src/harness/harnessIO.ts - main - githubmirror/TypeScript

src/harness/harnessIO.ts
1 592 строки75 KB
Jake Bailey
Remove compiler runner libFiles option entirely (#63060)
28 янв 2026, 23:56
28 янв 2026, 23:56c1592ad
import * as Diff from "diff";
import fs from "fs";
import pathModule from "path";
import * as compiler from "./_namespaces/compiler.js";
import * as documents from "./_namespaces/documents.js";
import * as fakes from "./_namespaces/fakes.js";
import {
    RunnerBase,
    TypeWriterResult,
    TypeWriterWalker,
} from "./_namespaces/Harness.js";
import * as ts from "./_namespaces/ts.js";
import * as Utils from "./_namespaces/Utils.js";
import * as vfs from "./_namespaces/vfs.js";
import * as vpath from "./_namespaces/vpath.js";

export interface IO {
    newLine(): string;
    getCurrentDirectory(): string;
    useCaseSensitiveFileNames(): boolean;
    resolvePath(path: string): string | undefined;
    getFileSize(path: string): number;
    readFile(path: string): string | undefined;
    writeFile(path: string, contents: string): void;
    directoryName(path: string): string | undefined;
    getDirectories(path: string): string[];
    createDirectory(path: string): void;
    fileExists(fileName: string): boolean;
    directoryExists(path: string): boolean;
    deleteFile(fileName: string): void;
    enumerateTestFiles(runner: RunnerBase): string[];
    listFiles(path: string, filter?: RegExp, options?: { recursive?: boolean; }): string[];
    log(text: string): void;
    args(): string[];
    getExecutingFilePath(): string;
    getWorkspaceRoot(): string;
    exit(exitCode?: number): void;
    readDirectory(path: string, extension?: readonly string[], exclude?: readonly string[], include?: readonly string[], depth?: number): readonly string[];
    getAccessibleFileSystemEntries(dirname: string): ts.FileSystemEntries;
    tryEnableSourceMapsForHost?(): void;
    getEnvironmentVariable?(name: string): string;
    getMemoryUsage?(): number | undefined;
    joinPath(...components: string[]): string;
}

export let IO: IO;
export function setHarnessIO(io: IO): void {
    IO = io;
}

// harness always uses one kind of new line
// But note that `parseTestData` in `fourslash.ts` uses "\n"
export const harnessNewLine = "\r\n";

// Root for file paths that are stored in a virtual file system
export const virtualFileSystemRoot = "/";

function createNodeIO(): IO {
    const workspaceRoot = Utils.findUpRoot();

    function deleteFile(path: string) {
        try {
            fs.unlinkSync(path);
        }
        catch { /*ignore*/ }
    }

    function directoryName(path: string) {
        const dirPath = pathModule.dirname(path);
        // Node will just continue to repeat the root path, rather than return null
        return dirPath === path ? undefined : dirPath;
    }

    function joinPath(...components: string[]) {
        return pathModule.join(...components);
    }

    function enumerateTestFiles(runner: RunnerBase) {
        return runner.getTestFiles();
    }

    function listFiles(path: string, spec: RegExp | undefined, options: { recursive?: boolean; } = {}) {
        function filesInFolder(folder: string): string[] {
            const { files, directories } = ts.sys.getAccessibleFileSystemEntries!(folder);
            let paths: string[] = [];
            for (const file of files) {
                const pathToFile = pathModule.join(folder, file);
                if (!spec || file.match(spec)) {
                    paths.push(pathToFile);
                }
            }
            if (options.recursive) {
                for (const dir of directories) {
                    const pathToDir = pathModule.join(folder, dir);
                    paths = paths.concat(filesInFolder(pathToDir));
                }
            }
            return paths;
        }

        return filesInFolder(path);
    }

    function createDirectory(path: string) {
        try {
            fs.mkdirSync(path);
        }
        catch (e) {
            if (e.code === "ENOENT") {
                createDirectory(vpath.dirname(path));
                createDirectory(path);
            }
            else if (!ts.sys.directoryExists(path)) {
                throw e;
            }
        }
    }

    return {
        newLine: () => harnessNewLine,
        getCurrentDirectory: () => ts.sys.getCurrentDirectory(),
        useCaseSensitiveFileNames: () => ts.sys.useCaseSensitiveFileNames,
        resolvePath: (path: string) => ts.sys.resolvePath(path),
        getFileSize: (path: string) => ts.sys.getFileSize!(path),
        readFile: path => ts.sys.readFile(path),
        writeFile: (path, content) => ts.sys.writeFile(path, content),
        directoryName,
        getDirectories: path => ts.sys.getDirectories(path),
        createDirectory,
        fileExists: path => ts.sys.fileExists(path),
        directoryExists: path => ts.sys.directoryExists(path),
        deleteFile,
        listFiles,
        enumerateTestFiles,
        log: s => console.log(s),
        args: () => ts.sys.args,
        getExecutingFilePath: () => ts.sys.getExecutingFilePath(),
        getWorkspaceRoot: () => workspaceRoot,
        exit: exitCode => ts.sys.exit(exitCode),
        readDirectory: (path, extension, exclude, include, depth) => ts.sys.readDirectory(path, extension, exclude, include, depth),
        getAccessibleFileSystemEntries: ts.sys.getAccessibleFileSystemEntries!,
        tryEnableSourceMapsForHost: () => ts.sys.tryEnableSourceMapsForHost && ts.sys.tryEnableSourceMapsForHost(),
        getMemoryUsage: () => ts.sys.getMemoryUsage && ts.sys.getMemoryUsage(),
        getEnvironmentVariable: name => ts.sys.getEnvironmentVariable(name),
        joinPath,
    };
}

export function mockHash(s: string): string {
    return `hash-${s}`;
}

IO = createNodeIO();

if (IO.tryEnableSourceMapsForHost && /^development$/i.test(IO.getEnvironmentVariable!("NODE_ENV"))) {
    IO.tryEnableSourceMapsForHost();
}

export const libFolder = "built/local/";

export type SourceMapEmitterCallback = (
    emittedFile: string,
    emittedLine: number,
    emittedColumn: number,
    sourceFile: string,
    sourceLine: number,
    sourceColumn: number,
    sourceName: string,
) => void;

// Settings
/* eslint-disable prefer-const */
export let userSpecifiedRoot = "";
export let lightMode = false;
/* eslint-enable prefer-const */
export function setLightMode(flag: boolean): void {
    lightMode = flag;
}

/** Functionality for compiling TypeScript code */
export namespace Compiler {
    /** Aggregate various writes into a single array of lines. Useful for passing to the
     *  TypeScript compiler to fill with source code or errors.
     */
    export class WriterAggregator {
        public lines: string[] = [];
        public currentLine: string = undefined!;

        public Write(str: string): void {
            // out of memory usage concerns avoid using + or += if we're going to do any manipulation of this string later
            this.currentLine = [this.currentLine || "", str].join("");
        }

        public WriteLine(str: string): void {
            // out of memory usage concerns avoid using + or += if we're going to do any manipulation of this string later
            this.lines.push([this.currentLine || "", str].join(""));
            this.currentLine = undefined!;
        }

        public Close(): void {
            if (this.currentLine !== undefined) this.lines.push(this.currentLine);
            this.currentLine = undefined!;
        }

        public reset(): void {
            this.lines = [];
            this.currentLine = undefined!;
        }
    }

    export function createSourceFileAndAssertInvariants(
        fileName: string,
        sourceText: string,
        languageVersionOrOptions: ts.ScriptTarget | ts.CreateSourceFileOptions,
    ): ts.SourceFile {
        // We'll only assert invariants outside of light mode.
        const shouldAssertInvariants = !lightMode;

        // Only set the parent nodes if we're asserting invariants.  We don't need them otherwise.
        // Set ParseForTypeErrors like tsc.
        languageVersionOrOptions = typeof languageVersionOrOptions === "object" ? languageVersionOrOptions : { languageVersion: languageVersionOrOptions };
        languageVersionOrOptions = { ...languageVersionOrOptions, jsDocParsingMode: ts.JSDocParsingMode.ParseForTypeErrors };
        const result = ts.createSourceFile(fileName, sourceText, languageVersionOrOptions, /*setParentNodes:*/ shouldAssertInvariants);

        if (shouldAssertInvariants) {
            Utils.assertInvariants(result, /*parent:*/ undefined);
        }

        return result;
    }

    // Cache these between executions so we don't have to re-parse them for every test
    export const fourslashFileName = "fourslash.ts";
    export let fourslashSourceFile: ts.SourceFile;

    export function getCanonicalFileName(fileName: string): string {
        return fileName;
    }

    interface HarnessOptions {
        useCaseSensitiveFileNames?: boolean;
        baselineFile?: string;
        noTypesAndSymbols?: boolean;
        captureSuggestions?: boolean;
    }

    // Additional options not already in ts.optionDeclarations
    const harnessOptionDeclarations: ts.CommandLineOption[] = [
        { name: "allowNonTsExtensions", type: "boolean", defaultValueDescription: false },
        { name: "useCaseSensitiveFileNames", type: "boolean", defaultValueDescription: false },
        { name: "baselineFile", type: "string" },
        { name: "fileName", type: "string" },
        { name: "noErrorTruncation", type: "boolean", defaultValueDescription: false },
        { name: "suppressOutputPathCheck", type: "boolean", defaultValueDescription: false },
        { name: "noImplicitReferences", type: "boolean", defaultValueDescription: false },
        { name: "currentDirectory", type: "string" },
        { name: "symlink", type: "string" },
        { name: "link", type: "string" },
        { name: "noTypesAndSymbols", type: "boolean", defaultValueDescription: false },
        // Emitted js baseline will print full paths for every output file
        { name: "fullEmitPaths", type: "boolean", defaultValueDescription: false },
        { name: "noCheck", type: "boolean", defaultValueDescription: false },
        { name: "reportDiagnostics", type: "boolean", defaultValueDescription: false }, // used to enable error collection in `transpile` baselines
        { name: "captureSuggestions", type: "boolean", defaultValueDescription: false }, // Adds suggestion diagnostics to error baselines
    ];

    let optionsIndex: Map<string, ts.CommandLineOption>;
    function getCommandLineOption(name: string): ts.CommandLineOption | undefined {
        if (!optionsIndex) {
            optionsIndex = new Map<string, ts.CommandLineOption>();
            const optionDeclarations = harnessOptionDeclarations.concat(ts.optionDeclarations);
            for (const option of optionDeclarations) {
                optionsIndex.set(option.name.toLowerCase(), option);
            }
        }
        return optionsIndex.get(name.toLowerCase());
    }

    export function setCompilerOptionsFromHarnessSetting(settings: TestCaseParser.CompilerSettings, options: ts.CompilerOptions & HarnessOptions): void {
        for (const name in settings) {
            if (ts.hasProperty(settings, name)) {
                const value = settings[name];
                if (value === undefined) {
                    throw new Error(`Cannot have undefined value for compiler option '${name}'.`);
                }
                if (name === "typeScriptVersion") {
                    continue;
                }
                const option = getCommandLineOption(name);
                if (option) {
                    const errors: ts.Diagnostic[] = [];
                    options[option.name] = optionValue(option, value, errors);
                    if (errors.length > 0) {
                        throw new Error(`Unknown value '${value}' for compiler option '${name}'.`);
                    }
                }
                else {
                    throw new Error(`Unknown compiler option '${name}'.`);
                }
            }
        }
    }

    function optionValue(option: ts.CommandLineOption, value: string, errors: ts.Diagnostic[]): any {
        switch (option.type) {
            case "boolean":
                return value.toLowerCase() === "true";
            case "string":
                return value;
            case "number": {
                const numverValue = parseInt(value, 10);
                if (isNaN(numverValue)) {
                    throw new Error(`Value must be a number, got: ${JSON.stringify(value)}`);
                }
                return numverValue;
            }
            // If not a primitive, the possible types are specified in what is effectively a map of options.
            case "list":
            case "listOrElement":
                return ts.parseListTypeOption(option, value, errors);
            default:
                return ts.parseCustomTypeOption(option as ts.CommandLineOptionOfCustomType, value, errors);
        }
    }

    export interface TestFile {
        unitName: string;
        content: string;
        fileOptions?: any;
    }

    export type CompileFilesResult = compiler.CompilationResult & { repeat(newOptions: TestCaseParser.CompilerSettings): CompileFilesResult; };

    export function compileFiles(
        inputFiles: TestFile[],
        otherFiles: TestFile[],
        harnessSettings: TestCaseParser.CompilerSettings | undefined,
        compilerOptions: ts.CompilerOptions | undefined,
        // Current directory is needed for rwcRunner to be able to use currentDirectory defined in json file
        currentDirectory: string | undefined,
        symlinks?: vfs.FileSet,
    ): CompileFilesResult {
        const originalCurrentDirectory = currentDirectory;
        const options: ts.CompilerOptions & HarnessOptions = compilerOptions ? ts.cloneCompilerOptions(compilerOptions) : { noResolve: false };
        options.newLine = options.newLine || ts.NewLineKind.CarriageReturnLineFeed;
        options.noErrorTruncation = true;
        options.skipDefaultLibCheck = typeof options.skipDefaultLibCheck === "undefined" ? true : options.skipDefaultLibCheck;

        if (typeof currentDirectory === "undefined") {
            currentDirectory = vfs.srcFolder;
        }

        let typeScriptVersion: string | undefined;

        // Parse settings
        if (harnessSettings) {
            setCompilerOptionsFromHarnessSetting(harnessSettings, options);
            if (ts.isString(harnessSettings.typeScriptVersion) && harnessSettings.typeScriptVersion) {
                typeScriptVersion = harnessSettings.typeScriptVersion;
            }
        }

        const useCaseSensitiveFileNames = options.useCaseSensitiveFileNames !== undefined ? options.useCaseSensitiveFileNames : true;
        // When a tsconfig is present, root names passed to createProgram should already be absolute
        const programFileNames = inputFiles
            .map(file => options.configFile ? ts.getNormalizedAbsolutePath(file.unitName, currentDirectory) : file.unitName)
            .filter(fileName => !ts.fileExtensionIs(fileName, ts.Extension.Json));

        const docs = inputFiles.concat(otherFiles).map(documents.TextDocument.fromTestFile);
        const fs = vfs.createFromFileSystem(IO, !useCaseSensitiveFileNames, { documents: docs, cwd: currentDirectory });
        if (symlinks) {
            fs.apply(symlinks);
        }

        ts.assign(options, ts.convertToOptionsWithAbsolutePaths(options, path => ts.getNormalizedAbsolutePath(path, currentDirectory)));
        const host = new fakes.CompilerHost(fs, options);
        const result = compiler.compileFiles(host, programFileNames, options, typeScriptVersion, harnessSettings?.captureSuggestions === "true");
        result.symlinks = symlinks;
        (result as CompileFilesResult).repeat = newOptions => compileFiles(inputFiles, otherFiles, { ...harnessSettings, ...newOptions }, compilerOptions, originalCurrentDirectory, symlinks);
        return result as CompileFilesResult;
    }

    export interface DeclarationCompilationContext {
        declInputFiles: TestFile[];
        declOtherFiles: TestFile[];
        harnessSettings: TestCaseParser.CompilerSettings & HarnessOptions | undefined;
        options: ts.CompilerOptions;
        currentDirectory: string;
    }

    export function prepareDeclarationCompilationContext(
        inputFiles: readonly TestFile[],
        otherFiles: readonly TestFile[],
        result: compiler.CompilationResult,
        harnessSettings: TestCaseParser.CompilerSettings & HarnessOptions,
        options: ts.CompilerOptions,
        // Current directory is needed for rwcRunner to be able to use currentDirectory defined in json file
        currentDirectory: string | undefined,
    ): DeclarationCompilationContext | undefined {
        if (options.declaration && result.diagnostics.length === 0) {
            if (options.emitDeclarationOnly) {
                if (result.js.size > 0 || (result.dts.size === 0 && !options.noEmit)) {
                    throw new Error("Only declaration files should be generated when emitDeclarationOnly:true");
                }
            }
            else if (result.dts.size !== result.getNumberOfJsFiles(/*includeJson*/ false)) {
                throw new Error("There were no errors and declFiles generated did not match number of js files generated");
            }
        }

        const declInputFiles: TestFile[] = [];
        const declOtherFiles: TestFile[] = [];

        // if the .d.ts is non-empty, confirm it compiles correctly as well
        if (options.declaration && result.diagnostics.length === 0 && result.dts.size > 0) {
            ts.forEach(inputFiles, file => addDtsFile(file, declInputFiles));
            ts.forEach(otherFiles, file => addDtsFile(file, declOtherFiles));
            return { declInputFiles, declOtherFiles, harnessSettings, options, currentDirectory: currentDirectory || harnessSettings.currentDirectory };
        }

        function addDtsFile(file: TestFile, dtsFiles: TestFile[]) {
            if (vpath.isDeclaration(file.unitName) || vpath.isJson(file.unitName)) {
                dtsFiles.push(file);
            }
            else if (vpath.isTypeScript(file.unitName) || (vpath.isJavaScript(file.unitName) && ts.getAllowJSCompilerOption(options))) {
                const declFile = findResultCodeFile(file.unitName);
                if (declFile && !findUnit(declFile.file, declInputFiles) && !findUnit(declFile.file, declOtherFiles)) {
                    dtsFiles.push({
                        unitName: declFile.file,
                        content: Utils.removeByteOrderMark(declFile.text),
                    });
                }
            }
        }

        function findResultCodeFile(fileName: string) {
            const sourceFile = result.program!.getSourceFile(fileName)!;
            assert(sourceFile, "Program has no source file with name '" + fileName + "'");
            // Is this file going to be emitted separately
            let sourceFileName: string;
            const outFile = options.outFile;
            if (!outFile) {
                if (options.outDir) {
                    let sourceFilePath = ts.getNormalizedAbsolutePath(sourceFile.fileName, result.vfs.cwd());
                    sourceFilePath = sourceFilePath.replace(result.program!.getCommonSourceDirectory(), "");
                    sourceFileName = ts.combinePaths(options.outDir, sourceFilePath);
                }
                else {
                    sourceFileName = sourceFile.fileName;
                }
            }
            else {
                // Goes to single --out file
                sourceFileName = outFile;
            }

            const dTsFileName = ts.removeFileExtension(sourceFileName) + ts.getDeclarationEmitExtensionForPath(sourceFileName);
            return result.dts.get(dTsFileName);
        }

        function findUnit(fileName: string, units: TestFile[]) {
            return ts.forEach(units, unit => unit.unitName === fileName ? unit : undefined);
        }
    }

    export function compileDeclarationFiles(context: DeclarationCompilationContext | undefined, symlinks: vfs.FileSet | undefined): {
        declInputFiles: TestFile[];
        declOtherFiles: TestFile[];
        declResult: CompileFilesResult;
    } | undefined {
        if (!context) {
            return;
        }
        const { declInputFiles, declOtherFiles, harnessSettings, options, currentDirectory } = context;
        const output = compileFiles(declInputFiles, declOtherFiles, harnessSettings, options, currentDirectory, symlinks);
        return { declInputFiles, declOtherFiles, declResult: output };
    }

    export function minimalDiagnosticsToString(diagnostics: readonly ts.Diagnostic[], pretty?: boolean): string {
        const host = { getCanonicalFileName, getCurrentDirectory: () => "", getNewLine: () => IO.newLine() };
        return (pretty ? ts.formatDiagnosticsWithColorAndContext : ts.formatDiagnostics)(diagnostics, host);
    }

    export function getErrorBaseline(inputFiles: readonly TestFile[], diagnostics: readonly ts.Diagnostic[], pretty?: boolean): string {
        let outputLines = "";
        const gen = iterateErrorBaseline(inputFiles, diagnostics, { pretty });
        for (const value of gen) {
            const [, content] = value;
            outputLines += content;
        }
        if (pretty) {
            outputLines += Utils.removeTestPathPrefixes(ts.getErrorSummaryText(ts.getErrorCountForSummary(diagnostics), ts.getFilesInErrorForSummary(diagnostics), IO.newLine(), { getCurrentDirectory: () => "" }));
        }
        return outputLines;
    }

    export const diagnosticSummaryMarker = "__diagnosticSummary";
    export const globalErrorsMarker = "__globalErrors";
    export function* iterateErrorBaseline(inputFiles: readonly TestFile[], diagnostics: readonly ts.Diagnostic[], options?: { pretty?: boolean; caseSensitive?: boolean; currentDirectory?: string; }): IterableIterator<[string, string, number]> {
        diagnostics = ts.toSorted(diagnostics, ts.compareDiagnostics);
        let outputLines = "";
        // Count up all errors that were found in files other than lib.d.ts so we don't miss any
        let totalErrorsReportedInNonLibraryNonTsconfigFiles = 0;

        let errorsReported = 0;

        let firstLine = true;
        function newLine() {
            if (firstLine) {
                firstLine = false;
                return "";
            }
            return "\r\n";
        }

        const formatDiagnsoticHost = {
            getCurrentDirectory: () => options && options.currentDirectory ? options.currentDirectory : "",
            getNewLine: () => IO.newLine(),
            getCanonicalFileName: ts.createGetCanonicalFileName(options && options.caseSensitive !== undefined ? options.caseSensitive : true),
        };

        function outputErrorText(error: ts.Diagnostic) {
            const message = ts.flattenDiagnosticMessageText(error.messageText, IO.newLine());

            const errLines = Utils.removeTestPathPrefixes(message)
                .split("\n")
                .map(s => s.length > 0 && s.charAt(s.length - 1) === "\r" ? s.substr(0, s.length - 1) : s)
                .filter(s => s.length > 0)
                .map(s => "!!! " + ts.diagnosticCategoryName(error) + " TS" + error.code + ": " + s);
            if (error.relatedInformation) {
                for (const info of error.relatedInformation) {
                    let location = info.file ? " " + ts.formatLocation(info.file, info.start!, formatDiagnsoticHost, ts.identity) : "";
                    location = Utils.removeTestPathPrefixes(location);
                    if (location && isDefaultLibraryFile(info.file!.fileName)) {
                        location = location.replace(/(lib.*\.d\.ts):\d+:\d+/i, "$1:--:--");
                    }
                    errLines.push(`!!! related TS${info.code}${location}: ${ts.flattenDiagnosticMessageText(info.messageText, IO.newLine())}`);
                }
            }
            errLines.forEach(e => outputLines += newLine() + e);
            errorsReported++;

            // do not count errors from lib.d.ts here, they are computed separately as numLibraryDiagnostics
            // if lib.d.ts is explicitly included in input files and there are some errors in it (i.e. because of duplicate identifiers)
            // then they will be added twice thus triggering 'total errors' assertion with condition
            // Similarly for tsconfig, which may be in the input files and contain errors.
            // 'totalErrorsReportedInNonLibraryNonTsconfigFiles + numLibraryDiagnostics + numTsconfigDiagnostics, diagnostics.length

            if (!error.file || !isDefaultLibraryFile(error.file.fileName) && !vpath.isTsConfigFile(error.file.fileName)) {
                totalErrorsReportedInNonLibraryNonTsconfigFiles++;
            }
        }

        let topDiagnostics = minimalDiagnosticsToString(diagnostics, options && options.pretty);
        topDiagnostics = Utils.removeTestPathPrefixes(topDiagnostics);
        topDiagnostics = topDiagnostics.replace(/^(lib.*\.d\.ts)\(\d+,\d+\)/gim, "$1(--,--)");

        yield [diagnosticSummaryMarker, topDiagnostics + IO.newLine() + IO.newLine(), diagnostics.length];

        // Report global errors
        const globalErrors = diagnostics.filter(err => !err.file);
        globalErrors.forEach(outputErrorText);
        yield [globalErrorsMarker, outputLines, errorsReported];
        outputLines = "";
        errorsReported = 0;

        // 'merge' the lines of each input file with any errors associated with it
        const dupeCase = new Map<string, number>();
        for (const inputFile of inputFiles.filter(f => f.content !== undefined)) {
            // Filter down to the errors in the file
            const fileErrors = diagnostics.filter((e): e is ts.DiagnosticWithLocation => {
                const errFn = e.file;
                return !!errFn && ts.comparePaths(Utils.removeTestPathPrefixes(errFn.fileName), Utils.removeTestPathPrefixes(inputFile.unitName), options && options.currentDirectory || "", !(options && options.caseSensitive)) === ts.Comparison.EqualTo;
            });

            // Header
            outputLines += newLine() + "==== " + Utils.removeTestPathPrefixes(inputFile.unitName) + " (" + fileErrors.length + " errors) ====";

            // Make sure we emit something for every error
            let markedErrorCount = 0;
            // For each line, emit the line followed by any error squiggles matching this line
            // Note: IE JS engine incorrectly handles consecutive delimiters here when using RegExp split, so
            // we have to string-based splitting instead and try to figure out the delimiting chars

            const lineStarts = ts.computeLineStarts(inputFile.content);
            let lines = inputFile.content.split("\n");
            if (lines.length === 1) {
                lines = lines[0].split("\r");
            }

            lines.forEach((line, lineIndex) => {
                if (line.length > 0 && line.charAt(line.length - 1) === "\r") {
                    line = line.substr(0, line.length - 1);
                }

                const thisLineStart = lineStarts[lineIndex];
                let nextLineStart: number;
                // On the last line of the file, fake the next line start number so that we handle errors on the last character of the file correctly
                if (lineIndex === lines.length - 1) {
                    nextLineStart = inputFile.content.length;
                }
                else {
                    nextLineStart = lineStarts[lineIndex + 1];
                }
                // Emit this line from the original file
                outputLines += newLine() + "    " + line;
                fileErrors.forEach(errDiagnostic => {
                    const err = errDiagnostic as ts.TextSpan; // TODO: GH#18217
                    // Does any error start or continue on to this line? Emit squiggles
                    const end = ts.textSpanEnd(err);
                    if ((end >= thisLineStart) && ((err.start < nextLineStart) || (lineIndex === lines.length - 1))) {
                        // How many characters from the start of this line the error starts at (could be positive or negative)
                        const relativeOffset = err.start - thisLineStart;
                        // How many characters of the error are on this line (might be longer than this line in reality)
                        const length = (end - err.start) - Math.max(0, thisLineStart - err.start);
                        // Calculate the start of the squiggle
                        const squiggleStart = Math.max(0, relativeOffset);
                        // TODO/REVIEW: this doesn't work quite right in the browser if a multi file test has files whose names are just the right length relative to one another
                        outputLines += newLine() + "    " + line.substr(0, squiggleStart).replace(/\S/g, " ") + new Array(Math.min(length, line.length - squiggleStart) + 1).join("~");

                        // If the error ended here, or we're at the end of the file, emit its message
                        if ((lineIndex === lines.length - 1) || nextLineStart > end) {
                            // Just like above, we need to do a split on a string instead of on a regex
                            // because the JS engine does regexes wrong

                            outputErrorText(errDiagnostic);
                            markedErrorCount++;
                        }
                    }
                });
            });

            // Verify we didn't miss any errors in this file
            assert.equal(markedErrorCount, fileErrors.length, "count of errors in " + inputFile.unitName);
            const isDupe = dupeCase.has(sanitizeTestFilePath(inputFile.unitName));
            yield [checkDuplicatedFileName(inputFile.unitName, dupeCase), outputLines, errorsReported];
            if (isDupe && !(options && options.caseSensitive)) {
                // Case-duplicated files on a case-insensitive build will have errors reported in both the dupe and the original
                // thanks to the canse-insensitive path comparison on the error file path - We only want to count those errors once
                // for the assert below, so we subtract them here.
                totalErrorsReportedInNonLibraryNonTsconfigFiles -= errorsReported;
            }
            outputLines = "";
            errorsReported = 0;
        }

        const numLibraryDiagnostics = ts.countWhere(diagnostics, diagnostic => {
            return !!diagnostic.file && (isDefaultLibraryFile(diagnostic.file.fileName) || isBuiltFile(diagnostic.file.fileName));
        });

        const numTsconfigDiagnostics = ts.countWhere(diagnostics, diagnostic => {
            return !!diagnostic.file && (vpath.isTsConfigFile(diagnostic.file.fileName));
        });

        // Verify we didn't miss any errors in total
        assert.equal(totalErrorsReportedInNonLibraryNonTsconfigFiles + numLibraryDiagnostics + numTsconfigDiagnostics, diagnostics.length, "total number of errors");
    }

    export function doErrorBaseline(baselinePath: string, inputFiles: readonly TestFile[], errors: readonly ts.Diagnostic[], pretty?: boolean): void {
        Baseline.runBaseline(baselinePath.replace(/\.tsx?$/, ".errors.txt"), !errors || (errors.length === 0) ? null : getErrorBaseline(inputFiles, errors, pretty)); // eslint-disable-line no-restricted-syntax
    }

    export function doTypeAndSymbolBaseline(
        baselinePath: string,
        header: string,
        program: ts.Program,
        allFiles: { unitName: string; content: string; }[],
        opts?: Baseline.BaselineOptions,
        multifile?: boolean,
        skipTypeBaselines?: boolean,
        skipSymbolBaselines?: boolean,
        hasErrorBaseline?: boolean,
    ): void {
        // The full walker simulates the types that you would get from doing a full
        // compile.  The pull walker simulates the types you get when you just do
        // a type query for a random node (like how the LS would do it).  Most of the
        // time, these will be the same.  However, occasionally, they can be different.
        // Specifically, when the compiler internally depends on symbol IDs to order
        // things, then we may see different results because symbols can be created in a
        // different order with 'pull' operations, and thus can produce slightly differing
        // output.
        //
        // For example, with a full type check, we may see a type displayed as: number | string
        // But with a pull type check, we may see it as:                        string | number
        //
        // These types are equivalent, but depend on what order the compiler observed
        // certain parts of the program.

        const fullWalker = new TypeWriterWalker(program, !!hasErrorBaseline);

        // Produce baselines.  The first gives the types for all expressions.
        // The second gives symbols for all identifiers.
        let typesError: Error | undefined, symbolsError: Error | undefined;
        try {
            checkBaseLines(/*isSymbolBaseLine*/ false);
        }
        catch (e) {
            typesError = e;
        }

        try {
            checkBaseLines(/*isSymbolBaseLine*/ true);
        }
        catch (e) {
            symbolsError = e;
        }

        if (typesError && symbolsError) {
            throw new Error(typesError.stack + IO.newLine() + symbolsError.stack);
        }

        if (typesError) {
            throw typesError;
        }

        if (symbolsError) {
            throw symbolsError;
        }

        return;

        function checkBaseLines(isSymbolBaseLine: boolean) {
            const fullExtension = isSymbolBaseLine ? ".symbols" : ".types";
            // When calling this function from rwc-runner, the baselinePath will have no extension.
            // As rwc test- file is stored in json which ".json" will get stripped off.
            // When calling this function from compiler-runner, the baselinePath will then has either ".ts" or ".tsx" extension
            const outputFileName = ts.endsWith(baselinePath, ts.Extension.Ts) || ts.endsWith(baselinePath, ts.Extension.Tsx) ?
                baselinePath.replace(/\.tsx?/, "") : baselinePath;

            if (!multifile) {
                const fullBaseLine = generateBaseLine(isSymbolBaseLine, isSymbolBaseLine ? skipSymbolBaselines : skipTypeBaselines);
                Baseline.runBaseline(outputFileName + fullExtension, fullBaseLine, opts);
            }
            else {
                Baseline.runMultifileBaseline(outputFileName, fullExtension, () => {
                    return iterateBaseLine(isSymbolBaseLine, isSymbolBaseLine ? skipSymbolBaselines : skipTypeBaselines);
                }, opts);
            }
        }

        function generateBaseLine(isSymbolBaseline: boolean, skipBaseline?: boolean): string | null { // eslint-disable-line no-restricted-syntax
            let result = "";
            const perfLines: string[] = [];
            const prePerformanceValues = getPerformanceBaselineValues();
            const gen = iterateBaseLine(isSymbolBaseline, skipBaseline);
            for (const value of gen) {
                const [, content] = value;
                result += content;
            }
            const postPerformanceValues = getPerformanceBaselineValues();

            if (!isSymbolBaseline) {
                const perfStats: [name: string, reportThreshold: number, beforeValue: number, afterValue: number][] = [];
                perfStats.push(["Strict subtype cache", 1000, prePerformanceValues.strictSubtype, postPerformanceValues.strictSubtype]);
                perfStats.push(["Subtype cache", 1000, prePerformanceValues.subtype, postPerformanceValues.subtype]);
                perfStats.push(["Identity cache", 1000, prePerformanceValues.identity, postPerformanceValues.identity]);
                perfStats.push(["Assignability cache", 1000, prePerformanceValues.assignability, postPerformanceValues.assignability]);
                perfStats.push(["Type Count", 1000, prePerformanceValues.typeCount, postPerformanceValues.typeCount]);
                perfStats.push(["Instantiation count", 1500, prePerformanceValues.instantiation, postPerformanceValues.instantiation]);
                perfStats.push(["Symbol count", 45000, prePerformanceValues.symbol, postPerformanceValues.symbol]);

                if (perfStats.some(([, threshold, , postValue]) => postValue >= threshold)) {
                    perfLines.push(`=== Performance Stats ===`);
                    for (const [name, threshold, preValue, postValue] of perfStats) {
                        if (postValue >= threshold) {
                            const preString = valueToString(preValue);
                            const postString = valueToString(postValue);
                            if (preString === postString) {
                                perfLines.push(`${name}: ${preString}`);
                            }
                            else {
                                perfLines.push(`${name}: ${preString} -> ${postString}`);
                            }
                        }
                    }
                    perfLines.push("");
                    perfLines.push("");
                }
            }

            return result ? (`//// [${header}] ////\r\n\r\n${perfLines.join("\n")}${result}`) : null; // eslint-disable-line no-restricted-syntax

            function valueToString(value: number) {
                return roundToHumanLogarithm(value).toLocaleString("en-US");
            }
        }

        /**
         * Rounds to a number like 10, 25, 50, 100, 250, 500, 1000, etc
         */
        function roundToHumanLogarithm(n: number) {
            if (n < 10) return 0;
            const powerOfTen = Math.floor(Math.log10(n));
            const basePowerOfTen = Math.pow(10, powerOfTen);
            const multipliers = [1, 2.5, 5, 10];
            const closestMultiplier = multipliers.reduce((prev, curr) => {
                return Math.abs(curr * basePowerOfTen - n) < Math.abs(prev * basePowerOfTen - n) ? curr : prev;
            });
            return closestMultiplier * basePowerOfTen;
        }

        function getPerformanceBaselineValues() {
            const checker = program.getTypeChecker();
            const caches = checker.getRelationCacheSizes();
            return {
                strictSubtype: caches.strictSubtype,
                subtype: caches.subtype,
                identity: caches.identity,
                assignability: caches.assignable,
                typeCount: checker.getTypeCount(),
                instantiation: checker.getInstantiationCount(),
                symbol: checker.getSymbolCount(),
            };
        }

        function* iterateBaseLine(isSymbolBaseline: boolean, skipBaseline?: boolean): IterableIterator<[string, string]> {
            if (skipBaseline) {
                return;
            }
            const dupeCase = new Map<string, number>();

            for (const file of allFiles) {
                const { unitName } = file;
                let typeLines = "=== " + unitName + " ===\r\n";
                const codeLines = ts.flatMap(file.content.split(/\r?\n/), e => e.split(/[\r\u2028\u2029]/));
                const gen: IterableIterator<TypeWriterResult> = isSymbolBaseline ? fullWalker.getSymbols(unitName) : fullWalker.getTypes(unitName);
                let lastIndexWritten: number | undefined;
                for (const result of gen) {
                    if (isSymbolBaseline && !result.symbol) {
                        return;
                    }
                    if (lastIndexWritten === undefined) {
                        typeLines += codeLines.slice(0, result.line + 1).join("\r\n") + "\r\n";
                    }
                    else if (result.line !== lastIndexWritten) {
                        if (!((lastIndexWritten + 1 < codeLines.length) && (codeLines[lastIndexWritten + 1].match(/^\s*[{|}]\s*$/) || codeLines[lastIndexWritten + 1].trim() === ""))) {
                            typeLines += "\r\n";
                        }
                        typeLines += codeLines.slice(lastIndexWritten + 1, result.line + 1).join("\r\n") + "\r\n";
                    }
                    lastIndexWritten = result.line;
                    const typeOrSymbolString = isSymbolBaseline ? result.symbol : result.type;
                    const lineText = result.sourceText.replace(/\r?\n/g, "");
                    const formattedLine = lineText + " : " + typeOrSymbolString;
                    typeLines += ">" + formattedLine + "\r\n";
                    if (result.underline) {
                        typeLines += ">" + " ".repeat(lineText.length) + " : " + result.underline + "\r\n";
                    }
                }

                lastIndexWritten ??= -1;
                if (lastIndexWritten + 1 < codeLines.length) {
                    if (!((lastIndexWritten + 1 < codeLines.length) && (codeLines[lastIndexWritten + 1].match(/^\s*[{|}]\s*$/) || codeLines[lastIndexWritten + 1].trim() === ""))) {
                        typeLines += "\r\n";
                    }
                    typeLines += codeLines.slice(lastIndexWritten + 1).join("\r\n");
                }
                typeLines += "\r\n";
                yield [checkDuplicatedFileName(unitName, dupeCase), Utils.removeTestPathPrefixes(typeLines)];
            }
        }
    }

    export function doSourcemapBaseline(baselinePath: string, options: ts.CompilerOptions, result: compiler.CompilationResult, harnessSettings: TestCaseParser.CompilerSettings): void {
        const declMaps = ts.getAreDeclarationMapsEnabled(options);
        if (options.inlineSourceMap) {
            if (result.maps.size > 0 && !declMaps) {
                throw new Error("No sourcemap files should be generated if inlineSourceMaps was set.");
            }
            return;
        }
        else if (options.sourceMap || declMaps) {
            if (result.maps.size !== ((options.sourceMap ? result.getNumberOfJsFiles(/*includeJson*/ false) : 0) + (declMaps ? result.getNumberOfJsFiles(/*includeJson*/ true) : 0))) {
                throw new Error("Number of sourcemap files should be same as js files.");
            }

            let sourceMapCode: string | null; // eslint-disable-line no-restricted-syntax
            if ((options.noEmitOnError && result.diagnostics.length !== 0) || result.maps.size === 0) {
                // We need to return null here or the runBaseLine will actually create a empty file.
                // Baselining isn't required here because there is no output.
                sourceMapCode = null; // eslint-disable-line no-restricted-syntax
            }
            else {
                sourceMapCode = "";
                result.maps.forEach(sourceMap => {
                    if (sourceMapCode) sourceMapCode += "\r\n";
                    sourceMapCode += fileOutput(sourceMap, harnessSettings);
                    if (!options.inlineSourceMap) {
                        sourceMapCode += createSourceMapPreviewLink(sourceMap.text, result);
                    }
                });
            }
            Baseline.runBaseline(baselinePath.replace(/\.tsx?/, ".js.map"), sourceMapCode);
        }
    }

    function createSourceMapPreviewLink(sourcemap: string, result: compiler.CompilationResult) {
        const sourcemapJSON = JSON.parse(sourcemap);
        const outputJSFile = result.outputs.find(td => td.file.endsWith(sourcemapJSON.file));
        if (!outputJSFile) return "";

        const sourceTDs = ts.map(sourcemapJSON.sources, (s: string) => result.inputs.find(td => td.file.endsWith(s)));
        const anyUnfoundSources = ts.contains(sourceTDs, /*value*/ undefined);
        if (anyUnfoundSources) return "";

        const hash = "#base64," + ts.map([outputJSFile.text, sourcemap].concat(sourceTDs.map(td => td!.text)), s => ts.convertToBase64(decodeURIComponent(encodeURIComponent(s)))).join(",");
        return "\n//// https://sokra.github.io/source-map-visualization" + hash + "\n";
    }

    export function doJsEmitBaseline(
        baselinePath: string,
        header: string,
        options: ts.CompilerOptions,
        result: CompileFilesResult,
        tsConfigFiles: readonly TestFile[],
        toBeCompiled: readonly TestFile[],
        otherFiles: readonly TestFile[],
        harnessSettings: TestCaseParser.CompilerSettings,
    ): void {
        if (!options.noEmit && !options.emitDeclarationOnly && result.js.size === 0 && result.diagnostics.length === 0) {
            throw new Error("Expected at least one js file to be emitted or at least one error to be created.");
        }

        // check js output
        let tsCode = "";
        const tsSources = otherFiles.concat(toBeCompiled);
        tsCode += "//// [" + header + "] ////\r\n\r\n";

        for (let i = 0; i < tsSources.length; i++) {
            tsCode += "//// [" + ts.getBaseFileName(tsSources[i].unitName) + "]\r\n";
            tsCode += tsSources[i].content + (i < (tsSources.length - 1) ? "\r\n" : "");
        }

        let jsCode = "";
        result.js.forEach(file => {
            if (jsCode.length && jsCode.charCodeAt(jsCode.length - 1) !== ts.CharacterCodes.lineFeed) {
                jsCode += "\r\n";
            }
            if (!result.diagnostics.length && !ts.endsWith(file.file, ts.Extension.Json)) {
                const fileParseResult = ts.createSourceFile(file.file, file.text, ts.getEmitScriptTarget(options), /*setParentNodes*/ false, ts.endsWith(file.file, "x") ? ts.ScriptKind.JSX : ts.ScriptKind.JS);
                if (ts.length(fileParseResult.parseDiagnostics)) {
                    jsCode += getErrorBaseline([file.asTestFile()], fileParseResult.parseDiagnostics);
                    return;
                }
            }
            jsCode += fileOutput(file, harnessSettings);
        });

        if (result.dts.size > 0) {
            jsCode += "\r\n\r\n";
            result.dts.forEach(declFile => {
                jsCode += fileOutput(declFile, harnessSettings);
            });
        }

        const declFileContext = prepareDeclarationCompilationContext(
            toBeCompiled,
            otherFiles,
            result,
            harnessSettings,
            options,
            /*currentDirectory*/ undefined,
        );
        const declFileCompilationResult = compileDeclarationFiles(declFileContext, result.symlinks);

        if (declFileCompilationResult && declFileCompilationResult.declResult.diagnostics.length) {
            jsCode += "\r\n\r\n//// [DtsFileErrors]\r\n";
            jsCode += "\r\n\r\n";
            jsCode += getErrorBaseline(tsConfigFiles.concat(declFileCompilationResult.declInputFiles, declFileCompilationResult.declOtherFiles), declFileCompilationResult.declResult.diagnostics);
        }
        else if (!options.noCheck && !options.noEmit) {
            const withoutChecking = result.repeat({ noCheck: "true" });
            compareResultFileSets(withoutChecking.dts, result.dts);
            compareResultFileSets(withoutChecking.js, result.js);
        }

        // eslint-disable-next-line no-restricted-syntax
        Baseline.runBaseline(baselinePath.replace(/\.tsx?/, ts.Extension.Js), jsCode.length > 0 ? tsCode + "\r\n\r\n" + jsCode : null);

        function compareResultFileSets(a: ReadonlyMap<string, documents.TextDocument>, b: ReadonlyMap<string, documents.TextDocument>) {
            a.forEach((doc, key) => {
                const original = b.get(key);
                if (!original) {
                    jsCode += `\r\n\r\n!!!! File ${Utils.removeTestPathPrefixes(doc.file)} missing from original emit, but present in noCheck emit\r\n`;
                    jsCode += fileOutput(doc, harnessSettings);
                }
                else if (original.text !== doc.text) {
                    jsCode += `\r\n\r\n!!!! File ${Utils.removeTestPathPrefixes(doc.file)} differs from original emit in noCheck emit\r\n`;
                    const expected = original.text;
                    const actual = doc.text;
                    const patch = Diff.createTwoFilesPatch("Expected", "Actual", expected, actual, "The full check baseline", "with noCheck set");
                    const fileName = harnessSettings.fullEmitPaths ? Utils.removeTestPathPrefixes(doc.file) : ts.getBaseFileName(doc.file);
                    jsCode += "//// [" + fileName + "]\r\n";
                    jsCode += patch;
                }
            });
        }
    }

    function fileOutput(file: documents.TextDocument, harnessSettings: TestCaseParser.CompilerSettings): string {
        const fileName = harnessSettings.fullEmitPaths ? Utils.removeTestPathPrefixes(file.file) : ts.getBaseFileName(file.file);
        return "//// [" + fileName + "]\r\n" + file.text;
    }

    export function collateOutputs(outputFiles: readonly documents.TextDocument[]): string {
        const gen = iterateOutputs(outputFiles);
        // Emit them
        let result = "";
        for (const value of gen) {
            // Some extra spacing if this isn't the first file
            if (result.length) {
                result += "\r\n\r\n";
            }
            // FileName header + content
            const [, content] = value;
            result += content;
        }
        return result;
    }

    export function* iterateOutputs(outputFiles: Iterable<documents.TextDocument>): IterableIterator<[string, string]> {
        // Collect, test, and sort the fileNames
        const files = ts.arrayFrom(outputFiles);
        files.slice().sort((a, b) => ts.compareStringsCaseSensitive(cleanName(a.file), cleanName(b.file)));
        const dupeCase = new Map<string, number>();
        // Yield them
        for (const outputFile of files) {
            yield [checkDuplicatedFileName(outputFile.file, dupeCase), "/*====== " + outputFile.file + " ======*/\r\n" + Utils.removeByteOrderMark(outputFile.text)];
        }

        function cleanName(fn: string) {
            const lastSlash = ts.normalizeSlashes(fn).lastIndexOf("/");
            return fn.substr(lastSlash + 1).toLowerCase();
        }
    }

    function checkDuplicatedFileName(resultName: string, dupeCase: Map<string, number>): string {
        resultName = sanitizeTestFilePath(resultName);
        if (dupeCase.has(resultName)) {
            // A different baseline filename should be manufactured if the names differ only in case, for windows compat
            const count = 1 + dupeCase.get(resultName)!;
            dupeCase.set(resultName, count);
            resultName = `${resultName}.dupe${count}`;
        }
        else {
            dupeCase.set(resultName, 0);
        }
        return resultName;
    }

    export function sanitizeTestFilePath(name: string): string {
        const path = ts.toPath(ts.normalizeSlashes(name.replace(/[\^<>:"|?*%]/g, "_")).replace(/\.\.\//g, "__dotdot/"), "", Utils.canonicalizeForHarness);
        if (ts.startsWith(path, "/")) {
            return path.substring(1);
        }
        return path;
    }
}

export interface FileBasedTest {
    file: string;
    configurations?: FileBasedTestConfiguration[];
}

export interface FileBasedTestConfiguration {
    [key: string]: string;
}

function splitVaryBySettingValue(text: string, varyBy: string): string[] | undefined {
    if (!text) return undefined;

    let star = false;
    const includes: string[] = [];
    const excludes: string[] = [];
    for (let s of text.split(/,/)) {
        s = s.trim().toLowerCase();
        if (s.length === 0) continue;
        if (s === "*") {
            star = true;
        }
        else if (ts.startsWith(s, "-") || ts.startsWith(s, "!")) {
            excludes.push(s.slice(1));
        }
        else {
            includes.push(s);
        }
    }

    // do nothing if the setting has no variations
    if (includes.length <= 1 && !star && excludes.length === 0) {
        return undefined;
    }

    const variations: { key: string; value?: string | number; }[] = [];
    const values = getVaryByStarSettingValues(varyBy);

    // add (and deduplicate) all included entries
    for (const include of includes) {
        const value = values?.get(include);
        if (ts.findIndex(variations, v => v.key === include || value !== undefined && v.value === value) === -1) {
            variations.push({ key: include, value });
        }
    }

    if (star && values) {
        // add all entries
        for (const [key, value] of ts.arrayFrom(values.entries())) {
            if (ts.findIndex(variations, v => v.key === key || v.value === value) === -1) {
                variations.push({ key, value });
            }
        }
    }

    // remove all excluded entries
    for (const exclude of excludes) {
        const value = values?.get(exclude);
        let index: number;
        while ((index = ts.findIndex(variations, v => v.key === exclude || value !== undefined && v.value === value)) >= 0) {
            ts.orderedRemoveItemAt(variations, index);
        }
    }

    if (variations.length === 0) {
        throw new Error(`Variations in test option '@${varyBy}' resulted in an empty set.`);
    }

    return ts.map(variations, v => v.key);
}

function computeFileBasedTestConfigurationVariations(configurations: FileBasedTestConfiguration[], variationState: FileBasedTestConfiguration, varyByEntries: [string, string[]][], offset: number) {
    if (offset >= varyByEntries.length) {
        // make a copy of the current variation state
        configurations.push({ ...variationState });
        return;
    }

    const [varyBy, entries] = varyByEntries[offset];
    for (const entry of entries) {
        // set or overwrite the variation, then compute the next variation
        variationState[varyBy] = entry;
        computeFileBasedTestConfigurationVariations(configurations, variationState, varyByEntries, offset + 1);
    }
}

let booleanVaryByStarSettingValues: Map<string, string | number> | undefined;

function getVaryByStarSettingValues(varyBy: string): ReadonlyMap<string, string | number> | undefined {
    const option = ts.forEach(ts.optionDeclarations, decl => ts.equateStringsCaseInsensitive(decl.name, varyBy) ? decl : undefined);
    if (option) {
        if (typeof option.type === "object") {
            return option.type;
        }
        if (option.type === "boolean") {
            return booleanVaryByStarSettingValues || (booleanVaryByStarSettingValues = new Map(Object.entries({
                true: 1,
                false: 0,
            })));
        }
    }
}

/**
 * Compute FileBasedTestConfiguration variations based on a supplied list of variable settings.
 */
export function getFileBasedTestConfigurations(settings: TestCaseParser.CompilerSettings, varyBy: readonly string[]): FileBasedTestConfiguration[] | undefined {
    let varyByEntries: [string, string[]][] | undefined;
    let variationCount = 1;
    for (const varyByKey of varyBy) {
        if (ts.hasProperty(settings, varyByKey)) {
            // we only consider variations when there are 2 or more variable entries.
            const entries = splitVaryBySettingValue(settings[varyByKey], varyByKey);
            if (entries) {
                if (!varyByEntries) varyByEntries = [];
                variationCount *= entries.length;
                if (variationCount > 25) throw new Error(`Provided test options exceeded the maximum number of variations: ${varyBy.map(v => `'@${v}'`).join(", ")}`);
                varyByEntries.push([varyByKey, entries]);
            }
        }
    }

    if (!varyByEntries) return undefined;

    const configurations: FileBasedTestConfiguration[] = [];
    computeFileBasedTestConfigurationVariations(configurations, /*variationState*/ {}, varyByEntries, /*offset*/ 0);
    return configurations;
}

/**
 * Compute a description for this configuration based on its entries
 */
export function getFileBasedTestConfigurationDescription(configuration: FileBasedTestConfiguration): string {
    let name = "";
    if (configuration) {
        const keys = Object.keys(configuration).sort();
        for (const key of keys) {
            if (name) name += ", ";
            name += `@${key}: ${configuration[key]}`;
        }
    }
    return name;
}

export namespace TestCaseParser {
    /** all the necessary information to set the right compiler settings */
    export interface CompilerSettings {
        [name: string]: string;
    }

    /** All the necessary information to turn a multi file test into useful units for later compilation */
    export interface TestUnitData {
        content: string;
        name: string;
        fileOptions: any;
        originalFilePath: string;
        references: string[];
    }

    // Regex for parsing options in the format "@Alpha: Value of any sort"
    const optionRegex = /^\/{2}\s*@(\w+)\s*:\s*([^\r\n]*)/gm; // multiple matches on multiple lines
    const linkRegex = /^\/{2}\s*@link\s*:\s*([^\r\n]*)\s*->\s*([^\r\n]*)/gm; // multiple matches on multiple lines

    export function parseSymlinkFromTest(line: string, symlinks: vfs.FileSet | undefined, absoluteRootDir?: string): vfs.FileSet | undefined {
        const linkMetaData = linkRegex.exec(line);
        linkRegex.lastIndex = 0;
        if (!linkMetaData) return undefined;

        if (!symlinks) symlinks = {};
        symlinks[ts.getNormalizedAbsolutePath(linkMetaData[2].trim(), absoluteRootDir)] = new vfs.Symlink(ts.getNormalizedAbsolutePath(linkMetaData[1].trim(), absoluteRootDir));
        return symlinks;
    }

    export function extractCompilerSettings(content: string): CompilerSettings {
        const opts: CompilerSettings = {};

        let match: RegExpExecArray | null; // eslint-disable-line no-restricted-syntax
        while ((match = optionRegex.exec(content)) !== null) { // eslint-disable-line no-restricted-syntax
            opts[match[1]] = match[2].trim();
        }

        return opts;
    }

    export interface TestCaseContent {
        settings: CompilerSettings;
        testUnitData: TestUnitData[];
        tsConfig: ts.ParsedCommandLine | undefined;
        tsConfigFileUnitData: TestUnitData | undefined;
        symlinks?: vfs.FileSet;
    }

    /** Given a test file containing // @FileName directives, return an array of named units of code to be added to an existing compiler instance */
    export function makeUnitsFromTest(code: string, fileName: string, settings: CompilerSettings = extractCompilerSettings(code)): TestCaseContent {
        // List of all the subfiles we've parsed out
        const testUnitData: TestUnitData[] = [];

        const lines = Utils.splitContentByNewlines(code);

        // Stuff related to the subfile we're parsing
        let currentFileContent: string | undefined;
        let currentFileOptions: any = {};
        let currentFileName: any;
        let refs: string[] = [];
        let symlinks: vfs.FileSet | undefined;

        for (const line of lines) {
            let testMetaData: RegExpExecArray | null; // eslint-disable-line no-restricted-syntax
            const possiblySymlinks = parseSymlinkFromTest(line, symlinks, vfs.srcFolder);
            if (possiblySymlinks) {
                symlinks = possiblySymlinks;
            }
            else if (testMetaData = optionRegex.exec(line)) {
                // Comment line, check for global/file @options and record them
                optionRegex.lastIndex = 0;
                const metaDataName = testMetaData[1].toLowerCase();
                currentFileOptions[testMetaData[1]] = testMetaData[2].trim();
                if (metaDataName !== "filename") {
                    continue;
                }

                // New metadata statement after having collected some code to go with the previous metadata
                if (currentFileName) {
                    // Store result file
                    const newTestFile = {
                        content: currentFileContent!, // TODO: GH#18217
                        name: currentFileName,
                        fileOptions: currentFileOptions,
                        originalFilePath: fileName,
                        references: refs,
                    };
                    testUnitData.push(newTestFile);

                    // Reset local data
                    currentFileContent = undefined;
                    currentFileOptions = {};
                    currentFileName = testMetaData[2].trim();
                    refs = [];
                }
                else {
                    // First metadata marker in the file
                    currentFileName = testMetaData[2].trim();
                    if (currentFileContent && ts.skipTrivia(currentFileContent, 0, /*stopAfterLineBreak*/ false, /*stopAtComments*/ false) !== currentFileContent.length) {
                        throw new Error("Non-comment test content appears before the first '// @Filename' directive");
                    }
                    currentFileContent = "";
                }
            }
            else {
                // Subfile content line
                // Append to the current subfile content, inserting a newline needed
                if (currentFileContent === undefined) {
                    currentFileContent = "";
                }
                else if (currentFileContent !== "") {
                    // End-of-line
                    currentFileContent = currentFileContent + "\n";
                }
                currentFileContent = currentFileContent + line;
            }
        }

        // normalize the fileName for the single file case
        currentFileName = testUnitData.length > 0 || currentFileName ? currentFileName : ts.getBaseFileName(fileName);

        // EOF, push whatever remains
        const newTestFile2 = {
            content: currentFileContent || "",
            name: currentFileName,
            fileOptions: currentFileOptions,
            originalFilePath: fileName,
            references: refs,
        };
        testUnitData.push(newTestFile2);

        // unit tests always list files explicitly
        const parseConfigHost: ts.ParseConfigHost = {
            useCaseSensitiveFileNames: false,
            readDirectory: (directory, extensions, excludes, includes, depth) => {
                return ts.matchFiles(directory, extensions, excludes, includes, /*useCaseSensitiveFileNames*/ false, "", depth, dir => {
                    const files: string[] = [];
                    const directories = new Set<string>();
                    for (const unit of testUnitData) {
                        const fileName = ts.getNormalizedAbsolutePath(unit.name, vfs.srcFolder);
                        if (fileName.toLowerCase().startsWith(dir.toLowerCase())) {
                            let path = fileName.substring(dir.length);
                            if (path.startsWith("/")) {
                                path = path.substring(1);
                            }
                            if (path.includes("/")) {
                                const directoryName = path.substring(0, path.indexOf("/"));
                                directories.add(directoryName);
                            }
                            else {
                                files.push(path);
                            }
                        }
                    }
                    return { files, directories: ts.arrayFrom(directories) };
                }, ts.identity);
            },
            fileExists: fileName => testUnitData.some(data => data.name.toLowerCase() === fileName.toLowerCase()),
            readFile: name => ts.forEach(testUnitData, data => data.name.toLowerCase() === name.toLowerCase() ? data.content : undefined),
        };

        // check if project has tsconfig.json in the list of files
        let tsConfig: ts.ParsedCommandLine | undefined;
        let tsConfigFileUnitData: TestUnitData | undefined;
        for (let i = 0; i < testUnitData.length; i++) {
            const data = testUnitData[i];
            if (getConfigNameFromFileName(data.name)) {
                const configJson = ts.parseJsonText(data.name, data.content);
                assert.isTrue(configJson.endOfFileToken !== undefined);
                const configFileName = ts.getNormalizedAbsolutePath(data.name, vfs.srcFolder);
                const configDir = ts.getDirectoryPath(configFileName);
                tsConfig = ts.parseJsonSourceFileConfigFileContent(configJson, parseConfigHost, configDir, /*existingOptions*/ undefined, configFileName);
                tsConfigFileUnitData = data;

                // delete entry from the list
                ts.orderedRemoveItemAt(testUnitData, i);

                break;
            }
        }
        return { settings, testUnitData, tsConfig, tsConfigFileUnitData, symlinks };
    }
}

/** Support class for baseline files */
export namespace Baseline {
    const noContent = "<no content>";

    export interface BaselineOptions {
        Subfolder?: string;
        Baselinefolder?: string;
        PrintDiff?: true;
    }

    export function localPath(fileName: string, baselineFolder?: string, subfolder?: string): string {
        if (baselineFolder === undefined) {
            return baselinePath(fileName, "local", "tests/baselines", subfolder);
        }
        else {
            return baselinePath(fileName, "local", baselineFolder, subfolder);
        }
    }

    function referencePath(fileName: string, baselineFolder?: string, subfolder?: string) {
        if (baselineFolder === undefined) {
            return baselinePath(fileName, "reference", "tests/baselines", subfolder);
        }
        else {
            return baselinePath(fileName, "reference", baselineFolder, subfolder);
        }
    }

    function baselinePath(fileName: string, type: string, baselineFolder: string, subfolder?: string) {
        if (subfolder !== undefined) {
            return userSpecifiedRoot + baselineFolder + "/" + subfolder + "/" + type + "/" + fileName;
        }
        else {
            return userSpecifiedRoot + baselineFolder + "/" + type + "/" + fileName;
        }
    }

    const fileCache: { [idx: string]: boolean; } = {};

    function compareToBaseline(actual: string | null, relativeFileName: string, opts: BaselineOptions | undefined) { // eslint-disable-line no-restricted-syntax
        // actual is now either undefined (the generator had an error), null (no file requested),
        // or some real output of the function
        if (actual === undefined) {
            // Nothing to do
            return undefined!; // TODO: GH#18217
        }

        const refFileName = referencePath(relativeFileName, opts && opts.Baselinefolder, opts && opts.Subfolder);

        // eslint-disable-next-line no-restricted-syntax
        if (actual === null) {
            actual = noContent;
        }

        let expected = "<no content>";
        if (IO.fileExists(refFileName)) {
            expected = IO.readFile(refFileName)!; // TODO: GH#18217
        }

        return { expected, actual };
    }

    function writeComparison(expected: string, actual: string, relativeFileName: string, actualFileName: string, opts?: BaselineOptions) {
        // For now this is written using TypeScript, because sys is not available when running old test cases.
        // But we need to move to sys once we have
        // Creates the directory including its parent if not already present
        function createDirectoryStructure(dirName: string) {
            if (fileCache[dirName] || IO.directoryExists(dirName)) {
                fileCache[dirName] = true;
                return;
            }

            const parentDirectory = IO.directoryName(dirName)!; // TODO: GH#18217
            if (parentDirectory !== "" && parentDirectory !== dirName) {
                createDirectoryStructure(parentDirectory);
            }
            IO.createDirectory(dirName);
            fileCache[dirName] = true;
        }

        // Create folders if needed
        createDirectoryStructure(IO.directoryName(actualFileName)!); // TODO: GH#18217

        // Delete the actual file in case it fails
        if (IO.fileExists(actualFileName)) {
            IO.deleteFile(actualFileName);
        }

        const encodedActual = Utils.encodeString(actual);
        if (expected !== encodedActual) {
            if (actual === noContent) {
                IO.writeFile(actualFileName + ".delete", "");
            }
            else {
                IO.writeFile(actualFileName, encodedActual);
            }
            const errorMessage = getBaselineFileChangedErrorMessage(relativeFileName);
            if (opts && opts.PrintDiff) {
                const patch = Diff.createTwoFilesPatch("Expected", "Actual", expected, actual, "The current baseline", "The new version");
                throw new Error(`${errorMessage}${ts.ForegroundColorEscapeSequences.Grey}\n\n${patch}`);
            }
            else {
                if (!IO.fileExists(expected)) {
                    throw new Error(`New baseline created at ${IO.joinPath("tests", "baselines", "local", relativeFileName)}`);
                }
                else {
                    throw new Error(errorMessage);
                }
            }
        }
    }

    function getBaselineFileChangedErrorMessage(relativeFileName: string): string {
        return `The baseline file ${relativeFileName} has changed. (Run "hereby baseline-accept" if the new baseline is correct.)`;
    }

    export function runBaseline(relativeFileName: string, actual: string | null, opts?: BaselineOptions): void { // eslint-disable-line no-restricted-syntax
        const actualFileName = localPath(relativeFileName, opts && opts.Baselinefolder, opts && opts.Subfolder);
        if (actual === undefined) {
            throw new Error('The generated content was "undefined". Return "null" if no baselining is required."');
        }
        const comparison = compareToBaseline(actual, relativeFileName, opts);
        writeComparison(comparison.expected, comparison.actual, relativeFileName, actualFileName, opts);
    }

    export function runMultifileBaseline(relativeFileBase: string, extension: string, generateContent: () => IterableIterator<[string, string, number]> | IterableIterator<[string, string]> | null, opts?: BaselineOptions, referencedExtensions?: string[]): void { // eslint-disable-line no-restricted-syntax
        const gen = generateContent();
        const writtenFiles = new Map<string, true>();
        const errors: Error[] = [];

        // eslint-disable-next-line no-restricted-syntax
        if (gen !== null) {
            for (const value of gen) {
                const [name, content, count] = value as [string, string, number | undefined];
                if (count === 0) continue; // Allow error reporter to skip writing files without errors
                const relativeFileName = relativeFileBase + "/" + name + extension;
                const actualFileName = localPath(relativeFileName, opts && opts.Baselinefolder, opts && opts.Subfolder);
                const comparison = compareToBaseline(content, relativeFileName, opts);
                try {
                    writeComparison(comparison.expected, comparison.actual, relativeFileName, actualFileName);
                }
                catch (e) {
                    errors.push(e);
                }
                writtenFiles.set(relativeFileName, true);
            }
        }

        const referenceDir = referencePath(relativeFileBase, opts && opts.Baselinefolder, opts && opts.Subfolder);
        let existing = IO.readDirectory(referenceDir, referencedExtensions || [extension]);
        if (extension === ".ts" || referencedExtensions && referencedExtensions.includes(".ts") && !referencedExtensions.includes(".d.ts")) {
            // special-case and filter .d.ts out of .ts results
            existing = existing.filter(f => !ts.endsWith(f, ".d.ts"));
        }
        const missing: string[] = [];
        for (const name of existing) {
            const localCopy = name.substring(referenceDir.length - relativeFileBase.length);
            if (!writtenFiles.has(localCopy)) {
                missing.push(localCopy);
            }
        }
        if (missing.length) {
            for (const file of missing) {
                IO.writeFile(localPath(file + ".delete", opts && opts.Baselinefolder, opts && opts.Subfolder), "");
            }
        }

        if (errors.length || missing.length) {
            let errorMsg = "";
            if (errors.length) {
                errorMsg += `The baseline for ${relativeFileBase} in ${errors.length} files has changed:${"\n    " + errors.slice(0, 5).map(e => e.message).join("\n    ") + (errors.length > 5 ? "\n" + `    and ${errors.length - 5} more` : "")}`;
            }
            if (errors.length && missing.length) {
                errorMsg += "\n";
            }
            if (missing.length) {
                const writtenFilesArray = ts.arrayFrom(writtenFiles.keys());
                errorMsg += `Baseline missing ${missing.length} files:${"\n    " + missing.slice(0, 5).join("\n    ") + (missing.length > 5 ? "\n" + `    and ${missing.length - 5} more` : "") + "\n"}Written ${writtenFiles.size} files:${"\n    " + writtenFilesArray.slice(0, 5).join("\n    ") + (writtenFilesArray.length > 5 ? "\n" + `    and ${writtenFilesArray.length - 5} more` : "")}`;
            }
            throw new Error(errorMsg);
        }
    }
}

export function isDefaultLibraryFile(filePath: string): boolean {
    // We need to make sure that the filePath is prefixed with "lib." not just containing "lib." and end with ".d.ts"
    const fileName = ts.getBaseFileName(ts.normalizeSlashes(filePath));
    return ts.startsWith(fileName, "lib.") && ts.endsWith(fileName, ts.Extension.Dts);
}

export function isBuiltFile(filePath: string): boolean {
    return filePath.indexOf(libFolder) === 0 ||
        filePath.indexOf(vpath.addTrailingSeparator(vfs.builtFolder)) === 0;
}

export function getDefaultLibraryFile(filePath: string, io: IO): Compiler.TestFile {
    const libFile = userSpecifiedRoot + libFolder + ts.getBaseFileName(ts.normalizeSlashes(filePath));
    return { unitName: libFile, content: io.readFile(libFile)! };
}

export function getConfigNameFromFileName(filename: string): "tsconfig.json" | "jsconfig.json" | undefined {
    const flc = ts.getBaseFileName(filename).toLowerCase();
    return ts.find(["tsconfig.json" as const, "jsconfig.json" as const], x => x === flc);
}

if (Error) (Error as any).stackTraceLimit = 100;