorlib]System.Action)
        .removeon void I1::remove_M01(class [mscorlib]System.Action)
    }
}

.class public auto ansi beforefieldinit C1
    extends System.Object
    implements I1
{
    .method private hidebysig specialname static
        void I1.add_M01 (
            class [mscorlib]System.Action 'value'
        ) cil managed 
    {
        .override method void I1::add_M01(class [mscorlib]System.Action)
        IL_0000: ret
    }

    .method private hidebysig specialname static
        void I1.remove_M01 (
            class [mscorlib]System.Action 'value'
        ) cil managed 
    {
        .override method void I1::remove_M01(class [mscorlib]System.Action)
        IL_0000: ret
    }

    .event [mscorlib]System.Action I1.M01
    {
        .addon void C1::I1.add_M01(class [mscorlib]System.Action)
        .removeon void C1::I1.remove_M01(class [mscorlib]System.Action)
    }

    .method public hidebysig specialname static 
        void add_M01 (
            class [mscorlib]System.Action 'value'
        ) cil managed 
    {
        IL_0000: ret
    }

    .method public hidebysig specialname static 
        void remove_M01 (
            class [mscorlib]System.Action 'value'
        ) cil managed 
    {
        IL_0000: ret
    }

    .event [mscorlib]System.Action M01
    {
        .addon void C1::add_M01(class [mscorlib]System.Action)
        .removeon void C1::remove_M01(class [mscorlib]System.Action)
    }

    .method public hidebysig specialname rtspecialname 
        instance void .ctor () cil managed 
    {
        IL_0000: ldarg.0
        IL_0001: call instance void System.Object::.ctor()
        IL_0006: ret
    }
}

.class public auto ansi beforefieldinit C2
    extends C1
    implements I1
{
    .method public hidebysig specialname static 
        void add_M01 (
            class [mscorlib]System.Action 'value'
        ) cil managed 
    {
        IL_0000: ret
    }

    .method public hidebysig specialname static 
        void remove_M01 (
            class [mscorlib]System.Action 'value'
        ) cil managed 
    {
        IL_0000: ret
    }

    .event [mscorlib]System.Action M01
    {
        .addon void C2::add_M01(class [mscorlib]System.Action)
        .removeon void C2::remove_M01(class [mscorlib]System.Action)
    }

    .method public hidebysig specialname rtspecialname 
        instance void .ctor () cil managed 
    {
        IL_0000: ldarg.0
        IL_0001: call instance void C1::.ctor()
        IL_0006: ret
    }
}
";
            var source1 =
@"
public class C3 : C2
{
}

public class C4 : C1, I1
{
}

public class C5 : C2, I1
{
}
";

            var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var c1 = compilation1.GlobalNamespace.GetTypeMember("C1");
            var m01 = c1.Interfaces().Single().GetMembers().OfType<EventSymbol>().Single();

            var c1M01 = (EventSymbol)c1.FindImplementationForInterfaceMember(m01);

            Assert.Equal("event System.Action C1.I1.M01", c1M01.ToTestDisplayString());

            Assert.Same(c1M01.AddMethod, c1.FindImplementationForInterfaceMember(m01.AddMethod));
            Assert.Same(c1M01.RemoveMethod, c1.FindImplementationForInterfaceMember(m01.RemoveMethod));
            Assert.Same(m01, c1M01.ExplicitInterfaceImplementations.Single());
            Assert.Same(m01.AddMethod, c1M01.AddMethod.ExplicitInterfaceImplementations.Single());
            Assert.Same(m01.RemoveMethod, c1M01.RemoveMethod.ExplicitInterfaceImplementations.Single());

            var c2 = compilation1.GlobalNamespace.GetTypeMember("C2");
            Assert.Same(c1M01, c2.FindImplementationForInterfaceMember(m01));
            Assert.Same(c1M01.AddMethod, c2.FindImplementationForInterfaceMember(m01.AddMethod));
            Assert.Same(c1M01.RemoveMethod, c2.FindImplementationForInterfaceMember(m01.RemoveMethod));

            var c3 = compilation1.GlobalNamespace.GetTypeMember("C3");
            Assert.Same(c1M01, c3.FindImplementationForInterfaceMember(m01));
            Assert.Same(c1M01.AddMethod, c3.FindImplementationForInterfaceMember(m01.AddMethod));
            Assert.Same(c1M01.RemoveMethod, c3.FindImplementationForInterfaceMember(m01.RemoveMethod));

            var c4 = compilation1.GlobalNamespace.GetTypeMember("C4");
            Assert.Same(c1M01, c4.FindImplementationForInterfaceMember(m01));
            Assert.Same(c1M01.AddMethod, c4.FindImplementationForInterfaceMember(m01.AddMethod));
            Assert.Same(c1M01.RemoveMethod, c4.FindImplementationForInterfaceMember(m01.RemoveMethod));

            var c5 = compilation1.GlobalNamespace.GetTypeMember("C5");

            var c2M01 = (EventSymbol)c5.FindImplementationForInterfaceMember(m01);
            Assert.Equal("event System.Action C2.M01", c2M01.ToTestDisplayString());
            Assert.Same(c2M01.AddMethod, c5.FindImplementationForInterfaceMember(m01.AddMethod));
            Assert.Same(c2M01.RemoveMethod, c5.FindImplementationForInterfaceMember(m01.RemoveMethod));

            compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (10,23): error CS8706: 'C2.M01.add' cannot implement interface member 'I1.M01.add' in type 'C5' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                // public class C5 : C2, I1
                Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, "I1").WithArguments("C2.M01.add", "I1.M01.add", "C5", "static abstract members in interfaces", "10.0", "11.0").WithLocation(10, 23),
                // (10,23): error CS8706: 'C2.M01.remove' cannot implement interface member 'I1.M01.remove' in type 'C5' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                // public class C5 : C2, I1
                Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, "I1").WithArguments("C2.M01.remove", "I1.M01.remove", "C5", "static abstract members in interfaces", "10.0", "11.0").WithLocation(10, 23),
                // (10,23): error CS8706: 'C2.M01' cannot implement interface member 'I1.M01' in type 'C5' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                // public class C5 : C2, I1
                Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, "I1").WithArguments("C2.M01", "I1.M01", "C5", "static abstract members in interfaces", "10.0", "11.0").WithLocation(10, 23)
                );
        }

        [Fact]
        public void ImplementAbstractStaticEvent_11()
        {
            // Non-abstract static virtual method. 
            scenario1();
            scenario2();
            scenario3();

            void scenario1()
            {
                var ilSource = @"
.class interface public auto ansi abstract I1
{
    .method public hidebysig specialname static virtual
        void add_M01 (
            class [mscorlib]System.Action 'value'
        ) cil managed 
    {
        IL_0000: ret
    }

    .method public hidebysig specialname static virtual
        void remove_M01 (
            class [mscorlib]System.Action 'value'
        ) cil managed 
    {
        IL_0000: ret
    }

    .event [mscorlib]System.Action M01
    {
        .addon void I1::add_M01(class [mscorlib]System.Action)
        .removeon void I1::remove_M01(class [mscorlib]System.Action)
    }
}
";

                var source1 =
@"
public class C1 : I1
{
}
";

                var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation1.VerifyEmitDiagnostics();

                var c1 = compilation1.GlobalNamespace.GetTypeMember("C1");
                var i1 = c1.Interfaces().Single();
                var m01 = i1.GetMembers().OfType<EventSymbol>().Single();

                Assert.Same(m01, c1.FindImplementationForInterfaceMember(m01));
                Assert.Same(m01, i1.FindImplementationForInterfaceMember(m01));
                Assert.Same(m01.AddMethod, c1.FindImplementationForInterfaceMember(m01.AddMethod));
                Assert.Same(m01.AddMethod, i1.FindImplementationForInterfaceMember(m01.AddMethod));
                Assert.Same(m01.RemoveMethod, c1.FindImplementationForInterfaceMember(m01.RemoveMethod));
                Assert.Same(m01.RemoveMethod, i1.FindImplementationForInterfaceMember(m01.RemoveMethod));

                compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.Regular10,
                                                     targetFramework: _supportingFramework);

                compilation1.VerifyEmitDiagnostics(
                    // (2,19): error CS8706: 'I1.M01.add' cannot implement interface member 'I1.M01.add' in type 'C1' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                    // public class C1 : I1
                    Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, "I1").WithArguments("I1.M01.add", "I1.M01.add", "C1", "static abstract members in interfaces", "10.0", "11.0").WithLocation(2, 19),
                    // (2,19): error CS8706: 'I1.M01.remove' cannot implement interface member 'I1.M01.remove' in type 'C1' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                    // public class C1 : I1
                    Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, "I1").WithArguments("I1.M01.remove", "I1.M01.remove", "C1", "static abstract members in interfaces", "10.0", "11.0").WithLocation(2, 19)
                    );

                var source2 =
@"
public class C1 : I1
{
   static event System.Action I1.M01 { add{} remove{} }
}
";

                var compilation2 = CreateCompilationWithIL(source2, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation2.VerifyEmitDiagnostics();

                c1 = compilation2.GlobalNamespace.GetTypeMember("C1");
                i1 = c1.Interfaces().Single();
                m01 = i1.GetMembers().OfType<EventSymbol>().Single();
                var c1m01 = c1.GetMembers().OfType<EventSymbol>().Single();

                Assert.Same(c1m01, c1.FindImplementationForInterfaceMember(m01));
                Assert.Same(m01, i1.FindImplementationForInterfaceMember(m01));
                Assert.Same(c1m01.AddMethod, c1.FindImplementationForInterfaceMember(m01.AddMethod));
                Assert.Same(m01.AddMethod, i1.FindImplementationForInterfaceMember(m01.AddMethod));
                Assert.Same(c1m01.RemoveMethod, c1.FindImplementationForInterfaceMember(m01.RemoveMethod));
                Assert.Same(m01.RemoveMethod, i1.FindImplementationForInterfaceMember(m01.RemoveMethod));

                var source3 =
@"
public class C1 : I1
{
   public static event System.Action M01 { add{} remove{} }
}
";

                var compilation3 = CreateCompilationWithIL(source3, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                CompileAndVerify(compilation3, sourceSymbolValidator: validate3, symbolValidator: validate3, verify: Verification.Skipped).VerifyDiagnostics();

                void validate3(ModuleSymbol module)
                {
                    var c = module.GlobalNamespace.GetTypeMember("C1");
                    Assert.Equal(1, c.GetMembers().OfType<EventSymbol>().Count());
                    Assert.Equal(2, c.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());

                    var m01 = c.Interfaces().Single().GetMembers().OfType<EventSymbol>().Single();
                    var c1m01 = c.GetMembers().OfType<EventSymbol>().Single();
                    Assert.Same(c1m01, c.FindImplementationForInterfaceMember(m01));
                    Assert.Same(c1m01.AddMethod, c.FindImplementationForInterfaceMember(m01.AddMethod));
                    Assert.Same(c1m01.RemoveMethod, c.FindImplementationForInterfaceMember(m01.RemoveMethod));
                }
            }

            void scenario2()
            {
                var ilSource = @"
.class interface public auto ansi abstract I1
{
    .method public hidebysig specialname abstract virtual static 
        void add_M01 (
            class [mscorlib]System.Action 'value'
        ) cil managed 
    {
    }

    .method public hidebysig specialname static virtual
        void remove_M01 (
            class [mscorlib]System.Action 'value'
        ) cil managed 
    {
        IL_0000: ret
    }

    .event [mscorlib]System.Action M01
    {
        .addon void I1::add_M01(class [mscorlib]System.Action)
        .removeon void I1::remove_M01(class [mscorlib]System.Action)
    }
}
";

                var source1 =
@"
public class C1 : I1
{
}
";

                var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation1.VerifyDiagnostics(
                    // (2,19): error CS0535: 'C1' does not implement interface member 'I1.M01'
                    // public class C1 : I1
                    Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C1", "I1.M01").WithLocation(2, 19)
                    );

                var c1 = compilation1.GlobalNamespace.GetTypeMember("C1");
                var i1 = c1.Interfaces().Single();
                var m01 = i1.GetMembers().OfType<EventSymbol>().Single();

                Assert.Null(c1.FindImplementationForInterfaceMember(m01));
                Assert.Null(i1.FindImplementationForInterfaceMember(m01));
                Assert.Null(c1.FindImplementationForInterfaceMember(m01.AddMethod));
                Assert.Null(i1.FindImplementationForInterfaceMember(m01.AddMethod));
                Assert.Same(m01.RemoveMethod, c1.FindImplementationForInterfaceMember(m01.RemoveMethod));
                Assert.Same(m01.RemoveMethod, i1.FindImplementationForInterfaceMember(m01.RemoveMethod));

                var source2 =
@"
public class C1 : I1
{
   static event System.Action I1.M01 { add {} }
}
";

                var compilation2 = CreateCompilationWithIL(source2, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation2.VerifyDiagnostics(
                    // (4,34): error CS0065: 'C1.I1.M01': event property must have both add and remove accessors
                    //    static event System.Action I1.M01 { add {} }
                    Diagnostic(ErrorCode.ERR_EventNeedsBothAccessors, "M01").WithArguments("C1.I1.M01").WithLocation(4, 34)
                    );

                c1 = compilation2.GlobalNamespace.GetTypeMember("C1");
                i1 = c1.Interfaces().Single();
                m01 = i1.GetMembers().OfType<EventSymbol>().Single();
                var c1M01 = c1.GetMembers().OfType<EventSymbol>().Single();

                Assert.Same(c1M01, c1.FindImplementationForInterfaceMember(m01));
                Assert.Same(c1M01.AddMethod, c1.FindImplementationForInterfaceMember(m01.AddMethod));
                Assert.Same(m01.RemoveMethod, c1.FindImplementationForInterfaceMember(m01.RemoveMethod));
                Assert.Same(m01, c1M01.ExplicitInterfaceImplementations.Single());
                Assert.Same(m01.AddMethod, c1M01.AddMethod.ExplicitInterfaceImplementations.Single());

                var source3 =
@"
public class C1 : I1
{
   public static event System.Action M01 { add{} remove{} }
}
";

                var compilation3 = CreateCompilationWithIL(source3, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                CompileAndVerify(compilation3, sourceSymbolValidator: validate3, symbolValidator: validate3, verify: Verification.Skipped).VerifyDiagnostics();

                void validate3(ModuleSymbol module)
                {
                    var c = module.GlobalNamespace.GetTypeMember("C1");

                    var m01 = c.Interfaces().Single().GetMembers().OfType<EventSymbol>().Single();
                    var m01Add = m01.AddMethod;

                    Assert.Equal(1, c.GetMembers().OfType<EventSymbol>().Count());
                    Assert.Equal(2, c.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());

                    var cM01 = (EventSymbol)c.FindImplementationForInterfaceMember(m01);

                    Assert.True(cM01.IsStatic);
                    Assert.False(cM01.IsAbstract);
                    Assert.False(cM01.IsVirtual);

                    Assert.Equal("event System.Action C1.M01", cM01.ToTestDisplayString());

                    var cM01Add = cM01.AddMethod;
                    Assert.Same(cM01Add, c.FindImplementationForInterfaceMember(m01Add));

                    Assert.True(cM01Add.IsStatic);
                    Assert.False(cM01Add.IsAbstract);
                    Assert.False(cM01Add.IsVirtual);
                    Assert.False(cM01Add.IsMetadataVirtual());
                    Assert.False(cM01Add.IsMetadataFinal);
                    Assert.False(cM01Add.IsMetadataNewSlot());
                    Assert.Equal(MethodKind.EventAdd, cM01Add.MethodKind);

                    Assert.Equal("void C1.M01.add", cM01Add.ToTestDisplayString());

                    var cM01Remove = cM01.RemoveMethod;

                    Assert.True(cM01Remove.IsStatic);
                    Assert.False(cM01Remove.IsAbstract);
                    Assert.False(cM01Remove.IsVirtual);
                    Assert.False(cM01Remove.IsMetadataVirtual());
                    Assert.False(cM01Remove.IsMetadataFinal);
                    Assert.False(cM01Remove.IsMetadataNewSlot());
                    Assert.Equal(MethodKind.EventRemove, cM01Remove.MethodKind);

                    Assert.Equal("void C1.M01.remove", cM01Remove.ToTestDisplayString());

                    Assert.Same(cM01Remove, c.FindImplementationForInterfaceMember(m01.RemoveMethod));

                    if (module is PEModuleSymbol)
                    {
                        Assert.Same(m01Add, cM01Add.ExplicitInterfaceImplementations.Single());
                        Assert.Same(m01, cM01.ExplicitInterfaceImplementations.Single());
                        Assert.Same(m01.RemoveMethod, cM01Remove.ExplicitInterfaceImplementations.Single());
                    }
                    else
                    {
                        Assert.Empty(cM01Add.ExplicitInterfaceImplementations);
                        Assert.Empty(cM01.ExplicitInterfaceImplementations);
                        Assert.Empty(cM01Remove.ExplicitInterfaceImplementations);
                    }
                }

                var source4 =
@"
public class C1 : I1
{
   static event System.Action I1.M01 { add{} remove{} }
}
";

                var compilation4 = CreateCompilationWithIL(source4, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation4.VerifyDiagnostics();

                c1 = compilation4.GlobalNamespace.GetTypeMember("C1");
                i1 = c1.Interfaces().Single();
                m01 = i1.GetMembers().OfType<EventSymbol>().Single();
                c1M01 = c1.GetMembers().OfType<EventSymbol>().Single();

                Assert.Same(c1M01, c1.FindImplementationForInterfaceMember(m01));
                Assert.Same(c1M01.AddMethod, c1.FindImplementationForInterfaceMember(m01.AddMethod));
                Assert.Same(c1M01.RemoveMethod, c1.FindImplementationForInterfaceMember(m01.RemoveMethod));
                Assert.Same(m01, c1M01.ExplicitInterfaceImplementations.Single());
                Assert.Same(m01.AddMethod, c1M01.AddMethod.ExplicitInterfaceImplementations.Single());
                Assert.Same(m01.RemoveMethod, c1M01.RemoveMethod.ExplicitInterfaceImplementations.Single());

                var source5 =
@"
public class C1 : I1
{
   public static event System.Action M01 { add{} }
}
";

                var compilation5 = CreateCompilationWithIL(source5, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation5.VerifyDiagnostics(
                    // (4,38): error CS0065: 'C1.M01': event property must have both add and remove accessors
                    //    public static event System.Action M01 { add{} }
                    Diagnostic(ErrorCode.ERR_EventNeedsBothAccessors, "M01").WithArguments("C1.M01").WithLocation(4, 38)
                    );

                c1 = compilation5.GlobalNamespace.GetTypeMember("C1");
                i1 = c1.Interfaces().Single();
                m01 = i1.GetMembers().OfType<EventSymbol>().Single();
                c1M01 = c1.GetMembers().OfType<EventSymbol>().Single();

                Assert.Same(c1M01, c1.FindImplementationForInterfaceMember(m01));
                Assert.Same(c1M01.AddMethod, c1.FindImplementationForInterfaceMember(m01.AddMethod));
                Assert.Same(m01.RemoveMethod, c1.FindImplementationForInterfaceMember(m01.RemoveMethod));

                var source6 =
@"
public class C1 : I1
{
   public static event System.Action M01 { remove{} }
}
";

                var compilation6 = CreateCompilationWithIL(source6, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation6.VerifyDiagnostics(
                    // (2,19): error CS0535: 'C1' does not implement interface member 'I1.M01.add'
                    // public class C1 : I1
                    Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C1", "I1.M01.add").WithLocation(2, 19),
                    // (4,38): error CS0065: 'C1.M01': event property must have both add and remove accessors
                    //    public static event System.Action M01 { remove{} }
                    Diagnostic(ErrorCode.ERR_EventNeedsBothAccessors, "M01").WithArguments("C1.M01").WithLocation(4, 38)
                    );

                c1 = compilation6.GlobalNamespace.GetTypeMember("C1");
                i1 = c1.Interfaces().Single();
                m01 = i1.GetMembers().OfType<EventSymbol>().Single();
                c1M01 = c1.GetMembers().OfType<EventSymbol>().Single();

                Assert.Same(c1M01, c1.FindImplementationForInterfaceMember(m01));
                Assert.Null(c1.FindImplementationForInterfaceMember(m01.AddMethod));
                Assert.Same(c1M01.RemoveMethod, c1.FindImplementationForInterfaceMember(m01.RemoveMethod));

                var source7 =
@"
public class C1 : I1
{
   static event System.Action I1.M01 { remove{} }
}
";

                var compilation7 = CreateCompilationWithIL(source7, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation7.VerifyDiagnostics(
                    // (2,19): error CS0535: 'C1' does not implement interface member 'I1.M01.add'
                    // public class C1 : I1
                    Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C1", "I1.M01.add").WithLocation(2, 19),
                    // (4,34): error CS0065: 'C1.I1.M01': event property must have both add and remove accessors
                    //    static event System.Action I1.M01 { remove{} }
                    Diagnostic(ErrorCode.ERR_EventNeedsBothAccessors, "M01").WithArguments("C1.I1.M01").WithLocation(4, 34)
                    );

                c1 = compilation7.GlobalNamespace.GetTypeMember("C1");
                i1 = c1.Interfaces().Single();
                m01 = i1.GetMembers().OfType<EventSymbol>().Single();
                c1M01 = c1.GetMembers().OfType<EventSymbol>().Single();

                Assert.Same(c1M01, c1.FindImplementationForInterfaceMember(m01));
                Assert.Null(c1.FindImplementationForInterfaceMember(m01.AddMethod));
                Assert.Same(c1M01.RemoveMethod, c1.FindImplementationForInterfaceMember(m01.RemoveMethod));
                Assert.Same(m01, c1M01.ExplicitInterfaceImplementations.Single());
                Assert.Same(m01.RemoveMethod, c1M01.RemoveMethod.ExplicitInterfaceImplementations.Single());
            }

            void scenario3()
            {
                var ilSource = @"
.class interface public auto ansi abstract I1
{
    .method public hidebysig specialname static virtual
        void add_M01 (
            class [mscorlib]System.Action 'value'
        ) cil managed 
    {
        IL_0000: ret
    }

    .method public hidebysig specialname abstract virtual static 
        void remove_M01 (
            class [mscorlib]System.Action 'value'
        ) cil managed 
    {
    }

    .event [mscorlib]System.Action M01
    {
        .addon void I1::add_M01(class [mscorlib]System.Action)
        .removeon void I1::remove_M01(class [mscorlib]System.Action)
    }
}
";

                var source1 =
@"
public class C1 : I1
{
}
";

                var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation1.VerifyDiagnostics(
                    // (2,19): error CS0535: 'C1' does not implement interface member 'I1.M01'
                    // public class C1 : I1
                    Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C1", "I1.M01").WithLocation(2, 19)
                    );

                var c1 = compilation1.GlobalNamespace.GetTypeMember("C1");
                var i1 = c1.Interfaces().Single();
                var m01 = i1.GetMembers().OfType<EventSymbol>().Single();

                Assert.Null(c1.FindImplementationForInterfaceMember(m01));
                Assert.Null(i1.FindImplementationForInterfaceMember(m01));
                Assert.Null(c1.FindImplementationForInterfaceMember(m01.RemoveMethod));
                Assert.Null(i1.FindImplementationForInterfaceMember(m01.RemoveMethod));
                Assert.Same(m01.AddMethod, c1.FindImplementationForInterfaceMember(m01.AddMethod));
                Assert.Same(m01.AddMethod, i1.FindImplementationForInterfaceMember(m01.AddMethod));

                var source2 =
@"
public class C1 : I1
{
   static event System.Action I1.M01 { remove {} }
}
";

                var compilation2 = CreateCompilationWithIL(source2, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation2.VerifyDiagnostics(
                    // (4,34): error CS0065: 'C1.I1.M01': event property must have both add and remove accessors
                    //    static event System.Action I1.M01 { add {} }
                    Diagnostic(ErrorCode.ERR_EventNeedsBothAccessors, "M01").WithArguments("C1.I1.M01").WithLocation(4, 34)
                    );

                c1 = compilation2.GlobalNamespace.GetTypeMember("C1");
                i1 = c1.Interfaces().Single();
                m01 = i1.GetMembers().OfType<EventSymbol>().Single();
                var c1M01 = c1.GetMembers().OfType<EventSymbol>().Single();

                Assert.Same(c1M01, c1.FindImplementationForInterfaceMember(m01));
                Assert.Same(c1M01.RemoveMethod, c1.FindImplementationForInterfaceMember(m01.RemoveMethod));
                Assert.Same(m01.AddMethod, c1.FindImplementationForInterfaceMember(m01.AddMethod));
                Assert.Same(m01, c1M01.ExplicitInterfaceImplementations.Single());
                Assert.Same(m01.RemoveMethod, c1M01.RemoveMethod.ExplicitInterfaceImplementations.Single());

                var source3 =
@"
public class C1 : I1
{
   public static event System.Action M01 { add{} remove{} }
}
";

                var compilation3 = CreateCompilationWithIL(source3, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                CompileAndVerify(compilation3, sourceSymbolValidator: validate3, symbolValidator: validate3, verify: Verification.Skipped).VerifyDiagnostics();

                void validate3(ModuleSymbol module)
                {
                    var c = module.GlobalNamespace.GetTypeMember("C1");

                    var m01 = c.Interfaces().Single().GetMembers().OfType<EventSymbol>().Single();
                    var m01Remove = m01.RemoveMethod;

                    Assert.Equal(1, c.GetMembers().OfType<EventSymbol>().Count());
                    Assert.Equal(2, c.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());

                    var cM01 = (EventSymbol)c.FindImplementationForInterfaceMember(m01);

                    Assert.True(cM01.IsStatic);
                    Assert.False(cM01.IsAbstract);
                    Assert.False(cM01.IsVirtual);

                    Assert.Equal("event System.Action C1.M01", cM01.ToTestDisplayString());

                    var cM01Remove = cM01.RemoveMethod;
                    Assert.Same(cM01Remove, c.FindImplementationForInterfaceMember(m01Remove));

                    Assert.True(cM01Remove.IsStatic);
                    Assert.False(cM01Remove.IsAbstract);
                    Assert.False(cM01Remove.IsVirtual);
                    Assert.False(cM01Remove.IsMetadataVirtual());
                    Assert.False(cM01Remove.IsMetadataFinal);
                    Assert.False(cM01Remove.IsMetadataNewSlot());
                    Assert.Equal(MethodKind.EventRemove, cM01Remove.MethodKind);

                    Assert.Equal("void C1.M01.remove", cM01Remove.ToTestDisplayString());

                    var cM01Add = cM01.AddMethod;

                    Assert.True(cM01Add.IsStatic);
                    Assert.False(cM01Add.IsAbstract);
                    Assert.False(cM01Add.IsVirtual);
                    Assert.False(cM01Add.IsMetadataVirtual());
                    Assert.False(cM01Add.IsMetadataFinal);
                    Assert.False(cM01Add.IsMetadataNewSlot());
                    Assert.Equal(MethodKind.EventAdd, cM01Add.MethodKind);

                    Assert.Equal("void C1.M01.add", cM01Add.ToTestDisplayString());

                    Assert.Same(cM01Add, c.FindImplementationForInterfaceMember(m01.AddMethod));

                    if (module is PEModuleSymbol)
                    {
                        Assert.Same(m01Remove, cM01Remove.ExplicitInterfaceImplementations.Single());
                        Assert.Same(m01, cM01.ExplicitInterfaceImplementations.Single());
                        Assert.Same(m01.AddMethod, cM01Add.ExplicitInterfaceImplementations.Single());
                    }
                    else
                    {
                        Assert.Empty(cM01Remove.ExplicitInterfaceImplementations);
                        Assert.Empty(cM01.ExplicitInterfaceImplementations);
                        Assert.Empty(cM01Add.ExplicitInterfaceImplementations);
                    }
                }

                var source4 =
@"
public class C1 : I1
{
   static event System.Action I1.M01 { add{} remove{} }
}
";

                var compilation4 = CreateCompilationWithIL(source4, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation4.VerifyDiagnostics();

                c1 = compilation4.GlobalNamespace.GetTypeMember("C1");
                i1 = c1.Interfaces().Single();
                m01 = i1.GetMembers().OfType<EventSymbol>().Single();
                c1M01 = c1.GetMembers().OfType<EventSymbol>().Single();

                Assert.Same(c1M01, c1.FindImplementationForInterfaceMember(m01));
                Assert.Same(c1M01.RemoveMethod, c1.FindImplementationForInterfaceMember(m01.RemoveMethod));
                Assert.Same(c1M01.AddMethod, c1.FindImplementationForInterfaceMember(m01.AddMethod));
                Assert.Same(m01, c1M01.ExplicitInterfaceImplementations.Single());
                Assert.Same(m01.RemoveMethod, c1M01.RemoveMethod.ExplicitInterfaceImplementations.Single());
                Assert.Same(m01.AddMethod, c1M01.AddMethod.ExplicitInterfaceImplementations.Single());

                var source5 =
@"
public class C1 : I1
{
   public static event System.Action M01 { remove{} }
}
";

                var compilation5 = CreateCompilationWithIL(source5, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation5.VerifyDiagnostics(
                    // (4,38): error CS0065: 'C1.M01': event property must have both add and remove accessors
                    //    public static event System.Action M01 { remove{} }
                    Diagnostic(ErrorCode.ERR_EventNeedsBothAccessors, "M01").WithArguments("C1.M01").WithLocation(4, 38)
                    );

                c1 = compilation5.GlobalNamespace.GetTypeMember("C1");
                i1 = c1.Interfaces().Single();
                m01 = i1.GetMembers().OfType<EventSymbol>().Single();
                c1M01 = c1.GetMembers().OfType<EventSymbol>().Single();

                Assert.Same(c1M01, c1.FindImplementationForInterfaceMember(m01));
                Assert.Same(c1M01.RemoveMethod, c1.FindImplementationForInterfaceMember(m01.RemoveMethod));
                Assert.Same(m01.AddMethod, c1.FindImplementationForInterfaceMember(m01.AddMethod));

                var source6 =
@"
public class C1 : I1
{
   public static event System.Action M01 { add{} }
}
";

                var compilation6 = CreateCompilationWithIL(source6, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation6.VerifyDiagnostics(
                    // (2,19): error CS0535: 'C1' does not implement interface member 'I1.M01.remove'
                    // public class C1 : I1
                    Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C1", "I1.M01.remove").WithLocation(2, 19),
                    // (4,38): error CS0065: 'C1.M01': event property must have both add and remove accessors
                    //    public static event System.Action M01 { remove{} }
                    Diagnostic(ErrorCode.ERR_EventNeedsBothAccessors, "M01").WithArguments("C1.M01").WithLocation(4, 38)
                    );

                c1 = compilation6.GlobalNamespace.GetTypeMember("C1");
                i1 = c1.Interfaces().Single();
                m01 = i1.GetMembers().OfType<EventSymbol>().Single();
                c1M01 = c1.GetMembers().OfType<EventSymbol>().Single();

                Assert.Same(c1M01, c1.FindImplementationForInterfaceMember(m01));
                Assert.Same(c1M01.AddMethod, c1.FindImplementationForInterfaceMember(m01.AddMethod));
                Assert.Null(c1.FindImplementationForInterfaceMember(m01.RemoveMethod));

                var source7 =
@"
public class C1 : I1
{
   static event System.Action I1.M01 { add{} }
}
";

                var compilation7 = CreateCompilationWithIL(source7, ilSource, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation7.VerifyDiagnostics(
                    // (2,19): error CS0535: 'C1' does not implement interface member 'I1.M01.remove'
                    // public class C1 : I1
                    Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1").WithArguments("C1", "I1.M01.remove").WithLocation(2, 19),
                    // (4,34): error CS0065: 'C1.I1.M01': event property must have both add and remove accessors
                    //    static event System.Action I1.M01 { add{} }
                    Diagnostic(ErrorCode.ERR_EventNeedsBothAccessors, "M01").WithArguments("C1.I1.M01").WithLocation(4, 34)
                    );

                c1 = compilation7.GlobalNamespace.GetTypeMember("C1");
                i1 = c1.Interfaces().Single();
                m01 = i1.GetMembers().OfType<EventSymbol>().Single();
                c1M01 = c1.GetMembers().OfType<EventSymbol>().Single();

                Assert.Same(c1M01, c1.FindImplementationForInterfaceMember(m01));
                Assert.Same(c1M01.AddMethod, c1.FindImplementationForInterfaceMember(m01.AddMethod));
                Assert.Null(c1.FindImplementationForInterfaceMember(m01.RemoveMethod));
                Assert.Same(m01, c1M01.ExplicitInterfaceImplementations.Single());
                Assert.Same(m01.AddMethod, c1M01.AddMethod.ExplicitInterfaceImplementations.Single());
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticEvent_12(bool isVirtual)
        {
            // Default interface implementation for a static method
            var (modifier, body) = GetILModifierAndBody(isVirtual);

            var ilSource = @"
.class interface public auto ansi abstract I1
{
    .method public hidebysig specialname " + modifier + @" virtual static 
        void add_M01 (
            class [mscorlib]System.Action 'value'
        ) cil managed 
    " + body + @"

    .method public hidebysig specialname " + modifier + @" virtual static 
        void remove_M01 (
            class [mscorlib]System.Action 'value'
        ) cil managed 
    " + body + @"

    .event [mscorlib]System.Action M01
    {
        .addon void I1::add_M01(class [mscorlib]System.Action)
        .removeon void I1::remove_M01(class [mscorlib]System.Action)
    }
}

.class interface public auto ansi abstract I2
    implements I1
{
    .method private hidebysig specialname static
        void I1.add_M01 (
            class [mscorlib]System.Action 'value'
        ) cil managed 
    {
        .override method void I1::add_M01(class [mscorlib]System.Action)
        IL_0000: ret
    }

    .method private hidebysig specialname static
        void I1.remove_M01 (
            class [mscorlib]System.Action 'value'
        ) cil managed 
    {
        .override method void I1::remove_M01(class [mscorlib]System.Action)
        IL_0000: ret
    }

    .event [mscorlib]System.Action I1.M01
    {
        .addon void I2::I1.add_M01(class [mscorlib]System.Action)
        .removeon void I2::I1.remove_M01(class [mscorlib]System.Action)
    }
}
";

            var source1 =
@"
public class C1 : I2
{
}
";

            var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyEmitDiagnostics();

            var c1 = compilation1.GlobalNamespace.GetTypeMember("C1");
            var i2 = c1.Interfaces().Single();
            var i1 = i2.Interfaces().Single();
            var m01 = i1.GetMembers().OfType<EventSymbol>().Single();
            var i2M01 = i2.GetMembers().OfType<EventSymbol>().Single();

            Assert.Same(i2M01, c1.FindImplementationForInterfaceMember(m01));
            Assert.Same(i2M01, i2.FindImplementationForInterfaceMember(m01));
            Assert.Same(i2M01.AddMethod, c1.FindImplementationForInterfaceMember(m01.AddMethod));
            Assert.Same(i2M01.AddMethod, i2.FindImplementationForInterfaceMember(m01.AddMethod));
            Assert.Same(i2M01.RemoveMethod, c1.FindImplementationForInterfaceMember(m01.RemoveMethod));
            Assert.Same(i2M01.RemoveMethod, i2.FindImplementationForInterfaceMember(m01.RemoveMethod));

            Assert.Same(m01, i2M01.ExplicitInterfaceImplementations.Single());
            Assert.Same(m01.AddMethod, i2M01.AddMethod.ExplicitInterfaceImplementations.Single());
            Assert.Same(m01.RemoveMethod, i2M01.RemoveMethod.ExplicitInterfaceImplementations.Single());
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticEvent_13(bool isVirtual)
        {
            // A forwarding method is added for an implicit implementation declared in base class. 
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"#pragma warning disable CS0067 // WRN_UnreferencedEvent
public interface I1
{
    " + modifier + @" static event System.Action M01;
}

class C1
{
    public static event System.Action M01 { add => throw null; remove{} }
}

class C2 : C1, I1
{
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var m01 = module.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<EventSymbol>().Single();
                var c2 = module.GlobalNamespace.GetTypeMember("C2");

                var c2M01 = (EventSymbol)c2.FindImplementationForInterfaceMember(m01);
                var c2M01Add = (MethodSymbol)c2.FindImplementationForInterfaceMember(m01.AddMethod);
                var c2M01Remove = (MethodSymbol)c2.FindImplementationForInterfaceMember(m01.RemoveMethod);

                Assert.True(c2M01Add.IsStatic);
                Assert.False(c2M01Add.IsAbstract);
                Assert.False(c2M01Add.IsVirtual);
                Assert.False(c2M01Add.IsMetadataVirtual());
                Assert.False(c2M01Add.IsMetadataFinal);
                Assert.False(c2M01Add.IsMetadataNewSlot());

                Assert.True(c2M01Remove.IsStatic);
                Assert.False(c2M01Remove.IsAbstract);
                Assert.False(c2M01Remove.IsVirtual);
                Assert.False(c2M01Remove.IsMetadataVirtual());
                Assert.False(c2M01Remove.IsMetadataFinal);
                Assert.False(c2M01Remove.IsMetadataNewSlot());

                if (module is PEModuleSymbol)
                {
                    Assert.Equal(MethodKind.ExplicitInterfaceImplementation, c2M01Add.MethodKind);
                    Assert.False(c2M01Add.HasRuntimeSpecialName);
                    Assert.False(c2M01Add.HasSpecialName);
                    Assert.Equal("void C2.I1.add_M01(System.Action value)", c2M01Add.ToTestDisplayString());
                    Assert.Same(m01.AddMethod, c2M01Add.ExplicitInterfaceImplementations.Single());

                    Assert.Equal(MethodKind.ExplicitInterfaceImplementation, c2M01Remove.MethodKind);
                    Assert.False(c2M01Remove.HasRuntimeSpecialName);
                    Assert.False(c2M01Remove.HasSpecialName);
                    Assert.Equal("void C2.I1.remove_M01(System.Action value)", c2M01Remove.ToTestDisplayString());
                    Assert.Same(m01.RemoveMethod, c2M01Remove.ExplicitInterfaceImplementations.Single());

                    // Forwarding methods for accessors aren't tied to a property
                    Assert.Null(c2M01);

                    var c1M01 = module.GlobalNamespace.GetMember<EventSymbol>("C1.M01");
                    var c1M01Add = c1M01.AddMethod;
                    var c1M01Remove = c1M01.RemoveMethod;

                    Assert.True(c1M01.IsStatic);
                    Assert.False(c1M01.IsAbstract);
                    Assert.False(c1M01.IsVirtual);
                    Assert.Empty(c1M01.ExplicitInterfaceImplementations);

                    Assert.True(c1M01Add.IsStatic);
                    Assert.False(c1M01Add.IsAbstract);
                    Assert.False(c1M01Add.IsVirtual);
                    Assert.False(c1M01Add.IsMetadataVirtual());
                    Assert.False(c1M01Add.IsMetadataFinal);
                    Assert.False(c1M01Add.IsMetadataNewSlot());
                    Assert.Equal(MethodKind.EventAdd, c1M01Add.MethodKind);
                    Assert.False(c1M01Add.HasRuntimeSpecialName);
                    Assert.True(c1M01Add.HasSpecialName);
                    Assert.Empty(c1M01Add.ExplicitInterfaceImplementations);

                    Assert.True(c1M01Remove.IsStatic);
                    Assert.False(c1M01Remove.IsAbstract);
                    Assert.False(c1M01Remove.IsVirtual);
                    Assert.False(c1M01Remove.IsMetadataVirtual());
                    Assert.False(c1M01Remove.IsMetadataFinal);
                    Assert.False(c1M01Remove.IsMetadataNewSlot());
                    Assert.Equal(MethodKind.EventRemove, c1M01Remove.MethodKind);
                    Assert.False(c1M01Remove.HasRuntimeSpecialName);
                    Assert.True(c1M01Remove.HasSpecialName);
                    Assert.Empty(c1M01Remove.ExplicitInterfaceImplementations);
                }
                else
                {
                    Assert.True(c2M01.IsStatic);
                    Assert.False(c2M01.IsAbstract);
                    Assert.False(c2M01.IsVirtual);

                    Assert.Equal("event System.Action C1.M01", c2M01.ToTestDisplayString());
                    Assert.Empty(c2M01.ExplicitInterfaceImplementations);

                    Assert.Equal(MethodKind.EventAdd, c2M01Add.MethodKind);
                    Assert.False(c2M01Add.HasRuntimeSpecialName);
                    Assert.True(c2M01Add.HasSpecialName);
                    Assert.Same(c2M01.AddMethod, c2M01Add);
                    Assert.Empty(c2M01Add.ExplicitInterfaceImplementations);

                    Assert.Equal(MethodKind.EventRemove, c2M01Remove.MethodKind);
                    Assert.False(c2M01Remove.HasRuntimeSpecialName);
                    Assert.True(c2M01Remove.HasSpecialName);
                    Assert.Same(c2M01.RemoveMethod, c2M01Remove);
                    Assert.Empty(c2M01Remove.ExplicitInterfaceImplementations);
                }
            }

            verifier.VerifyIL("C2.I1.add_M01",
@"
{
  // Code size        7 (0x7)
  .maxstack  1
  IL_0000:  ldarg.0
  IL_0001:  call       ""void C1.M01.add""
  IL_0006:  ret
}
");

            verifier.VerifyIL("C2.I1.remove_M01",
@"
{
  // Code size        7 (0x7)
  .maxstack  1
  IL_0000:  ldarg.0
  IL_0001:  call       ""void C1.M01.remove""
  IL_0006:  ret
}
");
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticEvent_14(bool isVirtual)
        {
            // A forwarding method is added for an implicit implementation with modopt mismatch. 
            var (modifier, body) = GetILModifierAndBody(isVirtual);

            var ilSource = @"
.class interface public auto ansi abstract I1
{
    .method public hidebysig specialname " + modifier + @" virtual static 
        void add_M01 (
            class [mscorlib]System.Action`1<int32 modopt(I1)> 'value'
        ) cil managed 
    " + body + @"

    .method public hidebysig specialname " + modifier + @" virtual static 
        void remove_M01 (
            class [mscorlib]System.Action`1<int32 modopt(I1)> 'value'
        ) cil managed 
    " + body + @"

    .event class [mscorlib]System.Action`1<int32 modopt(I1)> M01
    {
        .addon void I1::add_M01(class [mscorlib]System.Action`1<int32 modopt(I1)>)
        .removeon void I1::remove_M01(class [mscorlib]System.Action`1<int32 modopt(I1)>)
    }
}

.class interface public auto ansi abstract I2
{
    .method public hidebysig specialname abstract virtual static 
        void add_M02 (
            class [mscorlib]System.Action modopt(I1) 'value'
        ) cil managed 
    {
    }

    .method public hidebysig specialname abstract virtual static 
        void modopt(I2) remove_M02 (
            class [mscorlib]System.Action 'value'
        ) cil managed 
    {
    }

    .event class [mscorlib]System.Action M02
    {
        .addon void I2::add_M02(class [mscorlib]System.Action modopt(I1))
        .removeon void modopt(I2) I2::remove_M02(class [mscorlib]System.Action)
    }
}
";

            var source1 =
@"
class C1 : I1
{
    public static event System.Action<int> M01 { add => throw null; remove{} }
}

class C2 : I1
{
    static event System.Action<int> I1.M01 { add => throw null; remove{} }
}

#pragma warning disable CS0067 // The event 'C3.M02' is never used

class C3 : I2
{
    public static event System.Action M02;
}

class C4 : I2
{
    static event System.Action I2.M02 { add => throw null; remove{} }
}
";

            var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var c1 = module.GlobalNamespace.GetTypeMember("C1");
                var m01 = c1.Interfaces().Single().GetMembers().OfType<EventSymbol>().Single();

                var c1M01 = c1.GetMembers().OfType<EventSymbol>().Single();
                var c1M01Add = c1M01.AddMethod;
                var c1M01Remove = c1M01.RemoveMethod;

                Assert.Equal("event System.Action<System.Int32> C1.M01", c1M01.ToTestDisplayString());
                Assert.Empty(c1M01.ExplicitInterfaceImplementations);
                Assert.True(c1M01.IsStatic);
                Assert.False(c1M01.IsAbstract);
                Assert.False(c1M01.IsVirtual);

                Assert.Equal(MethodKind.EventAdd, c1M01Add.MethodKind);
                Assert.Equal("void C1.M01.add", c1M01Add.ToTestDisplayString());
                Assert.Equal("System.Action<System.Int32> value", c1M01Add.Parameters.Single().ToTestDisplayString());
                Assert.Empty(c1M01Add.ExplicitInterfaceImplementations);
                Assert.True(c1M01Add.IsStatic);
                Assert.False(c1M01Add.IsAbstract);
                Assert.False(c1M01Add.IsVirtual);
                Assert.False(c1M01Add.IsMetadataVirtual());
                Assert.False(c1M01Add.IsMetadataFinal);
                Assert.False(c1M01Add.IsMetadataNewSlot());

                Assert.Equal(MethodKind.EventRemove, c1M01Remove.MethodKind);
                Assert.Equal("void C1.M01.remove", c1M01Remove.ToTestDisplayString());
                Assert.Equal("System.Action<System.Int32> value", c1M01Remove.Parameters.Single().ToTestDisplayString());
                Assert.Empty(c1M01Remove.ExplicitInterfaceImplementations);
                Assert.True(c1M01Remove.IsStatic);
                Assert.False(c1M01Remove.IsAbstract);
                Assert.False(c1M01Remove.IsVirtual);
                Assert.False(c1M01Remove.IsMetadataVirtual());
                Assert.False(c1M01Remove.IsMetadataFinal);
                Assert.False(c1M01Remove.IsMetadataNewSlot());

                if (module is PEModuleSymbol)
                {
                    c1M01Add = (MethodSymbol)c1.FindImplementationForInterfaceMember(m01.AddMethod);
                    Assert.Equal(MethodKind.ExplicitInterfaceImplementation, c1M01Add.MethodKind);
                    Assert.Equal("void C1.I1.add_M01(System.Action<System.Int32 modopt(I1)> value)", c1M01Add.ToTestDisplayString());
                    Assert.Same(m01.AddMethod, c1M01Add.ExplicitInterfaceImplementations.Single());

                    Assert.True(c1M01Add.IsStatic);
                    Assert.False(c1M01Add.IsAbstract);
                    Assert.False(c1M01Add.IsVirtual);
                    Assert.False(c1M01Add.IsMetadataVirtual());
                    Assert.False(c1M01Add.IsMetadataFinal);
                    Assert.False(c1M01Add.IsMetadataNewSlot());

                    c1M01Remove = (MethodSymbol)c1.FindImplementationForInterfaceMember(m01.RemoveMethod);
                    Assert.Equal(MethodKind.ExplicitInterfaceImplementation, c1M01Remove.MethodKind);
                    Assert.Equal("void C1.I1.remove_M01(System.Action<System.Int32 modopt(I1)> value)", c1M01Remove.ToTestDisplayString());
                    Assert.Same(m01.RemoveMethod, c1M01Remove.ExplicitInterfaceImplementations.Single());

                    Assert.True(c1M01Remove.IsStatic);
                    Assert.False(c1M01Remove.IsAbstract);
                    Assert.False(c1M01Remove.IsVirtual);
                    Assert.False(c1M01Remove.IsMetadataVirtual());
                    Assert.False(c1M01Remove.IsMetadataFinal);
                    Assert.False(c1M01Remove.IsMetadataNewSlot());

                    // Forwarding methods aren't tied to an event  
                    Assert.Null(c1.FindImplementationForInterfaceMember(m01));
                }
                else
                {
                    Assert.Same(c1M01, c1.FindImplementationForInterfaceMember(m01));
                    Assert.Same(c1M01Add, c1.FindImplementationForInterfaceMember(m01.AddMethod));
                    Assert.Same(c1M01Remove, c1.FindImplementationForInterfaceMember(m01.RemoveMethod));
                }

                var c2 = module.GlobalNamespace.GetTypeMember("C2");

                var c2M01 = (EventSymbol)c2.FindImplementationForInterfaceMember(m01);
                var c2M01Add = c2M01.AddMethod;
                var c2M01Remove = c2M01.RemoveMethod;

                Assert.Equal("event System.Action<System.Int32 modopt(I1)> C2.I1.M01", c2M01.ToTestDisplayString());

                Assert.True(c2M01.IsStatic);
                Assert.False(c2M01.IsAbstract);
                Assert.False(c2M01.IsVirtual);
                Assert.Same(m01, c2M01.ExplicitInterfaceImplementations.Single());

                Assert.True(c2M01Add.IsStatic);
                Assert.False(c2M01Add.IsAbstract);
                Assert.False(c2M01Add.IsVirtual);
                Assert.False(c2M01Add.IsMetadataVirtual());
                Assert.False(c2M01Add.IsMetadataFinal);
                Assert.False(c2M01Add.IsMetadataNewSlot());
                Assert.Equal(MethodKind.EventAdd, c2M01Add.MethodKind);
                Assert.Equal("void C2.I1.M01.add", c2M01Add.ToTestDisplayString());
                Assert.Equal("System.Action<System.Int32 modopt(I1)> value", c2M01Add.Parameters.Single().ToTestDisplayString());
                Assert.Same(m01.AddMethod, c2M01Add.ExplicitInterfaceImplementations.Single());
                Assert.Same(c2M01Add, c2.FindImplementationForInterfaceMember(m01.AddMethod));

                Assert.True(c2M01Remove.IsStatic);
                Assert.False(c2M01Remove.IsAbstract);
                Assert.False(c2M01Remove.IsVirtual);
                Assert.False(c2M01Remove.IsMetadataVirtual());
                Assert.False(c2M01Remove.IsMetadataFinal);
                Assert.False(c2M01Remove.IsMetadataNewSlot());
                Assert.Equal(MethodKind.EventRemove, c2M01Remove.MethodKind);
                Assert.Equal("void C2.I1.M01.remove", c2M01Remove.ToTestDisplayString());
                Assert.Equal("System.Action<System.Int32 modopt(I1)> value", c2M01Remove.Parameters.Single().ToTestDisplayString());
                Assert.Same(m01.RemoveMethod, c2M01Remove.ExplicitInterfaceImplementations.Single());
                Assert.Same(c2M01Remove, c2.FindImplementationForInterfaceMember(m01.RemoveMethod));

                Assert.Same(c2M01, c2.GetMembers().OfType<EventSymbol>().Single());
                Assert.Equal(2, c2.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());

                var c3 = module.GlobalNamespace.GetTypeMember("C3");
                var m02 = c3.Interfaces().Single().GetMembers().OfType<EventSymbol>().Single();

                var c3M02 = c3.GetMembers().OfType<EventSymbol>().Single();
                var c3M02Add = c3M02.AddMethod;
                var c3M02Remove = c3M02.RemoveMethod;

                Assert.Equal("event System.Action C3.M02", c3M02.ToTestDisplayString());
                Assert.Empty(c3M02.ExplicitInterfaceImplementations);
                Assert.True(c3M02.IsStatic);
                Assert.False(c3M02.IsAbstract);
                Assert.False(c3M02.IsVirtual);

                Assert.Equal(MethodKind.EventAdd, c3M02Add.MethodKind);
                Assert.Equal("void C3.M02.add", c3M02Add.ToTestDisplayString());
                Assert.Equal("System.Action value", c3M02Add.Parameters.Single().ToTestDisplayString());
                Assert.Empty(c3M02Add.ExplicitInterfaceImplementations);
                Assert.True(c3M02Add.IsStatic);
                Assert.False(c3M02Add.IsAbstract);
                Assert.False(c3M02Add.IsVirtual);
                Assert.False(c3M02Add.IsMetadataVirtual());
                Assert.False(c3M02Add.IsMetadataFinal);
                Assert.False(c3M02Add.IsMetadataNewSlot());

                Assert.Equal(MethodKind.EventRemove, c3M02Remove.MethodKind);
                Assert.Equal("void C3.M02.remove", c3M02Remove.ToTestDisplayString());
                Assert.Equal("System.Void", c3M02Remove.ReturnTypeWithAnnotations.ToTestDisplayString());
                Assert.Empty(c3M02Remove.ExplicitInterfaceImplementations);
                Assert.True(c3M02Remove.IsStatic);
                Assert.False(c3M02Remove.IsAbstract);
                Assert.False(c3M02Remove.IsVirtual);
                Assert.False(c3M02Remove.IsMetadataVirtual());
                Assert.False(c3M02Remove.IsMetadataFinal);
                Assert.False(c3M02Remove.IsMetadataNewSlot());

                if (module is PEModuleSymbol)
                {
                    c3M02Add = (MethodSymbol)c3.FindImplementationForInterfaceMember(m02.AddMethod);
                    Assert.Equal(MethodKind.ExplicitInterfaceImplementation, c3M02Add.MethodKind);
                    Assert.Equal("void C3.I2.add_M02(System.Action modopt(I1) value)", c3M02Add.ToTestDisplayString());
                    Assert.Same(m02.AddMethod, c3M02Add.ExplicitInterfaceImplementations.Single());

                    Assert.True(c3M02Add.IsStatic);
                    Assert.False(c3M02Add.IsAbstract);
                    Assert.False(c3M02Add.IsVirtual);
                    Assert.False(c3M02Add.IsMetadataVirtual());
                    Assert.False(c3M02Add.IsMetadataFinal);
                    Assert.False(c3M02Add.IsMetadataNewSlot());

                    c3M02Remove = (MethodSymbol)c3.FindImplementationForInterfaceMember(m02.RemoveMethod);
                    Assert.Equal(MethodKind.ExplicitInterfaceImplementation, c3M02Remove.MethodKind);
                    Assert.Equal("void modopt(I2) C3.I2.remove_M02(System.Action value)", c3M02Remove.ToTestDisplayString());
                    Assert.Same(m02.RemoveMethod, c3M02Remove.ExplicitInterfaceImplementations.Single());

                    Assert.True(c3M02Remove.IsStatic);
                    Assert.False(c3M02Remove.IsAbstract);
                    Assert.False(c3M02Remove.IsVirtual);
                    Assert.False(c3M02Remove.IsMetadataVirtual());
                    Assert.False(c3M02Remove.IsMetadataFinal);
                    Assert.False(c3M02Remove.IsMetadataNewSlot());

                    // Forwarding methods aren't tied to an event  
                    Assert.Null(c3.FindImplementationForInterfaceMember(m02));
                }
                else
                {
                    Assert.Same(c3M02, c3.FindImplementationForInterfaceMember(m02));
                    Assert.Same(c3M02Add, c3.FindImplementationForInterfaceMember(m02.AddMethod));
                    Assert.Same(c3M02Remove, c3.FindImplementationForInterfaceMember(m02.RemoveMethod));
                }

                var c4 = module.GlobalNamespace.GetTypeMember("C4");

                var c4M02 = (EventSymbol)c4.FindImplementationForInterfaceMember(m02);
                var c4M02Add = c4M02.AddMethod;
                var c4M02Remove = c4M02.RemoveMethod;

                Assert.Equal("event System.Action C4.I2.M02", c4M02.ToTestDisplayString());

                // Signatures of accessors are lacking custom modifiers due to https://github.com/dotnet/roslyn/issues/53390.

                Assert.True(c4M02.IsStatic);
                Assert.False(c4M02.IsAbstract);
                Assert.False(c4M02.IsVirtual);
                Assert.Same(m02, c4M02.ExplicitInterfaceImplementations.Single());

                Assert.True(c4M02Add.IsStatic);
                Assert.False(c4M02Add.IsAbstract);
                Assert.False(c4M02Add.IsVirtual);
                Assert.False(c4M02Add.IsMetadataVirtual());
                Assert.False(c4M02Add.IsMetadataFinal);
                Assert.False(c4M02Add.IsMetadataNewSlot());
                Assert.Equal(MethodKind.EventAdd, c4M02Add.MethodKind);
                Assert.Equal("void C4.I2.M02.add", c4M02Add.ToTestDisplayString());
                Assert.Equal("System.Action value", c4M02Add.Parameters.Single().ToTestDisplayString());
                Assert.Equal("System.Void", c4M02Add.ReturnTypeWithAnnotations.ToTestDisplayString());
                Assert.Same(m02.AddMethod, c4M02Add.ExplicitInterfaceImplementations.Single());
                Assert.Same(c4M02Add, c4.FindImplementationForInterfaceMember(m02.AddMethod));

                Assert.True(c4M02Remove.IsStatic);
                Assert.False(c4M02Remove.IsAbstract);
                Assert.False(c4M02Remove.IsVirtual);
                Assert.False(c4M02Remove.IsMetadataVirtual());
                Assert.False(c4M02Remove.IsMetadataFinal);
                Assert.False(c4M02Remove.IsMetadataNewSlot());
                Assert.Equal(MethodKind.EventRemove, c4M02Remove.MethodKind);
                Assert.Equal("void C4.I2.M02.remove", c4M02Remove.ToTestDisplayString());
                Assert.Equal("System.Action value", c4M02Remove.Parameters.Single().ToTestDisplayString());
                Assert.Equal("System.Void", c4M02Remove.ReturnTypeWithAnnotations.ToTestDisplayString());
                Assert.Same(m02.RemoveMethod, c4M02Remove.ExplicitInterfaceImplementations.Single());
                Assert.Same(c4M02Remove, c4.FindImplementationForInterfaceMember(m02.RemoveMethod));

                Assert.Same(c4M02, c4.GetMembers().OfType<EventSymbol>().Single());
                Assert.Equal(2, c4.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());
            }

            verifier.VerifyIL("C1.I1.add_M01",
@"
{
  // Code size        7 (0x7)
  .maxstack  1
  IL_0000:  ldarg.0
  IL_0001:  call       ""void C1.M01.add""
  IL_0006:  ret
}
");

            verifier.VerifyIL("C1.I1.remove_M01",
@"
{
  // Code size        7 (0x7)
  .maxstack  1
  IL_0000:  ldarg.0
  IL_0001:  call       ""void C1.M01.remove""
  IL_0006:  ret
}
");

            verifier.VerifyIL("C3.I2.add_M02",
@"
{
  // Code size        7 (0x7)
  .maxstack  1
  IL_0000:  ldarg.0
  IL_0001:  call       ""void C3.M02.add""
  IL_0006:  ret
}
");

            verifier.VerifyIL("C3.I2.remove_M02",
@"
{
  // Code size        7 (0x7)
  .maxstack  1
  IL_0000:  ldarg.0
  IL_0001:  call       ""void C3.M02.remove""
  IL_0006:  ret
}
");
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticEvent_15(bool isVirtual)
        {
            // A forwarding method isn't created if base class implements interface exactly the same way. 
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"#pragma warning disable CS0067 // WRN_UnreferencedEvent
public interface I1
{
    " + modifier + @" static event System.Action M01;
    " + modifier + @" static event System.Action M02;
}

public class C1
{
    public static event System.Action M01 { add => throw null; remove{} }
}

public class C2 : C1, I1
{
    static event System.Action I1.M02 { add => throw null; remove{} }
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C3 : C2, I1
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.RegularPreview, TestOptions.Regular10 })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                         parseOptions: parseOptions,
                                                         targetFramework: _supportingFramework,
                                                         references: new[] { reference });
                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c3 = module.GlobalNamespace.GetTypeMember("C3");
                Assert.Empty(c3.GetMembers().OfType<EventSymbol>());
                Assert.Empty(c3.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()));

                var m01 = c3.Interfaces().Single().GetMembers("M01").OfType<EventSymbol>().Single();

                var c1M01 = c3.BaseType().BaseType().GetMember<EventSymbol>("M01");
                Assert.Equal("event System.Action C1.M01", c1M01.ToTestDisplayString());

                Assert.True(c1M01.IsStatic);
                Assert.False(c1M01.IsAbstract);
                Assert.False(c1M01.IsVirtual);

                Assert.Empty(c1M01.ExplicitInterfaceImplementations);

                var c1M01Add = c1M01.AddMethod;
                Assert.True(c1M01Add.IsStatic);
                Assert.False(c1M01Add.IsAbstract);
                Assert.False(c1M01Add.IsVirtual);
                Assert.False(c1M01Add.IsMetadataVirtual());
                Assert.False(c1M01Add.IsMetadataFinal);
                Assert.False(c1M01Add.IsMetadataNewSlot());

                Assert.Empty(c1M01Add.ExplicitInterfaceImplementations);

                var c1M01Remove = c1M01.RemoveMethod;
                Assert.True(c1M01Remove.IsStatic);
                Assert.False(c1M01Remove.IsAbstract);
                Assert.False(c1M01Remove.IsVirtual);
                Assert.False(c1M01Remove.IsMetadataVirtual());
                Assert.False(c1M01Remove.IsMetadataFinal);
                Assert.False(c1M01Remove.IsMetadataNewSlot());

                Assert.Empty(c1M01Remove.ExplicitInterfaceImplementations);

                if (c1M01.ContainingModule is PEModuleSymbol)
                {
                    var c2M01Add = c3.FindImplementationForInterfaceMember(m01.AddMethod);
                    Assert.Equal("void C2.I1.add_M01(System.Action value)", c2M01Add.ToTestDisplayString());

                    var c2M01Remove = c3.FindImplementationForInterfaceMember(m01.RemoveMethod);
                    Assert.Equal("void C2.I1.remove_M01(System.Action value)", c2M01Remove.ToTestDisplayString());

                    // Forwarding methods for accessors aren't tied to an event
                    Assert.Null(c3.FindImplementationForInterfaceMember(m01));
                }
                else
                {
                    Assert.Same(c1M01, c3.FindImplementationForInterfaceMember(m01));
                    Assert.Same(c1M01.AddMethod, c3.FindImplementationForInterfaceMember(m01.AddMethod));
                    Assert.Same(c1M01.RemoveMethod, c3.FindImplementationForInterfaceMember(m01.RemoveMethod));
                }

                var m02 = c3.Interfaces().Single().GetMembers("M02").OfType<EventSymbol>().Single();

                var c2M02 = c3.BaseType().GetMember<EventSymbol>("I1.M02");
                Assert.Equal("event System.Action C2.I1.M02", c2M02.ToTestDisplayString());
                Assert.Same(c2M02, c3.FindImplementationForInterfaceMember(m02));
                Assert.Same(c2M02.AddMethod, c3.FindImplementationForInterfaceMember(m02.AddMethod));
                Assert.Same(c2M02.RemoveMethod, c3.FindImplementationForInterfaceMember(m02.RemoveMethod));
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticEvent_16(bool isVirtual)
        {
            // A new implicit implementation is properly considered.
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var source1 =
@"#pragma warning disable CS0067 // WRN_UnreferencedEvent
public interface I1
{
    " + modifier + @" static event System.Action M01;
}

public class C1 : I1
{
    public static event System.Action M01 { add{} remove => throw null; }
}

public class C2 : C1
{
    new public static event System.Action M01 { add{} remove => throw null; }
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C3 : C2, I1
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                        parseOptions: TestOptions.RegularPreview,
                                                        targetFramework: _supportingFramework,
                                                        references: new[] { reference });
                var verifier = CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

                verifier.VerifyIL("C3.I1.add_M01",
@"
{
  // Code size        7 (0x7)
  .maxstack  1
  IL_0000:  ldarg.0
  IL_0001:  call       ""void C2.M01.add""
  IL_0006:  ret
}
");

                verifier.VerifyIL("C3.I1.remove_M01",
@"
{
  // Code size        7 (0x7)
  .maxstack  1
  IL_0000:  ldarg.0
  IL_0001:  call       ""void C2.M01.remove""
  IL_0006:  ret
}
");
            }

            void validate(ModuleSymbol module)
            {
                var c3 = module.GlobalNamespace.GetTypeMember("C3");
                var m01 = c3.Interfaces().Single().GetMembers().OfType<EventSymbol>().Single();

                var c2M01 = c3.BaseType().GetMember<EventSymbol>("M01");
                var c2M01Add = c2M01.AddMethod;
                var c2M01Remove = c2M01.RemoveMethod;
                Assert.Equal("event System.Action C2.M01", c2M01.ToTestDisplayString());

                Assert.True(c2M01.IsStatic);
                Assert.False(c2M01.IsAbstract);
                Assert.False(c2M01.IsVirtual);
                Assert.Empty(c2M01.ExplicitInterfaceImplementations);

                Assert.True(c2M01Add.IsStatic);
                Assert.False(c2M01Add.IsAbstract);
                Assert.False(c2M01Add.IsVirtual);
                Assert.False(c2M01Add.IsMetadataVirtual());
                Assert.False(c2M01Add.IsMetadataFinal);
                Assert.False(c2M01Add.IsMetadataNewSlot());
                Assert.Empty(c2M01Add.ExplicitInterfaceImplementations);

                Assert.True(c2M01Remove.IsStatic);
                Assert.False(c2M01Remove.IsAbstract);
                Assert.False(c2M01Remove.IsVirtual);
                Assert.False(c2M01Remove.IsMetadataVirtual());
                Assert.False(c2M01Remove.IsMetadataFinal);
                Assert.False(c2M01Remove.IsMetadataNewSlot());
                Assert.Empty(c2M01Remove.ExplicitInterfaceImplementations);

                if (module is PEModuleSymbol)
                {
                    var c3M01 = (EventSymbol)c3.FindImplementationForInterfaceMember(m01);
                    // Forwarding methods for accessors aren't tied to an event
                    Assert.Null(c3M01);

                    var c3M01Add = (MethodSymbol)c3.FindImplementationForInterfaceMember(m01.AddMethod);
                    Assert.Equal("void C3.I1.add_M01(System.Action value)", c3M01Add.ToTestDisplayString());
                    Assert.Same(m01.AddMethod, c3M01Add.ExplicitInterfaceImplementations.Single());

                    var c3M01Remove = (MethodSymbol)c3.FindImplementationForInterfaceMember(m01.RemoveMethod);
                    Assert.Equal("void C3.I1.remove_M01(System.Action value)", c3M01Remove.ToTestDisplayString());
                    Assert.Same(m01.RemoveMethod, c3M01Remove.ExplicitInterfaceImplementations.Single());
                }
                else
                {
                    Assert.Same(c2M01, c3.FindImplementationForInterfaceMember(m01));
                    Assert.Same(c2M01Add, c3.FindImplementationForInterfaceMember(m01.AddMethod));
                    Assert.Same(c2M01Remove, c3.FindImplementationForInterfaceMember(m01.RemoveMethod));
                }
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticEvent_19(bool genericFirst, bool isVirtual)
        {
            // An "ambiguity" in implicit/explicit implementation declared in generic base class.
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var generic =
@"
    public static event System.Action<T> M01 { add{} remove{} }
";
            var nonGeneric =
@"
    static event System.Action<int> I1.M01 { add{} remove{} }
";
            var source1 =
@"#pragma warning disable CS0067 // WRN_UnreferencedEvent
public interface I1
{
    " + modifier + @" static event System.Action<int> M01;
}

public class C1<T> : I1
{
" + (genericFirst ? generic + nonGeneric : nonGeneric + generic) + @"
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { CreateCompilation("", targetFramework: _supportingFramework).ToMetadataReference() });

            Assert.Equal(2, compilation1.GlobalNamespace.GetTypeMember("C1").GetMembers().OfType<EventSymbol>().Where(m => m.Name.Contains("M01")).Count());
            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C2 : C1<int>, I1
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.Regular10, TestOptions.RegularPreview })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: parseOptions,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { reference });

                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c2 = module.GlobalNamespace.GetTypeMember("C2");
                var m01 = c2.Interfaces().Single().GetMembers().OfType<EventSymbol>().Single();

                Assert.True(m01.ContainingModule is RetargetingModuleSymbol or PEModuleSymbol);

                var c1M01 = (EventSymbol)c2.FindImplementationForInterfaceMember(m01);
                Assert.Equal("event System.Action<System.Int32> C1<T>.I1.M01", c1M01.OriginalDefinition.ToTestDisplayString());
                Assert.Same(m01, c1M01.ExplicitInterfaceImplementations.Single());
                Assert.Same(c1M01, c2.BaseType().FindImplementationForInterfaceMember(m01));
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticEvent_20(bool genericFirst, bool isVirtual)
        {
            // Same as ImplementAbstractStaticEvent_19 only interface is generic too.
            var (modifier, _) = GetModifierAndBody(isVirtual);

            var generic =
@"
    static event System.Action<T> I1<T>.M01 { add{} remove{} }
";
            var nonGeneric =
@"
    public static event System.Action<int> M01 { add{} remove{} }
";
            var source1 =
@"#pragma warning disable CS0067 // WRN_UnreferencedEvent
public interface I1<T>
{
    " + modifier + @" static event System.Action<T> M01;
}

public class C1<T> : I1<T>
{
" + (genericFirst ? generic + nonGeneric : nonGeneric + generic) + @"
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { CreateCompilation("", targetFramework: _supportingFramework).ToMetadataReference() });

            Assert.Equal(2, compilation1.GlobalNamespace.GetTypeMember("C1").GetMembers().OfType<EventSymbol>().Where(m => m.Name.Contains("M01")).Count());

            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C2 : C1<int>, I1<int>
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.Regular10, TestOptions.RegularPreview })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: parseOptions,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { reference });

                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c2 = module.GlobalNamespace.GetTypeMember("C2");
                var m01 = c2.Interfaces().Single().GetMembers().OfType<EventSymbol>().Single();

                Assert.True(m01.ContainingModule is RetargetingModuleSymbol or PEModuleSymbol);

                var c1M01 = (EventSymbol)c2.FindImplementationForInterfaceMember(m01);
                Assert.Equal("event System.Action<T> C1<T>.I1<T>.M01", c1M01.OriginalDefinition.ToTestDisplayString());
                Assert.Equal(m01, c1M01.ExplicitInterfaceImplementations.Single());
                Assert.Same(c1M01, c2.BaseType().FindImplementationForInterfaceMember(m01));
            }
        }

        private static string ConversionOperatorName(string op, bool isChecked = false) =>
            (op, isChecked) switch
            {
                ("implicit", _) => WellKnownMemberNames.ImplicitConversionName,
                ("explicit", false) => WellKnownMemberNames.ExplicitConversionName,
                ("explicit", true) => WellKnownMemberNames.CheckedExplicitConversionName,
                _ => throw TestExceptionUtilities.UnexpectedValue(op)
            };

        internal static string GetConversionOperatorName(string op, bool isChecked, out string checkedKeyword)
        {
            string opName = ConversionOperatorName(op, isChecked: false);
            checkedKeyword = "";

            if (isChecked)
            {
                string checkedName = ConversionOperatorName(op, isChecked: true);

                if (checkedName == opName)
                {
                    return null; // There is no checked form
                }
                else
                {
                    opName = checkedName;
                    checkedKeyword = "checked ";
                }
            }

            return opName;
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticConversionOperator_01([CombinatorialValues("implicit", "explicit")] string op, bool structure, bool isChecked)
        {
            string opName = GetConversionOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var typeKeyword = structure ? "struct" : "class";

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    abstract static " + op + @" operator " + checkedKeyword + @"int(T x);
}

" + typeKeyword + @"
    C1 : I1<C1>
{}

" + typeKeyword + @"
    C2 : I1<C2>
{
    public " + op + @" operator " + checkedKeyword + @"int(C2 x) => throw null;
}

" + typeKeyword + @"
    C3 : I1<C3>
{
    static " + op + @" operator " + checkedKeyword + @"int(C3 x) => throw null;
}

" + typeKeyword + @"
    C4 : I1<C4>
{
    " + op + @" I1<C4>.operator " + checkedKeyword + @"int(C4 x) => throw null;
}

" + typeKeyword + @"
    C5 : I1<C5>
{
    public static " + op + @" operator " + checkedKeyword + @"long(C5 x) => throw null;
}

" + typeKeyword + @"
    C6 : I1<C6>
{
    static " + op + @" I1<C6>.operator " + checkedKeyword + @"long(C6 x) => throw null;
}

" + typeKeyword + @"
    C7 : I1<C7>
{
    public static int " + opName + @"(C7 x) => throw null;
}

" + typeKeyword + @"
    C8 : I1<C8>
{
    static int I1<C8>." + opName + @"(C8 x) => throw null;
}

public interface I2<T> where T : I2<T>
{
    abstract static int " + opName + @"(T x);
}

" + typeKeyword + @"
    C9 : I2<C9>
{
    public static " + op + @" operator " + checkedKeyword + @"int(C9 x) => throw null;
}

" + typeKeyword + @"
    C10 : I2<C10>
{
    static " + op + @" I2<C10>.operator " + checkedKeyword + @"int(C10 x) => throw null;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (8,10): error CS0535: 'C1' does not implement interface member 'I1<C1>.explicit operator int(C1)'
                //     C1 : I1<C1>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C1>").WithArguments("C1", "I1<C1>." + op + " operator " + checkedKeyword + "int(C1)").WithLocation(8, 10),
                // (12,10): error CS8928: 'C2' does not implement static interface member 'I1<C2>.explicit operator int(C2)'. 'C2.explicit operator int(C2)' cannot implement the interface member because it is not static.
                //     C2 : I1<C2>
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberNotStatic, "I1<C2>").WithArguments("C2", "I1<C2>." + op + " operator " + checkedKeyword + "int(C2)", "C2." + op + " operator " + checkedKeyword + "int(C2)").WithLocation(12, 10),
                // (14,30): error CS0558: User-defined operator 'C2.explicit operator int(C2)' must be declared static and public
                //     public explicit operator int(C2 x) => throw null;
                Diagnostic(ErrorCode.ERR_OperatorsMustBeStaticAndPublic, "int").WithArguments("C2." + op + " operator " + checkedKeyword + "int(C2)").WithLocation(14, 30 + checkedKeyword.Length),
                // (18,10): error CS0737: 'C3' does not implement interface member 'I1<C3>.explicit operator int(C3)'. 'C3.explicit operator int(C3)' cannot implement an interface member because it is not public.
                //     C3 : I1<C3>
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberNotPublic, "I1<C3>").WithArguments("C3", "I1<C3>." + op + " operator " + checkedKeyword + "int(C3)", "C3." + op + " operator " + checkedKeyword + "int(C3)").WithLocation(18, 10),
                // (20,30): error CS0558: User-defined operator 'C3.explicit operator int(C3)' must be declared static and public
                //     static explicit operator int(C3 x) => throw null;
                Diagnostic(ErrorCode.ERR_OperatorsMustBeStaticAndPublic, "int").WithArguments("C3." + op + " operator " + checkedKeyword + "int(C3)").WithLocation(20, 30 + checkedKeyword.Length),
                // (24,10): error CS0535: 'C4' does not implement interface member 'I1<C4>.explicit operator int(C4)'
                //     C4 : I1<C4>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C4>").WithArguments("C4", "I1<C4>." + op + " operator " + checkedKeyword + "int(C4)").WithLocation(24, 10),
                // (26,30): error CS8930: Explicit implementation of a user-defined operator 'C4.explicit operator int(C4)' must be declared static
                //     explicit I1<C4>.operator int(C4 x) => throw null;
                Diagnostic(ErrorCode.ERR_ExplicitImplementationOfOperatorsMustBeStatic, "int").WithArguments("C4." + op + " operator " + checkedKeyword + "int(C4)").WithLocation(26, 30 + checkedKeyword.Length),
                // (26,30): error CS0539: 'C4.explicit operator int(C4)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     explicit I1<C4>.operator int(C4 x) => throw null;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "int").WithArguments("C4." + op + " operator " + checkedKeyword + "int(C4)").WithLocation(26, 30 + checkedKeyword.Length),
                // (30,10): error CS0738: 'C5' does not implement interface member 'I1<C5>.explicit operator int(C5)'. 'C5.explicit operator long(C5)' cannot implement 'I1<C5>.explicit operator int(C5)' because it does not have the matching return type of 'int'.
                //     C5 : I1<C5>
                Diagnostic(ErrorCode.ERR_CloseUnimplementedInterfaceMemberWrongReturnType, "I1<C5>").WithArguments("C5", "I1<C5>." + op + " operator " + checkedKeyword + "int(C5)", "C5." + op + " operator " + checkedKeyword + "long(C5)", "int").WithLocation(30, 10),
                // (36,10): error CS0535: 'C6' does not implement interface member 'I1<C6>.explicit operator int(C6)'
                //     C6 : I1<C6>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C6>").WithArguments("C6", "I1<C6>." + op + " operator " + checkedKeyword + "int(C6)").WithLocation(36, 10),
                // (38,37): error CS9334: 'C6.explicit operator long(C6)' return type must be 'int' to match implemented member 'I1<C6>.explicit operator int(C6)'
                //     static explicit I1<C6>.operator long(C6 x) => throw null;
                Diagnostic(ErrorCode.ERR_ExplicitInterfaceMemberReturnTypeMismatch, "long").WithArguments("C6." + op + " operator " + checkedKeyword + "long(C6)", "int", "I1<C6>." + op + " operator " + checkedKeyword + "int(C6)").WithLocation(38, 37 + checkedKeyword.Length),
                // (42,10): error CS0535: 'C7' does not implement interface member 'I1<C7>.explicit operator int(C7)'
                //     C7 : I1<C7>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C7>").WithArguments("C7", "I1<C7>." + op + " operator " + checkedKeyword + "int(C7)").WithLocation(42, 10),
                // (48,10): error CS0535: 'C8' does not implement interface member 'I1<C8>.explicit operator int(C8)'
                //     C8 : I1<C8>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C8>").WithArguments("C8", "I1<C8>." + op + " operator " + checkedKeyword + "int(C8)").WithLocation(48, 10),
                // (50,23): error CS0539: 'C8.op_Explicit(C8)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static int I1<C8>.op_Explicit(C8 x) => throw null;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, opName).WithArguments("C8." + opName + "(C8)").WithLocation(50, 23),
                // (59,10): error CS0535: 'C9' does not implement interface member 'I2<C9>.op_Explicit(C9)'
                //     C9 : I2<C9>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I2<C9>").WithArguments("C9", "I2<C9>." + opName + "(C9)").WithLocation(59, 10),
                // (65,11): error CS0535: 'C10' does not implement interface member 'I2<C10>.op_Explicit(C10)'
                //     C10 : I2<C10>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I2<C10>").WithArguments("C10", "I2<C10>." + opName + "(C10)").WithLocation(65, 11),
                // (67,38): error CS0539: 'C10.explicit operator int(C10)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static explicit I2<C10>.operator int(C10 x) => throw null;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "int").WithArguments("C10." + op + " operator " + checkedKeyword + "int(C10)").WithLocation(67, 38 + checkedKeyword.Length)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementVirtualStaticConversionOperator_01([CombinatorialValues("implicit", "explicit")] string op, bool structure, bool isChecked)
        {
            string opName = GetConversionOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var typeKeyword = structure ? "struct" : "class";

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    virtual static " + op + @" operator " + checkedKeyword + @"int(T x) => default;
}

" + typeKeyword + @"
    C1 : I1<C1>
{}

" + typeKeyword + @"
    C2 : I1<C2>
{
    public " + op + @" operator " + checkedKeyword + @"int(C2 x) => throw null;
}

" + typeKeyword + @"
    C3 : I1<C3>
{
    static " + op + @" operator " + checkedKeyword + @"int(C3 x) => throw null;
}

" + typeKeyword + @"
    C4 : I1<C4>
{
    " + op + @" I1<C4>.operator " + checkedKeyword + @"int(C4 x) => throw null;
}

" + typeKeyword + @"
    C5 : I1<C5>
{
    public static " + op + @" operator " + checkedKeyword + @"long(C5 x) => throw null;
}

" + typeKeyword + @"
    C6 : I1<C6>
{
    static " + op + @" I1<C6>.operator " + checkedKeyword + @"long(C6 x) => throw null;
}

" + typeKeyword + @"
    C7 : I1<C7>
{
    public static int " + opName + @"(C7 x) => throw null;
}

" + typeKeyword + @"
    C8 : I1<C8>
{
    static int I1<C8>." + opName + @"(C8 x) => throw null;
}

public interface I2<T> where T : I2<T>
{
    virtual static int " + opName + @"(T x) => default;
}

" + typeKeyword + @"
    C9 : I2<C9>
{
    public static " + op + @" operator " + checkedKeyword + @"int(C9 x) => throw null;
}

" + typeKeyword + @"
    C10 : I2<C10>
{
    static " + op + @" I2<C10>.operator " + checkedKeyword + @"int(C10 x) => throw null;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (14,30): error CS0558: User-defined operator 'C2.explicit operator int(C2)' must be declared static and public
                //     public explicit operator int(C2 x) => throw null;
                Diagnostic(ErrorCode.ERR_OperatorsMustBeStaticAndPublic, "int").WithArguments("C2." + op + " operator " + checkedKeyword + "int(C2)").WithLocation(14, 30 + checkedKeyword.Length),
                // (20,30): error CS0558: User-defined operator 'C3.explicit operator int(C3)' must be declared static and public
                //     static explicit operator int(C3 x) => throw null;
                Diagnostic(ErrorCode.ERR_OperatorsMustBeStaticAndPublic, "int").WithArguments("C3." + op + " operator " + checkedKeyword + "int(C3)").WithLocation(20, 30 + checkedKeyword.Length),
                // (26,30): error CS8930: Explicit implementation of a user-defined operator 'C4.explicit operator int(C4)' must be declared static
                //     explicit I1<C4>.operator int(C4 x) => throw null;
                Diagnostic(ErrorCode.ERR_ExplicitImplementationOfOperatorsMustBeStatic, "int").WithArguments("C4." + op + " operator " + checkedKeyword + "int(C4)").WithLocation(26, 30 + checkedKeyword.Length),
                // (26,30): error CS0539: 'C4.explicit operator int(C4)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     explicit I1<C4>.operator int(C4 x) => throw null;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "int").WithArguments("C4." + op + " operator " + checkedKeyword + "int(C4)").WithLocation(26, 30 + checkedKeyword.Length),
                // (38,37): error CS9334: 'C6.explicit operator long(C6)' return type must be 'int' to match implemented member 'I1<C6>.explicit operator int(C6)'
                //     static explicit I1<C6>.operator long(C6 x) => throw null;
                Diagnostic(ErrorCode.ERR_ExplicitInterfaceMemberReturnTypeMismatch, "long").WithArguments("C6." + op + " operator " + checkedKeyword + "long(C6)", "int", "I1<C6>." + op + " operator " + checkedKeyword + "int(C6)").WithLocation(38, 37 + checkedKeyword.Length),
                // (50,23): error CS0539: 'C8.op_Explicit(C8)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static int I1<C8>.op_Explicit(C8 x) => throw null;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, opName).WithArguments("C8." + opName + "(C8)").WithLocation(50, 23),
                // (67,38): error CS0539: 'C10.explicit operator int(C10)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static explicit I2<C10>.operator int(C10 x) => throw null;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "int").WithArguments("C10." + op + " operator " + checkedKeyword + "int(C10)").WithLocation(67, 38 + checkedKeyword.Length)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticConversionOperator_03([CombinatorialValues("implicit", "explicit")] string op, bool isChecked)
        {
            if (GetConversionOperatorName(op, isChecked, out string checkedKeyword) is null)
            {
                return;
            }

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    abstract static " + op + @" operator " + checkedKeyword + @"int(T x);
}

interface I2<T> : I1<T> where T : I1<T>
{}

interface I3<T> : I1<T> where T : I1<T>
{
    " + op + @" operator " + checkedKeyword + @"int(T x) => default;
}

interface I4<T> : I1<T> where T : I1<T>
{
    static " + op + @" operator " + checkedKeyword + @"int(T x) => default;
}

interface I5<T> : I1<T> where T : I1<T>
{
    " + op + @" I1<T>.operator " + checkedKeyword + @"int(T x) => default;
}

interface I6<T> : I1<T> where T : I1<T>
{
    static " + op + @" I1<T>.operator " + checkedKeyword + @"int(T x) => default;
}

interface I7<T> : I1<T> where T : I1<T>
{
    abstract static " + op + @" operator " + checkedKeyword + @"int(T x);
}

public interface I11<T> where T : I11<T>
{
    abstract static " + op + @" operator " + checkedKeyword + @"int(T x);
}

interface I8<T> : I11<T> where T : I8<T>
{
    " + op + @" operator " + checkedKeyword + @"int(T x) => default;
}

interface I9<T> : I11<T> where T : I9<T>
{
    static " + op + @" operator " + checkedKeyword + @"int(T x) => default;
}

interface I10<T> : I11<T> where T : I10<T>
{
    abstract static " + op + @" operator " + checkedKeyword + @"int(T x);
}

interface I12<T> : I11<T> where T : I12<T>
{
    static " + op + @" I11<T>.operator " + checkedKeyword + @"int(T x) => default;
}

interface I13<T> : I11<T> where T : I13<T>
{
    abstract static " + op + @" I11<T>.operator " + checkedKeyword + @"int(T x);
}

interface I14<T> : I1<T> where T : I1<T>
{
    abstract static " + op + @" I1<T>.operator " + checkedKeyword + @"int(T x);
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (12,23): error CS0556: User-defined conversion must convert to or from the enclosing type
                //     implicit operator int(T x) => default;
                Diagnostic(ErrorCode.ERR_ConversionNotInvolvingContainedType, "int").WithLocation(12, 23 + checkedKeyword.Length),
                // (12,23): error CS0567: Conversion, equality, or inequality operators declared in interfaces must be abstract or virtual
                //     implicit operator int(T x) => default;
                Diagnostic(ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators, "int").WithLocation(12, 23 + checkedKeyword.Length),
                // (17,30): error CS0556: User-defined conversion must convert to or from the enclosing type
                //     static implicit operator int(T x) => default;
                Diagnostic(ErrorCode.ERR_ConversionNotInvolvingContainedType, "int").WithLocation(17, 30 + checkedKeyword.Length),
                // (17,30): error CS0567: Conversion, equality, or inequality operators declared in interfaces must be abstract or virtual
                //     static implicit operator int(T x) => default;
                Diagnostic(ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators, "int").WithLocation(17, 30 + checkedKeyword.Length),
                // (22,29): error CS8930: Explicit implementation of a user-defined operator 'I5<T>.implicit operator int(T)' must be declared static
                //     implicit I1<T>.operator int(T x) => default;
                Diagnostic(ErrorCode.ERR_ExplicitImplementationOfOperatorsMustBeStatic, "int").WithArguments("I5<T>." + op + " operator " + checkedKeyword + "int(T)").WithLocation(22, 29 + checkedKeyword.Length),
                // (22,29): error CS0539: 'I5<T>.implicit operator int(T)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     implicit I1<T>.operator int(T x) => default;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "int").WithArguments("I5<T>." + op + " operator " + checkedKeyword + "int(T)").WithLocation(22, 29 + checkedKeyword.Length),
                // (32,39): error CS8931: User-defined conversion in an interface must convert to or from a type parameter on the enclosing type constrained to the enclosing type
                //     abstract static implicit operator int(T x);
                Diagnostic(ErrorCode.ERR_AbstractConversionNotInvolvingContainedType, "int").WithLocation(32, 39 + checkedKeyword.Length),
                // (42,23): error CS0556: User-defined conversion must convert to or from the enclosing type
                //     implicit operator int(T x) => default;
                Diagnostic(ErrorCode.ERR_ConversionNotInvolvingContainedType, "int").WithLocation(42, 23 + checkedKeyword.Length),
                // (42,23): error CS0567: Conversion, equality, or inequality operators declared in interfaces must be abstract or virtual
                //     implicit operator int(T x) => default;
                Diagnostic(ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators, "int").WithLocation(42, 23 + checkedKeyword.Length),
                // (47,30): error CS0556: User-defined conversion must convert to or from the enclosing type
                //     static implicit operator int(T x) => default;
                Diagnostic(ErrorCode.ERR_ConversionNotInvolvingContainedType, "int").WithLocation(47, 30 + checkedKeyword.Length),
                // (47,30): error CS0567: Conversion, equality, or inequality operators declared in interfaces must be abstract or virtual
                //     static implicit operator int(T x) => default;
                Diagnostic(ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators, "int").WithLocation(47, 30 + checkedKeyword.Length)
                );

            var i2 = compilation1.GlobalNamespace.GetTypeMember("I2");
            Assert.Null(i2.FindImplementationForInterfaceMember(i2.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single()));

            var i3 = compilation1.GlobalNamespace.GetTypeMember("I3");
            Assert.Null(i3.FindImplementationForInterfaceMember(i3.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single()));

            var i4 = compilation1.GlobalNamespace.GetTypeMember("I4");
            Assert.Null(i4.FindImplementationForInterfaceMember(i4.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single()));

            var i5 = compilation1.GlobalNamespace.GetTypeMember("I5");
            Assert.Null(i5.FindImplementationForInterfaceMember(i5.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single()));

            var i6 = compilation1.GlobalNamespace.GetTypeMember("I6");
            Assert.Same(i6.GetMembers().OfType<MethodSymbol>().Single(), i6.FindImplementationForInterfaceMember(i6.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single()));

            var i7 = compilation1.GlobalNamespace.GetTypeMember("I7");
            Assert.Null(i7.FindImplementationForInterfaceMember(i7.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single()));

            var i8 = compilation1.GlobalNamespace.GetTypeMember("I8");
            Assert.Null(i8.FindImplementationForInterfaceMember(i8.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single()));

            var i9 = compilation1.GlobalNamespace.GetTypeMember("I9");
            Assert.Null(i9.FindImplementationForInterfaceMember(i9.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single()));

            var i10 = compilation1.GlobalNamespace.GetTypeMember("I10");
            Assert.Null(i10.FindImplementationForInterfaceMember(i10.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single()));

            var i12 = compilation1.GlobalNamespace.GetTypeMember("I12");
            Assert.Same(i12.GetMembers().OfType<MethodSymbol>().Single(), i12.FindImplementationForInterfaceMember(i12.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single()));

            var i13 = compilation1.GlobalNamespace.GetTypeMember("I13");
            Assert.Null(i13.FindImplementationForInterfaceMember(i13.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single()));

            var i14 = compilation1.GlobalNamespace.GetTypeMember("I14");
            Assert.Null(i14.FindImplementationForInterfaceMember(i14.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single()));
        }

        [Theory]
        [CombinatorialData]
        public void ImplementVirtualStaticConversionOperator_03([CombinatorialValues("implicit", "explicit")] string op, bool isChecked)
        {
            if (GetConversionOperatorName(op, isChecked, out string checkedKeyword) is null)
            {
                return;
            }

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    virtual  static " + op + @" operator " + checkedKeyword + @"int(T x) => default;
}

interface I2<T> : I1<T> where T : I1<T>
{}

interface I3<T> : I1<T> where T : I1<T>
{
    " + op + @" operator " + checkedKeyword + @"int(T x) => default;
}

interface I4<T> : I1<T> where T : I1<T>
{
    static " + op + @" operator " + checkedKeyword + @"int(T x) => default;
}

interface I5<T> : I1<T> where T : I1<T>
{
    " + op + @" I1<T>.operator " + checkedKeyword + @"int(T x) => default;
}

interface I6<T> : I1<T> where T : I1<T>
{
    static " + op + @" I1<T>.operator " + checkedKeyword + @"int(T x) => default;
}

interface I7<T> : I1<T> where T : I1<T>
{
    virtual  static " + op + @" operator " + checkedKeyword + @"int(T x) => default;
}

public interface I11<T> where T : I11<T>
{
    virtual  static " + op + @" operator " + checkedKeyword + @"int(T x) => default;
}

interface I8<T> : I11<T> where T : I8<T>
{
    " + op + @" operator " + checkedKeyword + @"int(T x) => default;
}

interface I9<T> : I11<T> where T : I9<T>
{
    static " + op + @" operator " + checkedKeyword + @"int(T x) => default;
}

interface I10<T> : I11<T> where T : I10<T>
{
    virtual  static " + op + @" operator " + checkedKeyword + @"int(T x) => default;
}

interface I12<T> : I11<T> where T : I12<T>
{
    static " + op + @" I11<T>.operator " + checkedKeyword + @"int(T x) => default;
}

interface I13<T> : I11<T> where T : I13<T>
{
    virtual  static " + op + @" I11<T>.operator " + checkedKeyword + @"int(T x) => default;
}

interface I14<T> : I1<T> where T : I1<T>
{
    virtual  static " + op + @" I1<T>.operator " + checkedKeyword + @"int(T x) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (12,23): error CS0556: User-defined conversion must convert to or from the enclosing type
                //     implicit operator int(T x) => default;
                Diagnostic(ErrorCode.ERR_ConversionNotInvolvingContainedType, "int").WithLocation(12, 23 + checkedKeyword.Length),
                // (12,23): error CS0567: Conversion, equality, or inequality operators declared in interfaces must be abstract or virtual
                //     implicit operator int(T x) => default;
                Diagnostic(ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators, "int").WithLocation(12, 23 + checkedKeyword.Length),
                // (17,30): error CS0556: User-defined conversion must convert to or from the enclosing type
                //     static implicit operator int(T x) => default;
                Diagnostic(ErrorCode.ERR_ConversionNotInvolvingContainedType, "int").WithLocation(17, 30 + checkedKeyword.Length),
                // (17,30): error CS0567: Conversion, equality, or inequality operators declared in interfaces must be abstract or virtual
                //     static implicit operator int(T x) => default;
                Diagnostic(ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators, "int").WithLocation(17, 30 + checkedKeyword.Length),
                // (22,29): error CS8930: Explicit implementation of a user-defined operator 'I5<T>.implicit operator int(T)' must be declared static
                //     implicit I1<T>.operator int(T x) => default;
                Diagnostic(ErrorCode.ERR_ExplicitImplementationOfOperatorsMustBeStatic, "int").WithArguments("I5<T>." + op + " operator " + checkedKeyword + "int(T)").WithLocation(22, 29 + checkedKeyword.Length),
                // (22,29): error CS0539: 'I5<T>.implicit operator int(T)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     implicit I1<T>.operator int(T x) => default;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "int").WithArguments("I5<T>." + op + " operator " + checkedKeyword + "int(T)").WithLocation(22, 29 + checkedKeyword.Length),
                // (32,39): error CS8931: User-defined conversion in an interface must convert to or from a type parameter on the enclosing type constrained to the enclosing type
                //     virtual  static implicit operator int(T x) => default;
                Diagnostic(ErrorCode.ERR_AbstractConversionNotInvolvingContainedType, "int").WithLocation(32, 39 + checkedKeyword.Length),
                // (42,23): error CS0556: User-defined conversion must convert to or from the enclosing type
                //     implicit operator int(T x) => default;
                Diagnostic(ErrorCode.ERR_ConversionNotInvolvingContainedType, "int").WithLocation(42, 23 + checkedKeyword.Length),
                // (42,23): error CS0567: Conversion, equality, or inequality operators declared in interfaces must be abstract or virtual
                //     implicit operator int(T x) => default;
                Diagnostic(ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators, "int").WithLocation(42, 23 + checkedKeyword.Length),
                // (47,30): error CS0556: User-defined conversion must convert to or from the enclosing type
                //     static implicit operator int(T x) => default;
                Diagnostic(ErrorCode.ERR_ConversionNotInvolvingContainedType, "int").WithLocation(47, 30 + checkedKeyword.Length),
                // (47,30): error CS0567: Conversion, equality, or inequality operators declared in interfaces must be abstract or virtual
                //     static implicit operator int(T x) => default;
                Diagnostic(ErrorCode.ERR_InterfacesCantContainConversionOrEqualityOperators, "int").WithLocation(47, 30 + checkedKeyword.Length),
                // (62,46): error CS0106: The modifier 'virtual' is not valid for this item
                //     virtual  static implicit I11<T>.operator int(T x) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "int").WithArguments("virtual").WithLocation(62, 46 + checkedKeyword.Length),
                // (67,45): error CS0106: The modifier 'virtual' is not valid for this item
                //     virtual  static implicit I1<T>.operator int(T x) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "int").WithArguments("virtual").WithLocation(67, 45 + checkedKeyword.Length)
                );

            var i2 = compilation1.GlobalNamespace.GetTypeMember("I2");
            var m01 = i2.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();
            Assert.Equal(m01, i2.FindImplementationForInterfaceMember(m01));

            var i3 = compilation1.GlobalNamespace.GetTypeMember("I3");
            m01 = i3.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();
            Assert.Equal(m01, i3.FindImplementationForInterfaceMember(m01));

            var i4 = compilation1.GlobalNamespace.GetTypeMember("I4");
            m01 = i4.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();
            Assert.Equal(m01, i4.FindImplementationForInterfaceMember(m01));

            var i5 = compilation1.GlobalNamespace.GetTypeMember("I5");
            m01 = i5.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();
            Assert.Equal(m01, i5.FindImplementationForInterfaceMember(m01));

            var i6 = compilation1.GlobalNamespace.GetTypeMember("I6");
            Assert.Same(i6.GetMembers().OfType<MethodSymbol>().Single(), i6.FindImplementationForInterfaceMember(i6.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single()));

            var i7 = compilation1.GlobalNamespace.GetTypeMember("I7");
            m01 = i7.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();
            Assert.Equal(m01, i7.FindImplementationForInterfaceMember(m01));

            foreach (var name in new[] { "I8", "I9", "I10" })
            {
                var iX = compilation1.GlobalNamespace.GetTypeMember(name);
                var iXM = iX.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();
                Assert.Equal(iXM, iX.FindImplementationForInterfaceMember(iXM));
            }

            foreach (var name in new[] { "I12", "I13" })
            {
                var iX = compilation1.GlobalNamespace.GetTypeMember(name);
                var iXM = iX.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();
                Assert.Equal(iX.GetMembers().OfType<MethodSymbol>().Single(), iX.FindImplementationForInterfaceMember(iXM));
            }

            var i14 = compilation1.GlobalNamespace.GetTypeMember("I14");
            Assert.Same(i14.GetMembers().OfType<MethodSymbol>().Single(), i14.FindImplementationForInterfaceMember(i14.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single()));
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticConversionOperator_04([CombinatorialValues("implicit", "explicit")] string op, bool structure, bool isChecked, bool isVirtual)
        {
            if (GetConversionOperatorName(op, isChecked, out string checkedKeyword) is null)
            {
                return;
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);
            var typeKeyword = structure ? "struct" : "class";

            var source1 =
@"
public interface I2<T> where T : I2<T>
{
    " + modifier + @" static " + op + @" operator " + checkedKeyword + @"int(T x)" + body + @"
}
";
            var source2 =
typeKeyword + @"
    Test1 : I2<Test1>
{
    static " + op + @" I2<Test1>.operator " + checkedKeyword + @"int(Test1 x) => default;
}
" + typeKeyword + @"
    Test2: I2<Test2>
{
    public static " + op + @" operator " + checkedKeyword + @"int(Test2 x) => default;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.ToMetadataReference() });

            if (!isChecked)
            {
                compilation2.VerifyDiagnostics(
                    // (4,21): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     static implicit I2<Test1>.operator int(Test1 x) => default;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "I2<Test1>.").WithArguments("static abstract members in interfaces", "11.0").WithLocation(4, 21),
                    // (9,37): error CS8706: 'Test2.implicit operator int(Test2)' cannot implement interface member 'I2<Test2>.implicit operator int(Test2)' in type 'Test2' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                    //     public static implicit operator int(Test2 x) => default;
                    Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, "int").WithArguments("Test2." + op + " operator int(Test2)", "I2<Test2>." + op + " operator int(Test2)", "Test2", "static abstract members in interfaces", "10.0", "11.0").WithLocation(9, 37)
                    );
            }
            else
            {
                compilation2.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                    // (4,21): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     static explicit I2<Test1>.operator checked int(Test1 x) => default;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "I2<Test1>.").WithArguments("static abstract members in interfaces", "11.0").WithLocation(4, 21),
                    // (4,40): error CS8936: Feature 'checked user-defined operators' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     static explicit I2<Test1>.operator checked int(Test1 x) => default;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "checked").WithArguments("checked user-defined operators", "11.0").WithLocation(4, 40),
                    // (9,37): error CS8936: Feature 'checked user-defined operators' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     public static explicit operator checked int(Test2 x) => default;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "checked").WithArguments("checked user-defined operators", "11.0").WithLocation(9, 37),
                    // (9,45): error CS8706: 'Test2.explicit operator checked int(Test2)' cannot implement interface member 'I2<Test2>.explicit operator checked int(Test2)' in type 'Test2' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                    //     public static explicit operator checked int(Test2 x) => default;
                    Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, "int").WithArguments("Test2." + op + " operator checked int(Test2)", "I2<Test2>." + op + " operator checked int(Test2)", "Test2", "static abstract members in interfaces", "10.0", "11.0").WithLocation(9, 45)
                    );
            }

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            if (!isChecked)
            {
                compilation3.VerifyDiagnostics(
                    // (4,21): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     static implicit I2<Test1>.operator int(Test1 x) => default;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "I2<Test1>.").WithArguments("static abstract members in interfaces", "11.0").WithLocation(4, 21),
                    // (14,39): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                    //     virtual  static implicit operator int(T x) => throw null;
                    Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "int").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(14, 39)
                    );
            }
            else
            {
                compilation3.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                    // (4,21): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     static explicit I2<Test1>.operator checked int(Test1 x) => default;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "I2<Test1>.").WithArguments("static abstract members in interfaces", "11.0").WithLocation(4, 21),
                    // (4,40): error CS8936: Feature 'checked user-defined operators' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     static explicit I2<Test1>.operator checked int(Test1 x) => default;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "checked").WithArguments("checked user-defined operators", "11.0").WithLocation(4, 40),
                    // (9,37): error CS8936: Feature 'checked user-defined operators' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     public static explicit operator checked int(Test2 x) => default;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "checked").WithArguments("checked user-defined operators", "11.0").WithLocation(9, 37),
                    // (14,39): error CS8936: Feature 'checked user-defined operators' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     abstract static explicit operator checked int(T x);
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "checked").WithArguments("checked user-defined operators", "11.0").WithLocation(14, 39),
                    // (14,47): error CS8703: The modifier 'abstract' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                    //     abstract static explicit operator checked int(T x);
                    Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "int").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(14, 47)
                    );
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticConversionOperator_05([CombinatorialValues("implicit", "explicit")] string op, bool structure, bool isChecked, bool isVirtual)
        {
            if (GetConversionOperatorName(op, isChecked, out string checkedKeyword) is null)
            {
                return;
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);
            var typeKeyword = structure ? "struct" : "class";

            var source1 =
@"
public partial interface I1<T> where T : I1<T> 
{
    " + modifier + @" static " + op + @" operator " + checkedKeyword + @"int(T x)" + body + @"
}
";
            var source2 =
"partial " + typeKeyword + @"
    Test1: I1<Test1>
{
    public static " + op + @" operator " + checkedKeyword + @"int(Test1 x) => default;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (4,37): error CS8929: 'Test1.implicit operator int(Test1)' cannot implement interface member 'I1<Test1>.implicit operator int(Test1)' in type 'Test1' because the target runtime doesn't support static abstract members in interfaces.
                //     public static implicit operator int(Test1 x) => default;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfacesForMember, "int").WithArguments("Test1." + op + " operator " + checkedKeyword + "int(Test1)", "I1<Test1>." + op + " operator " + checkedKeyword + "int(Test1)", "Test1").WithLocation(4, 37 + checkedKeyword.Length)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation3.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (9,39): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static explicit operator int(T x);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "int").WithLocation(9, 39 + checkedKeyword.Length)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticConversionOperator_06([CombinatorialValues("implicit", "explicit")] string op, bool structure, bool isChecked, bool isVirtual)
        {
            if (GetConversionOperatorName(op, isChecked, out string checkedKeyword) is null)
            {
                return;
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);
            var typeKeyword = structure ? "struct" : "class";

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    " + modifier + @" static " + op + @" operator " + checkedKeyword + @"int(T x)" + body + @"
}
";
            var source2 =
typeKeyword + @"
    Test1 : I1<Test1>
{
    static " + op + @" I1<Test1>.operator " + checkedKeyword + @"int(Test1 x) => default;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (4,40): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     static explicit I1<Test1>.operator int(Test1 x) => default;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "int").WithLocation(4, 40 + checkedKeyword.Length)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation3.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (4,40): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     static explicit I1<Test1>.operator int(Test1 x) => default;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "int").WithLocation(4, 40 + checkedKeyword.Length),
                // (9,39): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static explicit operator int(T x);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "int").WithLocation(9, 39 + checkedKeyword.Length)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticConversionOperator_07([CombinatorialValues("implicit", "explicit")] string op, bool structure, bool isChecked, bool isVirtual)
        {
            // Basic implicit implementation scenario, MethodImpl is emitted

            string opName = GetConversionOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);
            var typeKeyword = structure ? "struct" : "class";

            var source1 =
@"
public partial interface I1<T> where T : I1<T>
{
    " + modifier + @" static " + op + @" operator " + checkedKeyword + @"int(T x)" + body + @"
    " + modifier + @" static " + op + @" operator " + checkedKeyword + @"long(T x)" + body + @"
}

partial " + typeKeyword + @"
    C : I1<C>
{
    public static " + op + @" operator " + checkedKeyword + @"long(C x) => default;
    public static " + op + @" operator " + checkedKeyword + @"int(C x) => default;
}
";
            if (isChecked)
            {
                source1 +=
@"
public partial interface I1<T> where T : I1<T>
{
    " + modifier + @" static " + op + @" operator int(T x)" + body + @"
    " + modifier + @" static " + op + @" operator long(T x)" + body + @"
}

partial " + typeKeyword + @"
    C : I1<C>
{
    public static " + op + @" operator long(C x) => default;
    public static " + op + @" operator int(C x) => default;
}
";
            }

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped,
                             emitOptions: EmitOptions.Default.WithEmitMetadataOnly(true).WithIncludePrivateMembers(false)).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var c = module.GlobalNamespace.GetTypeMember("C");
                var i1 = c.Interfaces().Single();
                Assert.Equal(isChecked ? 4 : 2, c.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());

                var m01 = i1.GetMembers().OfType<MethodSymbol>().First();

                var cM01 = (MethodSymbol)c.FindImplementationForInterfaceMember(m01);

                Assert.True(cM01.IsStatic);
                Assert.False(cM01.IsAbstract);
                Assert.False(cM01.IsVirtual);
                Assert.False(cM01.IsMetadataVirtual());
                Assert.False(cM01.IsMetadataFinal);
                Assert.False(cM01.IsMetadataNewSlot());
                Assert.Equal(MethodKind.Conversion, cM01.MethodKind);
                Assert.False(cM01.HasRuntimeSpecialName);
                Assert.True(cM01.HasSpecialName);

                Assert.Equal("System.Int32 C." + opName + "(C x)", cM01.ToTestDisplayString());

                if (module is PEModuleSymbol)
                {
                    Assert.Equal(m01, cM01.ExplicitInterfaceImplementations.Single());
                }
                else
                {
                    Assert.Empty(cM01.ExplicitInterfaceImplementations);
                }

                var m02 = i1.GetMembers().OfType<MethodSymbol>().ElementAt(1);

                var cM02 = (MethodSymbol)c.FindImplementationForInterfaceMember(m02);

                Assert.True(cM02.IsStatic);
                Assert.False(cM02.IsAbstract);
                Assert.False(cM02.IsVirtual);
                Assert.False(cM02.IsMetadataVirtual());
                Assert.False(cM02.IsMetadataFinal);
                Assert.False(cM02.IsMetadataNewSlot());
                Assert.Equal(MethodKind.Conversion, cM02.MethodKind);
                Assert.False(cM02.HasRuntimeSpecialName);
                Assert.True(cM02.HasSpecialName);

                Assert.Equal("System.Int64 C." + opName + "(C x)", cM02.ToTestDisplayString());

                if (module is PEModuleSymbol)
                {
                    Assert.Equal(m02, cM02.ExplicitInterfaceImplementations.Single());
                }
                else
                {
                    Assert.Empty(cM02.ExplicitInterfaceImplementations);
                }
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticConversionOperator_08([CombinatorialValues("implicit", "explicit")] string op, bool structure, bool isChecked, bool isVirtual)
        {
            // Basic explicit implementation scenario

            string opName = GetConversionOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);
            var typeKeyword = structure ? "struct" : "class";

            var source1 =
@"
partial interface I1<T> where T : I1<T>
{
    " + modifier + @" static " + op + @" operator " + checkedKeyword + @"C(T x)" + body + @"
    " + modifier + @" static " + op + @" operator " + checkedKeyword + @"int(T x)" + body + @"
}

partial " + typeKeyword + @"
    C : I1<C>
{
    static " + op + @" I1<C>.operator " + checkedKeyword + @"int(C x) => int.MaxValue;
    static " + op + @" I1<C>.operator " + checkedKeyword + @"C(C x) => default;
}
";
            if (isChecked)
            {
                source1 +=
@"
partial interface I1<T> where T : I1<T>
{
    " + modifier + @" static " + op + @" operator C(T x)" + body + @"
    " + modifier + @" static " + op + @" operator int(T x)" + body + @"
}

partial " + typeKeyword + @"
    C : I1<C>
{
    static " + op + @" I1<C>.operator int(C x) => int.MaxValue;
    static " + op + @" I1<C>.operator C(C x) => default;
}
";
            }

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var tree = compilation1.SyntaxTrees.Single();
            var model = compilation1.GetSemanticModel(tree);
            var node = tree.GetRoot().DescendantNodes().OfType<LiteralExpressionSyntax>().Where(l => l.ToString() == "default").First();

            Assert.Equal("default", node.ToString());
            Assert.Equal("C", model.GetTypeInfo(node).ConvertedType.ToTestDisplayString());

            var declaredSymbol = model.GetDeclaredSymbol(node.FirstAncestorOrSelf<ConversionOperatorDeclarationSyntax>());
            Assert.Equal("C C.I1<C>." + opName + "(C x)", declaredSymbol.ToTestDisplayString());
            Assert.DoesNotContain(opName, declaredSymbol.ContainingType.MemberNames);

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped,
                             emitOptions: EmitOptions.Default.WithEmitMetadataOnly(true).WithIncludePrivateMembers(false)).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var c = module.GlobalNamespace.GetTypeMember("C");
                Assert.Equal(isChecked ? 4 : 2, c.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Count());

                var m01 = c.Interfaces().Single().GetMembers().OfType<MethodSymbol>().First();
                var cM01 = (MethodSymbol)c.FindImplementationForInterfaceMember(m01);

                Assert.True(cM01.IsStatic);
                Assert.False(cM01.IsAbstract);
                Assert.False(cM01.IsVirtual);
                Assert.False(cM01.IsMetadataVirtual());
                Assert.False(cM01.IsMetadataFinal);
                Assert.False(cM01.IsMetadataNewSlot());
                Assert.Equal(MethodKind.ExplicitInterfaceImplementation, cM01.MethodKind);
                Assert.False(cM01.HasRuntimeSpecialName);
                Assert.False(cM01.HasSpecialName);

                Assert.Equal("C C.I1<C>." + opName + "(C x)", cM01.ToTestDisplayString());
                Assert.Equal(m01, cM01.ExplicitInterfaceImplementations.Single());

                var m02 = c.Interfaces().Single().GetMembers().OfType<MethodSymbol>().ElementAt(1);
                var cM02 = (MethodSymbol)c.FindImplementationForInterfaceMember(m02);

                Assert.True(cM02.IsStatic);
                Assert.False(cM02.IsAbstract);
                Assert.False(cM02.IsVirtual);
                Assert.False(cM02.IsMetadataVirtual());
                Assert.False(cM02.IsMetadataFinal);
                Assert.False(cM02.IsMetadataNewSlot());
                Assert.Equal(MethodKind.ExplicitInterfaceImplementation, cM02.MethodKind);
                Assert.False(cM02.HasRuntimeSpecialName);
                Assert.False(cM02.HasSpecialName);

                Assert.Equal("System.Int32 C.I1<C>." + opName + "(C x)", cM02.ToTestDisplayString());
                Assert.Equal(m02, cM02.ExplicitInterfaceImplementations.Single());
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticConversionOperator_09([CombinatorialValues("implicit", "explicit")] string op, bool isChecked, bool isVirtual)
        {
            // Explicit implementation from base is treated as an implementation

            string opName = GetConversionOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public partial interface I1<T> where T : I1<T>
{
    " + modifier + @" static " + op + @" operator " + checkedKeyword + @"int(T x)" + body + @"
}

public partial class C2 : I1<C2>
{
    static " + op + @" I1<C2>.operator " + checkedKeyword + @"int(C2 x) => default;
}
";
            if (isChecked)
            {
                source1 +=
@"
public partial interface I1<T> where T : I1<T>
{
    " + modifier + @" static " + op + @" operator int(T x)" + body + @"
}

public partial class C2 : I1<C2>
{
    static " + op + @" I1<C2>.operator int(C2 x) => default;
}
";
            }

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C3 : C2, I1<C2>
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.Regular10, TestOptions.RegularPreview })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                     parseOptions: parseOptions,
                                                     targetFramework: _supportingFramework,
                                                     references: new[] { reference });
                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c3 = module.GlobalNamespace.GetTypeMember("C3");
                Assert.Empty(c3.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()));
                var m01 = c3.Interfaces().Single().GetMembers(opName).OfType<MethodSymbol>().Single();

                var cM01 = (MethodSymbol)c3.FindImplementationForInterfaceMember(m01);

                Assert.Equal("System.Int32 C2.I1<C2>." + opName + "(C2 x)", cM01.ToTestDisplayString());
                Assert.Equal(m01, cM01.ExplicitInterfaceImplementations.Single());
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticConversionOperator_10([CombinatorialValues("implicit", "explicit")] string op, bool isChecked, bool isVirtual)
        {
            // Implicit implementation is considered only for types implementing interface in source.
            // In metadata, only explicit implementations are considered

            string opName = GetConversionOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var (modifier, body) = GetILModifierAndBody(isVirtual);

            var ilSource = @"
.class interface public auto ansi abstract I1`1<(class I1`1<!T>) T>
{
    // Methods
    .method public hidebysig specialname " + modifier + @" virtual static 
        int32 " + opName + @" (
            !T x
        ) cil managed 
    " + body + @"
}

.class public auto ansi beforefieldinit C1
    extends System.Object
    implements class I1`1<class C1>
{
    .method private hidebysig static 
        int32 'I1<C1>." + opName + @"' (
            class C1 x
        ) cil managed 
    {
        .override method int32 class I1`1<class C1>::" + opName + @"(!0)

        IL_0000: ldc.i4.0
        IL_0001: ret
    }

    .method public hidebysig static 
        specialname int32 " + opName + @" (
            class C1 x
        ) cil managed 
    {
        IL_0000: ldc.i4.0
        IL_0001: ret
    }

    .method public hidebysig specialname rtspecialname 
        instance void .ctor () cil managed 
    {
        // Method begins at RVA 0x2053
        // Code size 8 (0x8)
        .maxstack 8

        IL_0000: ldarg.0
        IL_0001: call instance void System.Object::.ctor()
        IL_0006: nop
        IL_0007: ret
    }
}

.class public auto ansi beforefieldinit C2
    extends C1
    implements class I1`1<class C1>
{
    .method public hidebysig static 
        specialname int32 " + opName + @" (
            class C1 x
        ) cil managed 
    {
        IL_0000: ldc.i4.0
        IL_0001: ret
    }

    .method public hidebysig specialname rtspecialname 
        instance void .ctor () cil managed 
    {
        IL_0000: ldarg.0
        IL_0001: call instance void C1::.ctor()
        IL_0006: ret
    }
}
";
            var source1 =
@"
public class C3 : C2
{
}

public class C4 : C1, I1<C1>
{
}

public class C5 : C2, I1<C1>
{
}
";

            var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var c1 = compilation1.GlobalNamespace.GetTypeMember("C1");
            var m01 = c1.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();

            Assert.Equal(MethodKind.Conversion, m01.MethodKind);
            Assert.Equal(MethodKind.Conversion, c1.GetMember<MethodSymbol>(opName).MethodKind);

            var c1M01 = (MethodSymbol)c1.FindImplementationForInterfaceMember(m01);

            Assert.Equal("System.Int32 C1.I1<C1>." + opName + "(C1 x)", c1M01.ToTestDisplayString());
            Assert.Equal(MethodKind.ExplicitInterfaceImplementation, c1M01.MethodKind);
            Assert.Equal(m01, c1M01.ExplicitInterfaceImplementations.Single());

            var c2 = compilation1.GlobalNamespace.GetTypeMember("C2");
            Assert.Same(c1M01, c2.FindImplementationForInterfaceMember(m01));

            var c3 = compilation1.GlobalNamespace.GetTypeMember("C3");
            Assert.Same(c1M01, c3.FindImplementationForInterfaceMember(m01));

            var c4 = compilation1.GlobalNamespace.GetTypeMember("C4");
            Assert.Same(c1M01, c4.FindImplementationForInterfaceMember(m01));

            var c5 = compilation1.GlobalNamespace.GetTypeMember("C5");

            var c2M01 = (MethodSymbol)c5.FindImplementationForInterfaceMember(m01);
            Assert.Equal("System.Int32 C2." + opName + "(C1 x)", c2M01.ToTestDisplayString());
            Assert.Equal(MethodKind.Conversion, c2M01.MethodKind);

            compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (10,23): error CS8706: 'C2.implicit operator int(C1)' cannot implement interface member 'I1<C1>.implicit operator int(C1)' in type 'C5' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                // public class C5 : C2, I1<C1>
                Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, "I1<C1>").WithArguments("C2." + op + " operator " + checkedKeyword + "int(C1)", "I1<C1>." + op + " operator " + checkedKeyword + "int(C1)", "C5", "static abstract members in interfaces", "10.0", "11.0").WithLocation(10, 23)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticConversionOperator_11([CombinatorialValues("implicit", "explicit")] string op, bool isChecked)
        {
            // Non-abstract static virtual method. 

            string opName = GetConversionOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var ilSource = @"
.class interface public auto ansi abstract I1`1<(class I1`1<!T>) T>
{
    // Methods
    .method public hidebysig specialname virtual static 
        int32 " + opName + @" (
            !T x
        ) cil managed 
    {
        IL_0000: ldc.i4.0
        IL_0001: ret
    }
}
";

            var source1 =
@"
public class C1 : I1<C1>
{
}
";

            var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyEmitDiagnostics();

            var c1 = compilation1.GlobalNamespace.GetTypeMember("C1");
            var i1 = c1.Interfaces().Single();
            var m01 = i1.GetMembers().OfType<MethodSymbol>().Single();

            Assert.Equal(MethodKind.Conversion, m01.MethodKind);
            Assert.Equal(m01, c1.FindImplementationForInterfaceMember(m01));
            Assert.Same(m01, i1.FindImplementationForInterfaceMember(m01));

            compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyEmitDiagnostics(
                // (2,19): error CS8706: 'I1<C1>.implicit operator int(C1)' cannot implement interface member 'I1<C1>.implicit operator int(C1)' in type 'C1' because feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version '11.0' or greater.
                // public class C1 : I1<C1>
                Diagnostic(ErrorCode.ERR_LanguageVersionDoesNotSupportInterfaceImplementationForMember, "I1<C1>").WithArguments("I1<C1>." + op + " operator " + checkedKeyword + "int(C1)", "I1<C1>." + op + " operator " + checkedKeyword + "int(C1)", "C1", "static abstract members in interfaces", "10.0", "11.0").WithLocation(2, 19)
                );

            var source2 =
@"
public class C1 : I1<C1>
{
    static " + op + @" I1<C1>.operator " + checkedKeyword + @"int(C1 x) => default;
}
";

            var compilation2 = CreateCompilationWithIL(source2, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation2.VerifyEmitDiagnostics();

            c1 = compilation2.GlobalNamespace.GetTypeMember("C1");
            m01 = c1.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();

            Assert.Equal("System.Int32 I1<C1>." + opName + "(C1 x)", m01.ToTestDisplayString());
            Assert.Equal("System.Int32 C1.I1<C1>." + opName + "(C1 x)", c1.FindImplementationForInterfaceMember(m01).ToTestDisplayString());
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticConversionOperator_12([CombinatorialValues("implicit", "explicit")] string op, bool isChecked, bool isVirtual)
        {
            // Default interface implementation for a static method

            string opName = GetConversionOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var (modifier, body) = GetILModifierAndBody(isVirtual);

            var ilSource = @"
.class interface public auto ansi abstract I1`1<(class I1`1<!T>) T>
{
    // Methods
    .method public hidebysig specialname " + modifier + @" virtual static 
        int32 " + opName + @" (
            !T x
        ) cil managed 
    " + body + @"
}

.class interface public auto ansi abstract I2`1<(class I1`1<!T>) T>
    implements class I1`1<!T>
{
    .method private hidebysig static 
        int32 'I1<!T>." + opName + @"' (
            !T x
        ) cil managed 
    {
        .override method int32 class I1`1<!T>::" + opName + @"(!0)

        IL_0000: ldc.i4.0
        IL_0001: ret
    }
}
";

            var source1 =
@"
public class C1 : I2<C1>
{
}
";

            var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyEmitDiagnostics();

            var c1 = compilation1.GlobalNamespace.GetTypeMember("C1");
            var i2 = c1.Interfaces().Single();
            var i1 = i2.Interfaces().Single();
            var m01 = i1.GetMembers().OfType<MethodSymbol>().Single();
            var i2M01 = i2.GetMembers().OfType<MethodSymbol>().Single();

            Assert.Equal(MethodKind.Conversion, m01.MethodKind);
            Assert.Equal(i2M01, c1.FindImplementationForInterfaceMember(m01));
            Assert.Equal(i2M01, i2.FindImplementationForInterfaceMember(m01));

            Assert.Equal(m01, i2M01.ExplicitInterfaceImplementations.Single());
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticConversionOperator_13([CombinatorialValues("implicit", "explicit")] string op, bool isChecked, bool isVirtual)
        {
            // A forwarding method is added for an implicit implementation declared in base class. 

            string opName = GetConversionOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public partial interface I1<T> where T : I1<T>
{
    " + modifier + @" static " + op + @" operator " + checkedKeyword + @"C1<T>(T x)" + body + @"
}

public partial class C1<T>
{
    public static " + op + @" operator " + checkedKeyword + @"C1<T>(T x) => default;
}

public class C2 : C1<C2>, I1<C2>
{
}
";
            if (isChecked)
            {
                source1 += @"
public partial interface I1<T> where T : I1<T>
{
    " + modifier + @" static " + op + @" operator C1<T>(T x)" + body + @"
}

public partial class C1<T>
{
    public static " + op + @" operator C1<T>(T x) => default;
}
";
            }

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var c2 = module.GlobalNamespace.GetTypeMember("C2");
                var i1 = c2.Interfaces().Single();
                var m01 = i1.GetMembers(opName).OfType<MethodSymbol>().Single();

                var c2M01 = (MethodSymbol)c2.FindImplementationForInterfaceMember(m01);

                Assert.True(c2M01.IsStatic);
                Assert.False(c2M01.IsAbstract);
                Assert.False(c2M01.IsVirtual);
                Assert.False(c2M01.IsMetadataVirtual());
                Assert.False(c2M01.IsMetadataFinal);
                Assert.False(c2M01.IsMetadataNewSlot());

                if (module is PEModuleSymbol)
                {
                    Assert.Equal(MethodKind.ExplicitInterfaceImplementation, c2M01.MethodKind);
                    Assert.False(c2M01.HasRuntimeSpecialName);
                    Assert.False(c2M01.HasSpecialName);

                    Assert.Equal("C1<C2> C2.I1<C2>." + opName + "(C2 x)", c2M01.ToTestDisplayString());
                    Assert.Equal(m01, c2M01.ExplicitInterfaceImplementations.Single());

                    var c1M01 = module.GlobalNamespace.GetMember<MethodSymbol>("C1." + opName);

                    Assert.True(c1M01.IsStatic);
                    Assert.False(c1M01.IsAbstract);
                    Assert.False(c1M01.IsVirtual);
                    Assert.False(c1M01.IsMetadataVirtual());
                    Assert.False(c1M01.IsMetadataFinal);
                    Assert.False(c1M01.IsMetadataNewSlot());
                    Assert.Equal(MethodKind.Conversion, c1M01.MethodKind);
                    Assert.False(c1M01.HasRuntimeSpecialName);
                    Assert.True(c1M01.HasSpecialName);
                    Assert.Empty(c1M01.ExplicitInterfaceImplementations);
                }
                else
                {
                    Assert.Equal(MethodKind.Conversion, c2M01.MethodKind);
                    Assert.False(c2M01.HasRuntimeSpecialName);
                    Assert.True(c2M01.HasSpecialName);

                    Assert.Equal("C1<C2> C1<C2>." + opName + "(C2 x)", c2M01.ToTestDisplayString());
                    Assert.Empty(c2M01.ExplicitInterfaceImplementations);
                }
            }

            verifier.VerifyIL("C2.I1<C2>." + opName + "(C2)",
@"
{
  // Code size        7 (0x7)
  .maxstack  1
  IL_0000:  ldarg.0
  IL_0001:  call       ""C1<C2> C1<C2>." + opName + @"(C2)""
  IL_0006:  ret
}
");
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticConversionOperator_14([CombinatorialValues("implicit", "explicit")] string op, bool isChecked, bool isVirtual)
        {
            // A forwarding method is added for an implicit implementation with modopt mismatch. 

            string opName = GetConversionOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var (modifier, body) = GetILModifierAndBody(isVirtual);

            var ilSource = @"
.class interface public auto ansi abstract I1`1<(class I1`1<!T>) T>
{
    // Methods
    .method public hidebysig specialname " + modifier + @" virtual static 
        int32 modopt(I1`1) " + opName + @" (
            !T x
        ) cil managed 
    " + body + @"
} 
";

            var source1 =
@"
partial class C1 : I1<C1>
{
    public static " + op + @" operator " + checkedKeyword + @"int(C1 x) => default;
}

class C2 : I1<C2>
{
    static " + op + @" I1<C2>.operator " + checkedKeyword + @"int(C2 x) => default;
}
";
            if (isChecked)
            {
                source1 +=
@"
partial class C1 : I1<C1>
{
    public static " + op + @" operator int(C1 x) => default;
}
";
            }

            var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var c1 = module.GlobalNamespace.GetTypeMember("C1");
                var m01 = c1.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();

                var c1M01 = (MethodSymbol)c1.FindImplementationForInterfaceMember(m01);

                Assert.True(c1M01.IsStatic);
                Assert.False(c1M01.IsAbstract);
                Assert.False(c1M01.IsVirtual);
                Assert.False(c1M01.IsMetadataVirtual());
                Assert.False(c1M01.IsMetadataFinal);
                Assert.False(c1M01.IsMetadataNewSlot());

                if (module is PEModuleSymbol)
                {
                    Assert.Equal(MethodKind.ExplicitInterfaceImplementation, c1M01.MethodKind);
                    Assert.Equal("System.Int32 modopt(I1<>) C1.I1<C1>." + opName + "(C1 x)", c1M01.ToTestDisplayString());
                    Assert.Equal(m01, c1M01.ExplicitInterfaceImplementations.Single());

                    c1M01 = module.GlobalNamespace.GetMember<MethodSymbol>("C1." + opName);
                    Assert.Equal("System.Int32 C1." + opName + "(C1 x)", c1M01.ToTestDisplayString());

                    Assert.True(c1M01.IsStatic);
                    Assert.False(c1M01.IsAbstract);
                    Assert.False(c1M01.IsVirtual);
                    Assert.False(c1M01.IsMetadataVirtual());
                    Assert.False(c1M01.IsMetadataFinal);
                    Assert.False(c1M01.IsMetadataNewSlot());
                    Assert.Equal(MethodKind.Conversion, c1M01.MethodKind);

                    Assert.Empty(c1M01.ExplicitInterfaceImplementations);
                }
                else
                {
                    Assert.Equal(MethodKind.Conversion, c1M01.MethodKind);
                    Assert.Equal("System.Int32 C1." + opName + "(C1 x)", c1M01.ToTestDisplayString());
                    Assert.Empty(c1M01.ExplicitInterfaceImplementations);
                }

                var c2 = module.GlobalNamespace.GetTypeMember("C2");
                m01 = c2.Interfaces().Single().GetMembers().OfType<MethodSymbol>().Single();
                var c2M01 = (MethodSymbol)c2.FindImplementationForInterfaceMember(m01);

                Assert.True(c2M01.IsStatic);
                Assert.False(c2M01.IsAbstract);
                Assert.False(c2M01.IsVirtual);
                Assert.False(c2M01.IsMetadataVirtual());
                Assert.False(c2M01.IsMetadataFinal);
                Assert.False(c2M01.IsMetadataNewSlot());
                Assert.Equal(MethodKind.ExplicitInterfaceImplementation, c2M01.MethodKind);

                Assert.Equal("System.Int32 modopt(I1<>) C2.I1<C2>." + opName + "(C2 x)", c2M01.ToTestDisplayString());
                Assert.Equal(m01, c2M01.ExplicitInterfaceImplementations.Single());

                Assert.Same(c2M01, c2.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Single());
            }

            verifier.VerifyIL("C1.I1<C1>." + opName + "(C1)",
@"
{
  // Code size        7 (0x7)
  .maxstack  1
  IL_0000:  ldarg.0
  IL_0001:  call       ""int C1." + opName + @"(C1)""
  IL_0006:  ret
}
");
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticConversionOperator_15([CombinatorialValues("implicit", "explicit")] string op, bool isChecked, bool isVirtual)
        {
            // A forwarding method isn't created if base class implements interface exactly the same way. 

            string opName = GetConversionOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public partial interface I1<T> where T : I1<T>
{
    " + modifier + @" static " + op + @" operator " + checkedKeyword + @"C1<T>(T x)" + body + @"
    " + modifier + @" static " + op + @" operator " + checkedKeyword + @"T(int x)" + body + @"
}

public partial class C1<T>
{
    public static " + op + @" operator " + checkedKeyword + @"C1<T>(T x) => default;
}

public partial class C2 : C1<C2>, I1<C2>
{
    static " + op + @" I1<C2>.operator " + checkedKeyword + @"C2(int x) => default;
}
";
            if (isChecked)
            {
                source1 +=
@"
public partial interface I1<T> where T : I1<T>
{
    " + modifier + @" static " + op + @" operator C1<T>(T x)" + body + @"
    " + modifier + @" static " + op + @" operator T(int x)" + body + @"
}

public partial class C1<T>
{
    public static " + op + @" operator C1<T>(T x) => default;
}

public partial class C2 : C1<C2>, I1<C2>
{
    static " + op + @" I1<C2>.operator C2(int x) => default;
}
";
            }

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var source2 =
@"
public class C3 : C2, I1<C2>
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.RegularPreview, TestOptions.Regular10 })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                         parseOptions: parseOptions,
                                                         targetFramework: _supportingFramework,
                                                         references: new[] { reference });
                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c3 = module.GlobalNamespace.GetTypeMember("C3");
                Assert.Empty(c3.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()));

                var m01 = c3.Interfaces().Single().GetMembers(opName).OfType<MethodSymbol>().First();

                var c1M01 = c3.BaseType().BaseType().GetMember<MethodSymbol>(opName);
                Assert.Equal("C1<C2> C1<C2>." + opName + "(C2 x)", c1M01.ToTestDisplayString());

                Assert.True(c1M01.IsStatic);
                Assert.False(c1M01.IsAbstract);
                Assert.False(c1M01.IsVirtual);
                Assert.False(c1M01.IsMetadataVirtual());
                Assert.False(c1M01.IsMetadataFinal);
                Assert.False(c1M01.IsMetadataNewSlot());

                Assert.Empty(c1M01.ExplicitInterfaceImplementations);

                if (c1M01.ContainingModule is PEModuleSymbol)
                {
                    var c2M01 = (MethodSymbol)c3.FindImplementationForInterfaceMember(m01);
                    Assert.Equal("C1<C2> C2.I1<C2>." + opName + "(C2 x)", c2M01.ToTestDisplayString());
                    Assert.Equal(m01, c2M01.ExplicitInterfaceImplementations.Single());
                }
                else
                {
                    Assert.Equal(c1M01, c3.FindImplementationForInterfaceMember(m01));
                }

                var m02 = c3.Interfaces().Single().GetMembers(opName).OfType<MethodSymbol>().ElementAt(1);

                var c2M02 = c3.BaseType().GetMembers("I1<C2>." + opName).OfType<MethodSymbol>().First();
                Assert.Equal("C2 C2.I1<C2>." + opName + "(System.Int32 x)", c2M02.ToTestDisplayString());
                Assert.Same(c2M02, c3.FindImplementationForInterfaceMember(m02));
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticConversionOperator_18([CombinatorialValues("implicit", "explicit")] string op, bool genericFirst, bool isChecked, bool isVirtual)
        {
            // An "ambiguity" in implicit implementation declared in generic base class plus interface is generic too.

            string opName = GetConversionOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);

            var generic =
@"
    public static " + op + @" operator " + checkedKeyword + @"U(C1<T, U> x) => default;
";
            var nonGeneric =
@"
    public static " + op + @" operator " + checkedKeyword + @"int(C1<T, U> x) => default;
";
            var source1 =
@"
public partial interface I1<T, U> where T : I1<T, U>
{
    " + modifier + @" static " + op + @" operator " + checkedKeyword + @"U(T x)" + body + @"
}

public partial class C1<T, U> : I1<C1<T, U>, U>
{
" + (genericFirst ? generic + nonGeneric : nonGeneric + generic) + @"
}
";
            if (isChecked)
            {
                source1 +=
@"
public partial interface I1<T, U> where T : I1<T, U>
{
    " + modifier + @" static " + op + @" operator U(T x)" + body + @"
}

public partial class C1<T, U> : I1<C1<T, U>, U>
{
    public static " + op + @" operator U(C1<T, U> x) => default;
    public static " + op + @" operator int(C1<T, U> x) => default;
}
";
            }

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { CreateCompilation("", targetFramework: _supportingFramework).ToMetadataReference() });

            compilation1.VerifyDiagnostics();
            Assert.Equal(2, compilation1.GlobalNamespace.GetTypeMember("C1").GetMembers().Where(m => m.Name.Contains(opName)).Count());

            var source2 =
@"
public class C2 : C1<int, int>, I1<C1<int, int>, int>
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.Regular10, TestOptions.RegularPreview })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: parseOptions,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { reference });

                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c2 = module.GlobalNamespace.GetTypeMember("C2");
                var m01 = c2.Interfaces().Single().GetMembers(opName).OfType<MethodSymbol>().Single();

                Assert.True(m01.ContainingModule is RetargetingModuleSymbol or PEModuleSymbol);

                var c1M01 = (MethodSymbol)c2.FindImplementationForInterfaceMember(m01);
                Assert.Equal("U C1<T, U>." + opName + "(C1<T, U> x)", c1M01.OriginalDefinition.ToTestDisplayString());

                var baseI1M01 = c2.BaseType().FindImplementationForInterfaceMember(m01);
                Assert.Equal("U C1<T, U>." + opName + "(C1<T, U> x)", baseI1M01.OriginalDefinition.ToTestDisplayString());

                Assert.Equal(c1M01, baseI1M01);

                if (c1M01.OriginalDefinition.ContainingModule is PEModuleSymbol)
                {
                    Assert.Equal(m01, c1M01.ExplicitInterfaceImplementations.Single());
                }
                else
                {
                    Assert.Empty(c1M01.ExplicitInterfaceImplementations);
                }
            }
        }

        [Theory]
        [CombinatorialData]
        public void ImplementAbstractStaticConversionOperator_20([CombinatorialValues("implicit", "explicit")] string op, bool genericFirst, bool isChecked, bool isVirtual)
        {
            // Same as ImplementAbstractStaticConversionOperator_18 only implementation is explicit in source.

            string opName = GetConversionOperatorName(op, isChecked, out string checkedKeyword);

            if (opName is null)
            {
                return;
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);

            var generic =
@"
    static " + op + @" I1<C1<T, U>, U>.operator " + checkedKeyword + @"U(C1<T, U> x) => default;
";
            var nonGeneric =
@"
    public static " + op + @" operator " + checkedKeyword + @"int(C1<T, U> x) => default;
";
            var source1 =
@"
public partial interface I1<T, U> where T : I1<T, U>
{
    " + modifier + @" static " + op + @" operator " + checkedKeyword + @"U(T x)" + body + @"
}

public partial class C1<T, U> : I1<C1<T, U>, U>
{
" + (genericFirst ? generic + nonGeneric : nonGeneric + generic) + @"
}
";
            if (isChecked)
            {
                source1 +=
@"
public partial interface I1<T, U> where T : I1<T, U>
{
    " + modifier + @" static " + op + @" operator U(T x)" + body + @"
}

public partial class C1<T, U> : I1<C1<T, U>, U>
{
    static " + op + @" I1<C1<T, U>, U>.operator U(C1<T, U> x) => default;
    public static " + op + @" operator int(C1<T, U> x) => default;
}
";
            }

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { CreateCompilation("", targetFramework: _supportingFramework).ToMetadataReference() });

            compilation1.VerifyDiagnostics();
            Assert.Equal(2, compilation1.GlobalNamespace.GetTypeMember("C1").GetMembers().Where(m => m.Name.Contains(opName)).Count());

            var source2 =
@"
public class C2 : C1<int, int>, I1<C1<int, int>, int>
{
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                foreach (var parseOptions in new[] { TestOptions.Regular10, TestOptions.RegularPreview })
                {
                    var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: parseOptions,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { reference });

                    CompileAndVerify(compilation2, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();
                }
            }

            void validate(ModuleSymbol module)
            {
                var c2 = module.GlobalNamespace.GetTypeMember("C2");
                var m01 = c2.Interfaces().Single().GetMembers(opName).OfType<MethodSymbol>().Single();

                Assert.True(m01.ContainingModule is RetargetingModuleSymbol or PEModuleSymbol);

                var c1M01 = (MethodSymbol)c2.FindImplementationForInterfaceMember(m01);
                Assert.Equal("U C1<T, U>.I1<C1<T, U>, U>." + opName + "(C1<T, U> x)", c1M01.OriginalDefinition.ToTestDisplayString());

                Assert.Equal(m01, c1M01.ExplicitInterfaceImplementations.Single());
                Assert.Same(c1M01, c2.BaseType().FindImplementationForInterfaceMember(m01));
            }
        }

        [Theory]
        [CombinatorialData]
        public void ExplicitImplementationModifiersConversionOperator_01([CombinatorialValues("implicit", "explicit")] string op)
        {
            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    abstract static " + op + @" operator int(T x);
}

class
    C1 : I1<C1>
{
    static " + op + @" I1<C1>.operator int(C1 x) => default;
}

class
    C2 : I1<C2>
{
    private static " + op + @" I1<C2>.operator int(C2 x) => default;
}

class
    C3 : I1<C3>
{
    protected static " + op + @" I1<C3>.operator int(C3 x) => default;
}

class
    C4 : I1<C4>
{
    internal static " + op + @" I1<C4>.operator int(C4 x) => default;
}

class
    C5 : I1<C5>
{
    protected internal static " + op + @" I1<C5>.operator int(C5 x) => default;
}

class
    C6 : I1<C6>
{
    private protected static " + op + @" I1<C6>.operator int(C6 x) => default;
}

class
    C7 : I1<C7>
{
    public static " + op + @" I1<C7>.operator int(C7 x) => default;
}

class
    C9 : I1<C9>
{
    async static " + op + @" I1<C9>.operator int(C9 x) => default;
}

class
    C10 : I1<C10>
{
    unsafe static " + op + @" I1<C10>.operator int(C10 x) => default;
}

class
    C11 : I1<C11>
{
    static readonly " + op + @" I1<C11>.operator int(C11 x) => default;
}

class
    C12 : I1<C12>
{
    extern static " + op + @" I1<C12>.operator int(C12 x);
}

class
    C13 : I1<C13>
{
    abstract static " + op + @" I1<C13>.operator int(C13 x) => default;
}

class
    C14 : I1<C14>
{
    virtual static " + op + @" I1<C14>.operator int(C14 x) => default;
}

class
    C15 : I1<C15>
{
    sealed static " + op + @" I1<C15>.operator int(C15 x) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll.WithAllowUnsafe(true),
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var c1 = compilation1.GlobalNamespace.GetTypeMember("C1");

            Assert.Equal(Accessibility.Private, c1.GetMembers().OfType<MethodSymbol>().Where(m => !m.IsConstructor()).Single().DeclaredAccessibility);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.WRN_ExternMethodNoImplementation).Verify(
                // (16,45): error CS0106: The modifier 'private' is not valid for this item
                //     private static explicit I1<C2>.operator int(C2 x) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "int").WithArguments("private").WithLocation(16, 45),
                // (22,47): error CS0106: The modifier 'protected' is not valid for this item
                //     protected static explicit I1<C3>.operator int(C3 x) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "int").WithArguments("protected").WithLocation(22, 47),
                // (28,46): error CS0106: The modifier 'internal' is not valid for this item
                //     internal static explicit I1<C4>.operator int(C4 x) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "int").WithArguments("internal").WithLocation(28, 46),
                // (34,56): error CS0106: The modifier 'protected internal' is not valid for this item
                //     protected internal static explicit I1<C5>.operator int(C5 x) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "int").WithArguments("protected internal").WithLocation(34, 56),
                // (40,55): error CS0106: The modifier 'private protected' is not valid for this item
                //     private protected static explicit I1<C6>.operator int(C6 x) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "int").WithArguments("private protected").WithLocation(40, 55),
                // (46,44): error CS0106: The modifier 'public' is not valid for this item
                //     public static explicit I1<C7>.operator int(C7 x) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "int").WithArguments("public").WithLocation(46, 44),
                // (52,43): error CS0106: The modifier 'async' is not valid for this item
                //     async static explicit I1<C9>.operator int(C9 x) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "int").WithArguments("async").WithLocation(52, 43),
                // (64,47): error CS0106: The modifier 'readonly' is not valid for this item
                //     static readonly explicit I1<C11>.operator int(C11 x) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "int").WithArguments("readonly").WithLocation(64, 47),
                // (76,47): error CS0106: The modifier 'abstract' is not valid for this item
                //     abstract static explicit I1<C13>.operator int(C13 x) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "int").WithArguments("abstract").WithLocation(76, 47),
                // (82,46): error CS0106: The modifier 'virtual' is not valid for this item
                //     virtual static explicit I1<C14>.operator int(C14 x) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "int").WithArguments("virtual").WithLocation(82, 46),
                // (88,45): error CS0106: The modifier 'sealed' is not valid for this item
                //     sealed static explicit I1<C15>.operator int(C15 x) => default;
                Diagnostic(ErrorCode.ERR_BadMemberFlag, "int").WithArguments("sealed").WithLocation(88, 45)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ExplicitInterfaceSpecifierErrorsConversionOperator_01([CombinatorialValues("implicit", "explicit")] string op)
        {
            var source1 =
@"
public interface I1<T> where T : struct, I1<T>
{
    abstract static " + op + @" operator int(T x);
}

class C1
{
    static " + op + @" I1<int>.operator int(int x) => default;
}

class C2 : I1<C2>
{
    static " + op + @" I1<C2>.operator int(C2 x) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (9,21): error CS0540: 'C1.I1<int>.implicit operator int(int)': containing type does not implement interface 'I1<int>'
                //     static implicit I1<int>.operator int(int x) => default;
                Diagnostic(ErrorCode.ERR_ClassDoesntImplementInterface, "I1<int>").WithArguments("C1.I1<int>." + op + " operator int(int)", "I1<int>").WithLocation(9, 21),
                // (9,21): error CS0315: The type 'int' cannot be used as type parameter 'T' in the generic type or method 'I1<T>'. There is no boxing conversion from 'int' to 'I1<int>'.
                //     static implicit I1<int>.operator int(int x) => default;
                Diagnostic(ErrorCode.ERR_GenericConstraintNotSatisfiedValType, "I1<int>").WithArguments("I1<T>", "I1<int>", "T", "int").WithLocation(9, 21),
                // (12,7): error CS0453: The type 'C2' must be a non-nullable value type in order to use it as parameter 'T' in the generic type or method 'I1<T>'
                // class C2 : I1<C2>
                Diagnostic(ErrorCode.ERR_ValConstraintNotSatisfied, "C2").WithArguments("I1<T>", "T", "C2").WithLocation(12, 7),
                // (14,21): error CS0453: The type 'C2' must be a non-nullable value type in order to use it as parameter 'T' in the generic type or method 'I1<T>'
                //     static implicit I1<C2>.operator int(C2 x) => default;
                Diagnostic(ErrorCode.ERR_ValConstraintNotSatisfied, "I1<C2>").WithArguments("I1<T>", "T", "C2").WithLocation(14, 21)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractConversionOperator_01([CombinatorialValues("implicit", "explicit")] string op, bool isChecked, bool isVirtual)
        {
            bool isExplicit = op == "explicit";

            if (isChecked && !isExplicit)
            {
                return;
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);
            string checkedKeyword = isChecked ? " checked " : "";
            string cast = (isExplicit ? "(int)" : "");

            var source1 =
@"
interface I1<T> where T : I1<T>
{
    " + modifier + @" static " + op + @" operator " + checkedKeyword + @"int(T x)" + body + @"

    static int M02(I1<T> x)
    {" + checkedKeyword + @"{
        return " + cast + @"x;
    }}

    int M03(I1<T> y)
    {" + checkedKeyword + @"{
        return " + cast + @"y;
    }}
}

class Test<T> where T : I1<T>
{
    static int MT1(I1<T> a)
    {" + checkedKeyword + @"{
        return " + cast + @"a;
    }}

    static void MT2()
    {" + checkedKeyword + @"{
        _ = (System.Linq.Expressions.Expression<System.Func<T, int>>)((T b) => " + cast + @"b);
    }}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var error = (op == "explicit" ? ErrorCode.ERR_NoExplicitConv : ErrorCode.ERR_NoImplicitConv);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (8,16): error CS0030: Cannot convert type 'I1<T>' to 'int'
                //         return (int)x;
                Diagnostic(error, cast + "x").WithArguments("I1<T>", "int").WithLocation(8, 16),
                // (13,16): error CS0030: Cannot convert type 'I1<T>' to 'int'
                //         return (int)y;
                Diagnostic(error, cast + "y").WithArguments("I1<T>", "int").WithLocation(13, 16),
                // (21,16): error CS0030: Cannot convert type 'I1<T>' to 'int'
                //         return (int)a;
                Diagnostic(error, cast + "a").WithArguments("I1<T>", "int").WithLocation(21, 16),
                // (26,80): error CS8927: An expression tree may not contain an access of static virtual or abstract interface member
                //         _ = (System.Linq.Expressions.Expression<System.Func<T, int>>)((T b) => (int)b);
                Diagnostic(ErrorCode.ERR_ExpressionTreeContainsAbstractStaticMemberAccess, cast + "b").WithLocation(26, 80)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractConversionOperatorForTupleEquality_01([CombinatorialValues("==", "!=")] string op, bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
interface I1
{
    " + modifier + @" static implicit operator bool(I1 x)" + body + @"


    static void M02((int, C<I1>) x)
    {
        _ = x " + op + @" x;
    }

    void M03((int, C<I1>) y)
    {
        _ = y " + op + @" y;
    }
}

class Test
{
    static void MT1((int, C<I1>) a)
    {
        _ = a " + op + @" a;
    }

    static void MT2<T>() where T : I1
    {
        _ = (System.Linq.Expressions.Expression<System.Action<(int, C<T>)>>)(((int, C<T>) b) => (b " + op + @" b).ToString());
    }
}

#pragma warning disable CS0660 // 'C<T>' defines operator == or operator != but does not override Object.Equals(object o)
#pragma warning disable CS0661 // 'C<T>' defines operator == or operator != but does not override Object.GetHashCode()

class C<T>
{
    public static T operator == (C<T> x, C<T> y) => default;
    public static T operator != (C<T> x, C<T> y) => default;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_GenericConstraintNotSatisfiedInterfaceWithStaticAbstractMembers).Verify(
                // (4,39): error CS0552: 'I1.implicit operator bool(I1)': user-defined conversions to or from an interface are not allowed
                //     abstract static implicit operator bool(I1 x);
                Diagnostic(ErrorCode.ERR_ConversionWithInterface, "bool").WithArguments("I1.implicit operator bool(I1)").WithLocation(4, 39),
                // (9,13): error CS0029: Cannot implicitly convert type 'I1' to 'bool'
                //         _ = x == x;
                Diagnostic(ErrorCode.ERR_NoImplicitConv, "x " + op + " x").WithArguments("I1", "bool").WithLocation(9, 13),
                // (14,13): error CS0029: Cannot implicitly convert type 'I1' to 'bool'
                //         _ = y == y;
                Diagnostic(ErrorCode.ERR_NoImplicitConv, "y " + op + " y").WithArguments("I1", "bool").WithLocation(14, 13),
                // (22,13): error CS0029: Cannot implicitly convert type 'I1' to 'bool'
                //         _ = a == a;
                Diagnostic(ErrorCode.ERR_NoImplicitConv, "a " + op + " a").WithArguments("I1", "bool").WithLocation(22, 13),
                // (27,98): error CS8382: An expression tree may not contain a tuple == or != operator
                //         _ = (System.Linq.Expressions.Expression<System.Action<(int, C<T>)>>)(((int, C<T>) b) => (b == b).ToString());
                Diagnostic(ErrorCode.ERR_ExpressionTreeContainsTupleBinOp, "b " + op + " b").WithLocation(27, 98)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractConversionOperator_03([CombinatorialValues("implicit", "explicit")] string op, bool isCheckedOperator, bool isCheckedContext, bool isVirtual)
        {
            string metadataName = GetConversionOperatorName(op, isCheckedOperator, out string checkedKeyword);

            if (metadataName is null)
            {
                return;
            }

            if (isCheckedOperator && !isCheckedContext)
            {
                metadataName = ConversionOperatorName(op, isChecked: false);
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);
            string contextKeyword = isCheckedContext ? " checked " : " unchecked ";
            bool needCast = op == "explicit";

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    " + modifier + @" static " + op + @" operator int(T x)" + body + @"
"
;
            if (isCheckedOperator)
            {
                source1 +=
@"
    " + modifier + @" static " + op + @" operator checked int(T x)" + body + @"
"
;
            }

            source1 +=
@"
}

class Test
{
    static int M02<T, U>(T x) where T : U where U : I1<T>
    {" + contextKeyword + @"{
        return " + (needCast ? "(int)" : "") + @"x;
    }}

    static int? M03<T, U>(T y) where T : U where U : I1<T>
    {" + contextKeyword + @"{
        return " + (needCast ? "(int?)" : "") + @"y;
    }}

    static int? M04<T, U>(T? y) where T : struct, U where U : I1<T>
    {" + contextKeyword + @"{
        return " + (needCast ? "(int?)" : "") + @"y;
    }}

    static int? M05<T, U>() where T : struct, U where U : I1<T>
    {" + contextKeyword + @"{
        return " + (needCast ? "(int?)" : "") + @"(T?)new T();
    }}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            compilation1 = CreateCompilation(source1, options: TestOptions.ReleaseDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>(T)",
@"
{
  // Code size       13 (0xd)
  .maxstack  1
  IL_0000:  ldarg.0
  IL_0001:  constrained. ""T""
  IL_0007:  call       ""int I1<T>." + metadataName + @"(T)""
  IL_000c:  ret
}
");
            verifier.VerifyIL("Test.M03<T, U>(T)",
@"
{
  // Code size       18 (0x12)
  .maxstack  1
  IL_0000:  ldarg.0
  IL_0001:  constrained. ""T""
  IL_0007:  call       ""int I1<T>." + metadataName + @"(T)""
  IL_000c:  newobj     ""int?..ctor(int)""
  IL_0011:  ret
}
");
            verifier.VerifyIL("Test.M04<T, U>(T?)",
@"
{
  // Code size       45 (0x2d)
  .maxstack  1
  .locals init (T? V_0,
                int? V_1)
  IL_0000:  ldarg.0
  IL_0001:  stloc.0
  IL_0002:  ldloca.s   V_0
  IL_0004:  call       ""readonly bool T?.HasValue.get""
  IL_0009:  brtrue.s   IL_0015
  IL_000b:  ldloca.s   V_1
  IL_000d:  initobj    ""int?""
  IL_0013:  ldloc.1
  IL_0014:  ret
  IL_0015:  ldloca.s   V_0
  IL_0017:  call       ""readonly T T?.GetValueOrDefault()""
  IL_001c:  constrained. ""T""
  IL_0022:  call       ""int I1<T>." + metadataName + @"(T)""
  IL_0027:  newobj     ""int?..ctor(int)""
  IL_002c:  ret
}
");
            verifier.VerifyIL("Test.M05<T, U>()",
@"
{
  // Code size       22 (0x16)
  .maxstack  1
  IL_0000:  call       ""T System.Activator.CreateInstance<T>()""
  IL_0005:  constrained. ""T""
  IL_000b:  call       ""int I1<T>." + metadataName + @"(T)""
  IL_0010:  newobj     ""int?..ctor(int)""
  IL_0015:  ret
}
");

            compilation1 = CreateCompilation(source1, options: TestOptions.ReleaseDll,
                                             parseOptions: TestOptions.RegularPreview,
                                             targetFramework: _supportingFramework);

            verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>(T)",
@"
{
  // Code size       13 (0xd)
  .maxstack  1
  IL_0000:  ldarg.0
  IL_0001:  constrained. ""T""
  IL_0007:  call       ""int I1<T>." + metadataName + @"(T)""
  IL_000c:  ret
}
");
            verifier.VerifyIL("Test.M03<T, U>(T)",
@"
{
  // Code size       18 (0x12)
  .maxstack  1
  IL_0000:  ldarg.0
  IL_0001:  constrained. ""T""
  IL_0007:  call       ""int I1<T>." + metadataName + @"(T)""
  IL_000c:  newobj     ""int?..ctor(int)""
  IL_0011:  ret
}
");
            verifier.VerifyIL("Test.M04<T, U>(T?)",
@"
{
  // Code size       45 (0x2d)
  .maxstack  1
  .locals init (T? V_0,
                int? V_1)
  IL_0000:  ldarg.0
  IL_0001:  stloc.0
  IL_0002:  ldloca.s   V_0
  IL_0004:  call       ""readonly bool T?.HasValue.get""
  IL_0009:  brtrue.s   IL_0015
  IL_000b:  ldloca.s   V_1
  IL_000d:  initobj    ""int?""
  IL_0013:  ldloc.1
  IL_0014:  ret
  IL_0015:  ldloca.s   V_0
  IL_0017:  call       ""readonly T T?.GetValueOrDefault()""
  IL_001c:  constrained. ""T""
  IL_0022:  call       ""int I1<T>." + metadataName + @"(T)""
  IL_0027:  newobj     ""int?..ctor(int)""
  IL_002c:  ret
}
");
            verifier.VerifyIL("Test.M05<T, U>()",
@"
{
  // Code size       22 (0x16)
  .maxstack  1
  IL_0000:  call       ""T System.Activator.CreateInstance<T>()""
  IL_0005:  constrained. ""T""
  IL_000b:  call       ""int I1<T>." + metadataName + @"(T)""
  IL_0010:  newobj     ""int?..ctor(int)""
  IL_0015:  ret
}
");

            var tree = compilation1.SyntaxTrees.Single();
            var model = compilation1.GetSemanticModel(tree);
            var node = tree.GetRoot().DescendantNodes().OfType<ReturnStatementSyntax>().First();

            Assert.Equal("return " + (needCast ? "(int)" : "") + @"x;", node.ToString());

            VerifyOperationTreeForNode(compilation1, model, node,
@"
IReturnOperation (OperationKind.Return, Type: null) (Syntax: 'return " + (needCast ? "(int)" : "") + @"x;')
  ReturnedValue: 
    IConversionOperation (TryCast: False, " + (isCheckedOperator && isCheckedContext ? "Checked" : "Unchecked") + @") (OperatorMethod: System.Int32 I1<T>." + metadataName + @"(T x) ConstrainedToType: T) (OperationKind.Conversion, Type: System.Int32" + (needCast ? "" : ", IsImplicit") + @") (Syntax: '" + (needCast ? "(int)" : "") + @"x')
      Conversion: CommonConversion (Exists: True, IsIdentity: False, IsNumeric: False, IsReference: False, IsUserDefined: True) (MethodSymbol: System.Int32 I1<T>." + metadataName + @"(T x))
      Operand: 
        IParameterReferenceOperation: x (OperationKind.ParameterReference, Type: T) (Syntax: 'x')
");
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractConversionOperatorForTupleEquality_03([CombinatorialValues("==", "!=")] string op, bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    " + modifier + @" static implicit operator bool (T x)" + body + @"
}

class Test
{
    static void M02<T, U>((int, C<T>) x) where T : U where U : I1<T>
    {
        _ = x " + op + @" x;
    }
}

#pragma warning disable CS0660 // 'C<T>' defines operator == or operator != but does not override Object.Equals(object o)
#pragma warning disable CS0661 // 'C<T>' defines operator == or operator != but does not override Object.GetHashCode()

class C<T>
{
    public static T operator == (C<T> x, C<T> y) => default;
    public static T operator != (C<T> x, C<T> y) => default;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            if (op == "==")
            {
                verifier.VerifyIL("Test.M02<T, U>(System.ValueTuple<int, C<T>>)",
@"
{
  // Code size       52 (0x34)
  .maxstack  2
  .locals init (System.ValueTuple<int, C<T>> V_0,
                System.ValueTuple<int, C<T>> V_1)
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  stloc.0
  IL_0003:  ldarg.0
  IL_0004:  stloc.1
  IL_0005:  ldloc.0
  IL_0006:  ldfld      ""int System.ValueTuple<int, C<T>>.Item1""
  IL_000b:  ldloc.1
  IL_000c:  ldfld      ""int System.ValueTuple<int, C<T>>.Item1""
  IL_0011:  bne.un.s   IL_0031
  IL_0013:  ldloc.0
  IL_0014:  ldfld      ""C<T> System.ValueTuple<int, C<T>>.Item2""
  IL_0019:  ldloc.1
  IL_001a:  ldfld      ""C<T> System.ValueTuple<int, C<T>>.Item2""
  IL_001f:  call       ""T C<T>.op_Equality(C<T>, C<T>)""
  IL_0024:  constrained. ""T""
  IL_002a:  call       ""bool I1<T>.op_Implicit(T)""
  IL_002f:  br.s       IL_0032
  IL_0031:  ldc.i4.0
  IL_0032:  pop
  IL_0033:  ret
}
");
            }
            else
            {
                verifier.VerifyIL("Test.M02<T, U>(System.ValueTuple<int, C<T>>)",
@"
{
  // Code size       52 (0x34)
  .maxstack  2
  .locals init (System.ValueTuple<int, C<T>> V_0,
                System.ValueTuple<int, C<T>> V_1)
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  stloc.0
  IL_0003:  ldarg.0
  IL_0004:  stloc.1
  IL_0005:  ldloc.0
  IL_0006:  ldfld      ""int System.ValueTuple<int, C<T>>.Item1""
  IL_000b:  ldloc.1
  IL_000c:  ldfld      ""int System.ValueTuple<int, C<T>>.Item1""
  IL_0011:  bne.un.s   IL_0031
  IL_0013:  ldloc.0
  IL_0014:  ldfld      ""C<T> System.ValueTuple<int, C<T>>.Item2""
  IL_0019:  ldloc.1
  IL_001a:  ldfld      ""C<T> System.ValueTuple<int, C<T>>.Item2""
  IL_001f:  call       ""T C<T>.op_Inequality(C<T>, C<T>)""
  IL_0024:  constrained. ""T""
  IL_002a:  call       ""bool I1<T>.op_Implicit(T)""
  IL_002f:  br.s       IL_0032
  IL_0031:  ldc.i4.1
  IL_0032:  pop
  IL_0033:  ret
}
");
            }

            compilation1 = CreateCompilation(source1, options: TestOptions.ReleaseDll,
                                             parseOptions: TestOptions.RegularPreview,
                                             targetFramework: _supportingFramework);

            verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            if (op == "==")
            {
                verifier.VerifyIL("Test.M02<T, U>(System.ValueTuple<int, C<T>>)",
@"
{
  // Code size       51 (0x33)
  .maxstack  2
  .locals init (System.ValueTuple<int, C<T>> V_0,
                System.ValueTuple<int, C<T>> V_1)
  IL_0000:  ldarg.0
  IL_0001:  stloc.0
  IL_0002:  ldarg.0
  IL_0003:  stloc.1
  IL_0004:  ldloc.0
  IL_0005:  ldfld      ""int System.ValueTuple<int, C<T>>.Item1""
  IL_000a:  ldloc.1
  IL_000b:  ldfld      ""int System.ValueTuple<int, C<T>>.Item1""
  IL_0010:  bne.un.s   IL_0030
  IL_0012:  ldloc.0
  IL_0013:  ldfld      ""C<T> System.ValueTuple<int, C<T>>.Item2""
  IL_0018:  ldloc.1
  IL_0019:  ldfld      ""C<T> System.ValueTuple<int, C<T>>.Item2""
  IL_001e:  call       ""T C<T>.op_Equality(C<T>, C<T>)""
  IL_0023:  constrained. ""T""
  IL_0029:  call       ""bool I1<T>.op_Implicit(T)""
  IL_002e:  br.s       IL_0031
  IL_0030:  ldc.i4.0
  IL_0031:  pop
  IL_0032:  ret
}
");
            }
            else
            {
                verifier.VerifyIL("Test.M02<T, U>(System.ValueTuple<int, C<T>>)",
@"
{
  // Code size       51 (0x33)
  .maxstack  2
  .locals init (System.ValueTuple<int, C<T>> V_0,
                System.ValueTuple<int, C<T>> V_1)
  IL_0000:  ldarg.0
  IL_0001:  stloc.0
  IL_0002:  ldarg.0
  IL_0003:  stloc.1
  IL_0004:  ldloc.0
  IL_0005:  ldfld      ""int System.ValueTuple<int, C<T>>.Item1""
  IL_000a:  ldloc.1
  IL_000b:  ldfld      ""int System.ValueTuple<int, C<T>>.Item1""
  IL_0010:  bne.un.s   IL_0030
  IL_0012:  ldloc.0
  IL_0013:  ldfld      ""C<T> System.ValueTuple<int, C<T>>.Item2""
  IL_0018:  ldloc.1
  IL_0019:  ldfld      ""C<T> System.ValueTuple<int, C<T>>.Item2""
  IL_001e:  call       ""T C<T>.op_Inequality(C<T>, C<T>)""
  IL_0023:  constrained. ""T""
  IL_0029:  call       ""bool I1<T>.op_Implicit(T)""
  IL_002e:  br.s       IL_0031
  IL_0030:  ldc.i4.1
  IL_0031:  pop
  IL_0032:  ret
}
");
            }

            var tree = compilation1.SyntaxTrees.Single();
            var model = compilation1.GetSemanticModel(tree);
            var node = tree.GetRoot().DescendantNodes().OfType<BinaryExpressionSyntax>().First();

            Assert.Equal("x " + op + " x", node.ToString());
            VerifyOperationTreeForNode(compilation1, model, node,
// Information about user-defined operators isn't exposed today.
@"
ITupleBinaryOperation (BinaryOperatorKind." + (op == "==" ? "Equals" : "NotEquals") + @") (OperationKind.TupleBinary, Type: System.Boolean) (Syntax: 'x " + op + @" x')
  Left: 
    IParameterReferenceOperation: x (OperationKind.ParameterReference, Type: (System.Int32, C<T>)) (Syntax: 'x')
  Right: 
    IParameterReferenceOperation: x (OperationKind.ParameterReference, Type: (System.Int32, C<T>)) (Syntax: 'x')
");
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractConversionOperator_04([CombinatorialValues("implicit", "explicit")] string op, bool isChecked, bool isVirtual)
        {
            bool needCast = op == "explicit";

            if (isChecked && !needCast)
            {
                return;
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);
            string checkedKeyword = isChecked ? " checked " : "";

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    " + modifier + @" static " + op + @" operator " + checkedKeyword + @"int(T x)" + body + @"
}
";
            var source2 =
@"
class Test
{
    static int M02<T>(T x) where T : I1<T>
    {" + checkedKeyword + @"{
        return " + (needCast ? "(int)" : "") + @"x;
    }}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (6,16): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //         return (int)x;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, (needCast ? "(int)" : "") + "x").WithLocation(6, 16)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation3.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (12,39): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static explicit operator int(T x);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "int").WithLocation(12, 39 + checkedKeyword.Length)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractConversionOperatorForTupleEquality_04([CombinatorialValues("==", "!=")] string op, bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    " + modifier + @" static implicit operator bool(T x)" + body + @"
}
";
            var source2 =
@"
class Test
{
    static void M02<T>((int, C<T>) x) where T : I1<T>
    {
        _ = x " + op + @" x;
    }
}

#pragma warning disable CS0660 // 'C<T>' defines operator == or operator != but does not override Object.Equals(object o)
#pragma warning disable CS0661 // 'C<T>' defines operator == or operator != but does not override Object.GetHashCode()

class C<T>
{
    public static T operator == (C<T> x, C<T> y) => default;
    public static T operator != (C<T> x, C<T> y) => default;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (6,13): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //         _ = x == x;
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "x " + op + " x").WithLocation(6, 13)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: TargetFramework.Mscorlib461Extended);

            compilation3.VerifyDiagnostics(
                // (21,39): error CS8919: Target runtime doesn't support static abstract members in interfaces.
                //     abstract static implicit operator bool(T x);
                Diagnostic(ErrorCode.ERR_RuntimeDoesNotSupportStaticAbstractMembersInInterfaces, "bool").WithLocation(21, 39)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractConversionOperator_06([CombinatorialValues("implicit", "explicit")] string op, bool isChecked, bool isVirtual)
        {
            bool needCast = op == "explicit";

            if (isChecked && !needCast)
            {
                return;
            }

            var (modifier, body) = GetModifierAndBody(isVirtual);
            string checkedKeyword = isChecked ? " checked " : "";

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    " + modifier + @" static " + op + @" operator " + checkedKeyword + @"int(T x)" + body + @"
}
";
            var source2 =
@"
class Test
{
    static int M02<T>(T x) where T : I1<T>
    {" + checkedKeyword + @"{
        return " + (needCast ? "(int)" : "") + @"x;
    }}
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.ToMetadataReference() });

            if (isChecked)
            {
                compilation2.VerifyDiagnostics(
                    // (6,16): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //         return (int)x;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, (needCast ? "(int)" : "") + "x").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 16),
                    // (6,16): error CS8936: Feature 'checked user-defined operators' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //         return (int)x;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "(int)x").WithArguments("checked user-defined operators", "11.0").WithLocation(6, 16)
                    );
            }
            else
            {
                compilation2.VerifyDiagnostics(
                    // (6,16): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //         return x;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, (needCast ? "(int)" : "") + "x").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 16)
                    );
            }

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            if (isChecked)
            {
                compilation3.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                    // (12,40): error CS8936: Feature 'checked user-defined operators' is not available in C# 10.0. Please use language version 11.0 or greater.
                    //     virtual  static explicit operator  checked int(T x) => throw null;
                    Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "checked").WithArguments("checked user-defined operators", "11.0").WithLocation(12, 40),
                    // (12,48): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                    //     virtual  static explicit operator  checked int(T x) => throw null;
                    Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "int").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(12, 48)
                    );
            }
            else
            {
                compilation3.VerifyDiagnostics(
                    // (12,39): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                    //     virtual  static implicit operator int(T x) => throw null;
                    Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "int").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(12, 39)
                    );
            }
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractConversionOperatorForTupleEquality_06([CombinatorialValues("==", "!=")] string op, bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    " + modifier + @" static implicit operator bool(T x)" + body + @"
}
";
            var source2 =
@"
class Test
{
    static void M02<T>((int, C<T>) x) where T : I1<T>
    {
        _ = x " + op + @" x;
    }
}

#pragma warning disable CS0660 // 'C<T>' defines operator == or operator != but does not override Object.Equals(object o)
#pragma warning disable CS0661 // 'C<T>' defines operator == or operator != but does not override Object.GetHashCode()

class C<T>
{
    public static T operator == (C<T> x, C<T> y) => default;
    public static T operator != (C<T> x, C<T> y) => default;
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation1.ToMetadataReference() });

            compilation2.VerifyDiagnostics(
                // (6,13): error CS8936: Feature 'static abstract members in interfaces' is not available in C# 10.0. Please use language version 11.0 or greater.
                //         _ = x == x;
                Diagnostic(ErrorCode.ERR_FeatureNotAvailableInVersion10, "x " + op + " x").WithArguments("static abstract members in interfaces", "11.0").WithLocation(6, 13)
                );

            var compilation3 = CreateCompilation(source2 + source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.Regular10,
                                                 targetFramework: _supportingFramework);

            compilation3.VerifyDiagnostics(
                // (21,39): error CS8703: The modifier 'virtual' is not valid for this item in C# 10.0. Please use language version '11.0' or greater.
                //     virtual  static implicit operator bool(T x) => throw null;
                Diagnostic(ErrorCode.ERR_InvalidModifierForLanguageVersion, "bool").WithArguments(modifier.Trim(), "10.0", "11.0").WithLocation(21, 39)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractConversionOperator_07([CombinatorialValues("implicit", "explicit")] string op, bool isVirtual)
        {
            // Same as ConsumeAbstractConversionOperator_03 only direction of conversion is flipped

            var (modifier, body) = GetModifierAndBody(isVirtual);
            string metadataName = ConversionOperatorName(op);
            bool needCast = op == "explicit";

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    " + modifier + @" static " + op + @" operator T(int x)" + body + @"
}

class Test
{
    static T M02<T, U>(int x) where T : U where U : I1<T>
    {
        return " + (needCast ? "(T)" : "") + @"x;
    }

    static T? M03<T, U>(int y) where T : struct, U where U : I1<T>
    {
        return " + (needCast ? "(T?)" : "") + @"y;
    }

    static T? M04<T, U>(int? y) where T : struct, U where U : I1<T>
    {
        return " + (needCast ? "(T?)" : "") + @"y;
    }

    static T? M05<T, U>() where T : struct, U where U : I1<T>
    {
        return " + (needCast ? "(T?)" : "") + @"(T?)0;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>(int)",
@"
{
  // Code size       18 (0x12)
  .maxstack  1
  .locals init (T V_0)
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""T I1<T>." + metadataName + @"(int)""
  IL_000d:  stloc.0
  IL_000e:  br.s       IL_0010
  IL_0010:  ldloc.0
  IL_0011:  ret
}
");
            verifier.VerifyIL("Test.M03<T, U>(int)",
@"
{
  // Code size       23 (0x17)
  .maxstack  1
  .locals init (T? V_0)
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""T I1<T>." + metadataName + @"(int)""
  IL_000d:  newobj     ""T?..ctor(T)""
  IL_0012:  stloc.0
  IL_0013:  br.s       IL_0015
  IL_0015:  ldloc.0
  IL_0016:  ret
}
");
            verifier.VerifyIL("Test.M04<T, U>(int?)",
@"
{
  // Code size       51 (0x33)
  .maxstack  1
  .locals init (int? V_0,
                T? V_1,
                T? V_2)
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  stloc.0
  IL_0003:  ldloca.s   V_0
  IL_0005:  call       ""readonly bool int?.HasValue.get""
  IL_000a:  brtrue.s   IL_0017
  IL_000c:  ldloca.s   V_1
  IL_000e:  initobj    ""T?""
  IL_0014:  ldloc.1
  IL_0015:  br.s       IL_002e
  IL_0017:  ldloca.s   V_0
  IL_0019:  call       ""readonly int int?.GetValueOrDefault()""
  IL_001e:  constrained. ""T""
  IL_0024:  call       ""T I1<T>." + metadataName + @"(int)""
  IL_0029:  newobj     ""T?..ctor(T)""
  IL_002e:  stloc.2
  IL_002f:  br.s       IL_0031
  IL_0031:  ldloc.2
  IL_0032:  ret
}
");
            verifier.VerifyIL("Test.M05<T, U>()",
@"
{
  // Code size       23 (0x17)
  .maxstack  1
  .locals init (T? V_0)
  IL_0000:  nop
  IL_0001:  ldc.i4.0
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""T I1<T>." + metadataName + @"(int)""
  IL_000d:  newobj     ""T?..ctor(T)""
  IL_0012:  stloc.0
  IL_0013:  br.s       IL_0015
  IL_0015:  ldloc.0
  IL_0016:  ret
}
");

            compilation1 = CreateCompilation(source1, options: TestOptions.ReleaseDll,
                                             parseOptions: TestOptions.RegularPreview,
                                             targetFramework: _supportingFramework);

            verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>(int)",
@"
{
  // Code size       13 (0xd)
  .maxstack  1
  IL_0000:  ldarg.0
  IL_0001:  constrained. ""T""
  IL_0007:  call       ""T I1<T>." + metadataName + @"(int)""
  IL_000c:  ret
}
");
            verifier.VerifyIL("Test.M03<T, U>(int)",
@"
{
  // Code size       18 (0x12)
  .maxstack  1
  IL_0000:  ldarg.0
  IL_0001:  constrained. ""T""
  IL_0007:  call       ""T I1<T>." + metadataName + @"(int)""
  IL_000c:  newobj     ""T?..ctor(T)""
  IL_0011:  ret
}
");
            verifier.VerifyIL("Test.M04<T, U>(int?)",
@"
{
  // Code size       45 (0x2d)
  .maxstack  1
  .locals init (int? V_0,
                T? V_1)
  IL_0000:  ldarg.0
  IL_0001:  stloc.0
  IL_0002:  ldloca.s   V_0
  IL_0004:  call       ""readonly bool int?.HasValue.get""
  IL_0009:  brtrue.s   IL_0015
  IL_000b:  ldloca.s   V_1
  IL_000d:  initobj    ""T?""
  IL_0013:  ldloc.1
  IL_0014:  ret
  IL_0015:  ldloca.s   V_0
  IL_0017:  call       ""readonly int int?.GetValueOrDefault()""
  IL_001c:  constrained. ""T""
  IL_0022:  call       ""T I1<T>." + metadataName + @"(int)""
  IL_0027:  newobj     ""T?..ctor(T)""
  IL_002c:  ret
}
");
            verifier.VerifyIL("Test.M05<T, U>()",
@"
{
  // Code size       18 (0x12)
  .maxstack  1
  IL_0000:  ldc.i4.0
  IL_0001:  constrained. ""T""
  IL_0007:  call       ""T I1<T>." + metadataName + @"(int)""
  IL_000c:  newobj     ""T?..ctor(T)""
  IL_0011:  ret
}
");

            var tree = compilation1.SyntaxTrees.Single();
            var model = compilation1.GetSemanticModel(tree);
            var node = tree.GetRoot().DescendantNodes().OfType<ReturnStatementSyntax>().First();

            Assert.Equal("return " + (needCast ? "(T)" : "") + @"x;", node.ToString());

            VerifyOperationTreeForNode(compilation1, model, node,
@"
IReturnOperation (OperationKind.Return, Type: null) (Syntax: 'return " + (needCast ? "(T)" : "") + @"x;')
  ReturnedValue: 
    IConversionOperation (TryCast: False, Unchecked) (OperatorMethod: T I1<T>." + metadataName + @"(System.Int32 x) ConstrainedToType: T) (OperationKind.Conversion, Type: T" + (needCast ? "" : ", IsImplicit") + @") (Syntax: '" + (needCast ? "(T)" : "") + @"x')
      Conversion: CommonConversion (Exists: True, IsIdentity: False, IsNumeric: False, IsReference: False, IsUserDefined: True) (MethodSymbol: T I1<T>." + metadataName + @"(System.Int32 x))
      Operand: 
        IParameterReferenceOperation: x (OperationKind.ParameterReference, Type: System.Int32) (Syntax: 'x')
");
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractConversionOperator_08([CombinatorialValues("implicit", "explicit")] string op, bool isVirtual)
        {
            // Don't look in interfaces of the effective base

            var (modifier, body) = GetModifierAndBody(isVirtual);
            string metadataName = ConversionOperatorName(op);
            bool needCast = op == "explicit";

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    " + modifier + @" static " + op + @" operator int(T x)" + body + @"
}

class C1<T> : I1<C1<T>>
{
    static " + op + @" I1<C1<T>>.operator int(C1<T> x) => default;
}

class Test
{
    static int M02<T, U>(T x) where T : U where U : C1<T>
    {
        return " + (needCast ? "(int)" : "") + @"x;
    }

    static int M03<T>(C1<T> y) where T : I1<C1<T>>
    {
        return " + (needCast ? "(int)" : "") + @"y;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var error = (op == "explicit" ? ErrorCode.ERR_NoExplicitConv : ErrorCode.ERR_NoImplicitConv);

            compilation1.VerifyDiagnostics(
                // (16,16): error CS0030: Cannot convert type 'T' to 'int'
                //         return (int)x;
                Diagnostic(error, (needCast ? "(int)" : "") + "x").WithArguments("T", "int").WithLocation(16, 16),
                // (21,16): error CS0030: Cannot convert type 'C1<T>' to 'int'
                //         return (int)y;
                Diagnostic(error, (needCast ? "(int)" : "") + "y").WithArguments("C1<T>", "int").WithLocation(21, 16)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractConversionOperator_09([CombinatorialValues("implicit", "explicit")] string op, bool isVirtual)
        {
            // Same as ConsumeAbstractConversionOperator_08 only direction of conversion is flipped

            var (modifier, body) = GetModifierAndBody(isVirtual);
            string metadataName = ConversionOperatorName(op);
            bool needCast = op == "explicit";

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    " + modifier + @" static " + op + @" operator T(int x)" + body + @"
}

class C1<T> : I1<C1<T>>
{
    static " + op + @" I1<C1<T>>.operator C1<T>(int x) => default;
}

class Test
{
    static T M02<T, U>(int x) where T : U where U : C1<T>
    {
        return " + (needCast ? "(T)" : "") + @"x;
    }

    static C1<T> M03<T>(int y) where T : I1<C1<T>>
    {
        return " + (needCast ? "(C1<T>)" : "") + @"y;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var error = (op == "explicit" ? ErrorCode.ERR_NoExplicitConv : ErrorCode.ERR_NoImplicitConv);

            compilation1.VerifyDiagnostics(
                // (16,16): error CS0030: Cannot convert type 'int' to 'T'
                //         return (T)x;
                Diagnostic(error, (needCast ? "(T)" : "") + "x").WithArguments("int", "T").WithLocation(16, 16),
                // (21,16): error CS0030: Cannot convert type 'int' to 'C1<T>'
                //         return (C1<T>)y;
                Diagnostic(error, (needCast ? "(C1<T>)" : "") + "y").WithArguments("int", "C1<T>").WithLocation(21, 16)
                );
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractConversionOperator_10([CombinatorialValues("implicit", "explicit")] string op, bool isVirtual)
        {
            // Look in base interfaces for source 

            var (modifier, body) = GetModifierAndBody(isVirtual);
            string metadataName = ConversionOperatorName(op);
            bool needCast = op == "explicit";

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    " + modifier + @" static " + op + @" operator int(T x)" + body + @"
}

public interface I2<T> : I1<T> where T : I1<T>
{}

class Test
{
    static int M02<T, U>(T x) where T : U where U : I2<T>
    {
        return " + (needCast ? "(int)" : "") + @"x;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>(T)",
@"
{
  // Code size       18 (0x12)
  .maxstack  1
  .locals init (int V_0)
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""int I1<T>." + metadataName + @"(T)""
  IL_000d:  stloc.0
  IL_000e:  br.s       IL_0010
  IL_0010:  ldloc.0
  IL_0011:  ret
}
");
        }

        [Theory]
        [InlineData("implicit", false)]
        [InlineData("implicit", true)]
        [InlineData("explicit", false)]
        [InlineData("explicit", true)]
        public void ConsumeAbstractConversionOperator_11(string op, bool useCast)
        {
            // Same as ConsumeAbstractConversionOperator_10 only direction of conversion is flipped
            // Look in base interfaces for destination for explicit cast in code

            string metadataName = ConversionOperatorName(op);

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    abstract static " + op + @" operator T(int x);
}

public interface I2<T> : I1<T> where T : I1<T>
{}

class Test
{
    static T M02<T, U>(int x) where T : U where U : I2<T>
    {
        return " + (useCast ? "(T)" : "") + @"x;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            if (useCast)
            {
                var verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

                verifier.VerifyIL("Test.M02<T, U>(int)",
    @"
{
  // Code size       18 (0x12)
  .maxstack  1
  .locals init (T V_0)
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""T I1<T>." + metadataName + @"(int)""
  IL_000d:  stloc.0
  IL_000e:  br.s       IL_0010
  IL_0010:  ldloc.0
  IL_0011:  ret
}
");
            }
            else
            {
                compilation1.VerifyDiagnostics(
                    // (14,16): error CS0266: Cannot implicitly convert type 'int' to 'T'. An explicit conversion exists (are you missing a cast?)
                    //         return x;
                    Diagnostic(ErrorCode.ERR_NoImplicitConvCast, "x").WithArguments("int", "T").WithLocation(14, 16)
                    );
            }
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractConversionOperator_12([CombinatorialValues("implicit", "explicit")] string op, bool isVirtual)
        {
            // Ignore duplicate candidates

            var (modifier, body) = GetModifierAndBody(isVirtual);
            string metadataName = ConversionOperatorName(op);
            bool needCast = op == "explicit";

            var source1 =
@"
public interface I1<T, U> where T : I1<T, U> where U : I1<T, U>
{
    " + modifier + @" static " + op + @" operator U(T x)" + body + @"
}

class Test
{
    static U M02<T, U>(T x) where T : I1<T, U> where U : I1<T, U>
    {
        return " + (needCast ? "(U)" : "") + @"x;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>(T)",
@"
{
  // Code size       18 (0x12)
  .maxstack  1
  .locals init (U V_0)
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  constrained. ""T""
  IL_0008:  call       ""U I1<T, U>." + metadataName + @"(T)""
  IL_000d:  stloc.0
  IL_000e:  br.s       IL_0010
  IL_0010:  ldloc.0
  IL_0011:  ret
}
");
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractConversionOperator_13([CombinatorialValues("implicit", "explicit")] string op)
        {
            // Look in effective base

            string metadataName = ConversionOperatorName(op);
            bool needCast = op == "explicit";

            var source1 =
@"
public class C1<T>
{
    public static " + op + @" operator int(C1<T> x) => default;
}

class Test
{
    static int M02<T, U>(T x) where T : U where U : C1<T>
    {
        return " + (needCast ? "(int)" : "") + @"x;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>(T)",
@"
{
  // Code size       17 (0x11)
  .maxstack  1
  .locals init (int V_0)
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  box        ""T""
  IL_0007:  call       ""int C1<T>." + metadataName + @"(C1<T>)""
  IL_000c:  stloc.0
  IL_000d:  br.s       IL_000f
  IL_000f:  ldloc.0
  IL_0010:  ret
}
");
        }

        [Fact]
        public void ConsumeAbstractConversionOperator_14()
        {
            // Same as ConsumeAbstractConversionOperator_13 only direction of conversion is flipped
            var source1 =
@"
public class C1<T>
{
    public static explicit operator C1<T>(int x) => default;
}

class Test
{
    static T M02<T, U>(int x) where T : U where U : C1<T>
    {
        return (T)x;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                    parseOptions: TestOptions.RegularPreview,
                                                    targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>(int)",
@"
{
  // Code size       17 (0x11)
  .maxstack  1
  .locals init (T V_0)
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  call       ""C1<T> C1<T>.op_Explicit(int)""
  IL_0007:  unbox.any  ""T""
  IL_000c:  stloc.0
  IL_000d:  br.s       IL_000f
  IL_000f:  ldloc.0
  IL_0010:  ret
}
");
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractConversionOperator_15([CombinatorialValues("implicit", "explicit")] string op, bool isVirtual)
        {
            // If there is an applicable candidate in effective base class, interfaces are not looked at.

            var (modifier, body) = GetModifierAndBody(isVirtual);
            string metadataName = ConversionOperatorName(op);
            bool needCast = op == "explicit";

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    " + modifier + @" static " + op + @" operator int(T x)" + body + @"
}

public class C1 : I1<C1>
{
    public static " + op + @" operator int(C1 x) => default;
}

class Test
{
    static int M02<T, U>(T x) where T : U where U : C1, I1<C1>
    {
        return " + (needCast ? "(int)" : "") + @"x;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>(T)",
@"
{
  // Code size       17 (0x11)
  .maxstack  1
  .locals init (int V_0)
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  box        ""T""
  IL_0007:  call       ""int C1." + metadataName + @"(C1)""
  IL_000c:  stloc.0
  IL_000d:  br.s       IL_000f
  IL_000f:  ldloc.0
  IL_0010:  ret
}
");
        }

        [Fact]
        public void ConsumeAbstractConversionOperator_16()
        {
            // Same as ConsumeAbstractConversionOperator_15 only direction of conversion is flipped

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    abstract static explicit operator T(int x);
}

public class C1 : I1<C1>
{
    public static explicit operator C1(int x) => default;
}

class Test
{
    static T M02<T, U>(int x) where T : U where U : C1, I1<C1>
    {
        return (T)x;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                    parseOptions: TestOptions.RegularPreview,
                                                    targetFramework: _supportingFramework);

            var verifier = CompileAndVerify(compilation1, verify: Verification.Skipped).VerifyDiagnostics();

            verifier.VerifyIL("Test.M02<T, U>(int)",
@"
{
  // Code size       17 (0x11)
  .maxstack  1
  .locals init (T V_0)
  IL_0000:  nop
  IL_0001:  ldarg.0
  IL_0002:  call       ""C1 C1.op_Explicit(int)""
  IL_0007:  unbox.any  ""T""
  IL_000c:  stloc.0
  IL_000d:  br.s       IL_000f
  IL_000f:  ldloc.0
  IL_0010:  ret
}
");
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractConversionOperator_17([CombinatorialValues("implicit", "explicit")] string op, bool isVirtual)
        {
            // If there is no applicable candidate in effective base class, look in interfaces.

            var (modifier, body) = GetModifierAndBody(isVirtual);
            bool needCast = op == "explicit";

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    " + modifier + @"  static " + op + @" operator int(T x)" + body + @"
}

public class C1 
{
}

class Test
{
    static int M02<T, U>(T x) where T : U where U : C1, I1<T>
    {
        return " + (needCast ? "(int)" : "") + @"x;
    }

    static int M03<T, U>(T y) where T : U where U : I1<T>
    {
        return " + (needCast ? "(int)" : "") + @"y;
    }

    static void Main()
    {
        var c2 = new C2();
        M02<C2, C2>(c2);
        M03<C2, C2>(c2);
    }
}

public class C2 : C1, I1<C2>
{
    public static " + op + @" operator int(C2 x)
    {
        System.Console.WriteLine(""C2 conversion"");
        return default;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugExe,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, verify: Verification.Skipped, expectedOutput: !Execute(isVirtual) ? null : @"
C2 conversion
C2 conversion
").VerifyDiagnostics();
        }

        [Theory]
        [CombinatorialData]
        public void ConsumeAbstractConversionOperator_18([CombinatorialValues("implicit", "explicit")] string op, bool isVirtual)
        {
            // Same as ConsumeAbstractConversionOperator_17 only direction of conversion is flipped

            var (modifier, body) = GetModifierAndBody(isVirtual);
            bool needCast = op == "explicit";

            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    " + modifier + @" static " + op + @" operator T(int x)" + body + @"
}

public class C1 
{
}

class Test
{
    static T M02<T, U>(int x) where T : U where U : C1, I1<T>
    {
        return " + (needCast ? "(T)" : "") + @"x;
    }

    static T M03<T, U>(int y) where T : U where U : I1<T>
    {
        return " + (needCast ? "(T)" : "") + @"y;
    }

    static void Main()
    {
        M02<C2, C2>(0);
        M03<C2, C2>(1);
    }
}

public class C2 : C1, I1<C2>
{
    public static " + op + @" operator C2(int x)
    {
        System.Console.WriteLine(""C2 conversion"");
        return default;
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugExe,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, verify: Verification.Skipped, expectedOutput: !Execute(isVirtual) ? null : @"
C2 conversion
C2 conversion
").VerifyDiagnostics();
        }

        [Fact]
        [WorkItem(56753, "https://github.com/dotnet/roslyn/issues/56753")]
        public void ConsumeAbstractConversionOperator_19()
        {
            var source1 =
@"
interface I1 { }

abstract class Base : I1 {}

interface I2<T> where T : class, I2<T>
{ 
    public static abstract implicit operator T(string value);
}

class Derived : Base, I2<Derived>
{
    public static implicit operator Derived(string value)
    { 
        System.Console.WriteLine(""Derived conversion"");
        return default;
    }
}

static class Util 
{
    static void Method1<T>(string value) where T : Base, I2<T>
    {
        var newT = (T)value;
    }

    static void Method2<T>(string value) where T : class, I1, I2<T>
    {
        var newT = (T)value;
    }

    static void Main()
    {
        Method1<Derived>("""");
        Method2<Derived>("""");
    }
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugExe,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, verify: Verification.Skipped, expectedOutput: !Execute(isVirtual: false) ? null : @"
Derived conversion
Derived conversion
").VerifyDiagnostics();
        }

        [Theory]
        [CombinatorialData]
        [WorkItem(53802, "https://github.com/dotnet/roslyn/issues/53802")]
        public void TestAmbiguousImplementationMethod_01(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 = @"
public interface Interface<T, U>
{
    " + modifier + @" static void Method(int i)" + body + @"
    " + modifier + @" static void Method(T i)" + body + @"
    " + modifier + @" static void Method(U i)" + body + @"
}

public class Base<T> : Interface<T, T>
{
    public static void Method(int i) { }
    public static void Method(T i) { }
}

public class Derived : Base<int>, Interface<int, int>
{
}

class YetAnother : Interface<int, int>
{
    public static void Method(int i) { }
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var b = module.GlobalNamespace.GetTypeMember("Base");
                var bI = b.Interfaces().Single();
                var biMethods = bI.GetMembers();

                Assert.Equal("void Interface<T, U>.Method(System.Int32 i)", biMethods[0].OriginalDefinition.ToTestDisplayString());
                Assert.Equal("void Interface<T, U>.Method(T i)", biMethods[1].OriginalDefinition.ToTestDisplayString());
                Assert.Equal("void Interface<T, U>.Method(U i)", biMethods[2].OriginalDefinition.ToTestDisplayString());

                var bM1 = b.FindImplementationForInterfaceMember(biMethods[0]);

                Assert.Equal("void Base<T>.Method(System.Int32 i)", bM1.ToTestDisplayString());

                var bM2 = b.FindImplementationForInterfaceMember(biMethods[1]);

                Assert.Equal("void Base<T>.Method(T i)", bM2.ToTestDisplayString());
                Assert.Same(bM2, b.FindImplementationForInterfaceMember(biMethods[2]));

                var bM1Impl = ((MethodSymbol)bM1).ExplicitInterfaceImplementations;
                var bM2Impl = ((MethodSymbol)bM2).ExplicitInterfaceImplementations;

                if (module is PEModuleSymbol)
                {
                    Assert.Equal(biMethods[0], bM1Impl.Single());

                    Assert.Equal(2, bM2Impl.Length);
                    Assert.Equal(biMethods[1], bM2Impl[0]);
                    Assert.Equal(biMethods[2], bM2Impl[1]);
                }
                else
                {
                    Assert.Empty(bM1Impl);
                    Assert.Empty(bM2Impl);
                }

                var d = module.GlobalNamespace.GetTypeMember("Derived");
                var dB = d.BaseTypeNoUseSiteDiagnostics;
                var dI = d.Interfaces().Single();
                var diMethods = dI.GetMembers();

                Assert.Equal("void Interface<T, U>.Method(System.Int32 i)", diMethods[0].OriginalDefinition.ToTestDisplayString());
                Assert.Equal("void Interface<T, U>.Method(T i)", diMethods[1].OriginalDefinition.ToTestDisplayString());
                Assert.Equal("void Interface<T, U>.Method(U i)", diMethods[2].OriginalDefinition.ToTestDisplayString());

                var dM1 = d.FindImplementationForInterfaceMember(diMethods[0]);

                Assert.Same(bM1, dM1.OriginalDefinition);

                var dM2 = d.FindImplementationForInterfaceMember(diMethods[1]);

                Assert.Same(bM2, dM2.OriginalDefinition);
                Assert.Same(bM2, d.FindImplementationForInterfaceMember(diMethods[2]).OriginalDefinition);
            }
        }

        [Theory]
        [CombinatorialData]
        [WorkItem(53802, "https://github.com/dotnet/roslyn/issues/53802")]
        public void TestAmbiguousImplementationMethod_02(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source0 = @"
public interface Interface<T, U>
{
    " + modifier + @" static void Method(int i)" + body + @"
    " + modifier + @" static void Method(T i)" + body + @"
    " + modifier + @" static void Method(U i)" + body + @"
}

public class Base<T> : Interface<T, T>
{
    public static void Method(int i) { }
    public static void Method(T i) { }
}
";

            var compilation0 = CreateCompilation(source0, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation0.VerifyDiagnostics();

            var source1 = @"
public class Derived : Base<int>, Interface<int, int>
{
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation0.EmitToImageReference() });

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                var d = module.GlobalNamespace.GetTypeMember("Derived");
                var dB = d.BaseTypeNoUseSiteDiagnostics;
                var dI = d.Interfaces().Single();
                var diMethods = dI.GetMembers();

                Assert.Equal("void Interface<T, U>.Method(System.Int32 i)", diMethods[0].OriginalDefinition.ToTestDisplayString());
                Assert.Equal("void Interface<T, U>.Method(T i)", diMethods[1].OriginalDefinition.ToTestDisplayString());
                Assert.Equal("void Interface<T, U>.Method(U i)", diMethods[2].OriginalDefinition.ToTestDisplayString());

                var dM1 = d.FindImplementationForInterfaceMember(diMethods[0]);

                Assert.Equal("void Base<T>.Method(System.Int32 i)", dM1.OriginalDefinition.ToTestDisplayString());

                var dM2 = d.FindImplementationForInterfaceMember(diMethods[1]);

                Assert.Equal("void Base<T>.Method(T i)", dM2.OriginalDefinition.ToTestDisplayString());
                Assert.Same(dM2, d.FindImplementationForInterfaceMember(diMethods[2]));

                var dM1Impl = ((MethodSymbol)dM1).ExplicitInterfaceImplementations;
                var dM2Impl = ((MethodSymbol)dM2).ExplicitInterfaceImplementations;

                Assert.Equal(diMethods[0], dM1Impl.Single());

                Assert.Equal(2, dM2Impl.Length);
                Assert.Equal(diMethods[1], dM2Impl[0]);
                Assert.Equal(diMethods[2], dM2Impl[1]);
            }
        }

        [Theory]
        [CombinatorialData]
        [WorkItem(53802, "https://github.com/dotnet/roslyn/issues/53802")]
        public void TestAmbiguousImplementationMethod_03(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source0 = @"
public interface Interface<T, U>
{
    " + modifier + @" static void Method(int i)" + body + @"
    " + modifier + @" static void Method(T i)" + body + @"
    " + modifier + @" static void Method(U i)" + body + @"
}

public class Base<T> : Interface<T, T>
{
    public static void Method(int i) { }
    public static void Method(T i) { }
}
";

            var compilation0 = CreateCompilation(source0, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { CreateEmptyCompilation("").ToMetadataReference() });

            compilation0.VerifyDiagnostics();

            var source1 = @"
public class Derived : Base<int>, Interface<int, int>
{
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework,
                                                 references: new[] { compilation0.ToMetadataReference() });

            var d = compilation1.GlobalNamespace.GetTypeMember("Derived");
            var dB = d.BaseTypeNoUseSiteDiagnostics;
            var dI = d.Interfaces().Single();
            var diMethods = dI.GetMembers();

            Assert.IsType<RetargetingNamedTypeSymbol>(dB.OriginalDefinition);

            Assert.Equal("void Interface<T, U>.Method(System.Int32 i)", diMethods[0].OriginalDefinition.ToTestDisplayString());
            Assert.Equal("void Interface<T, U>.Method(T i)", diMethods[1].OriginalDefinition.ToTestDisplayString());
            Assert.Equal("void Interface<T, U>.Method(U i)", diMethods[2].OriginalDefinition.ToTestDisplayString());

            var dM1 = d.FindImplementationForInterfaceMember(diMethods[0]);

            Assert.Equal("void Base<T>.Method(System.Int32 i)", dM1.OriginalDefinition.ToTestDisplayString());

            var dM2 = d.FindImplementationForInterfaceMember(diMethods[1]);

            Assert.Equal("void Base<T>.Method(T i)", dM2.OriginalDefinition.ToTestDisplayString());
            Assert.Equal(dM2, d.FindImplementationForInterfaceMember(diMethods[2]));

            var dM1Impl = ((MethodSymbol)dM1).ExplicitInterfaceImplementations;
            var dM2Impl = ((MethodSymbol)dM2).ExplicitInterfaceImplementations;

            Assert.Empty(dM1Impl);
            Assert.Empty(dM2Impl);
        }

        [Fact]
        [WorkItem(53802, "https://github.com/dotnet/roslyn/issues/53802")]
        public void TestAmbiguousImplementationMethod_04()
        {
            var source2 = @"
public interface Interface<T, U>
{
    abstract static void Method(int i);
    abstract static void Method(T i);
    abstract static void Method(U i);
}

class Other : Interface<int, int>
{
    static void Interface<int, int>.Method(int i) { }
}
";

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation2.VerifyDiagnostics(
                // (9,15): error CS0535: 'Other' does not implement interface member 'Interface<int, int>.Method(int)'
                // class Other : Interface<int, int>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "Interface<int, int>").WithArguments("Other", "Interface<int, int>.Method(int)").WithLocation(9, 15),
                // (9,15): error CS0535: 'Other' does not implement interface member 'Interface<int, int>.Method(int)'
                // class Other : Interface<int, int>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "Interface<int, int>").WithArguments("Other", "Interface<int, int>.Method(int)").WithLocation(9, 15),
                // (11,37): warning CS0473: Explicit interface implementation 'Other.Interface<int, int>.Method(int)' matches more than one interface member. Which interface member is actually chosen is implementation-dependent. Consider using a non-explicit implementation instead.
                //     static void Interface<int, int>.Method(int i) { }
                Diagnostic(ErrorCode.WRN_ExplicitImplCollision, "Method").WithArguments("Other.Interface<int, int>.Method(int)").WithLocation(11, 37)
                );
        }

        [Fact]
        [WorkItem(53802, "https://github.com/dotnet/roslyn/issues/53802")]
        public void TestAmbiguousImplementationMethod_05()
        {
            var source2 = @"
public interface Interface<T, U>
{
    virtual static void Method(int i){}
    virtual static void Method(T i){}
    virtual static void Method(U i){}
}

class Other : Interface<int, int>
{
    static void Interface<int, int>.Method(int i) { }
}
";

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation2.VerifyDiagnostics(
                // (11,37): warning CS0473: Explicit interface implementation 'Other.Interface<int, int>.Method(int)' matches more than one interface member. Which interface member is actually chosen is implementation-dependent. Consider using a non-explicit implementation instead.
                //     static void Interface<int, int>.Method(int i) { }
                Diagnostic(ErrorCode.WRN_ExplicitImplCollision, "Method").WithArguments("Other.Interface<int, int>.Method(int)").WithLocation(11, 37)
                );
        }

        [Theory]
        [CombinatorialData]
        public void UnmanagedCallersOnly_01(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source2 = @"
using System.Runtime.InteropServices;

public interface I1
{
    [UnmanagedCallersOnly] " + modifier + @" static void M1()" + body + @"
    [UnmanagedCallersOnly] " + modifier + @" static int operator +(I1 x)" + body + @"
    [UnmanagedCallersOnly] " + modifier + @" static int operator +(I1 x, I1 y)" + body + @"
}

public interface I2<T> where T : I2<T>
{
    [UnmanagedCallersOnly] abstract static implicit operator int(T i);
    [UnmanagedCallersOnly] abstract static explicit operator T(int i);
}
";

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation2.VerifyDiagnostics(
                // (6,6): error CS8896: 'UnmanagedCallersOnly' can only be applied to ordinary static non-abstract, non-virtual methods or static local functions.
                //     [UnmanagedCallersOnly] abstract static void M1();
                Diagnostic(ErrorCode.ERR_UnmanagedCallersOnlyRequiresStatic, "UnmanagedCallersOnly").WithLocation(6, 6),
                // (7,6): error CS8896: 'UnmanagedCallersOnly' can only be applied to ordinary static non-abstract, non-virtual methods or static local functions.
                //     [UnmanagedCallersOnly] abstract static int operator +(I1 x);
                Diagnostic(ErrorCode.ERR_UnmanagedCallersOnlyRequiresStatic, "UnmanagedCallersOnly").WithLocation(7, 6),
                // (8,6): error CS8896: 'UnmanagedCallersOnly' can only be applied to ordinary static non-abstract, non-virtual methods or static local functions.
                //     [UnmanagedCallersOnly] abstract static int operator +(I1 x, I1 y);
                Diagnostic(ErrorCode.ERR_UnmanagedCallersOnlyRequiresStatic, "UnmanagedCallersOnly").WithLocation(8, 6),
                // (13,6): error CS8896: 'UnmanagedCallersOnly' can only be applied to ordinary static non-abstract, non-virtual methods or static local functions.
                //     [UnmanagedCallersOnly] abstract static implicit operator int(T i);
                Diagnostic(ErrorCode.ERR_UnmanagedCallersOnlyRequiresStatic, "UnmanagedCallersOnly").WithLocation(13, 6),
                // (14,6): error CS8896: 'UnmanagedCallersOnly' can only be applied to ordinary static non-abstract, non-virtual methods or static local functions.
                //     [UnmanagedCallersOnly] abstract static explicit operator T(int i);
                Diagnostic(ErrorCode.ERR_UnmanagedCallersOnlyRequiresStatic, "UnmanagedCallersOnly").WithLocation(14, 6)
                );
        }

        [Theory]
        [CombinatorialData]
        [WorkItem(54113, "https://github.com/dotnet/roslyn/issues/54113")]
        public void UnmanagedCallersOnly_02(bool isVirtual)
        {
            string modifier, body;

            if (isVirtual)
            {
                modifier = "";
                body =
@"
{
  // [System.Runtime.InteropServices.UnmanagedCallersOnly]
  .custom instance void System.Runtime.InteropServices.UnmanagedCallersOnlyAttribute::.ctor() = (
      01 00 00 00
  )

  .maxstack  8
  IL_0000:  ldnull
  IL_0001:  throw
}
";
            }
            else
            {
                modifier = "abstract";
                body =
@"{
  // [System.Runtime.InteropServices.UnmanagedCallersOnly]
  .custom instance void System.Runtime.InteropServices.UnmanagedCallersOnlyAttribute::.ctor() = (
      01 00 00 00
  )
}
";
            }

            var ilSource = @"
.class public auto ansi sealed beforefieldinit System.Runtime.InteropServices.UnmanagedCallersOnlyAttribute
    extends [mscorlib]System.Attribute
{
    .custom instance void [mscorlib]System.AttributeUsageAttribute::.ctor(valuetype [mscorlib]System.AttributeTargets) = (
        01 00 40 00 00 00 01 00 54 02 09 49 6e 68 65 72
        69 74 65 64 00
    )
    .field public class [mscorlib]System.Type[] CallConvs
    .field public string EntryPoint

    .method public hidebysig specialname rtspecialname 
        instance void .ctor () cil managed 
    {
        ldarg.0
        call instance void [mscorlib]System.Attribute::.ctor()
        ret
    }
}

.class interface public auto ansi abstract I1
{
    .method public hidebysig " + modifier + @" virtual static 
        void M1 () cil managed 
    " + body + @"

    .method public hidebysig specialname " + modifier + @" virtual static 
        int32 op_UnaryPlus (
            class I1 x
        ) cil managed 
    " + body + @"

    .method public hidebysig specialname " + modifier + @" virtual static 
        int32 op_Addition (
            class I1 x,
            class I1 y
        ) cil managed 
    " + body + @"
}

.class interface public auto ansi abstract I2`1<(class I2`1<!T>) T>
{
    .method public hidebysig specialname " + modifier + @" virtual static 
        int32 op_Implicit (
            !T i
        ) cil managed 
    " + body + @"

    .method public hidebysig specialname " + modifier + @" virtual static 
        !T op_Explicit (
            int32 i
        ) cil managed 
    " + body + @"
}
";

            var source1 =
@"
class Test
{
    static void M02<T>(T x, T y) where T : I1
    {
        T.M1();
        _ = +x;
        _ = x + y;
    }

    static int M03<T>(T x) where T : I2<T>
    {
        _ = (T)x;
        return x;
    }
}
";
            var compilation1 = CreateCompilationWithIL(source1, ilSource, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (6,11): error CS0570: 'I1.M1()' is not supported by the language
                //         T.M1();
                Diagnostic(ErrorCode.ERR_BindToBogus, "M1").WithArguments("I1.M1()").WithLocation(6, 11),
                // (7,13): error CS0570: 'I1.operator +(I1)' is not supported by the language
                //         _ = +x;
                Diagnostic(ErrorCode.ERR_BindToBogus, "+x").WithArguments("I1.operator +(I1)").WithLocation(7, 13),
                // (8,13): error CS0570: 'I1.operator +(I1, I1)' is not supported by the language
                //         _ = x + y;
                Diagnostic(ErrorCode.ERR_BindToBogus, "x + y").WithArguments("I1.operator +(I1, I1)").WithLocation(8, 13),
                // (14,16): error CS0570: 'I2<T>.implicit operator int(T)' is not supported by the language
                //         return x;
                Diagnostic(ErrorCode.ERR_BindToBogus, "x").WithArguments("I2<T>.implicit operator int(T)").WithLocation(14, 16)
                );
        }

        [Theory]
        [CombinatorialData]
        public void UnmanagedCallersOnly_03(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source2 = @"
using System.Runtime.InteropServices;

public interface I1<T> where T : I1<T>
{
    " + modifier + @" static void M1()" + body + @"
    " + modifier + @" static int operator +(T x)" + body + @"
    " + modifier + @" static int operator +(T x, T y)" + body + @"
    " + modifier + @" static implicit operator int(T i)" + body + @"
    " + modifier + @" static explicit operator T(int i)" + body + @"
}

class C : I1<C>
{
    [UnmanagedCallersOnly] public static void M1() {}
    [UnmanagedCallersOnly] public static int operator +(C x) => 0;
    [UnmanagedCallersOnly] public static int operator +(C x, C y) => 0;
    [UnmanagedCallersOnly] public static implicit operator int(C i) => 0;
    [UnmanagedCallersOnly] public static explicit operator C(int i) => null;
}
";

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation2.VerifyDiagnostics(
                // (15,47): error CS8932: 'UnmanagedCallersOnly' method 'C.M1()' cannot implement interface member 'I1<C>.M1()' in type 'C'
                //     [UnmanagedCallersOnly] public static void M1() {}
                Diagnostic(ErrorCode.ERR_InterfaceImplementedByUnmanagedCallersOnlyMethod, "M1").WithArguments("C.M1()", "I1<C>.M1()", "C").WithLocation(15, 47),
                // (16,6): error CS8896: 'UnmanagedCallersOnly' can only be applied to ordinary static non-abstract, non-virtual methods or static local functions.
                //     [UnmanagedCallersOnly] public static int operator +(C x) => 0;
                Diagnostic(ErrorCode.ERR_UnmanagedCallersOnlyRequiresStatic, "UnmanagedCallersOnly").WithLocation(16, 6),
                // (17,6): error CS8896: 'UnmanagedCallersOnly' can only be applied to ordinary static non-abstract, non-virtual methods or static local functions.
                //     [UnmanagedCallersOnly] public static int operator +(C x, C y) => 0;
                Diagnostic(ErrorCode.ERR_UnmanagedCallersOnlyRequiresStatic, "UnmanagedCallersOnly").WithLocation(17, 6),
                // (18,6): error CS8896: 'UnmanagedCallersOnly' can only be applied to ordinary static non-abstract, non-virtual methods or static local functions.
                //     [UnmanagedCallersOnly] public static implicit operator int(C i) => 0;
                Diagnostic(ErrorCode.ERR_UnmanagedCallersOnlyRequiresStatic, "UnmanagedCallersOnly").WithLocation(18, 6),
                // (19,6): error CS8896: 'UnmanagedCallersOnly' can only be applied to ordinary static non-abstract, non-virtual methods or static local functions.
                //     [UnmanagedCallersOnly] public static explicit operator C(int i) => null;
                Diagnostic(ErrorCode.ERR_UnmanagedCallersOnlyRequiresStatic, "UnmanagedCallersOnly").WithLocation(19, 6)
                );
        }

        [Theory]
        [CombinatorialData]
        public void UnmanagedCallersOnly_04(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source2 = @"
using System.Runtime.InteropServices;

public interface I1<T> where T : I1<T>
{
    " + modifier + @" static void M1()" + body + @"
    " + modifier + @" static int operator +(T x)" + body + @"
    " + modifier + @" static int operator +(T x, T y)" + body + @"
    " + modifier + @" static implicit operator int(T i)" + body + @"
    " + modifier + @" static explicit operator T(int i)" + body + @"
}

class C : I1<C>
{
    [UnmanagedCallersOnly] static void I1<C>.M1() {}
    [UnmanagedCallersOnly] static int I1<C>.operator +(C x) => 0;
    [UnmanagedCallersOnly] static int I1<C>.operator +(C x, C y) => 0;
    [UnmanagedCallersOnly] static implicit I1<C>.operator int(C i) => 0;
    [UnmanagedCallersOnly] static explicit I1<C>.operator C(int i) => null;
}
";

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation2.VerifyDiagnostics(
                // (15,6): error CS8896: 'UnmanagedCallersOnly' can only be applied to ordinary static non-abstract, non-virtual methods or static local functions.
                //     [UnmanagedCallersOnly] static void I1<C>.M1() {}
                Diagnostic(ErrorCode.ERR_UnmanagedCallersOnlyRequiresStatic, "UnmanagedCallersOnly").WithLocation(15, 6),
                // (16,6): error CS8896: 'UnmanagedCallersOnly' can only be applied to ordinary static non-abstract, non-virtual methods or static local functions.
                //     [UnmanagedCallersOnly] static int I1<C>.operator +(C x) => 0;
                Diagnostic(ErrorCode.ERR_UnmanagedCallersOnlyRequiresStatic, "UnmanagedCallersOnly").WithLocation(16, 6),
                // (17,6): error CS8896: 'UnmanagedCallersOnly' can only be applied to ordinary static non-abstract, non-virtual methods or static local functions.
                //     [UnmanagedCallersOnly] static int I1<C>.operator +(C x, C y) => 0;
                Diagnostic(ErrorCode.ERR_UnmanagedCallersOnlyRequiresStatic, "UnmanagedCallersOnly").WithLocation(17, 6),
                // (18,6): error CS8896: 'UnmanagedCallersOnly' can only be applied to ordinary static non-abstract, non-virtual methods or static local functions.
                //     [UnmanagedCallersOnly] static implicit I1<C>.operator int(C i) => 0;
                Diagnostic(ErrorCode.ERR_UnmanagedCallersOnlyRequiresStatic, "UnmanagedCallersOnly").WithLocation(18, 6),
                // (19,6): error CS8896: 'UnmanagedCallersOnly' can only be applied to ordinary static non-abstract, non-virtual methods or static local functions.
                //     [UnmanagedCallersOnly] static explicit I1<C>.operator C(int i) => null;
                Diagnostic(ErrorCode.ERR_UnmanagedCallersOnlyRequiresStatic, "UnmanagedCallersOnly").WithLocation(19, 6)
                );
        }

        [Theory]
        [InlineData("+", "op_UnaryPlus")]
        [InlineData("!", "op_LogicalNot")]
        [InlineData("~", "op_OnesComplement")]
        public void UnaryOperators_Checked_Unsupported_01(string op, string name)
        {
            unaryOperators_Checked_Unsupported_01(op, name, isVirtual: false);
            unaryOperators_Checked_Unsupported_01(op, name, isVirtual: true);

            void unaryOperators_Checked_Unsupported_01(string op, string name, bool isVirtual)
            {
                var (modifier, body) = GetModifierAndBody(isVirtual);

                var source1 =
@"
interface C 
{
    public static " + modifier + @" C operator checked " + op + @"(C x)" + body + @"
}
";

                var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation1.VerifyDiagnostics(
                    // (4,39): error CS9150: User-defined operator '+' cannot be declared checked
                    //     public static abstract C operator checked +(C x);
                    Diagnostic(ErrorCode.ERR_OperatorCantBeChecked, "checked").WithArguments(op).WithLocation(4, 39)
                    );

                var c = compilation1.SourceModule.GlobalNamespace.GetTypeMember("C");
                var opSymbol = c.GetMembers().OfType<MethodSymbol>().Where(m => m.MethodKind != MethodKind.Constructor).Single();

                Assert.Equal(MethodKind.UserDefinedOperator, opSymbol.MethodKind);
                Assert.Equal(name, opSymbol.Name);
                Assert.Equal("C C." + name + "(C x)", opSymbol.ToTestDisplayString());
                Assert.Equal("C.operator " + op + "(C)", opSymbol.ToDisplayString());
            }
        }

        [Theory]
        [CombinatorialData]
        public void UnaryOperators_Checked_Unsupported_02(bool isVirtual)
        {
            var (modifier, body) = GetModifierAndBody(isVirtual);

            var source1 =
@"
interface C 
{
    public static " + modifier + @" bool operator checked true(C x)" + body + @"
    public static " + modifier + @" bool operator checked false(C x)" + body + @"
}
";
            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,42): error CS9150: User-defined operator 'true' cannot be declared checked
                //     public static abstract bool operator checked true(C x);
                Diagnostic(ErrorCode.ERR_OperatorCantBeChecked, "checked").WithArguments("true").WithLocation(4, 42),
                // (5,42): error CS9150: User-defined operator 'false' cannot be declared checked
                //     public static abstract bool operator checked false(C x);
                Diagnostic(ErrorCode.ERR_OperatorCantBeChecked, "checked").WithArguments("false").WithLocation(5, 42)
                );

            var c = compilation1.SourceModule.GlobalNamespace.GetTypeMember("C");
            var opSymbols = c.GetMembers().OfType<MethodSymbol>().Where(m => m.MethodKind != MethodKind.Constructor).ToArray();
            Assert.Equal(2, opSymbols.Length);

            var opSymbol1 = opSymbols[0];
            Assert.Equal(MethodKind.UserDefinedOperator, opSymbol1.MethodKind);
            Assert.Equal("op_True", opSymbol1.Name);
            Assert.Equal("System.Boolean C.op_True(C x)", opSymbol1.ToTestDisplayString());
            Assert.Equal("C.operator true(C)", opSymbol1.ToDisplayString());

            var opSymbol2 = opSymbols[1];
            Assert.Equal(MethodKind.UserDefinedOperator, opSymbol2.MethodKind);
            Assert.Equal("op_False", opSymbol2.Name);
            Assert.Equal("System.Boolean C.op_False(C x)", opSymbol2.ToTestDisplayString());
            Assert.Equal("C.operator false(C)", opSymbol2.ToDisplayString());
        }

        [Theory]
        [InlineData("-")]
        [InlineData("++")]
        [InlineData("--")]
        public void ImplementAbstractStaticUnaryOperator_16(string op)
        {
            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    abstract static T operator checked " + op + @"(T x);
}

public class C1 : I1<C1>
{
    public static C1 operator " + op + @"(C1 x) => default;
}

public class C2 : I1<C2>
{
    static C2 I1<C2>.operator " + op + @"(C2 x) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (7,19): error CS0535: 'C1' does not implement interface member 'I1<C1>.operator checked --(C1)'
                // public class C1 : I1<C1>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C1>").WithArguments("C1", "I1<C1>.operator checked " + op + "(C1)").WithLocation(7, 19),
                // (12,19): error CS0535: 'C2' does not implement interface member 'I1<C2>.operator checked --(C2)'
                // public class C2 : I1<C2>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C2>").WithArguments("C2", "I1<C2>.operator checked " + op + "(C2)").WithLocation(12, 19),
                // (14,31): error CS0539: 'C2.operator --(C2)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static C2 I1<C2>.operator --(C2 x) => default;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, op).WithArguments("C2.operator " + op + "(C2)").WithLocation(14, 31)
                );
        }

        [Theory]
        [InlineData("-")]
        [InlineData("++")]
        [InlineData("--")]
        public void ImplementVirtualStaticUnaryOperator_16(string op)
        {
            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    virtual static T operator checked " + op + @"(T x) => throw null;
}

public class C1 : I1<C1>
{
    public static C1 operator " + op + @"(C1 x) => default;
}

public class C2 : I1<C2>
{
    static C2 I1<C2>.operator " + op + @"(C2 x) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (14,31): error CS0539: 'C2.operator --(C2)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static C2 I1<C2>.operator --(C2 x) => default;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, op).WithArguments("C2.operator " + op + "(C2)").WithLocation(14, 31)
                );
        }

        [Theory]
        [InlineData("-")]
        [InlineData("++")]
        [InlineData("--")]
        public void ImplementAbstractStaticUnaryOperator_17(string op)
        {
            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    abstract static T operator " + op + @"(T x);
}

public class C1 : I1<C1>
{
    public static C1 operator checked " + op + @"(C1 x) => default;
}

public class C2 : I1<C2>
{
    static C2 I1<C2>.operator checked" + op + @"(C2 x) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (7,19): error CS0535: 'C1' does not implement interface member 'I1<C1>.operator --(C1)'
                // public class C1 : I1<C1>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C1>").WithArguments("C1", "I1<C1>.operator " + op + "(C1)").WithLocation(7, 19),
                // (12,19): error CS0535: 'C2' does not implement interface member 'I1<C2>.operator --(C2)'
                // public class C2 : I1<C2>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C2>").WithArguments("C2", "I1<C2>.operator " + op + "(C2)").WithLocation(12, 19),
                // (14,38): error CS0539: 'C2.operator checked --(C2)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static C2 I1<C2>.operator checked--(C2 x) => default;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, op).WithArguments("C2.operator checked " + op + "(C2)").WithLocation(14, 38)
                );
        }

        [Theory]
        [InlineData("-")]
        [InlineData("++")]
        [InlineData("--")]
        public void ImplementVirtualStaticUnaryOperator_17(string op)
        {
            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    virtual static T operator " + op + @"(T x) => throw null;
}

public class C1 : I1<C1>
{
    public static C1 operator checked " + op + @"(C1 x) => default;
}

public class C2 : I1<C2>
{
    static C2 I1<C2>.operator checked" + op + @"(C2 x) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (14,38): error CS0539: 'C2.operator checked --(C2)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static C2 I1<C2>.operator checked--(C2 x) => default;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, op).WithArguments("C2.operator checked " + op + "(C2)").WithLocation(14, 38)
                );
        }

        [Theory]
        [InlineData("%", "op_Modulus")]
        [InlineData("&", "op_BitwiseAnd")]
        [InlineData("|", "op_BitwiseOr")]
        [InlineData("^", "op_ExclusiveOr")]
        [InlineData("<<", "op_LeftShift")]
        [InlineData(">>", "op_RightShift")]
        [InlineData(">>>", "op_UnsignedRightShift")]
        [InlineData("==", "op_Equality")]
        [InlineData("!=", "op_Inequality")]
        [InlineData(">", "op_GreaterThan")]
        [InlineData("<", "op_LessThan")]
        [InlineData(">=", "op_GreaterThanOrEqual")]
        [InlineData("<=", "op_LessThanOrEqual")]
        public void BinaryOperators_Checked_Unsupported_01(string op, string name)
        {
            binaryOperators_Checked_Unsupported_01(op, name, isVirtual: false);
            binaryOperators_Checked_Unsupported_01(op, name, isVirtual: true);

            void binaryOperators_Checked_Unsupported_01(string op, string name, bool isVirtual)
            {
                var (modifier, body) = GetModifierAndBody(isVirtual);

                var source1 =
@"
interface C 
{
    public static " + modifier + @" C operator checked " + op + @"(C x, int y)" + body + @"
}
";

                var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                     parseOptions: TestOptions.RegularPreview,
                                                     targetFramework: _supportingFramework);

                compilation1.GetDiagnostics().Where(d => d.Code is not ((int)ErrorCode.ERR_OperatorNeedsMatch or (int)ErrorCode.WRN_EqualityOpWithoutEquals or
                                                                        (int)ErrorCode.WRN_EqualityOpWithoutGetHashCode or (int)ErrorCode.ERR_BadAbstractEqualityOperatorSignature)).Verify(
                    // (4,39): error CS9150: User-defined operator '%' cannot be declared checked
                    //     public static abstract C operator checked %(C x, int y);
                    Diagnostic(ErrorCode.ERR_OperatorCantBeChecked, "checked").WithArguments(op).WithLocation(4, 39)
                    );

                var c = compilation1.SourceModule.GlobalNamespace.GetTypeMember("C");
                var opSymbol = c.GetMembers().OfType<MethodSymbol>().Where(m => m.MethodKind != MethodKind.Constructor).Single();

                Assert.Equal(MethodKind.UserDefinedOperator, opSymbol.MethodKind);
                Assert.Equal(name, opSymbol.Name);
                Assert.Equal("C C." + name + "(C x, System.Int32 y)", opSymbol.ToTestDisplayString());
                Assert.Equal("C.operator " + op + "(C, int)", opSymbol.ToDisplayString());
            }
        }

        [Theory]
        [InlineData("+")]
        [InlineData("-")]
        [InlineData("*")]
        [InlineData("/")]
        public void ImplementAbstractStaticBinaryOperator_23(string op)
        {
            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    abstract static T operator checked " + op + @"(T x, int y);
}

public class C1 : I1<C1>
{
    public static C1 operator " + op + @"(C1 x, int y) => default;
}

public class C2 : I1<C2>
{
    static C2 I1<C2>.operator " + op + @"(C2 x, int y) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (7,19): error CS0535: 'C1' does not implement interface member 'I1<C1>.operator checked -(C1, int)'
                // public class C1 : I1<C1>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C1>").WithArguments("C1", "I1<C1>.operator checked " + op + "(C1, int)").WithLocation(7, 19),
                // (12,19): error CS0535: 'C2' does not implement interface member 'I1<C2>.operator checked -(C2, int)'
                // public class C2 : I1<C2>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C2>").WithArguments("C2", "I1<C2>.operator checked " + op + "(C2, int)").WithLocation(12, 19),
                // (14,31): error CS0539: 'C2.operator -(C2, int)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static C2 I1<C2>.operator -(C2 x, int y) => default;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, op).WithArguments("C2.operator " + op + "(C2, int)").WithLocation(14, 31)
                );
        }

        [Theory]
        [InlineData("+")]
        [InlineData("-")]
        [InlineData("*")]
        [InlineData("/")]
        public void ImplementVirtualStaticBinaryOperator_23(string op)
        {
            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    virtual static T operator checked " + op + @"(T x, int y) => throw null;
}

public class C1 : I1<C1>
{
    public static C1 operator " + op + @"(C1 x, int y) => default;
}

public class C2 : I1<C2>
{
    static C2 I1<C2>.operator " + op + @"(C2 x, int y) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (14,31): error CS0539: 'C2.operator -(C2, int)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static C2 I1<C2>.operator -(C2 x, int y) => default;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, op).WithArguments("C2.operator " + op + "(C2, int)").WithLocation(14, 31)
                );
        }

        [Theory]
        [InlineData("+")]
        [InlineData("-")]
        [InlineData("*")]
        [InlineData("/")]
        public void ImplementAbstractStaticBinaryOperator_24(string op)
        {
            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    abstract static T operator " + op + @"(T x, int y);
}

public class C1 : I1<C1>
{
    public static C1 operator checked " + op + @"(C1 x, int y) => default;
}

public class C2 : I1<C2>
{
    static C2 I1<C2>.operator checked" + op + @"(C2 x, int y) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (7,19): error CS0535: 'C1' does not implement interface member 'I1<C1>.operator -(C1, int)'
                // public class C1 : I1<C1>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C1>").WithArguments("C1", "I1<C1>.operator " + op + "(C1, int)").WithLocation(7, 19),
                // (12,19): error CS0535: 'C2' does not implement interface member 'I1<C2>.operator -(C2, int)'
                // public class C2 : I1<C2>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C2>").WithArguments("C2", "I1<C2>.operator " + op + "(C2, int)").WithLocation(12, 19),
                // (14,38): error CS0539: 'C2.operator checked -(C2, int)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static C2 I1<C2>.operator checked-(C2 x, int y) => default;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, op).WithArguments("C2.operator checked " + op + "(C2, int)").WithLocation(14, 38)
                );
        }

        [Theory]
        [InlineData("+")]
        [InlineData("-")]
        [InlineData("*")]
        [InlineData("/")]
        public void ImplementVirtualStaticBinaryOperator_24(string op)
        {
            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    virtual static T operator " + op + @"(T x, int y) => throw null;
}

public class C1 : I1<C1>
{
    public static C1 operator checked " + op + @"(C1 x, int y) => default;
}

public class C2 : I1<C2>
{
    static C2 I1<C2>.operator checked" + op + @"(C2 x, int y) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (14,38): error CS0539: 'C2.operator checked -(C2, int)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static C2 I1<C2>.operator checked-(C2 x, int y) => default;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, op).WithArguments("C2.operator checked " + op + "(C2, int)").WithLocation(14, 38)
                );
        }

        [Fact]
        public void ConversionOperators_Checked_Unsupported_01()
        {
            var source1 =
@"
interface C<T> where T : C<T> 
{
    public static abstract implicit operator checked int(T x);
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics(
                // (4,46): error CS9151: An 'implicit' user-defined conversion operator cannot be declared checked
                //     public static abstract implicit operator checked int(T x);
                Diagnostic(ErrorCode.ERR_ImplicitConversionOperatorCantBeChecked, "checked").WithLocation(4, 46)
                );

            var c = compilation1.SourceModule.GlobalNamespace.GetTypeMember("C");
            var opSymbol = c.GetMembers().OfType<MethodSymbol>().Where(m => m.MethodKind != MethodKind.Constructor).Single();

            Assert.Equal(MethodKind.Conversion, opSymbol.MethodKind);
            Assert.Equal("op_Implicit", opSymbol.Name);
            Assert.Equal("System.Int32 C<T>.op_Implicit(T x)", opSymbol.ToTestDisplayString());
            Assert.Equal("C<T>.implicit operator int(T)", opSymbol.ToDisplayString());
        }

        [Fact]
        public void ImplementAbstractStaticConversionOperator_21()
        {
            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    abstract static explicit operator checked int(T x);
}

public class C1 : I1<C1>
{
    public static explicit operator int(C1 x) => default;
}

public class C2 : I1<C2>
{
    static explicit I1<C2>.operator int(C2 x) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (7,19): error CS0535: 'C1' does not implement interface member 'I1<C1>.explicit operator checked int(C1)'
                // public class C1 : I1<C1>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C1>").WithArguments("C1", "I1<C1>.explicit operator checked int(C1)").WithLocation(7, 19),
                // (12,19): error CS0535: 'C2' does not implement interface member 'I1<C2>.explicit operator checked int(C2)'
                // public class C2 : I1<C2>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C2>").WithArguments("C2", "I1<C2>.explicit operator checked int(C2)").WithLocation(12, 19),
                // (14,37): error CS0539: 'C2.explicit operator int(C2)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static explicit I1<C2>.operator int(C2 x) => default;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "int").WithArguments("C2.explicit operator int(C2)").WithLocation(14, 37)
                );
        }

        [Fact]
        public void ImplementVirtualStaticConversionOperator_21()
        {
            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    virtual static explicit operator checked int(T x) => default;
}

public class C1 : I1<C1>
{
    public static explicit operator int(C1 x) => default;
}

public class C2 : I1<C2>
{
    static explicit I1<C2>.operator int(C2 x) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (14,37): error CS0539: 'C2.explicit operator int(C2)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static explicit I1<C2>.operator int(C2 x) => default;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "int").WithArguments("C2.explicit operator int(C2)").WithLocation(14, 37)
                );
        }

        [Fact]
        public void ImplementAbstractStaticConversionOperator_22()
        {
            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    abstract static explicit operator int(T x);
}

public class C1 : I1<C1>
{
    public static explicit operator checked int(C1 x) => default;
}

public class C2 : I1<C2>
{
    static explicit I1<C2>.operator checked int(C2 x) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (7,19): error CS0535: 'C1' does not implement interface member 'I1<C1>.explicit operator int(C1)'
                // public class C1 : I1<C1>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C1>").WithArguments("C1", "I1<C1>.explicit operator int(C1)").WithLocation(7, 19),
                // (12,19): error CS0535: 'C2' does not implement interface member 'I1<C2>.explicit operator int(C2)'
                // public class C2 : I1<C2>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C2>").WithArguments("C2", "I1<C2>.explicit operator int(C2)").WithLocation(12, 19),
                // (14,45): error CS0539: 'C2.explicit operator checked int(C2)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static explicit I1<C2>.operator checked int(C2 x) => default;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "int").WithArguments("C2.explicit operator checked int(C2)").WithLocation(14, 45)
                );
        }

        [Fact]
        public void ImplementVirtualStaticConversionOperator_22()
        {
            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    virtual static explicit operator int(T x) => default;
}

public class C1 : I1<C1>
{
    public static explicit operator checked int(C1 x) => default;
}

public class C2 : I1<C2>
{
    static explicit I1<C2>.operator checked int(C2 x) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (14,45): error CS0539: 'C2.explicit operator checked int(C2)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static explicit I1<C2>.operator checked int(C2 x) => default;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "int").WithArguments("C2.explicit operator checked int(C2)").WithLocation(14, 45)
                );
        }

        [Fact]
        public void ImplementAbstractStaticConversionOperator_23()
        {
            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    abstract static explicit operator checked int(T x);
}

public class C1 : I1<C1>
{
    public static implicit operator int(C1 x) => default;
}

public class C2 : I1<C2>
{
    static implicit I1<C2>.operator int(C2 x) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (7,19): error CS0535: 'C1' does not implement interface member 'I1<C1>.explicit operator checked int(C1)'
                // public class C1 : I1<C1>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C1>").WithArguments("C1", "I1<C1>.explicit operator checked int(C1)").WithLocation(7, 19),
                // (12,19): error CS0535: 'C2' does not implement interface member 'I1<C2>.explicit operator checked int(C2)'
                // public class C2 : I1<C2>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C2>").WithArguments("C2", "I1<C2>.explicit operator checked int(C2)").WithLocation(12, 19),
                // (14,37): error CS0539: 'C2.implicit operator int(C2)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static implicit I1<C2>.operator int(C2 x) => default;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "int").WithArguments("C2.implicit operator int(C2)").WithLocation(14, 37)
                );
        }

        [Fact]
        public void ImplementVirtualStaticConversionOperator_23()
        {
            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    virtual static explicit operator checked int(T x) => default;
}

public class C1 : I1<C1>
{
    public static implicit operator int(C1 x) => default;
}

public class C2 : I1<C2>
{
    static implicit I1<C2>.operator int(C2 x) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (14,37): error CS0539: 'C2.implicit operator int(C2)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static implicit I1<C2>.operator int(C2 x) => default;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "int").WithArguments("C2.implicit operator int(C2)").WithLocation(14, 37)
                );
        }

        [Fact]
        public void ImplementAbstractStaticConversionOperator_24()
        {
            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    abstract static implicit operator int(T x);
}

public class C1 : I1<C1>
{
    public static explicit operator checked int(C1 x) => default;
}

public class C2 : I1<C2>
{
    static explicit I1<C2>.operator checked int(C2 x) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (7,19): error CS0535: 'C1' does not implement interface member 'I1<C1>.implicit operator int(C1)'
                // public class C1 : I1<C1>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C1>").WithArguments("C1", "I1<C1>.implicit operator int(C1)").WithLocation(7, 19),
                // (12,19): error CS0535: 'C2' does not implement interface member 'I1<C2>.implicit operator int(C2)'
                // public class C2 : I1<C2>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C2>").WithArguments("C2", "I1<C2>.implicit operator int(C2)").WithLocation(12, 19),
                // (14,45): error CS0539: 'C2.explicit operator checked int(C2)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static explicit I1<C2>.operator checked int(C2 x) => default;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "int").WithArguments("C2.explicit operator checked int(C2)").WithLocation(14, 45)
                );
        }

        [Fact]
        public void ImplementVirtualStaticConversionOperator_24()
        {
            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    virtual static implicit operator int(T x) => default;
}

public class C1 : I1<C1>
{
    public static explicit operator checked int(C1 x) => default;
}

public class C2 : I1<C2>
{
    static explicit I1<C2>.operator checked int(C2 x) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (14,45): error CS0539: 'C2.explicit operator checked int(C2)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static explicit I1<C2>.operator checked int(C2 x) => default;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "int").WithArguments("C2.explicit operator checked int(C2)").WithLocation(14, 45)
                );
        }

        [Fact]
        public void ImplementAbstractStaticConversionOperator_25()
        {
            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    abstract static explicit operator int(T x);
}

public class C1 : I1<C1>
{
    public static implicit operator int(C1 x) => default;
}

public class C2 : I1<C2>
{
    static implicit I1<C2>.operator int(C2 x) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (7,19): error CS0535: 'C1' does not implement interface member 'I1<C1>.explicit operator int(C1)'
                // public class C1 : I1<C1>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C1>").WithArguments("C1", "I1<C1>.explicit operator int(C1)").WithLocation(7, 19),
                // (12,19): error CS0535: 'C2' does not implement interface member 'I1<C2>.explicit operator int(C2)'
                // public class C2 : I1<C2>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C2>").WithArguments("C2", "I1<C2>.explicit operator int(C2)").WithLocation(12, 19),
                // (14,37): error CS0539: 'C2.implicit operator int(C2)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static implicit I1<C2>.operator int(C2 x) => default;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "int").WithArguments("C2.implicit operator int(C2)").WithLocation(14, 37)
                );
        }

        [Fact]
        public void ImplementVirtualStaticConversionOperator_25()
        {
            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    virtual static explicit operator int(T x) => default;
}

public class C1 : I1<C1>
{
    public static implicit operator int(C1 x) => default;
}

public class C2 : I1<C2>
{
    static implicit I1<C2>.operator int(C2 x) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (14,37): error CS0539: 'C2.implicit operator int(C2)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static implicit I1<C2>.operator int(C2 x) => default;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "int").WithArguments("C2.implicit operator int(C2)").WithLocation(14, 37)
                );
        }

        [Fact]
        public void ImplementAbstractStaticConversionOperator_26()
        {
            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    abstract static implicit operator int(T x);
}

public class C1 : I1<C1>
{
    public static explicit operator int(C1 x) => default;
}

public class C2 : I1<C2>
{
    static explicit I1<C2>.operator int(C2 x) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (7,19): error CS0535: 'C1' does not implement interface member 'I1<C1>.implicit operator int(C1)'
                // public class C1 : I1<C1>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C1>").WithArguments("C1", "I1<C1>.implicit operator int(C1)").WithLocation(7, 19),
                // (12,19): error CS0535: 'C2' does not implement interface member 'I1<C2>.implicit operator int(C2)'
                // public class C2 : I1<C2>
                Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C2>").WithArguments("C2", "I1<C2>.implicit operator int(C2)").WithLocation(12, 19),
                // (14,37): error CS0539: 'C2.explicit operator int(C2)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static explicit I1<C2>.operator int(C2 x) => default;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "int").WithArguments("C2.explicit operator int(C2)").WithLocation(14, 37)
                );
        }

        [Fact]
        public void ImplementVirtualStaticConversionOperator_26()
        {
            var source1 =
@"
public interface I1<T> where T : I1<T>
{
    virtual static implicit operator int(T x) => default;
}

public class C1 : I1<C1>
{
    public static explicit operator int(C1 x) => default;
}

public class C2 : I1<C2>
{
    static explicit I1<C2>.operator int(C2 x) => default;
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.GetDiagnostics().Where(d => d.Code is not (int)ErrorCode.ERR_CheckedOperatorNeedsMatch).Verify(
                // (14,37): error CS0539: 'C2.explicit operator int(C2)' in explicit interface declaration is not found among members of the interface that can be implemented
                //     static explicit I1<C2>.operator int(C2 x) => default;
                Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "int").WithArguments("C2.explicit operator int(C2)").WithLocation(14, 37)
                );
        }

        [Fact]
        public void OperatorVsMethod_01()
        {
            var source1 =
@"
public interface I1<T1> where T1 : I1<T1>
{
    abstract static T1 operator +(T1 x, T1 y);
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var source2 =
@"
public interface I2<T2> : I1<T2> where T2 : I2<T2>
{
    abstract static T2 I1<T2>.op_Addition(T2 x, T2 y);
}

public interface I3<T3> : I1<T3> where T3 : I3<T3>
{
    static T3 I1<T3>.op_Addition(T3 x, T3 y) => throw null;
}

public class C4 : I1<C4>
{
    static C4 I1<C4>.op_Addition(C4 x, C4 y) => throw null;
}

public class C5 : I1<C5>
{
    public static C5 op_Addition(C5 x, C5 y) => throw null;
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                    parseOptions: TestOptions.RegularPreview,
                                                    targetFramework: _supportingFramework,
                                                    references: new[] { reference });

                compilation2.VerifyDiagnostics(
                    // (4,31): error CS0539: 'I2<T2>.op_Addition(T2, T2)' in explicit interface declaration is not found among members of the interface that can be implemented
                    //     abstract static T2 I1<T2>.op_Addition(T2 x, T2 y);
                    Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "op_Addition").WithArguments("I2<T2>.op_Addition(T2, T2)").WithLocation(4, 31),
                    // (9,22): error CS0539: 'I3<T3>.op_Addition(T3, T3)' in explicit interface declaration is not found among members of the interface that can be implemented
                    //     static T3 I1<T3>.op_Addition(T3 x, T3 y) => throw null;
                    Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "op_Addition").WithArguments("I3<T3>.op_Addition(T3, T3)").WithLocation(9, 22),
                    // (12,19): error CS0535: 'C4' does not implement interface member 'I1<C4>.operator +(C4, C4)'
                    // public class C4 : I1<C4>
                    Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C4>").WithArguments("C4", "I1<C4>.operator +(C4, C4)").WithLocation(12, 19),
                    // (14,22): error CS0539: 'C4.op_Addition(C4, C4)' in explicit interface declaration is not found among members of the interface that can be implemented
                    //     static C4 I1<C4>.op_Addition(C4 x, C4 y) => throw null;
                    Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "op_Addition").WithArguments("C4.op_Addition(C4, C4)").WithLocation(14, 22),
                    // (17,19): error CS0535: 'C5' does not implement interface member 'I1<C5>.operator +(C5, C5)'
                    // public class C5 : I1<C5>
                    Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C5>").WithArguments("C5", "I1<C5>.operator +(C5, C5)").WithLocation(17, 19)
                    );
            }
        }

        [Fact]
        public void OperatorVsMethod_02()
        {
            var source1 =
@"
public interface I1<T1> where T1 : I1<T1>
{
    abstract static T1 op_Addition(T1 x, T1 y);
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var source2 =
@"
public interface I2<T2> : I1<T2> where T2 : I2<T2>
{
    abstract static T2 I1<T2>.operator +(T2 x, T2 y);
}

public interface I3<T3> : I1<T3> where T3 : I3<T3>
{
    static T3 I1<T3>.operator +(T3 x, T3 y) => throw null;
}

public class C4 : I1<C4>
{
    static C4 I1<C4>.operator +(C4 x, C4 y) => throw null;
}

public class C5 : I1<C5>
{
    public static C5 operator +(C5 x, C5 y) => throw null;
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                    parseOptions: TestOptions.RegularPreview,
                                                    targetFramework: _supportingFramework,
                                                    references: new[] { reference });

                compilation2.VerifyDiagnostics(
                    // (4,40): error CS0539: 'I2<T2>.operator +(T2, T2)' in explicit interface declaration is not found among members of the interface that can be implemented
                    //     abstract static T2 I1<T2>.operator +(T2 x, T2 y);
                    Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "+").WithArguments("I2<T2>.operator +(T2, T2)").WithLocation(4, 40),
                    // (9,31): error CS0539: 'I3<T3>.operator +(T3, T3)' in explicit interface declaration is not found among members of the interface that can be implemented
                    //     static T3 I1<T3>.operator +(T3 x, T3 y) => throw null;
                    Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "+").WithArguments("I3<T3>.operator +(T3, T3)").WithLocation(9, 31),
                    // (12,19): error CS0535: 'C4' does not implement interface member 'I1<C4>.op_Addition(C4, C4)'
                    // public class C4 : I1<C4>
                    Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C4>").WithArguments("C4", "I1<C4>.op_Addition(C4, C4)").WithLocation(12, 19),
                    // (14,31): error CS0539: 'C4.operator +(C4, C4)' in explicit interface declaration is not found among members of the interface that can be implemented
                    //     static C4 I1<C4>.operator +(C4 x, C4 y) => throw null;
                    Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "+").WithArguments("C4.operator +(C4, C4)").WithLocation(14, 31),
                    // (17,19): error CS0535: 'C5' does not implement interface member 'I1<C5>.op_Addition(C5, C5)'
                    // public class C5 : I1<C5>
                    Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C5>").WithArguments("C5", "I1<C5>.op_Addition(C5, C5)").WithLocation(17, 19)
                    );
            }
        }

        [Fact]
        public void OperatorVsMethod_03()
        {
            var source1 =
@"
public interface I1<T1> where T1 : I1<T1>
{
    abstract static implicit operator int(T1 x);
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var source2 =
@"
public interface I2<T2> : I1<T2> where T2 : I2<T2>
{
    abstract static int I1<T2>.op_Implicit(T2 x);
}

public interface I3<T3> : I1<T3> where T3 : I3<T3>
{
    static int I1<T3>.op_Implicit(T3 x) => throw null;
}

public class C4 : I1<C4>
{
    static int I1<C4>.op_Implicit(C4 x) => throw null;
}

public class C5 : I1<C5>
{
    public static int op_Implicit(C5 x) => throw null;
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                    parseOptions: TestOptions.RegularPreview,
                                                    targetFramework: _supportingFramework,
                                                    references: new[] { reference });

                compilation2.VerifyDiagnostics(
                    // (4,32): error CS0539: 'I2<T2>.op_Implicit(T2)' in explicit interface declaration is not found among members of the interface that can be implemented
                    //     abstract static int I1<T2>.op_Implicit(T2 x);
                    Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "op_Implicit").WithArguments("I2<T2>.op_Implicit(T2)").WithLocation(4, 32),
                    // (9,23): error CS0539: 'I3<T3>.op_Implicit(T3)' in explicit interface declaration is not found among members of the interface that can be implemented
                    //     static int I1<T3>.op_Implicit(T3 x) => throw null;
                    Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "op_Implicit").WithArguments("I3<T3>.op_Implicit(T3)").WithLocation(9, 23),
                    // (12,19): error CS0535: 'C4' does not implement interface member 'I1<C4>.implicit operator int(C4)'
                    // public class C4 : I1<C4>
                    Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C4>").WithArguments("C4", "I1<C4>.implicit operator int(C4)").WithLocation(12, 19),
                    // (14,23): error CS0539: 'C4.op_Implicit(C4)' in explicit interface declaration is not found among members of the interface that can be implemented
                    //     static int I1<C4>.op_Implicit(C4 x) => throw null;
                    Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "op_Implicit").WithArguments("C4.op_Implicit(C4)").WithLocation(14, 23),
                    // (17,19): error CS0535: 'C5' does not implement interface member 'I1<C5>.implicit operator int(C5)'
                    // public class C5 : I1<C5>
                    Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C5>").WithArguments("C5", "I1<C5>.implicit operator int(C5)").WithLocation(17, 19)
                    );
            }
        }

        [Fact]
        public void OperatorVsMethod_04()
        {
            var source1 =
@"
public interface I1<T1> where T1 : I1<T1>
{
    abstract static int op_Implicit(T1 x);
}
";

            var compilation1 = CreateCompilation(source1, options: TestOptions.DebugDll,
                                                 parseOptions: TestOptions.RegularPreview,
                                                 targetFramework: _supportingFramework);

            compilation1.VerifyDiagnostics();

            var source2 =
@"
public interface I2<T2> : I1<T2> where T2 : I2<T2>
{
    abstract static implicit I1<T2>.operator int(T2 x);
}

public interface I3<T3> : I1<T3> where T3 : I3<T3>
{
    static implicit I1<T3>.operator int(T3 x) => throw null;
}

public class C4 : I1<C4>
{
    static implicit I1<C4>.operator int(C4 x) => throw null;
}

public class C5 : I1<C5>
{
    public static implicit operator int(C5 x) => throw null;
}
";

            foreach (var reference in new[] { compilation1.ToMetadataReference(), compilation1.EmitToImageReference() })
            {
                var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll,
                                                    parseOptions: TestOptions.RegularPreview,
                                                    targetFramework: _supportingFramework,
                                                    references: new[] { reference });

                compilation2.VerifyDiagnostics(
                    // (4,46): error CS0539: 'I2<T2>.implicit operator int(T2)' in explicit interface declaration is not found among members of the interface that can be implemented
                    //     abstract static implicit I1<T2>.operator int(T2 x);
                    Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "int").WithArguments("I2<T2>.implicit operator int(T2)").WithLocation(4, 46),
                    // (9,37): error CS0539: 'I3<T3>.implicit operator int(T3)' in explicit interface declaration is not found among members of the interface that can be implemented
                    //     static implicit I1<T3>.operator int(T3 x) => throw null;
                    Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "int").WithArguments("I3<T3>.implicit operator int(T3)").WithLocation(9, 37),
                    // (12,19): error CS0535: 'C4' does not implement interface member 'I1<C4>.op_Implicit(C4)'
                    // public class C4 : I1<C4>
                    Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C4>").WithArguments("C4", "I1<C4>.op_Implicit(C4)").WithLocation(12, 19),
                    // (14,37): error CS0539: 'C4.implicit operator int(C4)' in explicit interface declaration is not found among members of the interface that can be implemented
                    //     static implicit I1<C4>.operator int(C4 x) => throw null;
                    Diagnostic(ErrorCode.ERR_InterfaceMemberNotFound, "int").WithArguments("C4.implicit operator int(C4)").WithLocation(14, 37),
                    // (17,19): error CS0535: 'C5' does not implement interface member 'I1<C5>.op_Implicit(C5)'
                    // public class C5 : I1<C5>
                    Diagnostic(ErrorCode.ERR_UnimplementedInterfaceMember, "I1<C5>").WithArguments("C5", "I1<C5>.op_Implicit(C5)").WithLocation(17, 19)
                    );
            }
        }

        [Fact, WorkItem(65685, "https://github.com/dotnet/roslyn/issues/65685")]
        public void NoDuplicateConversionForImplicitAndExplicitImplementations()
        {
            CreateCompilation("""
                interface I1<T> where T : I1<T>
                {
                    static abstract T operator +(T a, T b);
                    static abstract T operator +(T a);
                }

                interface I2<T> where T : I2<T>
                {
                    static abstract implicit operator int(T t);
                }

                interface I3<T> where T : I3<T>
                {
                    static abstract explicit operator int(T t);
                    static abstract explicit operator checked int(T t);
                }

                class C12_1 : I1<C12_1>, I2<C12_1>
                {
                    static C12_1 I1<C12_1>.operator +(C12_1 a, C12_1 b) => a + b;
                    public static C12_1 operator +(C12_1 a, C12_1 b) => a;

                    static C12_1 I1<C12_1>.operator +(C12_1 a) => a;
                    public static C12_1 operator +(C12_1 a) => a;

                    static implicit I2<C12_1>.operator int(C12_1 t) => 1;
                    public static implicit operator int(C12_1 t) => 42;
                }

                class C12_2 : I1<C12_2>, I2<C12_2>
                {
                    public static C12_2 operator +(C12_2 a, C12_2 b) => a;
                    static C12_2 I1<C12_2>.operator +(C12_2 a, C12_2 b) => a + b;

                    public static C12_2 operator +(C12_2 a) => a;
                    static C12_2 I1<C12_2>.operator +(C12_2 a) => a;

                    public static implicit operator int(C12_2 t) => 42;
                    static implicit I2<C12_2>.operator int(C12_2 t) => 1;
                }

                class C3_1 : I3<C3_1>
                {
                    static explicit I3<C3_1>.operator int(C3_1 t) => 1;
                    public static explicit operator int(C3_1 t) => 1;

                    static explicit I3<C3_1>.operator checked int(C3_1 t) => 1;
                    public static explicit operator checked int(C3_1 t) => 1;
                }

                class C3_2 : I3<C3_2>
                {
                    public static explicit operator int(C3_2 t) => 1;
                    static explicit I3<C3_2>.operator int(C3_2 t) => 1;

                    public static explicit operator checked int(C3_2 t) => 1;
                    static explicit I3<C3_2>.operator checked int(C3_2 t) => 1;
                }

                class C23_1 : I2<C23_1>, I3<C23_1>
                {
                    static implicit I2<C23_1>.operator int(C23_1 t) => 1;
                    public static implicit operator int(C23_1 t) => 42;

                    static explicit I3<C23_1>.operator int(C23_1 t) => 1;
                    public static explicit operator int(C23_1 t) => 1;

                    static explicit I3<C23_1>.operator checked int(C23_1 t) => 1;
                    public static explicit operator checked int(C23_1 t) => 1;
                }

                class C23_2 : I2<C23_2>, I3<C23_2>
                {
                    public static implicit operator int(C23_2 t) => 42;
                    static implicit I2<C23_2>.operator int(C23_2 t) => 1;

                    public static explicit operator int(C23_2 t) => 1;
                    static explicit I3<C23_2>.operator int(C23_2 t) => 1;

                    public static explicit operator checked int(C23_2 t) => 1;
                    static explicit I3<C23_2>.operator checked int(C23_2 t) => 1;
                }
                """, options: TestOptions.DebugDll, parseOptions: TestOptions.RegularPreview, targetFramework: _supportingFramework).VerifyDiagnostics(
                    // (66,37): error CS0557: Duplicate user-defined conversion in type 'C23_1'
                    //     public static explicit operator int(C23_1 t) => 1;
                    Diagnostic(ErrorCode.ERR_DuplicateConversionInClass, "int").WithArguments("C23_1").WithLocation(66, 37),
                    // (69,45): error CS0557: Duplicate user-defined conversion in type 'C23_1'
                    //     public static explicit operator checked int(C23_1 t) => 1;
                    Diagnostic(ErrorCode.ERR_DuplicateConversionInClass, "int").WithArguments("C23_1").WithLocation(69, 45),
                    // (77,37): error CS0557: Duplicate user-defined conversion in type 'C23_2'
                    //     public static explicit operator int(C23_2 t) => 1;
                    Diagnostic(ErrorCode.ERR_DuplicateConversionInClass, "int").WithArguments("C23_2").WithLocation(77, 37),
                    // (80,45): error CS0557: Duplicate user-defined conversion in type 'C23_2'
                    //     public static explicit operator checked int(C23_2 t) => 1;
                    Diagnostic(ErrorCode.ERR_DuplicateConversionInClass, "int").WithArguments("C23_2").WithLocation(80, 45)
                );
        }

        [Fact]
        [WorkItem(66516, "https://github.com/dotnet/roslyn/issues/66516")]
        public void AbstractEntryPoint()
        {
            CreateCompilation("""
                interface IProgram
                {
                    static abstract void Main();
                }
                """, options: TestOptions.DebugExe, parseOptions: TestOptions.RegularPreview, targetFramework: _supportingFramework).VerifyDiagnostics(
                    // error CS5001: Program does not contain a static 'Main' method suitable for an entry point
                    Diagnostic(ErrorCode.ERR_NoEntryPoint).WithLocation(1, 1)
                );
        }

        [Fact]
        [WorkItem(66516, "https://github.com/dotnet/roslyn/issues/66516")]
        public void VirtualEntryPoint()
        {
            CreateCompilation("""
                using System;

                interface IProgram
                {
                    static virtual void Main() => Console.WriteLine("Hello World!, from IProgram");
                }
                """, options: TestOptions.DebugExe, parseOptions: TestOptions.RegularPreview, targetFramework: _supportingFramework).VerifyDiagnostics(
                    // error CS5001: Program does not contain a static 'Main' method suitable for an entry point
                    Diagnostic(ErrorCode.ERR_NoEntryPoint).WithLocation(1, 1)
                );
        }

        [Fact]
        [WorkItem(66516, "https://github.com/dotnet/roslyn/issues/66516")]
        public void AbstractEntryPointWithImplementation()
        {
            CompileAndVerify("""
                using System;

                interface IProgram
                {
                    static abstract void Main();
                }

                class Program : IProgram
                {
                    public static void Main() => Console.WriteLine("Hello World!");
                }
                """,
                expectedOutput: Execute(false) ? "Hello World!" : null,
                options: TestOptions.DebugExe,
                parseOptions: TestOptions.RegularPreview,
                targetFramework: _supportingFramework,
                verify: Verification.Skipped);
        }

        [Fact]
        [WorkItem(66516, "https://github.com/dotnet/roslyn/issues/66516")]
        public void AbstractEntryPointWithExplicitImplementation()
        {
            CreateCompilation("""
                using System;

                interface IProgram
                {
                    static abstract void Main();
                }

                class Program : IProgram
                {
                    static void IProgram.Main() => Console.WriteLine("Hello World!");
                }
                """, options: TestOptions.DebugExe, parseOptions: TestOptions.RegularPreview, targetFramework: _supportingFramework).VerifyDiagnostics(
                    // error CS5001: Program does not contain a static 'Main' method suitable for an entry point
                    Diagnostic(ErrorCode.ERR_NoEntryPoint).WithLocation(1, 1)
                );
        }

        [Fact]
        [WorkItem(66516, "https://github.com/dotnet/roslyn/issues/66516")]
        public void VirtualEntryPointWithImplementation()
        {
            CompileAndVerify("""
                using System;

                interface IProgram
                {
                    static virtual void Main() => Console.WriteLine("Hello World!, from IProgram");
                }

                class Program : IProgram
                {
                    public static void Main() => Console.WriteLine("Hello World!");
                }
                """,
                expectedOutput: Execute(false) ? "Hello World!" : null,
                options: TestOptions.DebugExe,
                parseOptions: TestOptions.RegularPreview,
                targetFramework: _supportingFramework,
                verify: Verification.Skipped);
        }

        [Fact]
        [WorkItem(66516, "https://github.com/dotnet/roslyn/issues/66516")]
        public void VirtualEntryPointWithExplicitImplementation()
        {
            CreateCompilation("""
                using System;

                interface IProgram
                {
                    static virtual void Main() => Console.WriteLine("Hello World!, from IProgram");
                }

                class Program : IProgram
                {
                    static void IProgram.Main() => Console.WriteLine("Hello World!");
                }
                """, options: TestOptions.DebugExe, parseOptions: TestOptions.RegularPreview, targetFramework: _supportingFramework).VerifyDiagnostics(
                    // error CS5001: Program does not contain a static 'Main' method suitable for an entry point
                    Diagnostic(ErrorCode.ERR_NoEntryPoint).WithLocation(1, 1)
                );
        }

        [WorkItem("https://github.com/dotnet/roslyn/issues/68767")]
        [Theory]
        [InlineData("I1", "+", "(in I1 x)")]
        [InlineData("I1", "-", "(in I1 x)")]
        [InlineData("I1", "!", "(in I1 x)")]
        [InlineData("I1", "~", "(in I1 x)")]
        [InlineData("I1", "++", "(in I1 x)")]
        [InlineData("I1", "--", "(in I1 x)")]
        [InlineData("I1", "+", "(in I1 x, I1 y)")]
        [InlineData("I1", "-", "(in I1 x, I1 y)")]
        [InlineData("I1", "*", "(in I1 x, I1 y)")]
        [InlineData("I1", "/", "(in I1 x, I1 y)")]
        [InlineData("I1", "%", "(in I1 x, I1 y)")]
        [InlineData("I1", "&", "(in I1 x, I1 y)")]
        [InlineData("I1", "|", "(in I1 x, I1 y)")]
        [InlineData("I1", "^", "(in I1 x, I1 y)")]
        [InlineData("I1", "<<", "(in I1 x, int y)")]
        [InlineData("I1", ">>", "(in I1 x, int y)")]
        [InlineData("I1", ">>>", "(in I1 x, int y)")]
        [InlineData("I1", "checked -", "(in I1 x)")]
        [InlineData("I1", "checked ++", "(in I1 x)")]
        [InlineData("I1", "checked --", "(in I1 x)")]
        [InlineData("I1", "checked +", "(in I1 x, I1 y)")]
        [InlineData("I1", "checked -", "(in I1 x, I1 y)")]
        [InlineData("I1", "checked *", "(in I1 x, I1 y)")]
        [InlineData("I1", "checked /", "(in I1 x, I1 y)")]
        public void InParameters_01(string type, string op, string paramList)
        {
            string source2 = InParameter_01_Source2(type, op, paramList);
            InParameter_01_Validate(InParameter_01_Source1_Abstract(type, op, paramList), source2);
            InParameter_01_Validate(InParameter_01_Source1_Virtual(type, op, paramList), source2);
        }

        private static string InParameter_01_Source1_Abstract(string type, string op, string paramList)
        {
            var source1 =
@"
public partial interface I1
{
    abstract static " + type + " operator " + op + " " + paramList + @";
}
";

            if (op.StartsWith("checked "))
            {
                source1 +=
@"
partial interface I1
{
    abstract static " + type + " operator " + op.Substring(8) + " " + paramList + @";
}
";
            }

            return source1;
        }

        private static string InParameter_01_Source1_Virtual(string type, string op, string paramList)
        {
            var source1 =
@"
public partial interface I1
{
    virtual static " + type + " operator " + op + " " + paramList + @" => throw null;
}
";

            if (op.StartsWith("checked "))
            {
                source1 +=
@"
partial interface I1
{
    virtual static " + type + " operator " + op.Substring(8) + " " + paramList + @" => throw null;
}
";
            }

            return source1;
        }

        private static string InParameter_01_Source2(string type, string op, string paramList)
        {
            var source2 =
@"
partial class C1 : I1
{
    static " + type + " I1.operator " + op + " " + paramList + @" => throw null;
}
";

            if (op.StartsWith("checked "))
            {
                source2 +=
@"
partial class C1
{
    static " + type + " I1.operator " + op.Substring(8) + " " + paramList + @" => throw null;
}
";
            }

            return source2;
        }

        private void InParameter_01_Validate(string source1, string source2)
        {
            var compilation1 = CreateCompilation(source1 + source2, options: TestOptions.DebugDll,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll, references: new[] { compilation1.ToMetadataReference() },
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation2, verify: Verification.Skipped).VerifyDiagnostics();

            var compilation3 = CreateCompilation(source2, options: TestOptions.DebugDll, references: new[] { compilation1.EmitToImageReference() },
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation3, verify: Verification.Skipped).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                foreach (var m01 in module.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<MethodSymbol>())
                {
                    var modifier = m01.Parameters.First().RefCustomModifiers.Single();
                    Assert.Equal("System.Runtime.InteropServices.InAttribute", modifier.Modifier.ToTestDisplayString());
                    Assert.False(modifier.IsOptional);

                    if (m01.ParameterCount > 1)
                    {
                        Assert.Empty(m01.Parameters.Last().RefCustomModifiers);
                    }
                }
            }
        }

        [WorkItem("https://github.com/dotnet/roslyn/issues/68767")]
        [Theory]
        [InlineData("I1", "+", "(I1 x, in I1 y)")]
        [InlineData("I1", "-", "(I1 x, in I1 y)")]
        [InlineData("I1", "*", "(I1 x, in I1 y)")]
        [InlineData("I1", "/", "(I1 x, in I1 y)")]
        [InlineData("I1", "%", "(I1 x, in I1 y)")]
        [InlineData("I1", "&", "(I1 x, in I1 y)")]
        [InlineData("I1", "|", "(I1 x, in I1 y)")]
        [InlineData("I1", "^", "(I1 x, in I1 y)")]
        [InlineData("I1", "<<", "(I1 x, in int y)")]
        [InlineData("I1", ">>", "(I1 x, in int y)")]
        [InlineData("I1", ">>>", "(I1 x, in int y)")]
        [InlineData("I1", "checked +", "(I1 x, in I1 y)")]
        [InlineData("I1", "checked -", "(I1 x, in I1 y)")]
        [InlineData("I1", "checked *", "(I1 x, in I1 y)")]
        [InlineData("I1", "checked /", "(I1 x, in I1 y)")]
        public void InParameters_02(string type, string op, string paramList)
        {
            string source2 = InParameter_01_Source2(type, op, paramList);
            InParameter_02_Validate(InParameter_01_Source1_Abstract(type, op, paramList), source2);
            InParameter_02_Validate(InParameter_01_Source1_Virtual(type, op, paramList), source2);
        }

        private void InParameter_02_Validate(string source1, string source2)
        {
            var compilation1 = CreateCompilation(source1 + source2, options: TestOptions.DebugDll,
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation1, sourceSymbolValidator: validate, symbolValidator: validate, verify: Verification.Skipped).VerifyDiagnostics();

            var compilation2 = CreateCompilation(source2, options: TestOptions.DebugDll, references: new[] { compilation1.ToMetadataReference() },
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation2, verify: Verification.Skipped).VerifyDiagnostics();

            var compilation3 = CreateCompilation(source2, options: TestOptions.DebugDll, references: new[] { compilation1.EmitToImageReference() },
                                                 targetFramework: _supportingFramework);

            CompileAndVerify(compilation3, verify: Verification.Skipped).VerifyDiagnostics();

            void validate(ModuleSymbol module)
            {
                foreach (var m01 in module.GlobalNamespace.GetTypeMember("I1").GetMembers().OfType<MethodSymbol>())
                {
                    var modifier = m01.Parameters.Last().RefCustomModifiers.Single();
                    Assert.Equal("System.Runtime.InteropServices.InAttribute", modifier.Modifier.ToTestDisplayString());
                    Assert.False(modifier.IsOptional);

                    Assert.Empty(m01.Parameters.First().RefCustomModifiers);
                }
            }
        }

        [WorkItem("https://github.com/dotnet/roslyn/issues/68767")]
        [Theory]
        [InlineData("bool", "true", "false", "(in I1<T> x)")]
        [InlineData("I1<T>", ">", "<", "(in I1<T> x, I1<T> y)")]
        [InlineData("I1<T>", ">=", "<=", "(in I1<T> x, I1<T> y)")]
        [InlineData("T", "==", "!=", "(in T x, T y)")]
        public void InParameters_03(string type, string op1, string op2, string paramList)
        {
            string source2 = InParameter_03_Source2(type, op1, op2, paramList);
            InParameter_01_Validate(InParameter_03_Source1_Abstract(type, op1, op2, paramList), source2);
            InParameter_01_Validate(InParameter_03_Source1_Virtual(type, op1, op2, paramList), source2);
        }

        private static string InParameter_03_Source1_Abstract(string type, string op1, string op2, string paramList)
        {
            var source1 =
@"
public partial interface I1<T> where T : I1<T>
{
    abstract static " + type + " operator " + op1 + " " + paramList + @";
    abstract static " + type + " operator " + op2 + " " + paramList + @";
}
";

            return source1;
        }

        private static string InParameter_03_Source1_Virtual(string type, string op1, string op2, string paramList)
        {
            var source1 =
@"
public partial interface I1<T> where T : I1<T>
{
    virtual static " + type + " operator " + op1 + " " + paramList + @" => throw null;
    virtual static " + type + " operator " + op2 + " " + paramList + @" => throw null;
}
";

            return source1;
        }

        private static string InParameter_03_Source2(string type, string op1, string op2, string paramList)
        {
            var source2 =
@"
partial class C1 : I1<C1>
{
    static " + type + " I1<C1>.operator " + op1 + " " + paramList + @" => throw null;
    static " + type + " I1<C1>.operator " + op2 + " " + paramList + @" => throw null;
}
";

            return source2.Replace("T", "C1");
        }

        [WorkItem("https://github.com/dotnet/roslyn/issues/68767")]
        [Theory]
        [InlineData("I1<T>", ">", "<", "(I1<T> x, in I1<T> y)")]
        [InlineData("I1<T>", ">=", "<=", "(I1<T> x, in I1<T> y)")]
        [InlineData("T", "==", "!=", "(T x, in T y)")]
        public void InParameters_04(string type, string op1, string op2, string paramList)
        {
            string source2 = InParameter_03_Source2(type, op1, op2, paramList);
            InParameter_02_Validate(InParameter_03_Source1_Abstract(type, op1, op2, paramList), source2);
            InParameter_02_Validate(InParameter_03_Source1_Virtual(type, op1, op2, paramList), source2);
        }

        [WorkItem("https://github.com/dotnet/roslyn/issues/68767")]
        [Fact]
        public void InParameters_05()
        {
            var source1_Abstract =
@"
public interface I1<T> where T : I1<T>
{
    abstract static implicit operator int(in T x);
    abstract static explicit operator T(in int x);
    abstract static explicit operator checked T(in int x);
}
";
            var source1_Virtual =
@"
public interface I1<T> where T : I1<T>
{
    virtual static implicit operator int(in T x) => throw null;
    virtual static explicit operator T(in int x) => throw null;
    virtual static explicit operator checked T(in int x) => throw null;
}
";

            var source2 =
@"
partial class C1 : I1<C1>
{
    static implicit I1<C1>.operator int(in C1 x) => throw null;
    static explicit I1<C1>.operator C1(in int x) => throw null;
    static explicit I1<C1>.operator checked C1(in int x) => throw null;
}
";

            InParameter_01_Validate(source1_Abstract, source2);
            InParameter_01_Validate(source1_Virtual, source2);
        }
    }
}