namespace FourSlash {
    import ArrayOrSingle = FourSlashInterface.ArrayOrSingle;

    export const enum FourSlashTestType {
        Native,
        Shims,
        ShimsWithPreprocess,
        Server,
        OH
    }

    // Represents a parsed source file with metadata
    interface FourSlashFile {
        // The contents of the file (with markers, etc stripped out)
        content: string;
        fileName: string;
        symlinks?: string[];
        version: number;
        // File-specific options (name/value pairs)
        fileOptions: Harness.TestCaseParser.CompilerSettings;
    }

    // Represents a set of parsed source files and options
    interface FourSlashData {
        // Global options (name/value pairs)
        globalOptions: Harness.TestCaseParser.CompilerSettings;

        files: FourSlashFile[];

        symlinks: vfs.FileSet | undefined;

        // A mapping from marker names to name/position pairs
        markerPositions: ts.ESMap<string, Marker>;

        markers: Marker[];

        /**
         * Inserted in source files by surrounding desired text
         * in a range with `[|` and `|]`. For example,
         *
         * [|text in range|]
         *
         * is a range with `text in range` "selected".
         */
        ranges: Range[];
        rangesByText?: ts.MultiMap<string, Range>;
    }

    export interface Marker {
        fileName: string;
        position: number;
        data?: {};
    }

    export interface Range extends ts.TextRange {
        fileName: string;
        marker?: Marker;
    }

    interface LocationInformation {
        position: number;
        sourcePosition: number;
        sourceLine: number;
        sourceColumn: number;
    }

    interface RangeLocationInformation extends LocationInformation {
        marker?: Marker;
    }

    interface ImplementationLocationInformation extends ts.ImplementationLocation {
        matched?: boolean;
    }

    export interface TextSpan {
        start: number;
        end: number;
    }

    // Name of testcase metadata including ts.CompilerOptions properties that will be used by globalOptions
    // To add additional option, add property into the testOptMetadataNames, refer the property in either globalMetadataNames or fileMetadataNames
    // Add cases into convertGlobalOptionsToCompilationsSettings function for the compiler to acknowledge such option from meta data
    const enum MetadataOptionNames {
        baselineFile = "baselinefile",
        emitThisFile = "emitthisfile",  // This flag is used for testing getEmitOutput feature. It allows test-cases to indicate what file to be output in multiple files project
        fileName = "filename",
        resolveReference = "resolvereference",  // This flag is used to specify entry file for resolve file references. The flag is only allow once per test file
        symlink = "symlink",
    }

    // List of allowed metadata names
    const fileMetadataNames = [MetadataOptionNames.fileName, MetadataOptionNames.emitThisFile, MetadataOptionNames.resolveReference, MetadataOptionNames.symlink];

    function convertGlobalOptionsToCompilerOptions(globalOptions: Harness.TestCaseParser.CompilerSettings): ts.CompilerOptions {
        const settings: ts.CompilerOptions = { target: ts.ScriptTarget.ES5 };
        Harness.Compiler.setCompilerOptionsFromHarnessSetting(globalOptions, settings);
        return settings;
    }

    export class TestCancellationToken implements ts.HostCancellationToken {
        // 0 - cancelled
        // >0 - not cancelled
        // <0 - not cancelled and value denotes number of isCancellationRequested after which token become cancelled
        private static readonly notCanceled = -1;
        private numberOfCallsBeforeCancellation = TestCancellationToken.notCanceled;

        public isCancellationRequested(): boolean {
            if (this.numberOfCallsBeforeCancellation < 0) {
                return false;
            }

            if (this.numberOfCallsBeforeCancellation > 0) {
                this.numberOfCallsBeforeCancellation--;
                return false;
            }

            return true;
        }

        public setCancelled(numberOfCalls = 0): void {
            ts.Debug.assert(numberOfCalls >= 0);
            this.numberOfCallsBeforeCancellation = numberOfCalls;
        }

        public resetCancelled(): void {
            this.numberOfCallsBeforeCancellation = TestCancellationToken.notCanceled;
        }
    }

    export function verifyOperationIsCancelled(f: () => void) {
        try {
            f();
        }
        catch (e) {
            if (e instanceof ts.OperationCanceledException) {
                return;
            }
        }

        throw new Error("Operation should be cancelled");
    }

    export function ignoreInterpolations(diagnostic: string | ts.DiagnosticMessage): FourSlashInterface.DiagnosticIgnoredInterpolations {
        return { template: typeof diagnostic === "string" ? diagnostic : diagnostic.message };
    }

    // This function creates IScriptSnapshot object for testing getPreProcessedFileInfo
    // Return object may lack some functionalities for other purposes.
    function createScriptSnapShot(sourceText: string): ts.IScriptSnapshot {
        return ts.ScriptSnapshot.fromString(sourceText);
    }

    const enum CallHierarchyItemDirection {
        Root,
        Incoming,
        Outgoing
    }

    export class TestState {
        // Language service instance
        private languageServiceAdapterHost: Harness.LanguageService.LanguageServiceAdapterHost;
        private languageService: ts.LanguageService;
        private cancellationToken: TestCancellationToken;
        private assertTextConsistent: ((fileName: string) => void) | undefined;

        // The current caret position in the active file
        public currentCaretPosition = 0;
        // The position of the end of the current selection, or -1 if nothing is selected
        public selectionEnd = -1;

        public lastKnownMarker: string | undefined;

        // The file that's currently 'opened'
        public activeFile!: FourSlashFile;

        // Whether or not we should format on keystrokes
        public enableFormatting = true;

        public formatCodeSettings: ts.FormatCodeSettings;

        private inputFiles = new ts.Map<string, string>();  // Map between inputFile's fileName and its content for easily looking up when resolving references

        private static getDisplayPartsJson(displayParts: ts.SymbolDisplayPart[] | undefined) {
            let result = "";
            ts.forEach(displayParts, part => {
                if (result) {
                    result += ",\n    ";
                }
                else {
                    result = "[\n    ";
                }
                result += JSON.stringify(part);
            });
            if (result) {
                result += "\n]";
            }

            return result;
        }

        // Add input file which has matched file name with the given reference-file path.
        // This is necessary when resolveReference flag is specified
        private addMatchedInputFile(referenceFilePath: string, extensions: readonly string[] | undefined) {
            const inputFiles = this.inputFiles;
            const languageServiceAdapterHost = this.languageServiceAdapterHost;
            const didAdd = tryAdd(referenceFilePath);
            if (extensions && !didAdd) {
                ts.forEach(extensions, ext => tryAdd(referenceFilePath + ext));
            }

            function tryAdd(path: string) {
                const inputFile = inputFiles.get(path);
                if (inputFile && !Harness.isDefaultLibraryFile(path)) {
                    languageServiceAdapterHost.addScript(path, inputFile, /*isRootFile*/ true);
                    return true;
                }
            }
        }

        private getLanguageServiceAdapter(testType: FourSlashTestType, cancellationToken: TestCancellationToken, compilationOptions: ts.CompilerOptions): Harness.LanguageService.LanguageServiceAdapter {
            switch (testType) {
                case FourSlashTestType.Native:
                    return new Harness.LanguageService.NativeLanguageServiceAdapter(cancellationToken, compilationOptions);
                case FourSlashTestType.OH:
                    return new Harness.LanguageService.NativeLanguageServiceAdapter(cancellationToken, { ...compilationOptions, ...{ packageManagerType: "ohpm" } });
                case FourSlashTestType.Shims:
                    return new Harness.LanguageService.ShimLanguageServiceAdapter(/*preprocessToResolve*/ false, cancellationToken, compilationOptions);
                case FourSlashTestType.ShimsWithPreprocess:
                    return new Harness.LanguageService.ShimLanguageServiceAdapter(/*preprocessToResolve*/ true, cancellationToken, compilationOptions);
                case FourSlashTestType.Server:
                    return new Harness.LanguageService.ServerLanguageServiceAdapter(cancellationToken, compilationOptions);
                default:
                    throw new Error("Unknown FourSlash test type: ");
            }
        }

        constructor(private originalInputFileName: string, private basePath: string, private testType: FourSlashTestType, public testData: FourSlashData) {
            // Create a new Services Adapter
            this.cancellationToken = new TestCancellationToken();
            let compilationOptions = convertGlobalOptionsToCompilerOptions(this.testData.globalOptions);
            compilationOptions.skipDefaultLibCheck = true;

            // Initialize the language service with all the scripts
            let startResolveFileRef: FourSlashFile | undefined;

            let configFileName: string | undefined;
            for (const file of testData.files) {
                // Create map between fileName and its content for easily looking up when resolveReference flag is specified
                this.inputFiles.set(file.fileName, file.content);
                if (isConfig(file)) {
                    const configJson = ts.parseConfigFileTextToJson(file.fileName, file.content);
                    if (configJson.config === undefined) {
                        throw new Error(`Failed to parse test ${file.fileName}: ${configJson.error!.messageText}`);
                    }

                    // Extend our existing compiler options so that we can also support tsconfig only options
                    if (configJson.config.compilerOptions) {
                        const baseDirectory = ts.normalizePath(ts.getDirectoryPath(file.fileName));
                        const tsConfig = ts.convertCompilerOptionsFromJson(configJson.config.compilerOptions, baseDirectory, file.fileName);

                        if (!tsConfig.errors || !tsConfig.errors.length) {
                            compilationOptions = ts.extend(tsConfig.options, compilationOptions);
                        }
                    }
                    configFileName = file.fileName;
                }

                if (!startResolveFileRef && file.fileOptions[MetadataOptionNames.resolveReference] === "true") {
                    startResolveFileRef = file;
                }
                else if (startResolveFileRef) {
                    // If entry point for resolving file references is already specified, report duplication error
                    throw new Error("There exists a Fourslash file which has resolveReference flag specified; remove duplicated resolveReference flag");
                }
            }

            let configParseResult: ts.ParsedCommandLine | undefined;
            if (configFileName) {
                const baseDir = ts.normalizePath(ts.getDirectoryPath(configFileName));
                const files: vfs.FileSet = { [baseDir]: {} };
                this.inputFiles.forEach((data, path) => {
                    const scriptInfo = new Harness.LanguageService.ScriptInfo(path, undefined!, /*isRootFile*/ false); // TODO: GH#18217
                    files[path] = new vfs.File(data, { meta: { scriptInfo } });
                });
                const fs = new vfs.FileSystem(/*ignoreCase*/ true, { cwd: baseDir, files });
                const host = new fakes.ParseConfigHost(fs);
                const jsonSourceFile = ts.parseJsonText(configFileName, this.inputFiles.get(configFileName)!);
                configParseResult = ts.parseJsonSourceFileConfigFileContent(jsonSourceFile, host, baseDir, compilationOptions, configFileName);
                compilationOptions = configParseResult.options;
            }

            if (compilationOptions.typeRoots) {
                compilationOptions.typeRoots = compilationOptions.typeRoots.map(p => ts.getNormalizedAbsolutePath(p, this.basePath));
            }

            const languageServiceAdapter = this.getLanguageServiceAdapter(testType, this.cancellationToken, compilationOptions);
            this.languageServiceAdapterHost = languageServiceAdapter.getHost();
            this.languageService = memoWrap(languageServiceAdapter.getLanguageService(), this); // Wrap the LS to cache some expensive operations certain tests call repeatedly
            if (this.testType === FourSlashTestType.Server) {
                this.assertTextConsistent = fileName => (languageServiceAdapter as Harness.LanguageService.ServerLanguageServiceAdapter).assertTextConsistent(fileName);
            }

            if (startResolveFileRef) {
                // Add the entry-point file itself into the languageServiceShimHost
                this.languageServiceAdapterHost.addScript(startResolveFileRef.fileName, startResolveFileRef.content, /*isRootFile*/ true);

                const resolvedResult = languageServiceAdapter.getPreProcessedFileInfo(startResolveFileRef.fileName, startResolveFileRef.content);
                const referencedFiles: ts.FileReference[] = resolvedResult.referencedFiles;
                const importedFiles: ts.FileReference[] = resolvedResult.importedFiles;

                // Add triple reference files into language-service host
                ts.forEach(referencedFiles, referenceFile => {
                    // Fourslash insert tests/cases/fourslash into inputFile.unitName so we will properly append the same base directory to refFile path
                    const referenceFilePath = this.basePath + "/" + referenceFile.fileName;
                    this.addMatchedInputFile(referenceFilePath, /* extensions */ undefined);
                });

                const exts = ts.flatten(ts.getSupportedExtensions(compilationOptions));
                // Add import files into language-service host
                ts.forEach(importedFiles, importedFile => {
                    // Fourslash insert tests/cases/fourslash into inputFile.unitName and import statement doesn't require ".ts"
                    // so convert them before making appropriate comparison
                    const importedFilePath = this.basePath + "/" + importedFile.fileName;
                    this.addMatchedInputFile(importedFilePath, exts);
                });

                // Check if no-default-lib flag is false and if so add default library
                if (!resolvedResult.isLibFile) {
                    this.languageServiceAdapterHost.addScript(Harness.Compiler.defaultLibFileName,
                        Harness.Compiler.getDefaultLibrarySourceFile()!.text, /*isRootFile*/ false);

                    compilationOptions.lib?.forEach(fileName => {
                        const libFile = Harness.Compiler.getDefaultLibrarySourceFile(fileName);
                        ts.Debug.assertIsDefined(libFile, `Could not find lib file '${fileName}'`);
                        if (libFile) {
                            this.languageServiceAdapterHost.addScript(fileName, libFile.text, /*isRootFile*/ false);
                        }
                    });
                }
            }
            else {
                // resolveReference file-option is not specified then do not resolve any files and include all inputFiles
                this.inputFiles.forEach((file, fileName) => {
                    if (!Harness.isDefaultLibraryFile(fileName)) {
                        // all files if config file not specified, otherwise root files from the config and typings cache files are root files
                        const isRootFile = !configParseResult ||
                            ts.contains(configParseResult.fileNames, fileName) ||
                            (ts.isDeclarationFileName(fileName) && ts.containsPath("/Library/Caches/typescript", fileName));
                        this.languageServiceAdapterHost.addScript(fileName, file, isRootFile);
                    }
                });

                if (!compilationOptions.noLib) {
                    const seen = new Set<string>();
                    const addSourceFile = (fileName: string) => {
                        if (seen.has(fileName)) return;
                        seen.add(fileName);
                        const libFile = Harness.Compiler.getDefaultLibrarySourceFile(fileName);
                        ts.Debug.assertIsDefined(libFile, `Could not find lib file '${fileName}'`);
                        this.languageServiceAdapterHost.addScript(fileName, libFile.text, /*isRootFile*/ false);
                        if (!ts.some(libFile.libReferenceDirectives)) return;
                        for (const directive of libFile.libReferenceDirectives) {
                            addSourceFile(`lib.${directive.fileName}.d.ts`);
                        }
                    };

                    addSourceFile(Harness.Compiler.defaultLibFileName);
                    compilationOptions.lib?.forEach(addSourceFile);
                }

                compilationOptions.ets?.libs.forEach(fileName => {
                    const content = ts.sys.readFile(fileName);
                    if (content) {
                        this.languageServiceAdapterHost.addScript(fileName, content, /*isRootFile*/ false);
                    }
                });
            }

            for (const file of testData.files) {
                ts.forEach(file.symlinks, link => {
                    this.languageServiceAdapterHost.vfs.mkdirpSync(vpath.dirname(link));
                    this.languageServiceAdapterHost.vfs.symlinkSync(file.fileName, link);
                });
            }

            if (testData.symlinks) {
                this.languageServiceAdapterHost.vfs.apply(testData.symlinks);
            }

            this.formatCodeSettings = ts.testFormatSettings;

            // Open the first file by default
            this.openFile(0);

            function memoWrap(ls: ts.LanguageService, target: TestState): ts.LanguageService {
                const cacheableMembers: (keyof typeof ls)[] = [
                    "getCompletionEntryDetails",
                    "getCompletionEntrySymbol",
                    "getQuickInfoAtPosition",
                    "getReferencesAtPosition",
                    "getDocumentHighlights",
                ];
                const proxy = {} as ts.LanguageService;
                const keys = ts.getAllKeys(ls);
                for (const k of keys) {
                    const key = k as keyof typeof ls;
                    if (cacheableMembers.indexOf(key) === -1) {
                        proxy[key] = (...args: any[]) => (ls[key] as Function)(...args);
                        continue;
                    }
                    const memo = Utils.memoize(
                        (_version: number, _active: string, _caret: number, _selectEnd: number, _marker: string | undefined, ...args: any[]) => (ls[key] as Function)(...args),
                        (...args) => args.map(a => a && typeof a === "object" ? JSON.stringify(a) : a).join("|,|")
                    );
                    proxy[key] = (...args: any[]) => memo(
                        target.languageServiceAdapterHost.getScriptInfo(target.activeFile.fileName)!.version,
                        target.activeFile.fileName,
                        target.currentCaretPosition,
                        target.selectionEnd,
                        target.lastKnownMarker,
                        ...args
                    );
                }
                return proxy;
            }
        }

        private getFileContent(fileName: string): string {
            return ts.Debug.checkDefined(this.tryGetFileContent(fileName));
        }
        private tryGetFileContent(fileName: string): string | undefined {
            const script = this.languageServiceAdapterHost.getScriptInfo(fileName);
            return script && script.content;
        }

        // Entry points from fourslash.ts
        public goToMarker(name: string | Marker = "") {
            const marker = ts.isString(name) ? this.getMarkerByName(name) : name;
            if (this.activeFile.fileName !== marker.fileName) {
                this.openFile(marker.fileName);
            }

            const content = this.getFileContent(marker.fileName);
            if (marker.position === -1 || marker.position > content.length) {
                throw new Error(`Marker "${name}" has been invalidated by unrecoverable edits to the file.`);
            }
            const mName = ts.isString(name) ? name : this.markerName(marker);
            this.lastKnownMarker = mName;
            this.goToPosition(marker.position);
        }

        public goToEachMarker(markers: readonly Marker[], action: (marker: Marker, index: number) => void) {
            assert(markers.length);
            for (let i = 0; i < markers.length; i++) {
                this.goToMarker(markers[i]);
                action(markers[i], i);
            }
        }

        public goToEachRange(action: (range: Range) => void) {
            const ranges = this.getRanges();
            assert(ranges.length);
            for (const range of ranges) {
                this.selectRange(range);
                action(range);
            }
        }

        public markerName(m: Marker): string {
            return ts.forEachEntry(this.testData.markerPositions, (marker, name) => {
                if (marker === m) {
                    return name;
                }
            })!;
        }

        public goToPosition(positionOrLineAndCharacter: number | ts.LineAndCharacter) {
            const pos = typeof positionOrLineAndCharacter === "number"
                ? positionOrLineAndCharacter
                : this.languageServiceAdapterHost.lineAndCharacterToPosition(this.activeFile.fileName, positionOrLineAndCharacter);
            this.currentCaretPosition = pos;
            this.selectionEnd = -1;
        }

        public select(startMarker: string, endMarker: string) {
            const start = this.getMarkerByName(startMarker), end = this.getMarkerByName(endMarker);
            ts.Debug.assert(start.fileName === end.fileName);
            if (this.activeFile.fileName !== start.fileName) {
                this.openFile(start.fileName);
            }
            this.goToPosition(start.position);
            this.selectionEnd = end.position;
        }

        public selectAllInFile(fileName: string) {
            this.openFile(fileName);
            this.goToPosition(0);
            this.selectionEnd = this.activeFile.content.length;
        }

        public selectRange(range: Range): void {
            this.goToRangeStart(range);
            this.selectionEnd = range.end;
        }

        public selectLine(index: number) {
            const lineStart = this.languageServiceAdapterHost.lineAndCharacterToPosition(this.activeFile.fileName, { line: index, character: 0 });
            const lineEnd = lineStart + this.getLineContent(index).length;
            this.selectRange({ fileName: this.activeFile.fileName, pos: lineStart, end: lineEnd });
        }

        public moveCaretRight(count = 1) {
            this.currentCaretPosition += count;
            this.currentCaretPosition = Math.min(this.currentCaretPosition, this.getFileContent(this.activeFile.fileName).length);
            this.selectionEnd = -1;
        }

        // Opens a file given its 0-based index or fileName
        public openFile(indexOrName: number | string, content?: string, scriptKindName?: string): void {
            const fileToOpen: FourSlashFile = this.findFile(indexOrName);
            fileToOpen.fileName = ts.normalizeSlashes(fileToOpen.fileName);
            this.activeFile = fileToOpen;
            // Let the host know that this file is now open
            this.languageServiceAdapterHost.openFile(fileToOpen.fileName, content, scriptKindName);
        }

        public verifyErrorExistsBetweenMarkers(startMarkerName: string, endMarkerName: string, shouldExist: boolean) {
            const startMarker = this.getMarkerByName(startMarkerName);
            const endMarker = this.getMarkerByName(endMarkerName);
            const predicate = (errorMinChar: number, errorLimChar: number, startPos: number, endPos: number) =>
                ((errorMinChar === startPos) && (errorLimChar === endPos)) ? true : false;

            const exists = this.anyErrorInRange(predicate, startMarker, endMarker);

            if (exists !== shouldExist) {
                this.printErrorLog(shouldExist, this.getAllDiagnostics());
                throw new Error(`${shouldExist ? "Expected" : "Did not expect"} failure between markers: '${startMarkerName}', '${endMarkerName}'`);
            }
        }

        public verifyOrganizeImports(newContent: string, mode?: ts.OrganizeImportsMode) {
            const changes = this.languageService.organizeImports({ fileName: this.activeFile.fileName, type: "file", mode }, this.formatCodeSettings, ts.emptyOptions);
            this.applyChanges(changes);
            this.verifyFileContent(this.activeFile.fileName, newContent);
        }

        private raiseError(message: string): never {
            throw new Error(this.messageAtLastKnownMarker(message));
        }

        private messageAtLastKnownMarker(message: string) {
            const locationDescription = this.lastKnownMarker !== undefined ? this.lastKnownMarker : this.getLineColStringAtPosition(this.currentCaretPosition);
            return `At marker '${locationDescription}': ${message}`;
        }

        private assertionMessageAtLastKnownMarker(msg: string) {
            return "\nMarker: " + this.lastKnownMarker + "\nChecking: " + msg + "\n\n";
        }

        private getDiagnostics(fileName: string, includeSuggestions = false): ts.Diagnostic[] {
            return [
                ...this.languageService.getSyntacticDiagnostics(fileName),
                ...this.languageService.getSemanticDiagnostics(fileName),
                ...(includeSuggestions ? this.languageService.getSuggestionDiagnostics(fileName) : ts.emptyArray),
            ];
        }

        private getAllDiagnostics(): readonly ts.Diagnostic[] {
            return ts.flatMap(this.languageServiceAdapterHost.getFilenames(), fileName => {
                if (!ts.isAnySupportedFileExtension(fileName)) {
                    return [];
                }

                const baseName = ts.getBaseFileName(fileName);
                if (baseName === "package.json" || baseName === "oh-package.json5" || baseName === "tsconfig.json" || baseName === "jsconfig.json") {
                    return [];
                }
                return this.getDiagnostics(fileName);
            });
        }

        public verifyErrorExistsAfterMarker(markerName: string, shouldExist: boolean, after: boolean) {
            const marker: Marker = this.getMarkerByName(markerName);
            let predicate: (errorMinChar: number, errorLimChar: number, startPos: number, endPos: number) => boolean;

            if (after) {
                predicate = (errorMinChar: number, errorLimChar: number, startPos: number) =>
                    ((errorMinChar >= startPos) && (errorLimChar >= startPos)) ? true : false;
            }
            else {
                predicate = (errorMinChar: number, errorLimChar: number, startPos: number) =>
                    ((errorMinChar <= startPos) && (errorLimChar <= startPos)) ? true : false;
            }

            const exists = this.anyErrorInRange(predicate, marker);
            const diagnostics = this.getAllDiagnostics();

            if (exists !== shouldExist) {
                this.printErrorLog(shouldExist, diagnostics);
                throw new Error(`${shouldExist ? "Expected" : "Did not expect"} failure at marker '${markerName}'`);
            }
        }

        private anyErrorInRange(predicate: (errorMinChar: number, errorLimChar: number, startPos: number, endPos: number | undefined) => boolean, startMarker: Marker, endMarker?: Marker): boolean {
            return this.getDiagnostics(startMarker.fileName).some(({ start, length }) =>
                predicate(start!, start! + length!, startMarker.position, endMarker === undefined ? undefined : endMarker.position)); // TODO: GH#18217
        }

        private printErrorLog(expectErrors: boolean, errors: readonly ts.Diagnostic[]): void {
            if (expectErrors) {
                Harness.IO.log("Expected error not found.  Error list is:");
            }
            else {
                Harness.IO.log("Unexpected error(s) found.  Error list is:");
            }

            for (const { start, length, messageText, file } of errors) {
                Harness.IO.log("  " + this.formatRange(file, start!, length!) + // TODO: GH#18217
                    ", message: " + ts.flattenDiagnosticMessageText(messageText, Harness.IO.newLine()) + "\n");
            }
        }

        private formatRange(file: ts.SourceFile | undefined, start: number, length: number) {
            if (file) {
                return `from: ${this.formatLineAndCharacterOfPosition(file, start)}, to: ${this.formatLineAndCharacterOfPosition(file, start + length)}`;
            }
            return "global";
        }

        private formatLineAndCharacterOfPosition(file: ts.SourceFile, pos: number) {
            if (file) {
                const { line, character } = ts.getLineAndCharacterOfPosition(file, pos);
                return `${line}:${character}`;
            }
            return "global";
        }

        private formatPosition(file: ts.SourceFile, pos: number) {
            if (file) {
                return file.fileName + "@" + pos;
            }
            return "global";
        }

        public verifyNoErrors() {
            ts.forEachKey(this.inputFiles, fileName => {
                if (!ts.isAnySupportedFileExtension(fileName)
                    || Harness.getConfigNameFromFileName(fileName)
                    // Can't get a Program in Server tests
                    || this.testType !== FourSlashTestType.Server && !ts.getAllowJSCompilerOption(this.getProgram().getCompilerOptions()) && !ts.resolutionExtensionIsTSOrJson(ts.extensionFromPath(fileName))
                    || ts.getBaseFileName(fileName) === "package.json") return;
                const errors = this.getDiagnostics(fileName).filter(e => e.category !== ts.DiagnosticCategory.Suggestion);
                if (errors.length) {
                    this.printErrorLog(/*expectErrors*/ false, errors);
                    const error = errors[0];
                    const message = typeof error.messageText === "string" ? error.messageText : error.messageText.messageText;
                    this.raiseError(`Found an error: ${this.formatPosition(error.file!, error.start!)}: ${message}`);
                }
            });
        }

        public verifyErrorExistsAtRange(range: Range, code: number, expectedMessage?: string) {
            const span = ts.createTextSpanFromRange(range);
            const hasMatchingError = ts.some(
                this.getDiagnostics(range.fileName),
                ({ code, messageText, start, length }) =>
                    code === code &&
                    (!expectedMessage || expectedMessage === messageText) &&
                    ts.isNumber(start) && ts.isNumber(length) &&
                    ts.textSpansEqual(span, { start, length }));

            if (!hasMatchingError) {
                this.raiseError(`No error with code ${code} found at provided range.`);
            }
        }

        public verifyNumberOfErrorsInCurrentFile(expected: number) {
            const errors = this.getDiagnostics(this.activeFile.fileName);
            const actual = errors.length;

            if (actual !== expected) {
                this.printErrorLog(/*expectErrors*/ false, errors);
                const errorMsg = "Actual number of errors (" + actual + ") does not match expected number (" + expected + ")";
                Harness.IO.log(errorMsg);
                this.raiseError(errorMsg);
            }
        }

        public verifyEval(expr: string, value: any) {
            const emit = this.languageService.getEmitOutput(this.activeFile.fileName);
            if (emit.outputFiles.length !== 1) {
                throw new Error("Expected exactly one output from emit of " + this.activeFile.fileName);
            }

            const evaluation = new Function(`${emit.outputFiles[0].text};\r\nreturn (${expr});`)(); // eslint-disable-line no-new-func
            if (evaluation !== value) {
                this.raiseError(`Expected evaluation of expression "${expr}" to equal "${value}", but got "${evaluation}"`);
            }
        }

        public verifyGoToDefinitionIs(endMarker: ArrayOrSingle<string>) {
            this.verifyGoToXWorker(/*startMarker*/ undefined, toArray(endMarker), () => this.getGoToDefinition());
        }

        public verifyGoToDefinition(arg0: any, endMarkerNames?: ArrayOrSingle<string | { marker: string, unverified?: boolean }> | { file: string, unverified?: boolean }) {
            this.verifyGoToX(arg0, endMarkerNames, () => this.getGoToDefinitionAndBoundSpan());
        }

        public verifyGoToSourceDefinition(startMarkerNames: ArrayOrSingle<string>, end?: ArrayOrSingle<string | { marker: string, unverified?: boolean }> | { file: string, unverified?: boolean }) {
            if (this.testType !== FourSlashTestType.Server) {
                this.raiseError("goToSourceDefinition may only be used in fourslash/server tests.");
            }
            this.verifyGoToX(startMarkerNames, end, () => (this.languageService as ts.server.SessionClient).getSourceDefinitionAndBoundSpan(this.activeFile.fileName, this.currentCaretPosition)!);
        }

        private getGoToDefinition(): readonly ts.DefinitionInfo[] {
            return this.languageService.getDefinitionAtPosition(this.activeFile.fileName, this.currentCaretPosition)!;
        }

        private getGoToDefinitionAndBoundSpan(): ts.DefinitionInfoAndBoundSpan {
            return this.languageService.getDefinitionAndBoundSpan(this.activeFile.fileName, this.currentCaretPosition)!;
        }

        public verifyGoToType(arg0: any, endMarkerNames?: ArrayOrSingle<string>) {
            this.verifyGoToX(arg0, endMarkerNames, () =>
                this.languageService.getTypeDefinitionAtPosition(this.activeFile.fileName, this.currentCaretPosition));
        }

        private verifyGoToX(arg0: any, endMarkerNames: ArrayOrSingle<string | { marker: string, unverified?: boolean }> | { file: string, unverified?: boolean } | undefined, getDefs: () => readonly ts.DefinitionInfo[] | ts.DefinitionInfoAndBoundSpan | undefined) {
            if (endMarkerNames) {
                this.verifyGoToXPlain(arg0, endMarkerNames, getDefs);
            }
            else if (ts.isArray(arg0)) {
                const pairs = arg0 as readonly [ArrayOrSingle<string>, ArrayOrSingle<string>][];
                for (const [start, end] of pairs) {
                    this.verifyGoToXPlain(start, end, getDefs);
                }
            }
            else {
                const obj: { [startMarkerName: string]: ArrayOrSingle<string> } = arg0;
                for (const startMarkerName in obj) {
                    if (ts.hasProperty(obj, startMarkerName)) {
                        this.verifyGoToXPlain(startMarkerName, obj[startMarkerName], getDefs);
                    }
                }
            }
        }

        private verifyGoToXPlain(startMarkerNames: ArrayOrSingle<string>, endMarkerNames: ArrayOrSingle<string | { marker: string, unverified?: boolean }> | { file: string, unverified?: boolean }, getDefs: () => readonly ts.DefinitionInfo[] | ts.DefinitionInfoAndBoundSpan | undefined) {
            for (const start of toArray(startMarkerNames)) {
                this.verifyGoToXSingle(start, endMarkerNames, getDefs);
            }
        }

        public verifyGoToDefinitionForMarkers(markerNames: string[]) {
            for (const markerName of markerNames) {
                this.verifyGoToXSingle(`${markerName}Reference`, `${markerName}Definition`, () => this.getGoToDefinition());
            }
        }

        private verifyGoToXSingle(startMarkerName: string, endMarkerNames: ArrayOrSingle<string | { marker: string, unverified?: boolean }> | { file: string, unverified?: boolean }, getDefs: () => readonly ts.DefinitionInfo[] | ts.DefinitionInfoAndBoundSpan | undefined) {
            this.goToMarker(startMarkerName);
            this.verifyGoToXWorker(startMarkerName, toArray(endMarkerNames), getDefs, startMarkerName);
        }

        private verifyGoToXWorker(startMarker: string | undefined, endMarkers: readonly (string | { marker?: string, file?: string, unverified?: boolean })[], getDefs: () => readonly ts.DefinitionInfo[] | ts.DefinitionInfoAndBoundSpan | undefined, startMarkerName?: string) {
            const defs = getDefs();
            let definitions: readonly ts.DefinitionInfo[];
            let testName: string;

            if (!defs || ts.isArray(defs)) {
                definitions = defs as ts.DefinitionInfo[] || [];
                testName = "goToDefinitions";
            }
            else {
                this.verifyDefinitionTextSpan(defs, startMarkerName!);

                definitions = defs.definitions!; // TODO: GH#18217
                testName = "goToDefinitionsAndBoundSpan";
            }

            if (endMarkers.length !== definitions.length) {
                const markers = definitions.map(d => ({ text: "HERE", fileName: d.fileName, position: d.textSpan.start }));
                const actual = this.renderMarkers(markers);
                this.raiseError(`${testName} failed - expected to find ${endMarkers.length} definitions but got ${definitions.length}\n\n${actual}`);
            }

            ts.zipWith(endMarkers, definitions, (endMarkerOrFileResult, definition, i) => {
                const markerName = typeof endMarkerOrFileResult === "string" ? endMarkerOrFileResult : endMarkerOrFileResult.marker;
                const marker = markerName !== undefined ? this.getMarkerByName(markerName) : undefined;
                const expectedFileName = marker?.fileName || typeof endMarkerOrFileResult !== "string" && endMarkerOrFileResult.file;
                ts.Debug.assert(typeof expectedFileName === "string");
                const expectedPosition = marker?.position || 0;
                if (ts.comparePaths(expectedFileName, definition.fileName, /*ignoreCase*/ true) !== ts.Comparison.EqualTo || expectedPosition !== definition.textSpan.start) {
                    const markers = [{ text: "EXPECTED", fileName: expectedFileName, position: expectedPosition }, { text: "ACTUAL", fileName: definition.fileName, position: definition.textSpan.start }];
                    const text = this.renderMarkers(markers);
                    this.raiseError(`${testName} failed for definition ${markerName || expectedFileName} (${i}): expected ${expectedFileName} at ${expectedPosition}, got ${definition.fileName} at ${definition.textSpan.start}\n\n${text}\n`);
                }
                if (definition.unverified && (typeof endMarkerOrFileResult === "string" || !endMarkerOrFileResult.unverified)) {
                    const isFileResult = typeof endMarkerOrFileResult !== "string" && !!endMarkerOrFileResult.file;
                    this.raiseError(
                        `${testName} failed for definition ${markerName || expectedFileName} (${i}): The actual definition was an \`unverified\` result. Use:\n\n` +
                        `    verify.goToDefinition(${startMarker === undefined ? "startMarker" : `"${startMarker}"`}, { ${isFileResult ? `file: "${expectedFileName}"` : `marker: "${markerName}"`}, unverified: true })\n\n` +
                        `if this is expected.`
                    );
                }
            });
        }

        private renderMarkers(markers: { text: string, fileName: string, position: number }[]) {
            const filesToDisplay = ts.deduplicate(markers.map(m => m.fileName), ts.equateValues);
            return filesToDisplay.map(fileName => {
                const markersToRender = markers.filter(m => m.fileName === fileName).sort((a, b) => b.position - a.position);
                let fileContent = this.tryGetFileContent(fileName) || "";
                for (const marker of markersToRender) {
                    fileContent = fileContent.slice(0, marker.position) + `\x1b[1;4m/*${marker.text}*/\x1b[0;31m` + fileContent.slice(marker.position);
                }
                return `// @Filename: ${fileName}\n${fileContent}`;
            }).join("\n\n");
        }

        private verifyDefinitionTextSpan(defs: ts.DefinitionInfoAndBoundSpan, startMarkerName: string) {
            const range = this.testData.ranges.find(range => this.markerName(range.marker!) === startMarkerName);

            if (!range && !defs.textSpan) {
                return;
            }

            if (!range) {
                const marker = this.getMarkerByName(startMarkerName);
                const startFile = marker.fileName;
                const fileContent = this.getFileContent(startFile);
                const spanContent = fileContent.slice(defs.textSpan.start, ts.textSpanEnd(defs.textSpan));
                const spanContentWithMarker = spanContent.slice(0, marker.position - defs.textSpan.start) + `/*${startMarkerName}*/` + spanContent.slice(marker.position - defs.textSpan.start);
                const suggestedFileContent = (fileContent.slice(0, defs.textSpan.start) + `\x1b[1;4m[|${spanContentWithMarker}|]\x1b[0;31m` + fileContent.slice(ts.textSpanEnd(defs.textSpan)))
                    .split(/\r?\n/).map(line => " ".repeat(6) + line).join(ts.sys.newLine);
                this.raiseError(`goToDefinitionsAndBoundSpan failed. Found a starting TextSpan around '${spanContent}' in '${startFile}' (at position ${defs.textSpan.start}). `
                    + `If this is the correct input span, put a fourslash range around it: \n\n${suggestedFileContent}\n`);
            }
            else {
                this.assertTextSpanEqualsRange(defs.textSpan, range, "goToDefinitionsAndBoundSpan failed");
            }
        }

        public verifyGetEmitOutputForCurrentFile(expected: string): void {
            const emit = this.languageService.getEmitOutput(this.activeFile.fileName);
            if (emit.outputFiles.length !== 1) {
                throw new Error("Expected exactly one output from emit of " + this.activeFile.fileName);
            }
            const actual = emit.outputFiles[0].text;
            if (actual !== expected) {
                this.raiseError(`Expected emit output to be "${expected}", but got "${actual}"`);
            }
        }

        public verifyGetEmitOutputContentsForCurrentFile(expected: ts.OutputFile[]): void {
            const emit = this.languageService.getEmitOutput(this.activeFile.fileName);
            assert.equal(emit.outputFiles.length, expected.length, "Number of emit output files");
            ts.zipWith(emit.outputFiles, expected, (outputFile, expected) => {
                assert.equal(outputFile.name, expected.name, "FileName");
                assert.equal(outputFile.text, expected.text, "Content");
            });
        }

        public verifyInlayHints(expected: readonly FourSlashInterface.VerifyInlayHintsOptions[], span: ts.TextSpan = { start: 0, length: this.activeFile.content.length }, preference?: ts.UserPreferences) {
            const hints = this.languageService.provideInlayHints(this.activeFile.fileName, span, preference);
            assert.equal(hints.length, expected.length, "Number of hints");

            const sortHints = (a: ts.InlayHint, b: ts.InlayHint) => {
                return a.position - b.position;
            };
            ts.zipWith(hints.sort(sortHints), [...expected].sort(sortHints), (actual, expected) => {
                assert.equal(actual.text, expected.text, "Text");
                assert.equal(actual.position, expected.position, "Position");
                assert.equal(actual.kind, expected.kind, "Kind");
                assert.equal(actual.whitespaceBefore, expected.whitespaceBefore, "whitespaceBefore");
                assert.equal(actual.whitespaceAfter, expected.whitespaceAfter, "whitespaceAfter");
            });
        }

        public verifyCompletions(options: FourSlashInterface.VerifyCompletionsOptions) {
            if (options.marker === undefined) {
                this.verifyCompletionsWorker(options);
            }
            else {
                for (const marker of toArray(options.marker)) {
                    this.goToMarker(marker);
                    this.verifyCompletionsWorker({ ...options, marker });
                }
            }
        }

        private verifyCompletionsWorker(options: FourSlashInterface.VerifyCompletionsOptions): void {
            const actualCompletions = this.getCompletionListAtCaret({ ...options.preferences, triggerCharacter: options.triggerCharacter })!;
            if (!actualCompletions) {
                if (ts.hasProperty(options, "exact") && (options.exact === undefined || ts.isArray(options.exact) && !options.exact.length)) {
                    return;
                }
                this.raiseError(`No completions at position '${this.currentCaretPosition}'.`);
            }

            if (actualCompletions.isNewIdentifierLocation !== (options.isNewIdentifierLocation || false)) {
                this.raiseError(`Expected 'isNewIdentifierLocation' to be ${options.isNewIdentifierLocation || false}, got ${actualCompletions.isNewIdentifierLocation}`);
            }

            if (ts.hasProperty(options, "isGlobalCompletion") && actualCompletions.isGlobalCompletion !== options.isGlobalCompletion) {
                this.raiseError(`Expected 'isGlobalCompletion to be ${options.isGlobalCompletion}, got ${actualCompletions.isGlobalCompletion}`);
            }

            if (ts.hasProperty(options, "optionalReplacementSpan")) {
                assert.deepEqual(
                    actualCompletions.optionalReplacementSpan && actualCompletions.optionalReplacementSpan,
                    options.optionalReplacementSpan && ts.createTextSpanFromRange(options.optionalReplacementSpan),
                    "Expected 'optionalReplacementSpan' properties to match");
            }

            const nameToEntries = new ts.Map<string, ts.CompletionEntry[]>();
            for (const entry of actualCompletions.entries) {
                const entries = nameToEntries.get(entry.name);
                if (!entries) {
                    nameToEntries.set(entry.name, [entry]);
                }
                else {
                    if (entries.some(e =>
                        e.source === entry.source &&
                        e.data?.exportName === entry.data?.exportName &&
                        e.data?.fileName === entry.data?.fileName &&
                        e.data?.moduleSpecifier === entry.data?.moduleSpecifier &&
                        e.data?.ambientModuleName === entry.data?.ambientModuleName
                    )) {
                        this.raiseError(`Duplicate completions for ${entry.name}`);
                    }
                    entries.push(entry);
                }
            }

            if (ts.hasProperty(options, "exact")) {
                ts.Debug.assert(!ts.hasProperty(options, "includes") && !ts.hasProperty(options, "excludes") && !ts.hasProperty(options, "unsorted"));
                if (options.exact === undefined) throw this.raiseError("Expected no completions");
                this.verifyCompletionsAreExactly(actualCompletions.entries, options.exact, options.marker);
            }
            else if (options.unsorted) {
                ts.Debug.assert(!ts.hasProperty(options, "includes") && !ts.hasProperty(options, "excludes"));
                for (const expectedEntry of options.unsorted) {
                    const name = typeof expectedEntry === "string" ? expectedEntry : expectedEntry.name;
                    const found = nameToEntries.get(name);
                    if (!found) throw this.raiseError(`Unsorted: completion '${name}' not found.`);
                    if (!found.length) throw this.raiseError(`Unsorted: no completions with name '${name}' remain unmatched.`);
                    this.verifyCompletionEntry(found.shift()!, expectedEntry);
                }
                if (actualCompletions.entries.length !== options.unsorted.length) {
                    const unmatched: string[] = [];
                    nameToEntries.forEach(entries => {
                        unmatched.push(...entries.map(e => e.name));
                    });
                    this.raiseError(`Additional completions found not included in 'unsorted': ${unmatched.join("\n")}`);
                }
            }
            else {
                if (options.includes) {
                    for (const include of toArray(options.includes)) {
                        const name = typeof include === "string" ? include : include.name;
                        const found = nameToEntries.get(name);
                        if (!found) throw this.raiseError(`Includes: completion '${name}' not found.`);
                        if (!found.length) throw this.raiseError(`Includes: no completions with name '${name}' remain unmatched.`);
                        this.verifyCompletionEntry(found.shift()!, include);
                    }
                }
                if (options.excludes) {
                    for (const exclude of toArray(options.excludes)) {
                        assert(typeof exclude === "string");
                        if (nameToEntries.has(exclude)) {
                            this.raiseError(`Excludes: unexpected completion '${exclude}' found.`);
                        }
                    }
                }
            }
        }

        private verifyCompletionEntry(actual: ts.CompletionEntry, expected: FourSlashInterface.ExpectedCompletionEntry) {
            expected = typeof expected === "string" ? { name: expected } : expected;

            if (actual.insertText !== expected.insertText) {
                this.raiseError(`At entry ${actual.name}: Completion insert text did not match: ${showTextDiff(expected.insertText || "", actual.insertText || "")}`);
            }
            const convertedReplacementSpan = expected.replacementSpan && ts.createTextSpanFromRange(expected.replacementSpan);
            if (convertedReplacementSpan?.length) {
                try {
                    assert.deepEqual(actual.replacementSpan, convertedReplacementSpan);
                }
                catch {
                    this.raiseError(`At entry ${actual.name}: Expected completion replacementSpan to be ${stringify(convertedReplacementSpan)}, got ${stringify(actual.replacementSpan)}`);
                }
            }

            if (expected.kind !== undefined || expected.kindModifiers !== undefined) {
                assert.equal(actual.kind, expected.kind, `At entry ${actual.name}: Expected 'kind' for ${actual.name} to match`);
                assert.equal(actual.kindModifiers, expected.kindModifiers || "", `At entry ${actual.name}:  Expected 'kindModifiers' for ${actual.name} to match`);
            }
            if (expected.isFromUncheckedFile !== undefined) {
                assert.equal<boolean | undefined>(actual.isFromUncheckedFile, expected.isFromUncheckedFile, `At entry ${actual.name}: Expected 'isFromUncheckedFile' properties to match`);
            }
            if (expected.isPackageJsonImport !== undefined) {
                assert.equal<boolean | undefined>(actual.isPackageJsonImport, expected.isPackageJsonImport, `At entry ${actual.name}: Expected 'isPackageJsonImport' properties to match`);
            }

            assert.equal(actual.labelDetails?.description, expected.labelDetails?.description, `At entry ${actual.name}: Expected 'labelDetails.description' properties to match`);
            assert.equal(actual.labelDetails?.detail, expected.labelDetails?.detail, `At entry ${actual.name}: Expected 'labelDetails.detail' properties to match`);
            assert.equal(actual.hasAction, expected.hasAction, `At entry ${actual.name}: Expected 'hasAction' properties to match`);
            assert.equal(actual.isRecommended, expected.isRecommended, `At entry ${actual.name}: Expected 'isRecommended' properties to match'`);
            assert.equal(actual.isSnippet, expected.isSnippet, `At entry ${actual.name}: Expected 'isSnippet' properties to match`);
            assert.equal(actual.source, expected.source, `At entry ${actual.name}: Expected 'source' values to match`);
            assert.equal(actual.sortText, expected.sortText || ts.Completions.SortText.LocationPriority, `At entry ${actual.name}: Expected 'sortText' properties to match`);
            if (expected.sourceDisplay && actual.sourceDisplay) {
                assert.equal(ts.displayPartsToString(actual.sourceDisplay), expected.sourceDisplay, `At entry ${actual.name}: Expected 'sourceDisplay' properties to match`);
            }

            if (expected.text !== undefined) {
                const actualDetails = ts.Debug.checkDefined(this.getCompletionEntryDetails(actual.name, actual.source, actual.data), `No completion details available for name '${actual.name}' and source '${actual.source}'`);
                assert.equal(ts.displayPartsToString(actualDetails.displayParts), expected.text, "Expected 'text' property to match 'displayParts' string");
                assert.equal(ts.displayPartsToString(actualDetails.documentation), expected.documentation || "", "Expected 'documentation' property to match 'documentation' display parts string");
                // TODO: GH#23587
                // assert.equal(actualDetails.kind, actual.kind);
                assert.equal(actualDetails.kindModifiers, actual.kindModifiers, "Expected 'kindModifiers' properties to match");
                assert.equal(actualDetails.source && ts.displayPartsToString(actualDetails.source), expected.sourceDisplay, "Expected 'sourceDisplay' property to match 'source' display parts string");
                if (!actual.sourceDisplay) {
                    assert.equal(actualDetails.sourceDisplay && ts.displayPartsToString(actualDetails.sourceDisplay), expected.sourceDisplay, "Expected 'sourceDisplay' property to match 'sourceDisplay' display parts string");
                }
                assert.deepEqual(actualDetails.tags, expected.tags);
            }
            else {
                assert(expected.documentation === undefined && expected.tags === undefined, "If specifying completion details, should specify 'text'");
            }
        }

        private verifyCompletionsAreExactly(actual: readonly ts.CompletionEntry[], expected: ArrayOrSingle<FourSlashInterface.ExpectedCompletionEntry> | FourSlashInterface.ExpectedExactCompletionsPlus, marker?: ArrayOrSingle<string | Marker>) {
            if (!ts.isArray(expected)) {
                expected = [expected];
            }

            // First pass: test that names are right. Then we'll test details.
            assert.deepEqual(actual.map(a => a.name), expected.map(e => typeof e === "string" ? e : e.name), marker ? "At marker " + JSON.stringify(marker) : undefined);

            ts.zipWith(actual, expected, (completion, expectedCompletion, index) => {
                const name = typeof expectedCompletion === "string" ? expectedCompletion : expectedCompletion.name;
                if (completion.name !== name) {
                    this.raiseError(`${marker ? JSON.stringify(marker) : ""} Expected completion at index ${index} to be ${name}, got ${completion.name}`);
                }
                this.verifyCompletionEntry(completion, expectedCompletion);
            });

            // All completions were correct in the sort order given. If that order was produced by a function
            // like `completion.globalsPlus`, ensure the "plus" array was sorted in the same way.
            const { plusArgument, plusFunctionName } = expected as FourSlashInterface.ExpectedExactCompletionsPlus;
            if (plusArgument) {
                assert.deepEqual(
                    plusArgument,
                    expected.filter(entry => plusArgument.includes(entry)),
                    `At marker ${JSON.stringify(marker)}: Argument to '${plusFunctionName}' was incorrectly sorted.`);
            }
        }

        /** Use `getProgram` instead of accessing this directly. */
        private _program: ts.Program | undefined | "missing";
        /** Use `getChecker` instead of accessing this directly. */
        private _checker: ts.TypeChecker | undefined;

        private getProgram(): ts.Program {
            if (!this._program) this._program = this.languageService.getProgram() || "missing";
            if (this._program === "missing") ts.Debug.fail("Could not retrieve program from language service");
            return this._program;
        }

        private getChecker() {
            return this._checker || (this._checker = this.getProgram().getTypeChecker());
        }

        private getSourceFile(): ts.SourceFile {
            const { fileName } = this.activeFile;
            const result = this.getProgram().getSourceFile(fileName);
            if (!result) {
                throw new Error(`Could not get source file ${fileName}`);
            }
            return result;
        }

        private getNode(): ts.Node {
            return ts.getTouchingPropertyName(this.getSourceFile(), this.currentCaretPosition);
        }

        private goToAndGetNode(range: Range): ts.Node {
            this.goToRangeStart(range);
            const node = this.getNode();
            this.verifyRange("touching property name", range, node);
            return node;
        }

        private verifyRange(desc: string, expected: ts.TextRange, actual: ts.Node) {
            const actualStart = actual.getStart();
            const actualEnd = actual.getEnd();
            if (actualStart !== expected.pos || actualEnd !== expected.end) {
                this.raiseError(`${desc} should be ${expected.pos}-${expected.end}, got ${actualStart}-${actualEnd}`);
            }
        }

        private verifySymbol(symbol: ts.Symbol, declarationRanges: Range[]) {
            const { declarations } = symbol;
            if (declarations?.length !== declarationRanges.length) {
                this.raiseError(`Expected to get ${declarationRanges.length} declarations, got ${declarations?.length}`);
            }

            ts.zipWith(declarations, declarationRanges, (decl, range) => {
                this.verifyRange("symbol declaration", range, decl);
            });
        }

        public verifySymbolAtLocation(startRange: Range, declarationRanges: Range[]): void {
            const node = this.goToAndGetNode(startRange);
            const symbol = this.getChecker().getSymbolAtLocation(node)!;
            if (!symbol) {
                this.raiseError("Could not get symbol at location");
            }
            this.verifySymbol(symbol, declarationRanges);
        }

        public symbolsInScope(range: Range): ts.Symbol[] {
            const node = this.goToAndGetNode(range);
            return this.getChecker().getSymbolsInScope(node, ts.SymbolFlags.Value | ts.SymbolFlags.Type | ts.SymbolFlags.Namespace);
        }

        public setTypesRegistry(map: ts.MapLike<void>): void {
            this.languageServiceAdapterHost.typesRegistry = new ts.Map(ts.getEntries(map));
        }

        public verifyTypeOfSymbolAtLocation(range: Range, symbol: ts.Symbol, expected: string): void {
            const node = this.goToAndGetNode(range);
            const checker = this.getChecker();
            const type = checker.getTypeOfSymbolAtLocation(symbol, node);

            const actual = checker.typeToString(type);
            if (actual !== expected) {
                this.raiseError(displayExpectedAndActualString(expected, actual));
            }
        }

        public verifyBaselineFindAllReferences(...markerNames: string[]) {
            ts.Debug.assert(markerNames.length > 0, "Must pass at least one marker name to `verifyBaselineFindAllReferences()`");
            this.verifyBaselineFindAllReferencesWorker("", markerNames);
        }

        // Used when a single test needs to produce multiple baselines
        public verifyBaselineFindAllReferencesMulti(seq: number, ...markerNames: string[]) {
            ts.Debug.assert(markerNames.length > 0, "Must pass at least one marker name to `baselineFindAllReferences()`");
            this.verifyBaselineFindAllReferencesWorker(`.${seq}`, markerNames);
        }

        private verifyBaselineFindAllReferencesWorker(suffix: string, markerNames: string[]) {
            const baseline = markerNames.map(markerName => {
                this.goToMarker(markerName);
                const marker = this.getMarkerByName(markerName);
                const references = this.languageService.findReferences(marker.fileName, marker.position);
                const refsByFile = references
                    ? ts.group(ts.sort(ts.flatMap(references, r => r.references), (a, b) => a.textSpan.start - b.textSpan.start), ref => ref.fileName)
                    : ts.emptyArray;

                // Write input files
                const baselineContent = this.getBaselineContentForGroupedReferences(refsByFile, markerName);

                // Write response JSON
                return baselineContent + JSON.stringify(references, undefined, 2);
            }).join("\n\n");
            Harness.Baseline.runBaseline(this.getBaselineFileNameForContainingTestFile(`${suffix}.baseline.jsonc`), baseline);
        }

        public verifyBaselineGetFileReferences(fileName: string) {
            const references = this.languageService.getFileReferences(fileName);
            const refsByFile = references
                ? ts.group(ts.sort(references, (a, b) => a.textSpan.start - b.textSpan.start), ref => ref.fileName)
                : ts.emptyArray;

            // Write input files
            let baselineContent = this.getBaselineContentForGroupedReferences(refsByFile);

            // Write response JSON
            baselineContent += JSON.stringify(references, undefined, 2);
            Harness.Baseline.runBaseline(this.getBaselineFileNameForContainingTestFile(".baseline.jsonc"), baselineContent);
        }

        private getBaselineContentForGroupedReferences(refsByFile: readonly (readonly ts.ReferenceEntry[])[], markerName?: string) {
            const marker = markerName !== undefined ? this.getMarkerByName(markerName) : undefined;
            let baselineContent = "";
            for (const group of refsByFile) {
                baselineContent += getBaselineContentForFile(group[0].fileName, this.getFileContent(group[0].fileName));
                baselineContent += "\n\n";
            }
            return baselineContent;

            function getBaselineContentForFile(fileName: string, content: string) {
                let newContent = `=== ${fileName} ===\n`;
                let pos = 0;
                for (const { textSpan } of refsByFile.find(refs => refs[0].fileName === fileName) ?? ts.emptyArray) {
                    const end = textSpan.start + textSpan.length;
                    if (fileName === marker?.fileName && pos <= marker.position && marker.position < textSpan.start) {
                        newContent += content.slice(pos, marker.position);
                        newContent += "/*FIND ALL REFS*/";
                        pos = marker.position;
                    }
                    newContent += content.slice(pos, textSpan.start);
                    pos = textSpan.start;
                    // It's easier to read if the /*FIND ALL REFS*/ comment is outside the range markers, which makes
                    // this code a bit more verbose than it would be if I were less picky about the baseline format.
                    if (fileName === marker?.fileName && marker.position === textSpan.start) {
                        newContent += "/*FIND ALL REFS*/";
                        newContent += "[|";
                    }
                    else if (fileName === marker?.fileName && ts.textSpanContainsPosition(textSpan, marker.position)) {
                        newContent += "[|";
                        newContent += content.slice(pos, marker.position);
                        newContent += "/*FIND ALL REFS*/";
                        pos = marker.position;
                    }
                    else {
                        newContent += "[|";
                    }
                    newContent += content.slice(pos, end);
                    newContent += "|]";
                    pos = end;
                }
                if (marker?.fileName === fileName && marker.position >= pos) {
                    newContent += content.slice(pos, marker.position);
                    newContent += "/*FIND ALL REFS*/";
                    pos = marker.position;
                }
                newContent += content.slice(pos);
                return newContent.split(/\r?\n/).map(l => "// " + l).join("\n");
            }
        }

        private assertObjectsEqual<T>(fullActual: T, fullExpected: T, msgPrefix = ""): void {
            const recur = <U>(actual: U, expected: U, path: string) => {
                const fail = (msg: string) => {
                    this.raiseError(`${msgPrefix} At ${path}: ${msg} ${displayExpectedAndActualString(stringify(fullExpected), stringify(fullActual))}`);
                };

                if ((actual === undefined) !== (expected === undefined)) {
                    fail(`Expected ${stringify(expected)}, got ${stringify(actual)}`);
                }

                for (const key in actual) {
                    if (ts.hasProperty(actual as any, key)) {
                        const ak = actual[key], ek = expected[key];
                        if (typeof ak === "object" && typeof ek === "object") {
                            recur(ak, ek, path ? path + "." + key : key);
                        }
                        else if (ak !== ek) {
                            fail(`Expected '${key}' to be '${stringify(ek)}', got '${stringify(ak)}'`);
                        }
                    }
                }

                for (const key in expected) {
                    if (ts.hasProperty(expected as any, key)) {
                        if (!ts.hasProperty(actual as any, key)) {
                            fail(`${msgPrefix}Missing property '${key}'`);
                        }
                    }
                }
            };

            if (fullActual === undefined || fullExpected === undefined) {
                if (fullActual === fullExpected) {
                    return;
                }
                this.raiseError(`${msgPrefix} ${displayExpectedAndActualString(stringify(fullExpected), stringify(fullActual))}`);
            }
            recur(fullActual, fullExpected, "");

        }

        public verifyDisplayPartsOfReferencedSymbol(expected: ts.SymbolDisplayPart[]) {
            const referencedSymbols = this.findReferencesAtCaret()!;

            if (referencedSymbols.length === 0) {
                this.raiseError("No referenced symbols found at current caret position");
            }
            else if (referencedSymbols.length > 1) {
                this.raiseError("More than one referenced symbol found");
            }

            assert.equal(TestState.getDisplayPartsJson(referencedSymbols[0].definition.displayParts),
                TestState.getDisplayPartsJson(expected), this.messageAtLastKnownMarker("referenced symbol definition display parts"));
        }

        private configure(preferences: ts.UserPreferences) {
            if (this.testType === FourSlashTestType.Server) {
                (this.languageService as ts.server.SessionClient).configure(preferences);
            }
        }

        private getCompletionListAtCaret(options?: ts.GetCompletionsAtPositionOptions): ts.CompletionInfo | undefined {
            if (options) {
                this.configure(options);
            }
            return this.languageService.getCompletionsAtPosition(
                this.activeFile.fileName,
                this.currentCaretPosition,
                options,
                this.formatCodeSettings);
        }

        private getCompletionEntryDetails(entryName: string, source: string | undefined, data: ts.CompletionEntryData | undefined, preferences?: ts.UserPreferences): ts.CompletionEntryDetails | undefined {
            if (preferences) {
                this.configure(preferences);
            }
            return this.languageService.getCompletionEntryDetails(this.activeFile.fileName, this.currentCaretPosition, entryName, this.formatCodeSettings, source, preferences, data);
        }

        private findReferencesAtCaret() {
            return this.languageService.findReferences(this.activeFile.fileName, this.currentCaretPosition);
        }

        public getSyntacticDiagnostics(expected: readonly FourSlashInterface.Diagnostic[]) {
            const diagnostics = this.languageService.getSyntacticDiagnostics(this.activeFile.fileName);
            this.testDiagnostics(expected, diagnostics, "error");
        }

        public getSemanticDiagnostics(expected: readonly FourSlashInterface.Diagnostic[]) {
            const diagnostics = this.languageService.getSemanticDiagnostics(this.activeFile.fileName);
            this.testDiagnostics(expected, diagnostics, "error");
        }

        public getSuggestionDiagnostics(expected: readonly FourSlashInterface.Diagnostic[]): void {
            this.testDiagnostics(expected, this.languageService.getSuggestionDiagnostics(this.activeFile.fileName), "suggestion");
        }

        private testDiagnostics(expected: readonly FourSlashInterface.Diagnostic[], diagnostics: readonly ts.Diagnostic[], category: string) {
            assert.deepEqual(ts.realizeDiagnostics(diagnostics, "\n"), expected.map((e): ts.RealizedDiagnostic => {
                const range = e.range || this.getRangesInFile()[0];
                if (!range) {
                    this.raiseError("Must provide a range for each expected diagnostic, or have one range in the fourslash source.");
                }
                return {
                    message: e.message,
                    category,
                    code: e.code,
                    ...ts.createTextSpanFromRange(range),
                    reportsUnnecessary: e.reportsUnnecessary,
                    reportsDeprecated: e.reportsDeprecated
                };
            }));
        }

        public verifyQuickInfoAt(markerName: string | Range, expectedText: string, expectedDocumentation?: string, expectedTags?: {name: string; text: string;}[]) {
            if (typeof markerName === "string") this.goToMarker(markerName);
            else this.goToRangeStart(markerName);

            this.verifyQuickInfoString(expectedText, expectedDocumentation, expectedTags);
        }

        public verifyQuickInfos(namesAndTexts: { [name: string]: string | [string, string] }) {
            for (const name in namesAndTexts) {
                if (ts.hasProperty(namesAndTexts, name)) {
                    const text = namesAndTexts[name];
                    if (ts.isArray(text)) {
                        assert(text.length === 2);
                        const [expectedText, expectedDocumentation] = text;
                        this.verifyQuickInfoAt(name, expectedText, expectedDocumentation);
                    }
                    else {
                        this.verifyQuickInfoAt(name, text);
                    }
                }
            }
        }

        public verifyQuickInfoString(expectedText: string, expectedDocumentation?: string, expectedTags?: { name: string; text: string; }[]) {
            if (expectedDocumentation === "") {
                throw new Error("Use 'undefined' instead of empty string for `expectedDocumentation`");
            }
            const actualQuickInfo = this.languageService.getQuickInfoAtPosition(this.activeFile.fileName, this.currentCaretPosition);
            const actualQuickInfoText = ts.displayPartsToString(actualQuickInfo?.displayParts);
            const actualQuickInfoDocumentation = ts.displayPartsToString(actualQuickInfo?.documentation);
            const actualQuickInfoTags = actualQuickInfo?.tags?.map(tag => ({ name: tag.name, text: ts.getTextOfJSDocTagInfo(tag) }));

            assert.equal(actualQuickInfoText, expectedText, this.messageAtLastKnownMarker("quick info text"));
            assert.equal(actualQuickInfoDocumentation, expectedDocumentation || "", this.assertionMessageAtLastKnownMarker("quick info doc"));
            if (!expectedTags) {
                // Skip if `expectedTags` is not given
            }
            else if (!actualQuickInfoTags) {
                assert.equal(actualQuickInfoTags, expectedTags, this.messageAtLastKnownMarker("QuickInfo tags"));
            }
            else {
                ts.zipWith(expectedTags, actualQuickInfoTags, (expectedTag, actualTag) => {
                    assert.equal(expectedTag.name, actualTag.name);
                    assert.equal(expectedTag.text, actualTag.text, this.messageAtLastKnownMarker("QuickInfo tag " + actualTag.name));
                });
            }
        }

        public verifyQuickInfoDisplayParts(kind: string, kindModifiers: string, textSpan: TextSpan,
            displayParts: ts.SymbolDisplayPart[],
            documentation: ts.SymbolDisplayPart[],
            tags: ts.JSDocTagInfo[] | undefined
        ) {

            const actualQuickInfo = this.languageService.getQuickInfoAtPosition(this.activeFile.fileName, this.currentCaretPosition)!;
            assert.equal(actualQuickInfo.kind, kind, this.messageAtLastKnownMarker("QuickInfo kind"));
            assert.equal(actualQuickInfo.kindModifiers, kindModifiers, this.messageAtLastKnownMarker("QuickInfo kindModifiers"));
            assert.equal(JSON.stringify(actualQuickInfo.textSpan), JSON.stringify(textSpan), this.messageAtLastKnownMarker("QuickInfo textSpan"));
            assert.equal(TestState.getDisplayPartsJson(actualQuickInfo.displayParts), TestState.getDisplayPartsJson(displayParts), this.messageAtLastKnownMarker("QuickInfo displayParts"));
            assert.equal(TestState.getDisplayPartsJson(actualQuickInfo.documentation), TestState.getDisplayPartsJson(documentation), this.messageAtLastKnownMarker("QuickInfo documentation"));
            if (!actualQuickInfo.tags || !tags) {
                assert.equal(actualQuickInfo.tags, tags, this.messageAtLastKnownMarker("QuickInfo tags"));
            }
            else {
                assert.equal(actualQuickInfo.tags.length, tags.length, this.messageAtLastKnownMarker("QuickInfo tags"));
                ts.zipWith(tags, actualQuickInfo.tags, (expectedTag, actualTag) => {
                    assert.equal(expectedTag.name, actualTag.name);
                    assert.equal(expectedTag.text, actualTag.text, this.messageAtLastKnownMarker("QuickInfo tag " + actualTag.name));
                });
            }
        }

        public verifyRangesAreRenameLocations(options?: Range[] | { findInStrings?: boolean, findInComments?: boolean, ranges?: Range[] }) {
            if (ts.isArray(options)) {
                this.verifyRenameLocations(options, options);
            }
            else {
                const ranges = options && options.ranges || this.getRanges();
                this.verifyRenameLocations(ranges, { ranges, ...options });
            }
        }

        public verifyRenameLocations(startRanges: ArrayOrSingle<Range>, options: FourSlashInterface.RenameLocationsOptions) {
            interface RangeMarkerData {
                id?: string;
                contextRangeIndex?: number,
                contextRangeDelta?: number
                contextRangeId?: string;
            }
            const { findInStrings = false, findInComments = false, ranges = this.getRanges(), providePrefixAndSuffixTextForRename = true } =
                ts.isArray(options)
                    ? { findInStrings: false, findInComments: false, ranges: options, providePrefixAndSuffixTextForRename: true }
                    : options;

            const _startRanges = toArray(startRanges);
            assert(_startRanges.length);
            for (const startRange of _startRanges) {
                this.goToRangeStart(startRange);

                const renameInfo = this.languageService.getRenameInfo(this.activeFile.fileName, this.currentCaretPosition, { providePrefixAndSuffixTextForRename });
                if (!renameInfo.canRename) {
                    this.raiseError("Expected rename to succeed, but it actually failed.");
                }

                const references = this.languageService.findRenameLocations(
                    this.activeFile.fileName, this.currentCaretPosition, findInStrings, findInComments, providePrefixAndSuffixTextForRename);

                const sort = (locations: readonly ts.RenameLocation[] | undefined) =>
                    locations && ts.sort(locations, (r1, r2) => ts.compareStringsCaseSensitive(r1.fileName, r2.fileName) || r1.textSpan.start - r2.textSpan.start);
                assert.deepEqual(sort(references), sort(ranges.map((rangeOrOptions): ts.RenameLocation => {
                    const { range, ...prefixSuffixText } = "range" in rangeOrOptions ? rangeOrOptions : { range: rangeOrOptions }; // eslint-disable-line local/no-in-operator
                    const { contextRangeIndex, contextRangeDelta, contextRangeId } = (range.marker && range.marker.data || {}) as RangeMarkerData;
                    let contextSpan: ts.TextSpan | undefined;
                    if (contextRangeDelta !== undefined) {
                        const allRanges = this.getRanges();
                        const index = allRanges.indexOf(range);
                        if (index !== -1) {
                            contextSpan = ts.createTextSpanFromRange(allRanges[index + contextRangeDelta]);
                        }
                    }
                    else if (contextRangeId !== undefined) {
                        const allRanges = this.getRanges();
                        const contextRange = ts.find(allRanges, range => (range.marker?.data as RangeMarkerData)?.id === contextRangeId);
                        if (contextRange) {
                            contextSpan = ts.createTextSpanFromRange(contextRange);
                        }
                    }
                    else if (contextRangeIndex !== undefined) {
                        contextSpan = ts.createTextSpanFromRange(this.getRanges()[contextRangeIndex]);
                    }
                    return {
                        fileName: range.fileName,
                        textSpan: ts.createTextSpanFromRange(range),
                        ...(contextSpan ? { contextSpan } : undefined),
                        ...prefixSuffixText
                    };
                })));
            }
        }

        public baselineRename(marker: string, options: FourSlashInterface.RenameOptions) {
            const { fileName, position } = this.getMarkerByName(marker);
            const locations = this.languageService.findRenameLocations(
                fileName,
                position,
                options.findInStrings ?? false,
                options.findInComments ?? false,
                options.providePrefixAndSuffixTextForRename);

            if (!locations) {
                this.raiseError(`baselineRename failed. Could not rename at the provided position.`);
            }

            const renamesByFile = ts.group(locations, l => l.fileName);
            const baselineContent = renamesByFile.map(renames => {
                const { fileName } = renames[0];
                const sortedRenames = ts.sort(renames, (a, b) => b.textSpan.start - a.textSpan.start);
                let baselineFileContent = this.getFileContent(fileName);
                for (const { textSpan } of sortedRenames) {
                    const isOriginalSpan = fileName === this.activeFile.fileName && ts.textSpanIntersectsWithPosition(textSpan, position);
                    baselineFileContent =
                        baselineFileContent.slice(0, textSpan.start) +
                        (isOriginalSpan ? "[|RENAME|]" : "RENAME") +
                        baselineFileContent.slice(textSpan.start + textSpan.length);
                }
                return `/*====== ${fileName} ======*/\n\n${baselineFileContent}`;
            }).join("\n\n") + "\n";

            Harness.Baseline.runBaseline(this.getBaselineFileNameForContainingTestFile(), baselineContent);
        }

        public verifyQuickInfoExists(negative: boolean) {
            const actualQuickInfo = this.languageService.getQuickInfoAtPosition(this.activeFile.fileName, this.currentCaretPosition);
            if (negative) {
                if (actualQuickInfo) {
                    this.raiseError("verifyQuickInfoExists failed. Expected quick info NOT to exist");
                }
            }
            else {
                if (!actualQuickInfo) {
                    this.raiseError("verifyQuickInfoExists failed. Expected quick info to exist");
                }
            }
        }

        public verifySignatureHelpPresence(expectPresent: boolean, triggerReason: ts.SignatureHelpTriggerReason | undefined, markers: readonly (string | Marker)[]) {
            if (markers.length) {
                for (const marker of markers) {
                    this.goToMarker(marker);
                    this.verifySignatureHelpPresence(expectPresent, triggerReason, ts.emptyArray);
                }
                return;
            }
            const actual = this.getSignatureHelp({ triggerReason });
            if (expectPresent !== !!actual) {
                if (actual) {
                    this.raiseError(`Expected no signature help, but got "${stringify(actual)}"`);
                }
                else {
                    this.raiseError("Expected signature help, but none was returned.");
                }
            }
        }

        public verifySignatureHelp(optionses: readonly FourSlashInterface.VerifySignatureHelpOptions[]) {
            for (const options of optionses) {
                if (options.marker === undefined) {
                    this.verifySignatureHelpWorker(options);
                }
                else {
                    for (const marker of toArray(options.marker)) {
                        this.goToMarker(marker);
                        this.verifySignatureHelpWorker(options);
                    }
                }
            }
        }

        private verifySignatureHelpWorker(options: FourSlashInterface.VerifySignatureHelpOptions) {
            const help = this.getSignatureHelp({ triggerReason: options.triggerReason })!;
            if (!help) {
                this.raiseError("Could not get a help signature");
            }

            const selectedItem = help.items[options.overrideSelectedItemIndex ?? help.selectedItemIndex];
            // Argument index may exceed number of parameters
            const currentParameter = selectedItem.parameters[help.argumentIndex] as ts.SignatureHelpParameter | undefined;

            assert.equal(help.items.length, options.overloadsCount || 1, this.assertionMessageAtLastKnownMarker("signature help overloads count"));

            assert.equal(ts.displayPartsToString(selectedItem.documentation), options.docComment || "", this.assertionMessageAtLastKnownMarker("current signature help doc comment"));

            if (options.text !== undefined) {
                assert.equal(
                    ts.displayPartsToString(selectedItem.prefixDisplayParts) +
                    selectedItem.parameters.map(p => ts.displayPartsToString(p.displayParts)).join(ts.displayPartsToString(selectedItem.separatorDisplayParts)) +
                    ts.displayPartsToString(selectedItem.suffixDisplayParts), options.text);
            }
            if (options.parameterName !== undefined) {
                assert.equal(currentParameter!.name, options.parameterName);
            }
            if (options.parameterSpan !== undefined) {
                assert.equal(ts.displayPartsToString(currentParameter!.displayParts), options.parameterSpan);
            }
            if (currentParameter) {
                assert.equal(ts.displayPartsToString(currentParameter.documentation), options.parameterDocComment || "", this.assertionMessageAtLastKnownMarker("current parameter Help DocComment"));
            }
            if (options.parameterCount !== undefined) {
                assert.equal(selectedItem.parameters.length, options.parameterCount);
            }
            if (options.argumentCount !== undefined) {
                assert.equal(help.argumentCount, options.argumentCount);
            }

            assert.equal(selectedItem.isVariadic, !!options.isVariadic);

            const actualTags = selectedItem.tags;
            assert.equal(actualTags.length, (options.tags || ts.emptyArray).length, this.assertionMessageAtLastKnownMarker("signature help tags"));
            ts.zipWith((options.tags || ts.emptyArray), actualTags, (expectedTag, actualTag) => {
                assert.equal(actualTag.name, expectedTag.name);
                assert.deepEqual(actualTag.text, expectedTag.text, this.assertionMessageAtLastKnownMarker("signature help tag " + actualTag.name));
            });

            const allKeys: readonly (keyof FourSlashInterface.VerifySignatureHelpOptions)[] = [
                "marker",
                "triggerReason",
                "overloadsCount",
                "docComment",
                "text",
                "parameterName",
                "parameterSpan",
                "parameterDocComment",
                "parameterCount",
                "isVariadic",
                "tags",
                "argumentCount",
                "overrideSelectedItemIndex"
            ];
            for (const key in options) {
                if (!ts.contains(allKeys, key)) {
                    ts.Debug.fail("Unexpected key " + key);
                }
            }
        }

        private validate(name: string, expected: string | undefined, actual: string | undefined) {
            if (expected && expected !== actual) {
                this.raiseError("Expected " + name + " '" + expected + "'.  Got '" + actual + "' instead.");
            }
        }

        public verifyRenameInfoSucceeded(
            displayName: string | undefined,
            fullDisplayName: string | undefined,
            kind: string | undefined,
            kindModifiers: string | undefined,
            fileToRename: string | undefined,
            expectedRange: Range | undefined,
            preferences: ts.UserPreferences | undefined): void {
            const renameInfo = this.languageService.getRenameInfo(this.activeFile.fileName, this.currentCaretPosition, preferences || { allowRenameOfImportPath: true });
            if (!renameInfo.canRename) {
                throw this.raiseError("Rename did not succeed");
            }

            this.validate("displayName", displayName, renameInfo.displayName);
            this.validate("fullDisplayName", fullDisplayName, renameInfo.fullDisplayName);
            this.validate("kind", kind, renameInfo.kind);
            this.validate("kindModifiers", kindModifiers, renameInfo.kindModifiers);
            this.validate("fileToRename", fileToRename, renameInfo.fileToRename);

            if (!expectedRange) {
                if (this.getRanges().length !== 1) {
                    this.raiseError("Expected a single range to be selected in the test file.");
                }
                expectedRange = this.getRanges()[0];
            }

            if (renameInfo.triggerSpan.start !== expectedRange.pos ||
                ts.textSpanEnd(renameInfo.triggerSpan) !== expectedRange.end) {
                this.raiseError("Expected triggerSpan [" + expectedRange.pos + "," + expectedRange.end + ").  Got [" +
                    renameInfo.triggerSpan.start + "," + ts.textSpanEnd(renameInfo.triggerSpan) + ") instead.");
            }
        }

        public verifyRenameInfoFailed(message?: string, preferences?: ts.UserPreferences) {
            const allowRenameOfImportPath = preferences?.allowRenameOfImportPath === undefined ? true : preferences.allowRenameOfImportPath;
            const renameInfo = this.languageService.getRenameInfo(this.activeFile.fileName, this.currentCaretPosition, { ...preferences, allowRenameOfImportPath });
            if (renameInfo.canRename) {
                throw this.raiseError("Rename was expected to fail");
            }
            this.validate("error", message, renameInfo.localizedErrorMessage);
        }

        private alignmentForExtraInfo = 50;

        private spanLines(file: FourSlashFile, spanInfo: ts.TextSpan, { selection = false, fullLines = false, lineNumbers = false } = {}) {
            if (selection) {
                fullLines = true;
            }

            let contextStartPos = spanInfo.start;
            let contextEndPos = contextStartPos + spanInfo.length;
            if (fullLines) {
                if (contextStartPos > 0) {
                    while (contextStartPos > 1) {
                        const ch = file.content.charCodeAt(contextStartPos - 1);
                        if (ch === ts.CharacterCodes.lineFeed || ch === ts.CharacterCodes.carriageReturn) {
                            break;
                        }
                        contextStartPos--;
                    }
                }
                if (contextEndPos < file.content.length) {
                    while (contextEndPos < file.content.length - 1) {
                        const ch = file.content.charCodeAt(contextEndPos);
                        if (ch === ts.CharacterCodes.lineFeed || ch === ts.CharacterCodes.carriageReturn) {
                            break;
                        }
                        contextEndPos++;
                    }
                }
            }

            let contextString: string;
            let contextLineMap: number[];
            let contextStart: ts.LineAndCharacter;
            let contextEnd: ts.LineAndCharacter;
            let selectionStart: ts.LineAndCharacter;
            let selectionEnd: ts.LineAndCharacter;
            let lineNumberPrefixLength: number;
            if (lineNumbers) {
                contextString = file.content;
                contextLineMap = ts.computeLineStarts(contextString);
                contextStart = ts.computeLineAndCharacterOfPosition(contextLineMap, contextStartPos);
                contextEnd = ts.computeLineAndCharacterOfPosition(contextLineMap, contextEndPos);
                selectionStart = ts.computeLineAndCharacterOfPosition(contextLineMap, spanInfo.start);
                selectionEnd = ts.computeLineAndCharacterOfPosition(contextLineMap, ts.textSpanEnd(spanInfo));
                lineNumberPrefixLength = (contextEnd.line + 1).toString().length + 2;
            }
            else {
                contextString = file.content.substring(contextStartPos, contextEndPos);
                contextLineMap = ts.computeLineStarts(contextString);
                contextStart = { line: 0, character: 0 };
                contextEnd = { line: contextLineMap.length - 1, character: 0 };
                selectionStart = selection ? ts.computeLineAndCharacterOfPosition(contextLineMap, spanInfo.start - contextStartPos) : contextStart;
                selectionEnd = selection ? ts.computeLineAndCharacterOfPosition(contextLineMap, ts.textSpanEnd(spanInfo) - contextStartPos) : contextEnd;
                lineNumberPrefixLength = 0;
            }

            const output: string[] = [];
            for (let lineNumber = contextStart.line; lineNumber <= contextEnd.line; lineNumber++) {
                const spanLine = contextString.substring(contextLineMap[lineNumber], contextLineMap[lineNumber + 1]);
                output.push(lineNumbers ? `${ts.padLeft(`${lineNumber + 1}: `, lineNumberPrefixLength)}${spanLine}` : spanLine);
                if (selection) {
                    if (lineNumber < selectionStart.line || lineNumber > selectionEnd.line) {
                        continue;
                    }

                    const isEmpty = selectionStart.line === selectionEnd.line && selectionStart.character === selectionEnd.character;
                    const selectionPadLength = lineNumber === selectionStart.line ? selectionStart.character : 0;
                    const selectionPad = " ".repeat(selectionPadLength + lineNumberPrefixLength);
                    const selectionLength = isEmpty ? 0 : Math.max(lineNumber < selectionEnd.line ? spanLine.trimRight().length - selectionPadLength : selectionEnd.character - selectionPadLength, 1);
                    const selectionLine = isEmpty ? "<" : "^".repeat(selectionLength);
                    output.push(`${selectionPad}${selectionLine}`);
                }
            }
            return output;
        }

        private spanInfoToString(spanInfo: ts.TextSpan, prefixString: string, file: FourSlashFile = this.activeFile) {
            let resultString = "SpanInfo: " + JSON.stringify(spanInfo);
            if (spanInfo) {
                const spanLines = this.spanLines(file, spanInfo);
                for (let i = 0; i < spanLines.length; i++) {
                    if (!i) {
                        resultString += "\n";
                    }
                    resultString += prefixString + spanLines[i];
                }
                resultString += "\n" + prefixString + ":=> (" + this.getLineColStringAtPosition(spanInfo.start, file) + ") to (" + this.getLineColStringAtPosition(ts.textSpanEnd(spanInfo), file) + ")";
            }

            return resultString;
        }

        private baselineCurrentFileLocations(getSpanAtPos: (pos: number) => ts.TextSpan): string {
            const fileLineMap = ts.computeLineStarts(this.activeFile.content);
            let nextLine = 0;
            let resultString = "";
            let currentLine: string;
            let previousSpanInfo: string | undefined;
            let startColumn: number | undefined;
            let length: number | undefined;
            const prefixString = "    >";

            let pos = 0;
            const addSpanInfoString = () => {
                if (previousSpanInfo) {
                    resultString += currentLine;
                    let thisLineMarker = ts.repeatString(" ", startColumn!) + ts.repeatString("~", length!);
                    thisLineMarker += ts.repeatString(" ", this.alignmentForExtraInfo - thisLineMarker.length - prefixString.length + 1);
                    resultString += thisLineMarker;
                    resultString += "=> Pos: (" + (pos - length!) + " to " + (pos - 1) + ") ";
                    resultString += " " + previousSpanInfo;
                    previousSpanInfo = undefined;
                }
            };

            for (; pos < this.activeFile.content.length; pos++) {
                if (pos === 0 || pos === fileLineMap[nextLine]) {
                    nextLine++;
                    addSpanInfoString();
                    if (resultString.length) {
                        resultString += "\n--------------------------------";
                    }
                    currentLine = "\n" + nextLine.toString() + ts.repeatString(" ", 3 - nextLine.toString().length) + ">" + this.activeFile.content.substring(pos, fileLineMap[nextLine]) + "\n    ";
                    startColumn = 0;
                    length = 0;
                }
                const spanInfo = this.spanInfoToString(getSpanAtPos(pos), prefixString);
                if (previousSpanInfo && previousSpanInfo !== spanInfo) {
                    addSpanInfoString();
                    previousSpanInfo = spanInfo;
                    startColumn = startColumn! + length!;
                    length = 1;
                }
                else {
                    previousSpanInfo = spanInfo;
                    length!++;
                }
            }
            addSpanInfoString();
            return resultString;
        }

        public getBreakpointStatementLocation(pos: number) {
            return this.languageService.getBreakpointStatementAtPosition(this.activeFile.fileName, pos);
        }

        public baselineCurrentFileBreakpointLocations() {
            const baselineFile = this.getBaselineFileNameForInternalFourslashFile().replace("breakpointValidation", "bpSpan");
            Harness.Baseline.runBaseline(baselineFile, this.baselineCurrentFileLocations(pos => this.getBreakpointStatementLocation(pos)!));
        }

        private getEmitFiles(): readonly FourSlashFile[] {
            // Find file to be emitted
            const emitFiles: FourSlashFile[] = [];  // List of FourSlashFile that has emitThisFile flag on

            const allFourSlashFiles = this.testData.files;
            for (const file of allFourSlashFiles) {
                if (file.fileOptions[MetadataOptionNames.emitThisFile] === "true") {
                    // Find a file with the flag emitThisFile turned on
                    emitFiles.push(file);
                }
            }

            // If there is not emiThisFile flag specified in the test file, throw an error
            if (emitFiles.length === 0) {
                this.raiseError("No emitThisFile is specified in the test file");
            }

            return emitFiles;
        }

        public verifyGetEmitOutput(expectedOutputFiles: readonly string[]): void {
            const outputFiles = ts.flatMap(this.getEmitFiles(), e => this.languageService.getEmitOutput(e.fileName).outputFiles);

            assert.deepEqual(outputFiles.map(f => f.name), expectedOutputFiles);

            for (const { name, text } of outputFiles) {
                const fromTestFile = this.getFileContent(name);
                if (fromTestFile !== text) {
                    this.raiseError(`Emit output for ${name} is not as expected: ${showTextDiff(fromTestFile, text)}`);
                }
            }
        }

        public baselineGetEmitOutput(): void {
            let resultString = "";
            // Loop through all the emittedFiles and emit them one by one
            for (const emitFile of this.getEmitFiles()) {
                const emitOutput = this.languageService.getEmitOutput(emitFile.fileName);
                // Print emitOutputStatus in readable format
                resultString += "EmitSkipped: " + emitOutput.emitSkipped + Harness.IO.newLine();

                if (emitOutput.emitSkipped) {
                    resultString += "Diagnostics:" + Harness.IO.newLine();
                    const diagnostics = ts.getPreEmitDiagnostics(this.languageService.getProgram()!); // TODO: GH#18217
                    for (const diagnostic of diagnostics) {
                        if (!ts.isString(diagnostic.messageText)) {
                            resultString += this.flattenChainedMessage(diagnostic.messageText);
                        }
                        else {
                            resultString += "  " + diagnostic.messageText + Harness.IO.newLine();
                        }
                    }
                }

                for (const outputFile of emitOutput.outputFiles) {
                    const fileName = "FileName : " + outputFile.name + Harness.IO.newLine();
                    resultString = resultString + Harness.IO.newLine() + fileName + outputFile.text;
                }
                resultString += Harness.IO.newLine();
            }

            Harness.Baseline.runBaseline(ts.Debug.checkDefined(this.testData.globalOptions[MetadataOptionNames.baselineFile]), resultString);
        }

        private flattenChainedMessage(diag: ts.DiagnosticMessageChain, indent = " ") {
            let result = "";
            result += indent + diag.messageText + Harness.IO.newLine();
            if (diag.next) {
                for (const kid of diag.next) {
                    result += this.flattenChainedMessage(kid, indent + " ");
                }
            }
            return result;
        }

        public baselineSyntacticDiagnostics() {
            const files = this.getCompilerTestFiles();
            const result = this.getSyntacticDiagnosticBaselineText(files);
            Harness.Baseline.runBaseline(this.getBaselineFileNameForContainingTestFile(), result);
        }

        private getCompilerTestFiles() {
            return ts.map(this.testData.files, ({ content, fileName }) => ({
                content, unitName: fileName
            }));
        }

        public baselineSyntacticAndSemanticDiagnostics() {
            const files = ts.filter(this.getCompilerTestFiles(), f => !ts.endsWith(f.unitName, ".json"));
            const result = this.getSyntacticDiagnosticBaselineText(files)
                + Harness.IO.newLine()
                + Harness.IO.newLine()
                + this.getSemanticDiagnosticBaselineText(files);
            Harness.Baseline.runBaseline(this.getBaselineFileNameForContainingTestFile(), result);
        }

        private getSyntacticDiagnosticBaselineText(files: Harness.Compiler.TestFile[]) {
            const diagnostics = ts.flatMap(files,
                file => this.languageService.getSyntacticDiagnostics(file.unitName)
            );
            const result = `Syntactic Diagnostics for file '${this.originalInputFileName}':`
                + Harness.IO.newLine()
                + Harness.Compiler.getErrorBaseline(files, diagnostics, /*pretty*/ false);
            return result;
        }

        private getSemanticDiagnosticBaselineText(files: Harness.Compiler.TestFile[]) {
            const diagnostics = ts.flatMap(files,
                file => this.languageService.getSemanticDiagnostics(file.unitName)
            );
            const result = `Semantic Diagnostics for file '${this.originalInputFileName}':`
                + Harness.IO.newLine()
                + Harness.Compiler.getErrorBaseline(files, diagnostics, /*pretty*/ false);
            return result;
        }

        public baselineQuickInfo() {
            const baselineFile = this.getBaselineFileNameForContainingTestFile();
            const result = ts.arrayFrom(this.testData.markerPositions.entries(), ([name, marker]) => ({
                marker: { ...marker, name },
                quickInfo: this.languageService.getQuickInfoAtPosition(marker.fileName, marker.position)
            }));
            Harness.Baseline.runBaseline(baselineFile, stringify(result));
        }

        public baselineSignatureHelp() {
            const baselineFile = this.getBaselineFileNameForContainingTestFile();
            const result = ts.arrayFrom(this.testData.markerPositions.entries(), ([name, marker]) => ({
                marker: { ...marker, name },
                signatureHelp: this.languageService.getSignatureHelpItems(marker.fileName, marker.position, /*options*/ undefined)
            }));
            Harness.Baseline.runBaseline(baselineFile, stringify(result));
        }

        public baselineCompletions(preferences?: ts.UserPreferences) {
            const baselineFile = this.getBaselineFileNameForContainingTestFile();
            const result = ts.arrayFrom(this.testData.markerPositions.entries(), ([name, marker]) => {
                this.goToMarker(marker);
                const completions = this.getCompletionListAtCaret(preferences);
                return {
                    marker: { ...marker, name },
                    completionList: {
                        ...completions,
                        entries: completions?.entries.map(entry => ({
                            ...entry,
                            ...this.getCompletionEntryDetails(entry.name, entry.source, entry.data, preferences)
                        })),
                    }
                };
            });
            Harness.Baseline.runBaseline(baselineFile, stringify(result));
        }

        public baselineSmartSelection() {
            const n = "\n";
            const baselineFile = this.getBaselineFileNameForContainingTestFile();
            const markers = this.getMarkers();
            const fileContent = this.activeFile.content;
            const text = markers.map(marker => {
                const baselineContent = [fileContent.slice(0, marker.position) + "/**/" + fileContent.slice(marker.position) + n];
                let selectionRange: ts.SelectionRange | undefined = this.languageService.getSmartSelectionRange(this.activeFile.fileName, marker.position);
                while (selectionRange) {
                    const { textSpan } = selectionRange;
                    let masked = Array.from(fileContent).map((char, index) => {
                        const charCode = char.charCodeAt(0);
                        if (index >= textSpan.start && index < ts.textSpanEnd(textSpan)) {
                            return char === " " ? "•" : ts.isLineBreak(charCode) ? `↲${n}` : char;
                        }
                        return ts.isLineBreak(charCode) ? char : " ";
                    }).join("");
                    masked = masked.replace(/^\s*$\r?\n?/gm, ""); // Remove blank lines
                    const isRealCharacter = (char: string) => char !== "•" && char !== "↲" && !ts.isWhiteSpaceLike(char.charCodeAt(0));
                    const leadingWidth = Array.from(masked).findIndex(isRealCharacter);
                    const trailingWidth = ts.findLastIndex(Array.from(masked), isRealCharacter);
                    masked = masked.slice(0, leadingWidth)
                        + masked.slice(leadingWidth, trailingWidth).replace(/•/g, " ").replace(/↲/g, "")
                        + masked.slice(trailingWidth);
                    baselineContent.push(masked);
                    selectionRange = selectionRange.parent;
                }
                return baselineContent.join(fileContent.includes("\n") ? n + n : n);
            }).join(n.repeat(2) + "=".repeat(80) + n.repeat(2));

            Harness.Baseline.runBaseline(baselineFile, text);
        }

        public printBreakpointLocation(pos: number) {
            Harness.IO.log("\n**Pos: " + pos + " " + this.spanInfoToString(this.getBreakpointStatementLocation(pos)!, "  "));
        }

        public printBreakpointAtCurrentLocation() {
            this.printBreakpointLocation(this.currentCaretPosition);
        }

        public printCurrentParameterHelp() {
            const help = this.languageService.getSignatureHelpItems(this.activeFile.fileName, this.currentCaretPosition, /*options*/ undefined);
            Harness.IO.log(stringify(help));
        }

        public printCurrentQuickInfo() {
            const quickInfo = this.languageService.getQuickInfoAtPosition(this.activeFile.fileName, this.currentCaretPosition)!;
            Harness.IO.log("Quick Info: " + quickInfo.displayParts!.map(part => part.text).join(""));
        }

        public printErrorList() {
            const syntacticErrors = this.languageService.getSyntacticDiagnostics(this.activeFile.fileName);
            const semanticErrors = this.languageService.getSemanticDiagnostics(this.activeFile.fileName);
            const errorList = ts.concatenate(syntacticErrors, semanticErrors);
            Harness.IO.log(`Error list (${errorList.length} errors)`);

            if (errorList.length) {
                errorList.forEach(err => {
                    Harness.IO.log(
                        "start: " + err.start +
                        ", length: " + err.length +
                        ", message: " + ts.flattenDiagnosticMessageText(err.messageText, Harness.IO.newLine()));
                });
            }
        }

        public printCurrentFileState(showWhitespace: boolean, makeCaretVisible: boolean) {
            for (const file of this.testData.files) {
                const active = (this.activeFile === file);
                Harness.IO.log(`=== Script (${file.fileName}) ${(active ? "(active, cursor at |)" : "")} ===`);
                let content = this.getFileContent(file.fileName);
                if (active) {
                    content = content.substr(0, this.currentCaretPosition) + (makeCaretVisible ? "|" : "") + content.substr(this.currentCaretPosition);
                }
                if (showWhitespace) {
                    content = makeWhitespaceVisible(content);
                }
                Harness.IO.log(content);
            }
        }

        public printCurrentSignatureHelp() {
            const help = this.getSignatureHelp(ts.emptyOptions)!;
            Harness.IO.log(stringify(help.items[help.selectedItemIndex]));
        }

        private getBaselineFileNameForInternalFourslashFile(ext = ".baseline") {
            return this.testData.globalOptions[MetadataOptionNames.baselineFile] ||
                ts.getBaseFileName(this.activeFile.fileName).replace(ts.Extension.Ts, ext);
        }

        private getBaselineFileNameForContainingTestFile(ext = ".baseline") {
            return this.testData.globalOptions[MetadataOptionNames.baselineFile] ||
                ts.getBaseFileName(this.originalInputFileName).replace(ts.Extension.Ts, ext);
        }

        private getSignatureHelp({ triggerReason }: FourSlashInterface.VerifySignatureHelpOptions): ts.SignatureHelpItems | undefined {
            return this.languageService.getSignatureHelpItems(this.activeFile.fileName, this.currentCaretPosition, {
                triggerReason
            });
        }

        public printCompletionListMembers(preferences: ts.UserPreferences | undefined) {
            const completions = this.getCompletionListAtCaret(preferences);
            this.printMembersOrCompletions(completions);
        }

        private printMembersOrCompletions(info: ts.CompletionInfo | undefined) {
            if (info === undefined) return "No completion info.";
            const { entries } = info;

            function pad(s: string, length: number) {
                return s + new Array(length - s.length + 1).join(" ");
            }
            function max<T>(arr: T[], selector: (x: T) => number): number {
                return arr.reduce((prev, x) => Math.max(prev, selector(x)), 0);
            }
            const longestNameLength = max(entries, m => m.name.length);
            const longestKindLength = max(entries, m => m.kind.length);
            entries.sort((m, n) => m.sortText > n.sortText ? 1 : m.sortText < n.sortText ? -1 : m.name > n.name ? 1 : m.name < n.name ? -1 : 0);
            const membersString = entries.map(m => `${pad(m.name, longestNameLength)} ${pad(m.kind, longestKindLength)} ${m.kindModifiers} ${m.isRecommended ? "recommended " : ""}${m.source === undefined ? "" : m.source}`).join("\n");
            Harness.IO.log(membersString);
        }

        public printContext() {
            ts.forEach(this.languageServiceAdapterHost.getFilenames(), Harness.IO.log);
        }

        public deleteChar(count = 1) {
            let offset = this.currentCaretPosition;
            const ch = "";

            const checkCadence = (count >> 2) + 1;

            for (let i = 0; i < count; i++) {
                this.editScriptAndUpdateMarkers(this.activeFile.fileName, offset, offset + 1, ch);

                if (i % checkCadence === 0) {
                    this.checkPostEditInvariants();
                }

                // Handle post-keystroke formatting
                if (this.enableFormatting) {
                    const edits = this.languageService.getFormattingEditsAfterKeystroke(this.activeFile.fileName, offset, ch, this.formatCodeSettings);
                    if (edits.length) {
                        offset += this.applyEdits(this.activeFile.fileName, edits);
                    }
                }
            }

            this.checkPostEditInvariants();
        }

        public replace(start: number, length: number, text: string) {
            this.editScriptAndUpdateMarkers(this.activeFile.fileName, start, start + length, text);
            this.checkPostEditInvariants();
        }

        public deleteLineRange(startIndex: number, endIndexInclusive: number) {
            const startPos = this.languageServiceAdapterHost.lineAndCharacterToPosition(this.activeFile.fileName, { line: startIndex, character: 0 });
            const endPos = this.languageServiceAdapterHost.lineAndCharacterToPosition(this.activeFile.fileName, { line: endIndexInclusive + 1, character: 0 });
            this.replace(startPos, endPos - startPos, "");
        }

        public deleteCharBehindMarker(count = 1) {
            let offset = this.currentCaretPosition;
            const ch = "";
            const checkCadence = (count >> 2) + 1;

            for (let i = 0; i < count; i++) {
                this.currentCaretPosition--;
                offset--;
                this.editScriptAndUpdateMarkers(this.activeFile.fileName, offset, offset + 1, ch);

                if (i % checkCadence === 0) {
                    this.checkPostEditInvariants();
                }

                // Don't need to examine formatting because there are no formatting changes on backspace.
            }

            this.checkPostEditInvariants();
        }

        // Enters lines of text at the current caret position
        public type(text: string, highFidelity = false) {
            let offset = this.currentCaretPosition;
            const prevChar = " ";
            const checkCadence = (text.length >> 2) + 1;
            const selection = this.getSelection();
            this.replace(selection.pos, selection.end - selection.pos, "");

            for (let i = 0; i < text.length; i++) {
                const ch = text.charAt(i);
                this.editScriptAndUpdateMarkers(this.activeFile.fileName, offset, offset, ch);
                if (highFidelity) {
                    this.languageService.getBraceMatchingAtPosition(this.activeFile.fileName, offset);
                }

                this.currentCaretPosition++;
                offset++;

                if (highFidelity) {
                    if (ch === "(" || ch === "," || ch === "<") {
                        /* Signature help*/
                        this.languageService.getSignatureHelpItems(this.activeFile.fileName, offset, {
                            triggerReason: {
                                kind: "characterTyped",
                                triggerCharacter: ch
                            }
                        });
                    }
                    else if (prevChar === " " && /A-Za-z_/.test(ch)) {
                        /* Completions */
                        this.languageService.getCompletionsAtPosition(this.activeFile.fileName, offset, ts.emptyOptions);
                    }

                    if (i % checkCadence === 0) {
                        this.checkPostEditInvariants();
                    }
                }

                // Handle post-keystroke formatting
                if (this.enableFormatting) {
                    const edits = this.languageService.getFormattingEditsAfterKeystroke(this.activeFile.fileName, offset, ch, this.formatCodeSettings);
                    if (edits.length) {
                        offset += this.applyEdits(this.activeFile.fileName, edits);
                    }
                }
            }

            this.checkPostEditInvariants();
        }

        // Enters text as if the user had pasted it
        public paste(text: string) {
            const start = this.currentCaretPosition;
            this.editScriptAndUpdateMarkers(this.activeFile.fileName, this.currentCaretPosition, this.currentCaretPosition, text);
            this.checkPostEditInvariants();
            const offset = this.currentCaretPosition += text.length;

            // Handle formatting
            if (this.enableFormatting) {
                const edits = this.languageService.getFormattingEditsForRange(this.activeFile.fileName, start, offset, this.formatCodeSettings);
                if (edits.length) {
                    this.applyEdits(this.activeFile.fileName, edits);
                }
            }


            this.checkPostEditInvariants();
        }

        private checkPostEditInvariants() {
            if (this.testType !== FourSlashTestType.Native) {
                // getSourcefile() results can not be serialized. Only perform these verifications
                // if running against a native LS object.
                return;
            }

            const incrementalSourceFile = this.languageService.getNonBoundSourceFile(this.activeFile.fileName);
            Utils.assertInvariants(incrementalSourceFile, /*parent:*/ undefined);

            const incrementalSyntaxDiagnostics = incrementalSourceFile.parseDiagnostics;

            // Check syntactic structure
            const content = this.getFileContent(this.activeFile.fileName);

            const options: ts.CreateSourceFileOptions = {
                languageVersion: ts.ScriptTarget.Latest,
                impliedNodeFormat: ts.getImpliedNodeFormatForFile(
                    ts.toPath(this.activeFile.fileName, this.languageServiceAdapterHost.sys.getCurrentDirectory(), ts.hostGetCanonicalFileName(this.languageServiceAdapterHost)),
                    /*cache*/ undefined,
                    this.languageServiceAdapterHost,
                    this.languageService.getProgram()?.getCompilerOptions() || {}
                ),
                setExternalModuleIndicator: ts.getSetExternalModuleIndicator(this.languageService.getProgram()?.getCompilerOptions() || {}),
            };
            const referenceSourceFile = ts.createLanguageServiceSourceFile(
                this.activeFile.fileName, createScriptSnapShot(content), options, /*version:*/ "0", /*setNodeParents:*/ false);
            const referenceSyntaxDiagnostics = referenceSourceFile.parseDiagnostics;

            Utils.assertDiagnosticsEquals(incrementalSyntaxDiagnostics, referenceSyntaxDiagnostics);
            Utils.assertStructuralEquals(incrementalSourceFile, referenceSourceFile);
        }

        /**
         * @returns The number of characters added to the file as a result of the edits.
         * May be negative.
         */
        private applyEdits(fileName: string, edits: readonly ts.TextChange[]): number {
            let runningOffset = 0;

            forEachTextChange(edits, edit => {
                const offsetStart = edit.span.start;
                const offsetEnd = offsetStart + edit.span.length;
                this.editScriptAndUpdateMarkers(fileName, offsetStart, offsetEnd, edit.newText);
                const editDelta = edit.newText.length - edit.span.length;
                if (offsetStart <= this.currentCaretPosition) {
                    if (offsetEnd <= this.currentCaretPosition) {
                        // The entirety of the edit span falls before the caret position, shift the caret accordingly
                        this.currentCaretPosition += editDelta;
                    }
                    else {
                        // The span being replaced includes the caret position, place the caret at the beginning of the span
                        this.currentCaretPosition = offsetStart;
                    }
                }
                runningOffset += editDelta;
            });

            return runningOffset;
        }

        public copyFormatOptions(): ts.FormatCodeSettings {
            return ts.clone(this.formatCodeSettings);
        }

        public setFormatOptions(formatCodeOptions: ts.FormatCodeOptions | ts.FormatCodeSettings): ts.FormatCodeSettings {
            const oldFormatCodeOptions = this.formatCodeSettings;
            this.formatCodeSettings = ts.toEditorSettings(formatCodeOptions);
            if (this.testType === FourSlashTestType.Server) {
                (this.languageService as ts.server.SessionClient).setFormattingOptions(this.formatCodeSettings);
            }
            return oldFormatCodeOptions;
        }

        public formatDocument() {
            const edits = this.languageService.getFormattingEditsForDocument(this.activeFile.fileName, this.formatCodeSettings);
            this.applyEdits(this.activeFile.fileName, edits);
        }

        public formatSelection(start: number, end: number) {
            const edits = this.languageService.getFormattingEditsForRange(this.activeFile.fileName, start, end, this.formatCodeSettings);
            this.applyEdits(this.activeFile.fileName, edits);
        }

        public formatOnType(pos: number, key: string) {
            const edits = this.languageService.getFormattingEditsAfterKeystroke(this.activeFile.fileName, pos, key, this.formatCodeSettings);
            this.applyEdits(this.activeFile.fileName, edits);
        }

        private editScriptAndUpdateMarkers(fileName: string, editStart: number, editEnd: number, newText: string) {
            this.languageServiceAdapterHost.editScript(fileName, editStart, editEnd, newText);
            if (this.assertTextConsistent) {
                this.assertTextConsistent(fileName);
            }
            for (const marker of this.testData.markers) {
                if (marker.fileName === fileName) {
                    marker.position = updatePosition(marker.position, editStart, editEnd, newText);
                }
            }

            for (const range of this.testData.ranges) {
                if (range.fileName === fileName) {
                    range.pos = updatePosition(range.pos, editStart, editEnd, newText);
                    range.end = updatePosition(range.end, editStart, editEnd, newText);
                }
            }
            this.testData.rangesByText = undefined;
        }

        private removeWhitespace(text: string): string {
            return text.replace(/\s/g, "");
        }

        public goToBOF() {
            this.goToPosition(0);
        }

        public goToEOF() {
            const len = this.getFileContent(this.activeFile.fileName).length;
            this.goToPosition(len);
        }

        public goToRangeStart({ fileName, pos }: Range) {
            this.openFile(fileName);
            this.goToPosition(pos);
        }

        public goToTypeDefinition(definitionIndex: number) {
            const definitions = this.languageService.getTypeDefinitionAtPosition(this.activeFile.fileName, this.currentCaretPosition)!;
            if (!definitions || !definitions.length) {
                this.raiseError("goToTypeDefinition failed - expected to find at least one definition location but got 0");
            }

            if (definitionIndex >= definitions.length) {
                this.raiseError(`goToTypeDefinition failed - definitionIndex value (${definitionIndex}) exceeds definition list size (${definitions.length})`);
            }

            const definition = definitions[definitionIndex];
            this.openFile(definition.fileName);
            this.currentCaretPosition = definition.textSpan.start;
        }

        public verifyTypeDefinitionsCount(negative: boolean, expectedCount: number) {
            const assertFn = negative ? assert.notEqual : assert.equal;

            const definitions = this.languageService.getTypeDefinitionAtPosition(this.activeFile.fileName, this.currentCaretPosition);
            const actualCount = definitions && definitions.length || 0;

            assertFn(actualCount, expectedCount, this.messageAtLastKnownMarker("Type definitions Count"));
        }

        public verifyImplementationListIsEmpty(negative: boolean) {
            const implementations = this.languageService.getImplementationAtPosition(this.activeFile.fileName, this.currentCaretPosition);

            if (negative) {
                assert.isTrue(implementations && implementations.length > 0, "Expected at least one implementation but got 0");
            }
            else {
                assert.isUndefined(implementations, "Expected implementation list to be empty but implementations returned");
            }
        }

        public verifyGoToDefinitionName(expectedName: string, expectedContainerName: string) {
            const definitions = this.languageService.getDefinitionAtPosition(this.activeFile.fileName, this.currentCaretPosition);
            const actualDefinitionName = definitions && definitions.length ? definitions[0].name : "";
            const actualDefinitionContainerName = definitions && definitions.length ? definitions[0].containerName : "";
            assert.equal(actualDefinitionName, expectedName, this.messageAtLastKnownMarker("Definition Info Name"));
            assert.equal(actualDefinitionContainerName, expectedContainerName, this.messageAtLastKnownMarker("Definition Info Container Name"));
        }

        public goToImplementation() {
            const implementations = this.languageService.getImplementationAtPosition(this.activeFile.fileName, this.currentCaretPosition)!;
            if (!implementations || !implementations.length) {
                this.raiseError("goToImplementation failed - expected to find at least one implementation location but got 0");
            }
            if (implementations.length > 1) {
                this.raiseError(`goToImplementation failed - more than 1 implementation returned (${implementations.length})`);
            }

            const implementation = implementations[0];
            this.openFile(implementation.fileName);
            this.currentCaretPosition = implementation.textSpan.start;
        }

        public verifyRangesInImplementationList(markerName: string) {
            this.goToMarker(markerName);
            const implementations: readonly ImplementationLocationInformation[] = this.languageService.getImplementationAtPosition(this.activeFile.fileName, this.currentCaretPosition)!;
            if (!implementations || !implementations.length) {
                this.raiseError("verifyRangesInImplementationList failed - expected to find at least one implementation location but got 0");
            }

            const duplicate = findDuplicatedElement(implementations, ts.documentSpansEqual);
            if (duplicate) {
                const { textSpan, fileName } = duplicate;
                this.raiseError(`Duplicate implementations returned for range (${textSpan.start}, ${ts.textSpanEnd(textSpan)}) in ${fileName}`);
            }

            const ranges = this.getRanges();

            if (!ranges || !ranges.length) {
                this.raiseError("verifyRangesInImplementationList failed - expected to find at least one range in test source");
            }

            const unsatisfiedRanges: Range[] = [];

            const delayedErrors: string[] = [];
            for (const range of ranges) {
                const length = range.end - range.pos;
                const matchingImpl = ts.find(implementations, impl =>
                    range.fileName === impl.fileName && range.pos === impl.textSpan.start && length === impl.textSpan.length);
                if (matchingImpl) {
                    if (range.marker && range.marker.data) {
                        const expected = range.marker.data as { displayParts?: ts.SymbolDisplayPart[], parts: string[], kind?: string };
                        if (expected.displayParts) {
                            if (!ts.arrayIsEqualTo(expected.displayParts, matchingImpl.displayParts, displayPartIsEqualTo)) {
                                delayedErrors.push(`Mismatched display parts: expected ${JSON.stringify(expected.displayParts)}, actual ${JSON.stringify(matchingImpl.displayParts)}`);
                            }
                        }
                        else if (expected.parts) {
                            const actualParts = matchingImpl.displayParts.map(p => p.text);
                            if (!ts.arrayIsEqualTo(expected.parts, actualParts)) {
                                delayedErrors.push(`Mismatched non-tagged display parts: expected ${JSON.stringify(expected.parts)}, actual ${JSON.stringify(actualParts)}`);
                            }
                        }
                        if (expected.kind !== undefined) {
                            if (expected.kind !== matchingImpl.kind) {
                                delayedErrors.push(`Mismatched kind: expected ${JSON.stringify(expected.kind)}, actual ${JSON.stringify(matchingImpl.kind)}`);
                            }
                        }
                    }

                    matchingImpl.matched = true;
                }
                else {
                    unsatisfiedRanges.push(range);
                }
            }
            if (delayedErrors.length) {
                this.raiseError(delayedErrors.join("\n"));
            }

            const unmatchedImplementations = implementations.filter(impl => !impl.matched);
            if (unmatchedImplementations.length || unsatisfiedRanges.length) {
                let error = "Not all ranges or implementations are satisfied";
                if (unsatisfiedRanges.length) {
                    error += "\nUnsatisfied ranges:";
                    for (const range of unsatisfiedRanges) {
                        error += `\n    (${range.pos}, ${range.end}) in ${range.fileName}: ${this.rangeText(range)}`;
                    }
                }

                if (unmatchedImplementations.length) {
                    error += "\nUnmatched implementations:";
                    for (const impl of unmatchedImplementations) {
                        const end = impl.textSpan.start + impl.textSpan.length;
                        error += `\n    (${impl.textSpan.start}, ${end}) in ${impl.fileName}: ${this.getFileContent(impl.fileName).slice(impl.textSpan.start, end)}`;
                    }
                }
                this.raiseError(error);
            }

            function displayPartIsEqualTo(a: ts.SymbolDisplayPart, b: ts.SymbolDisplayPart): boolean {
                return a.kind === b.kind && a.text === b.text;
            }
        }

        public getMarkers(): Marker[] {
            //  Return a copy of the list
            return this.testData.markers.slice(0);
        }

        public getMarkerNames(): string[] {
            return ts.arrayFrom(this.testData.markerPositions.keys());
        }

        public getRanges(): Range[] {
            return this.testData.ranges;
        }

        public getRangesInFile(fileName = this.activeFile.fileName) {
            return this.getRanges().filter(r => r.fileName === fileName);
        }

        public rangesByText(): ts.ESMap<string, Range[]> {
            if (this.testData.rangesByText) return this.testData.rangesByText;
            const result = ts.createMultiMap<Range>();
            this.testData.rangesByText = result;
            for (const range of this.getRanges()) {
                const text = this.rangeText(range);
                result.add(text, range);
            }
            return result;
        }

        private rangeText({ fileName, pos, end }: Range): string {
            return this.getFileContent(fileName).slice(pos, end);
        }

        public verifyCaretAtMarker(markerName = "") {
            const pos = this.getMarkerByName(markerName);
            if (pos.fileName !== this.activeFile.fileName) {
                throw new Error(`verifyCaretAtMarker failed - expected to be in file "${pos.fileName}", but was in file "${this.activeFile.fileName}"`);
            }
            if (pos.position !== this.currentCaretPosition) {
                throw new Error(`verifyCaretAtMarker failed - expected to be at marker "/*${markerName}*/, but was at position ${this.currentCaretPosition}(${this.getLineColStringAtPosition(this.currentCaretPosition)})`);
            }
        }

        private getIndentation(fileName: string, position: number, indentStyle: ts.IndentStyle, baseIndentSize: number): number {
            const formatOptions = ts.clone(this.formatCodeSettings);
            formatOptions.indentStyle = indentStyle;
            formatOptions.baseIndentSize = baseIndentSize;
            return this.languageService.getIndentationAtPosition(fileName, position, formatOptions);
        }

        public verifyIndentationAtCurrentPosition(numberOfSpaces: number, indentStyle: ts.IndentStyle = ts.IndentStyle.Smart, baseIndentSize = 0) {
            const actual = this.getIndentation(this.activeFile.fileName, this.currentCaretPosition, indentStyle, baseIndentSize);
            const lineCol = this.getLineColStringAtPosition(this.currentCaretPosition);
            if (actual !== numberOfSpaces) {
                this.raiseError(`verifyIndentationAtCurrentPosition failed at ${lineCol} - expected: ${numberOfSpaces}, actual: ${actual}`);
            }
        }

        public verifyIndentationAtPosition(fileName: string, position: number, numberOfSpaces: number, indentStyle: ts.IndentStyle = ts.IndentStyle.Smart, baseIndentSize = 0) {
            const actual = this.getIndentation(fileName, position, indentStyle, baseIndentSize);
            const lineCol = this.getLineColStringAtPosition(position);
            if (actual !== numberOfSpaces) {
                this.raiseError(`verifyIndentationAtPosition failed at ${lineCol} - expected: ${numberOfSpaces}, actual: ${actual}`);
            }
        }

        public verifyCurrentLineContent(text: string) {
            const actual = this.getCurrentLineContent();
            if (actual !== text) {
                throw new Error("verifyCurrentLineContent\n" + displayExpectedAndActualString(text, actual, /* quoted */ true));
            }
        }

        public verifyCurrentFileContent(text: string) {
            this.verifyFileContent(this.activeFile.fileName, text);
        }

        private verifyFileContent(fileName: string, text: string) {
            const actual = this.getFileContent(fileName);
            if (actual !== text) {
                throw new Error(`verifyFileContent failed:\n${showTextDiff(text, actual)}`);
            }
        }

        public verifyFormatDocumentChangesNothing(): void {
            const { fileName } = this.activeFile;
            const before = this.getFileContent(fileName);
            this.formatDocument();
            this.verifyFileContent(fileName, before);
        }

        public verifyTextAtCaretIs(text: string) {
            const actual = this.getFileContent(this.activeFile.fileName).substring(this.currentCaretPosition, this.currentCaretPosition + text.length);
            if (actual !== text) {
                throw new Error("verifyTextAtCaretIs\n" + displayExpectedAndActualString(text, actual, /* quoted */ true));
            }
        }

        public verifyCurrentNameOrDottedNameSpanText(text: string) {
            const span = this.languageService.getNameOrDottedNameSpan(this.activeFile.fileName, this.currentCaretPosition, this.currentCaretPosition);
            if (!span) {
                return this.raiseError("verifyCurrentNameOrDottedNameSpanText\n" + displayExpectedAndActualString("\"" + text + "\"", "undefined"));
            }

            const actual = this.getFileContent(this.activeFile.fileName).substring(span.start, ts.textSpanEnd(span));
            if (actual !== text) {
                this.raiseError("verifyCurrentNameOrDottedNameSpanText\n" + displayExpectedAndActualString(text, actual, /* quoted */ true));
            }
        }

        private getNameOrDottedNameSpan(pos: number) {
            return this.languageService.getNameOrDottedNameSpan(this.activeFile.fileName, pos, pos);
        }

        public baselineCurrentFileNameOrDottedNameSpans() {
            Harness.Baseline.runBaseline(
                this.testData.globalOptions[MetadataOptionNames.baselineFile],
                this.baselineCurrentFileLocations(pos => this.getNameOrDottedNameSpan(pos)!));
        }

        public printNameOrDottedNameSpans(pos: number) {
            Harness.IO.log(this.spanInfoToString(this.getNameOrDottedNameSpan(pos)!, "**"));
        }

        private classificationToIdentifier(classification: number){

            const tokenTypes: string[] = [];
            tokenTypes[ts.classifier.v2020.TokenType.class] = "class";
            tokenTypes[ts.classifier.v2020.TokenType.enum] = "enum";
            tokenTypes[ts.classifier.v2020.TokenType.interface] = "interface";
            tokenTypes[ts.classifier.v2020.TokenType.namespace] = "namespace";
            tokenTypes[ts.classifier.v2020.TokenType.typeParameter] = "typeParameter";
            tokenTypes[ts.classifier.v2020.TokenType.type] = "type";
            tokenTypes[ts.classifier.v2020.TokenType.parameter] = "parameter";
            tokenTypes[ts.classifier.v2020.TokenType.variable] = "variable";
            tokenTypes[ts.classifier.v2020.TokenType.enumMember] = "enumMember";
            tokenTypes[ts.classifier.v2020.TokenType.property] = "property";
            tokenTypes[ts.classifier.v2020.TokenType.function] = "function";
            tokenTypes[ts.classifier.v2020.TokenType.member] = "member";

            const tokenModifiers: string[] = [];
            tokenModifiers[ts.classifier.v2020.TokenModifier.async] = "async";
            tokenModifiers[ts.classifier.v2020.TokenModifier.declaration] = "declaration";
            tokenModifiers[ts.classifier.v2020.TokenModifier.readonly] = "readonly";
            tokenModifiers[ts.classifier.v2020.TokenModifier.static] = "static";
            tokenModifiers[ts.classifier.v2020.TokenModifier.local] = "local";
            tokenModifiers[ts.classifier.v2020.TokenModifier.defaultLibrary] = "defaultLibrary";


            function getTokenTypeFromClassification(tsClassification: number): number | undefined {
                if (tsClassification > ts.classifier.v2020.TokenEncodingConsts.modifierMask) {
                    return (tsClassification >> ts.classifier.v2020.TokenEncodingConsts.typeOffset) - 1;
                }
                return undefined;
            }

            function getTokenModifierFromClassification(tsClassification: number) {
                return tsClassification & ts.classifier.v2020.TokenEncodingConsts.modifierMask;
            }

            const typeIdx = getTokenTypeFromClassification(classification) || 0;
            const modSet = getTokenModifierFromClassification(classification);

            return [tokenTypes[typeIdx], ...tokenModifiers.filter((_, i) => modSet & 1 << i)].join(".");
        }

        private verifyClassifications(expected: { classificationType: string | number, text?: string; textSpan?: TextSpan }[], actual: (ts.ClassifiedSpan | ts.ClassifiedSpan2020)[] , sourceFileText: string) {
            if (actual.length !== expected.length) {
                this.raiseError("verifyClassifications failed - expected total classifications to be " + expected.length +
                    ", but was " + actual.length +
                    jsonMismatchString());
            }

            ts.zipWith(expected, actual, (expectedClassification, actualClassification) => {
                const expectedType = expectedClassification.classificationType;
                const actualType = typeof actualClassification.classificationType === "number"  ? this.classificationToIdentifier(actualClassification.classificationType) : actualClassification.classificationType;

                if (expectedType !== actualType) {
                    this.raiseError("verifyClassifications failed - expected classifications type to be " +
                        expectedType + ", but was " +
                        actualType +
                        jsonMismatchString());
                }

                const expectedSpan = expectedClassification.textSpan;
                const actualSpan = actualClassification.textSpan;

                if (expectedSpan) {
                    const expectedLength = expectedSpan.end - expectedSpan.start;

                    if (expectedSpan.start !== actualSpan.start || expectedLength !== actualSpan.length) {
                        this.raiseError("verifyClassifications failed - expected span of text to be " +
                            "{start=" + expectedSpan.start + ", length=" + expectedLength + "}, but was " +
                            "{start=" + actualSpan.start + ", length=" + actualSpan.length + "}" +
                            jsonMismatchString());
                    }
                }

                const actualText = this.activeFile.content.substr(actualSpan.start, actualSpan.length);
                if (expectedClassification.text !== actualText) {
                    this.raiseError("verifyClassifications failed - expected classified text to be " +
                        expectedClassification.text + ", but was " +
                        actualText +
                        jsonMismatchString());
                }
            });

            function jsonMismatchString() {
                const showActual = actual.map(({ classificationType, textSpan }) =>
                    ({ classificationType, text: sourceFileText.slice(textSpan.start, textSpan.start + textSpan.length) }));
                return Harness.IO.newLine() +
                    "expected: '" + Harness.IO.newLine() + stringify(expected) + "'" + Harness.IO.newLine() +
                    "actual:   '" + Harness.IO.newLine() + stringify(showActual) + "'";
            }
        }

        public verifyProjectInfo(expected: string[]) {
            if (this.testType === FourSlashTestType.Server) {
                const actual = (this.languageService as ts.server.SessionClient).getProjectInfo(
                    this.activeFile.fileName,
                    /* needFileNameList */ true
                );
                assert.equal(
                    expected.join(","),
                    actual.fileNames!.map(file => {
                        return file.replace(this.basePath + "/", "");
                    }).join(",")
                );
            }
        }

        public replaceWithSemanticClassifications(format: ts.SemanticClassificationFormat.TwentyTwenty) {
            const actual = this.languageService.getSemanticClassifications(this.activeFile.fileName,
                ts.createTextSpan(0, this.activeFile.content.length), format);
            const replacement = [`const c2 = classification("2020");`,`verify.semanticClassificationsAre("2020",`];
            for (const a of actual) {
                const identifier = this.classificationToIdentifier(a.classificationType as number);
                const text = this.activeFile.content.slice(a.textSpan.start, a.textSpan.start + a.textSpan.length);
                replacement.push(`    c2.semanticToken("${identifier}", "${text}"), `);
            }
            replacement.push(");");

            throw new Error("You need to change the source code of fourslash test to use replaceWithSemanticClassifications");

            // const fs = require("fs");
            // const testfilePath = this.originalInputFileName.slice(1);
            // const testfile = fs.readFileSync(testfilePath, "utf8");
            // const newfile = testfile.replace("verify.replaceWithSemanticClassifications(\"2020\")", replacement.join("\n"));
            // fs.writeFileSync(testfilePath, newfile);
        }

        public verifyEncodedSyntacticClassificationsLength(expected: number) {
            const actual = this.languageService.getEncodedSyntacticClassifications(this.activeFile.fileName, ts.createTextSpan(0, this.activeFile.content.length));
            if (actual.spans.length !== expected) {
                this.raiseError(`encodedSyntacticClassificationsLength failed - expected total spans to be ${expected} got ${actual.spans.length}`);
            }
        }

        public verifyEncodedSemanticClassificationsLength(format: ts.SemanticClassificationFormat, expected: number) {
            const actual = this.languageService.getEncodedSemanticClassifications(this.activeFile.fileName, ts.createTextSpan(0, this.activeFile.content.length), format);
            if (actual.spans.length !== expected) {
                this.raiseError(`encodedSemanticClassificationsLength failed - expected total spans to be ${expected} got ${actual.spans.length}`);
            }
        }

        public verifySemanticClassifications(format: ts.SemanticClassificationFormat, expected: { classificationType: string | number; text?: string }[]) {
            const actual = this.languageService.getSemanticClassifications(this.activeFile.fileName,
                ts.createTextSpan(0, this.activeFile.content.length), format);
            this.verifyClassifications(expected, actual, this.activeFile.content);
        }

        public verifySyntacticClassifications(expected: { classificationType: string; text: string }[]) {
            const actual = this.languageService.getSyntacticClassifications(this.activeFile.fileName,
                ts.createTextSpan(0, this.activeFile.content.length));

            this.verifyClassifications(expected, actual, this.activeFile.content);
        }

        public printOutliningSpans() {
            const spans = this.languageService.getOutliningSpans(this.activeFile.fileName);
            Harness.IO.log(`Outlining spans (${spans.length} items)\nResults:`);
            Harness.IO.log(stringify(spans));
            this.printOutliningSpansInline(spans);
        }

        private printOutliningSpansInline(spans: ts.OutliningSpan[]) {
            const allSpanInsets = [] as { text: string, pos: number }[];
            let annotated = this.activeFile.content;
            ts.forEach(spans, span => {
                allSpanInsets.push({ text: "[|", pos: span.textSpan.start });
                allSpanInsets.push({ text: "|]", pos: span.textSpan.start + span.textSpan.length });
            });

            const reverseSpans = allSpanInsets.sort((l, r) => r.pos - l.pos);
            ts.forEach(reverseSpans, span => {
               annotated = annotated.slice(0, span.pos) + span.text + annotated.slice(span.pos);
            });
            Harness.IO.log(`\nMockup:\n${annotated}`);
        }

        public verifyOutliningSpans(spans: Range[], kind?: "comment" | "region" | "code" | "imports") {
            const actual = this.languageService.getOutliningSpans(this.activeFile.fileName);

            const filterActual = ts.filter(actual, f => kind === undefined ? true : f.kind === kind);
            if (filterActual.length !== spans.length) {
                this.raiseError(`verifyOutliningSpans failed - expected total spans to be ${spans.length}, but was ${actual.length}\n\nFound Spans:\n\n${this.printOutliningSpansInline(actual)}`);
            }

            ts.zipWith(spans, filterActual, (expectedSpan, actualSpan, i) => {
                if (expectedSpan.pos !== actualSpan.textSpan.start || expectedSpan.end !== ts.textSpanEnd(actualSpan.textSpan)) {
                    return this.raiseError(`verifyOutliningSpans failed - span ${(i + 1)} expected: (${expectedSpan.pos},${expectedSpan.end}),  actual: (${actualSpan.textSpan.start},${ts.textSpanEnd(actualSpan.textSpan)})`);
                }
                if (kind !== undefined && actualSpan.kind !== kind) {
                    return this.raiseError(`verifyOutliningSpans failed - span ${(i + 1)} expected kind: ('${kind}'),  actual: ('${actualSpan.kind}')`);
                }
            });
        }

        public verifyOutliningHintSpans(spans: Range[]) {
            const actual = this.languageService.getOutliningSpans(this.activeFile.fileName);

            if (actual.length !== spans.length) {
                this.raiseError(`verifyOutliningHintSpans failed - expected total spans to be ${spans.length}, but was ${actual.length}`);
            }

            ts.zipWith(spans, actual, (expectedSpan, actualSpan, i) => {
                if (expectedSpan.pos !== actualSpan.hintSpan.start || expectedSpan.end !== ts.textSpanEnd(actualSpan.hintSpan)) {
                    return this.raiseError(`verifyOutliningSpans failed - span ${(i + 1)} expected: (${expectedSpan.pos},${expectedSpan.end}),  actual: (${actualSpan.hintSpan.start},${ts.textSpanEnd(actualSpan.hintSpan)})`);
                }
            });
        }

        public verifyTodoComments(descriptors: string[], spans: Range[]) {
            const actual = this.languageService.getTodoComments(this.activeFile.fileName,
                descriptors.map(d => ({ text: d, priority: 0 })));

            if (actual.length !== spans.length) {
                this.raiseError(`verifyTodoComments failed - expected total spans to be ${spans.length}, but was ${actual.length}`);
            }

            ts.zipWith(spans, actual, (expectedSpan, actualComment, i) => {
                const actualCommentSpan = ts.createTextSpan(actualComment.position, actualComment.message.length);

                if (expectedSpan.pos !== actualCommentSpan.start || expectedSpan.end !== ts.textSpanEnd(actualCommentSpan)) {
                    this.raiseError(`verifyOutliningSpans failed - span ${(i + 1)} expected: (${expectedSpan.pos},${expectedSpan.end}),  actual: (${actualCommentSpan.start},${ts.textSpanEnd(actualCommentSpan)})`);
                }
            });
        }

        /**
         * Finds and applies a code action corresponding to the supplied parameters.
         * If index is undefined, applies the unique code action available.
         * @param errorCode The error code that generated the code action.
         * @param index The nth (0-index-based) codeaction available generated by errorCode.
         */
        public getAndApplyCodeActions(errorCode?: number, index?: number) {
            const fileName = this.activeFile.fileName;
            const fixes = this.getCodeFixes(fileName, errorCode);
            if (index === undefined) {
                if (!(fixes && fixes.length === 1)) {
                    this.raiseError(`Should find exactly one codefix, but ${fixes ? fixes.length : "none"} found. ${fixes ? fixes.map(a => `${Harness.IO.newLine()} "${a.description}"`) : ""}`);
                }
                index = 0;
            }
            else {
                if (!(fixes && fixes.length >= index + 1)) {
                    this.raiseError(`Should find at least ${index + 1} codefix(es), but ${fixes ? fixes.length : "none"} found.`);
                }
            }

            this.applyChanges(fixes[index].changes);
        }

        public applyCodeActionFromCompletion(markerName: string, options: FourSlashInterface.VerifyCompletionActionOptions) {
            this.goToMarker(markerName);

            const details = this.getCompletionEntryDetails(options.name, options.source, options.data, options.preferences);
            if (!details) {
                const completions = this.getCompletionListAtCaret(options.preferences)?.entries;
                const matchingName = completions?.filter(e => e.name === options.name);
                const detailMessage = matchingName?.length
                    ? `\n  Found ${matchingName.length} with name '${options.name}' from source(s) ${matchingName.map(e => `'${e.source}'`).join(", ")}.`
                    : ` (In fact, there were no completions with name '${options.name}' at all.)`;
                return this.raiseError(`No completions were found for the given name, source/data, and preferences.` + detailMessage);
            }
            const codeActions = details.codeActions;
            if (codeActions?.length !== 1) {
                this.raiseError(`Expected one code action, got ${codeActions?.length ?? 0}`);
            }
            const codeAction = ts.first(codeActions);

            if (codeAction.description !== options.description) {
                this.raiseError(`Expected description to be:\n${options.description}\ngot:\n${codeActions[0].description}`);
            }
            this.applyChanges(codeAction.changes);

            this.verifyNewContentAfterChange(options, ts.flatMap(codeActions, a => a.changes.map(c => c.fileName)));
        }

        public verifyRangeIs(expectedText: string, includeWhiteSpace?: boolean) {
            this.verifyTextMatches(this.rangeText(this.getOnlyRange()), !!includeWhiteSpace, expectedText);
        }

        private getOnlyRange() {
            const ranges = this.getRanges();
            if (ranges.length !== 1) {
                this.raiseError("Exactly one range should be specified in the testfile.");
            }
            return ts.first(ranges);
        }

        private verifyTextMatches(actualText: string, includeWhitespace: boolean, expectedText: string) {
            const removeWhitespace = (s: string): string => includeWhitespace ? s : this.removeWhitespace(s);
            if (removeWhitespace(actualText) !== removeWhitespace(expectedText)) {
                this.raiseError(`Actual range text doesn't match expected text.\n${showTextDiff(expectedText, actualText)}`);
            }
        }

        /**
         * Compares expected text to the text that would be in the sole range
         * (ie: [|...|]) in the file after applying the codefix sole codefix
         * in the source file.
         */
        public verifyRangeAfterCodeFix(expectedText: string, includeWhiteSpace?: boolean, errorCode?: number, index?: number) {
            this.getAndApplyCodeActions(errorCode, index);
            this.verifyRangeIs(expectedText, includeWhiteSpace);
        }

        public verifyCodeFixAll({ fixId, fixAllDescription, newFileContent, commands: expectedCommands }: FourSlashInterface.VerifyCodeFixAllOptions): void {
            const fixWithId = ts.find(this.getCodeFixes(this.activeFile.fileName), a => a.fixId === fixId);
            ts.Debug.assert(fixWithId !== undefined, "No available code fix has the expected id. Fix All is not available if there is only one potentially fixable diagnostic present.", () =>
                `Expected '${fixId}'. Available actions:\n${ts.mapDefined(this.getCodeFixes(this.activeFile.fileName), a => `${a.fixName} (${a.fixId || "no fix id"})`).join("\n")}`);
            ts.Debug.assertEqual(fixWithId.fixAllDescription, fixAllDescription);

            const { changes, commands } = this.languageService.getCombinedCodeFix({ type: "file", fileName: this.activeFile.fileName }, fixId, this.formatCodeSettings, ts.emptyOptions);
            assert.deepEqual<readonly {}[] | undefined>(commands, expectedCommands);
            this.verifyNewContent({ newFileContent }, changes);
        }

        public verifyCodeFix(options: FourSlashInterface.VerifyCodeFixOptions) {
            const fileName = this.activeFile.fileName;
            const actions = this.getCodeFixes(fileName, options.errorCode, options.preferences);
            let index = options.index;
            if (index === undefined) {
                if (!(actions && actions.length === 1)) {
                    this.raiseError(`Should find exactly one codefix, but ${actions ? actions.length : "none"} found. ${actions ? actions.map(a => `${Harness.IO.newLine()} "${a.description}"`) : ""}`);
                }
                index = 0;
            }
            else {
                if (!(actions && actions.length >= index + 1)) {
                    this.raiseError(`Should find at least ${index + 1} codefix(es), but ${actions ? actions.length : "none"} found.`);
                }
            }

            const action = actions[index];

            if (typeof options.description === "string") {
                assert.equal(action.description, options.description);
            }
            else if (Array.isArray(options.description)) {
                const description = ts.formatStringFromArgs(options.description[0], options.description, 1);
                assert.equal(action.description, description);
            }
            else {
                assert.match(action.description, templateToRegExp(options.description.template));
            }
            assert.deepEqual(action.commands, options.commands);

            if (options.applyChanges) {
                for (const change of action.changes) {
                    this.applyEdits(change.fileName, change.textChanges);
                }
                this.verifyNewContentAfterChange(options, action.changes.map(c => c.fileName));
            }
            else {
                this.verifyNewContent(options, action.changes);
            }
        }

        private verifyNewContent({ newFileContent, newRangeContent }: FourSlashInterface.NewContentOptions, changes: readonly ts.FileTextChanges[]): void {
            if (newRangeContent !== undefined) {
                assert(newFileContent === undefined);
                assert(changes.length === 1, "Affected 0 or more than 1 file, must use 'newFileContent' instead of 'newRangeContent'");
                const change = ts.first(changes);
                assert(change.fileName = this.activeFile.fileName);
                const newText = ts.textChanges.applyChanges(this.getFileContent(this.activeFile.fileName), change.textChanges);
                const newRange = updateTextRangeForTextChanges(this.getOnlyRange(), change.textChanges);
                const actualText = newText.slice(newRange.pos, newRange.end);
                this.verifyTextMatches(actualText, /*includeWhitespace*/ true, newRangeContent);
            }
            else {
                if (newFileContent === undefined) throw ts.Debug.fail();
                if (typeof newFileContent !== "object") newFileContent = { [this.activeFile.fileName]: newFileContent };
                for (const change of changes) {
                    const expectedNewContent = newFileContent[change.fileName];
                    if (expectedNewContent === undefined) {
                        ts.Debug.fail(`Did not expect a change in ${change.fileName}`);
                    }
                    const oldText = this.tryGetFileContent(change.fileName);
                    ts.Debug.assert(!!change.isNewFile === (oldText === undefined));
                    const newContent = change.isNewFile ? ts.first(change.textChanges).newText : ts.textChanges.applyChanges(oldText!, change.textChanges);
                    this.verifyTextMatches(newContent, /*includeWhitespace*/ true, expectedNewContent);
                }
                for (const newFileName in newFileContent) {
                    ts.Debug.assert(changes.some(c => c.fileName === newFileName), "No change in file", () => newFileName);
                }
            }
        }

        private verifyNewContentAfterChange({ newFileContent, newRangeContent }: FourSlashInterface.NewContentOptions, changedFiles: readonly string[]) {
            const assertedChangedFiles = !newFileContent || typeof newFileContent === "string"
                ? [this.activeFile.fileName]
                : ts.getOwnKeys(newFileContent);
            assert.deepEqual(assertedChangedFiles, changedFiles);

            if (newFileContent !== undefined) {
                assert(!newRangeContent);
                if (typeof newFileContent === "string") {
                    this.verifyCurrentFileContent(newFileContent);
                }
                else {
                    for (const fileName in newFileContent) {
                        this.verifyFileContent(fileName, newFileContent[fileName]);
                    }
                }
            }
            else {
                this.verifyRangeIs(newRangeContent!, /*includeWhitespace*/ true);
            }
        }

        /**
         * Rerieves a codefix satisfying the parameters, or undefined if no such codefix is found.
         * @param fileName Path to file where error should be retrieved from.
         */
        private getCodeFixes(fileName: string, errorCode?: number, preferences: ts.UserPreferences = ts.emptyOptions, position?: number): readonly ts.CodeFixAction[] {
            const diagnosticsForCodeFix = this.getDiagnostics(fileName, /*includeSuggestions*/ true).map(diagnostic => ({
                start: diagnostic.start,
                length: diagnostic.length,
                code: diagnostic.code
            }));

            return ts.flatMap(ts.deduplicate(diagnosticsForCodeFix, ts.equalOwnProperties), diagnostic => {
                if (errorCode !== undefined && errorCode !== diagnostic.code) {
                    return;
                }
                if (position !== undefined && diagnostic.start !== undefined && diagnostic.length !== undefined) {
                    const span = ts.createTextRangeFromSpan({ start: diagnostic.start, length: diagnostic.length });
                    if (!ts.textRangeContainsPositionInclusive(span, position)) {
                        return;
                    }
                }
                return this.languageService.getCodeFixesAtPosition(fileName, diagnostic.start!, diagnostic.start! + diagnostic.length!, [diagnostic.code], this.formatCodeSettings, preferences);
            });
        }

        private applyChanges(changes: readonly ts.FileTextChanges[]): void {
            for (const change of changes) {
                this.applyEdits(change.fileName, change.textChanges);
            }
        }

        public verifyImportFixAtPosition(expectedTextArray: string[], errorCode: number | undefined, preferences: ts.UserPreferences | undefined) {
            const { fileName } = this.activeFile;
            const ranges = this.getRanges().filter(r => r.fileName === fileName);
            if (ranges.length > 1) {
                this.raiseError("Exactly one range should be specified in the testfile.");
            }
            const range = ts.firstOrUndefined(ranges);

            if (preferences) {
                this.configure(preferences);
            }

            const codeFixes = this.getCodeFixes(fileName, errorCode, preferences).filter(f => f.fixName === ts.codefix.importFixName);

            if (codeFixes.length === 0) {
                if (expectedTextArray.length !== 0) {
                    this.raiseError("No codefixes returned.");
                }
                return;
            }

            const actualTextArray: string[] = [];
            const scriptInfo = this.languageServiceAdapterHost.getScriptInfo(fileName)!;
            const originalContent = scriptInfo.content;
            for (const codeFix of codeFixes) {
                ts.Debug.assert(codeFix.changes.length === 1);
                const change = ts.first(codeFix.changes);
                ts.Debug.assert(change.fileName === fileName);
                this.applyEdits(change.fileName, change.textChanges);
                const text = range ? this.rangeText(range) : this.getFileContent(fileName);
                actualTextArray.push(text);

                // Undo changes to perform next fix
                const span = change.textChanges[0].span;
                 const deletedText = originalContent.substr(span.start, change.textChanges[0].span.length);
                 const insertedText = change.textChanges[0].newText;
                 this.editScriptAndUpdateMarkers(fileName, span.start, span.start + insertedText.length, deletedText);
            }
            if (expectedTextArray.length !== actualTextArray.length) {
                this.raiseError(`Expected ${expectedTextArray.length} import fixes, got ${actualTextArray.length}:\n\n${actualTextArray.join("\n\n" + "-".repeat(20) + "\n\n")}`);
            }
            ts.zipWith(expectedTextArray, actualTextArray, (expected, actual, index) => {
                if (expected !== actual) {
                    this.raiseError(`Import fix at index ${index} doesn't match.\n${showTextDiff(expected, actual)}`);
                }
            });
        }

        public verifyImportFixModuleSpecifiers(markerName: string, moduleSpecifiers: string[], preferences?: ts.UserPreferences) {
            const marker = this.getMarkerByName(markerName);
            const codeFixes = this.getCodeFixes(marker.fileName, ts.Diagnostics.Cannot_find_name_0.code, {
                includeCompletionsForModuleExports: true,
                includeCompletionsWithInsertText: true,
                ...preferences,
            }, marker.position).filter(f => f.fixName === ts.codefix.importFixName);

            const actualModuleSpecifiers = ts.mapDefined(codeFixes, fix => {
                return ts.forEach(ts.flatMap(fix.changes, c => c.textChanges), c => {
                    const match = /(?:from |require\()(['"])((?:(?!\1).)*)\1/.exec(c.newText);
                    return match?.[2];
                });
            });

            assert.deepEqual(actualModuleSpecifiers, moduleSpecifiers);
        }

        public verifyDocCommentTemplate(expected: ts.TextInsertion | undefined, options?: ts.DocCommentTemplateOptions) {
            const name = "verifyDocCommentTemplate";
            const actual = this.languageService.getDocCommentTemplateAtPosition(this.activeFile.fileName, this.currentCaretPosition, options || { generateReturnInDocTemplate: true })!;

            if (expected === undefined) {
                if (actual) {
                    this.raiseError(`${name} failed - expected no template but got {newText: "${actual.newText}", caretOffset: ${actual.caretOffset}}`);
                }

                return;
            }
            else {
                if (actual === undefined) {
                    this.raiseError(`${name} failed - expected the template {newText: "${expected.newText}", caretOffset: "${expected.caretOffset}"} but got nothing instead`);
                }

                if (actual.newText !== expected.newText) {
                    this.raiseError(`${name} failed for expected insertion.\n${showTextDiff(expected.newText, actual.newText)}`);
                }

                if (actual.caretOffset !== expected.caretOffset) {
                    this.raiseError(`${name} failed - expected caretOffset: ${expected.caretOffset}\nactual caretOffset:${actual.caretOffset}`);
                }
            }
        }

        public verifyBraceCompletionAtPosition(negative: boolean, openingBrace: string) {

            const openBraceMap = new ts.Map(ts.getEntries<ts.CharacterCodes>({
                "(": ts.CharacterCodes.openParen,
                "{": ts.CharacterCodes.openBrace,
                "[": ts.CharacterCodes.openBracket,
                "'": ts.CharacterCodes.singleQuote,
                '"': ts.CharacterCodes.doubleQuote,
                "`": ts.CharacterCodes.backtick,
                "<": ts.CharacterCodes.lessThan
            }));

            const charCode = openBraceMap.get(openingBrace);

            if (!charCode) {
                throw this.raiseError(`Invalid openingBrace '${openingBrace}' specified.`);
            }

            const position = this.currentCaretPosition;

            const validBraceCompletion = this.languageService.isValidBraceCompletionAtPosition(this.activeFile.fileName, position, charCode);

            if (!negative && !validBraceCompletion) {
                this.raiseError(`${position} is not a valid brace completion position for ${openingBrace}`);
            }

            if (negative && validBraceCompletion) {
                this.raiseError(`${position} is a valid brace completion position for ${openingBrace}`);
            }
        }

        public verifyJsxClosingTag(map: { [markerName: string]: ts.JsxClosingTagInfo | undefined }): void {
            for (const markerName in map) {
                this.goToMarker(markerName);
                const actual = this.languageService.getJsxClosingTagAtPosition(this.activeFile.fileName, this.currentCaretPosition);
                assert.deepEqual(actual, map[markerName], markerName);
            }
        }

        public verifyMatchingBracePosition(bracePosition: number, expectedMatchPosition: number) {
            const actual = this.languageService.getBraceMatchingAtPosition(this.activeFile.fileName, bracePosition);

            if (actual.length !== 2) {
                this.raiseError(`verifyMatchingBracePosition failed - expected result to contain 2 spans, but it had ${actual.length}`);
            }

            let actualMatchPosition = -1;
            if (bracePosition === actual[0].start) {
                actualMatchPosition = actual[1].start;
            }
            else if (bracePosition === actual[1].start) {
                actualMatchPosition = actual[0].start;
            }
            else {
                this.raiseError(`verifyMatchingBracePosition failed - could not find the brace position: ${bracePosition} in the returned list: (${actual[0].start},${ts.textSpanEnd(actual[0])}) and (${actual[1].start},${ts.textSpanEnd(actual[1])})`);
            }

            if (actualMatchPosition !== expectedMatchPosition) {
                this.raiseError(`verifyMatchingBracePosition failed - expected: ${actualMatchPosition},  actual: ${expectedMatchPosition}`);
            }
        }

        public verifyNoMatchingBracePosition(bracePosition: number) {
            const actual = this.languageService.getBraceMatchingAtPosition(this.activeFile.fileName, bracePosition);

            if (actual.length !== 0) {
                this.raiseError("verifyNoMatchingBracePosition failed - expected: 0 spans, actual: " + actual.length);
            }
        }

        public verifySpanOfEnclosingComment(negative: boolean, onlyMultiLineDiverges?: boolean) {
            const expected = !negative;
            const position = this.currentCaretPosition;
            const fileName = this.activeFile.fileName;
            const actual = !!this.languageService.getSpanOfEnclosingComment(fileName, position, /*onlyMultiLine*/ false);
            const actualOnlyMultiLine = !!this.languageService.getSpanOfEnclosingComment(fileName, position, /*onlyMultiLine*/ true);
            if (expected !== actual || onlyMultiLineDiverges === (actual === actualOnlyMultiLine)) {
                this.raiseError(`verifySpanOfEnclosingComment failed:
                position: '${position}'
                fileName: '${fileName}'
                onlyMultiLineDiverges: '${onlyMultiLineDiverges}'
                actual: '${actual}'
                actualOnlyMultiLine: '${actualOnlyMultiLine}'
                expected: '${expected}'.`);
            }
        }

        public verifyNavigateTo(options: readonly FourSlashInterface.VerifyNavigateToOptions[]): void {
            for (const { pattern, expected, fileName } of options) {
                const items = this.languageService.getNavigateToItems(pattern, /*maxResultCount*/ undefined, fileName);
                this.assertObjectsEqual(items, expected.map((e): ts.NavigateToItem => ({
                    name: e.name,
                    kind: e.kind,
                    kindModifiers: e.kindModifiers || "",
                    matchKind: e.matchKind || "exact",
                    isCaseSensitive: e.isCaseSensitive === undefined ? true : e.isCaseSensitive,
                    fileName: e.range.fileName,
                    textSpan: ts.createTextSpanFromRange(e.range),
                    containerName: e.containerName || "",
                    containerKind: e.containerKind || ts.ScriptElementKind.unknown,
                })));
            }
        }

        public verifyNavigationBar(json: any, options: { checkSpans?: boolean } | undefined) {
            this.verifyNavigationTreeOrBar(json, this.languageService.getNavigationBarItems(this.activeFile.fileName), "Bar", options);
        }

        public verifyNavigationTree(json: any, options: { checkSpans?: boolean } | undefined) {
            this.verifyNavigationTreeOrBar(json, this.languageService.getNavigationTree(this.activeFile.fileName), "Tree", options);
        }

        private verifyNavigationTreeOrBar(json: any, tree: any, name: "Tree" | "Bar", options: { checkSpans?: boolean } | undefined) {
            if (JSON.stringify(tree, replacer) !== JSON.stringify(json)) {
                this.raiseError(`verifyNavigation${name} failed - \n${showTextDiff(stringify(json), stringify(tree, replacer))}`);
            }

            function replacer(key: string, value: any) {
                switch (key) {
                    case "spans":
                    case "nameSpan":
                        return options && options.checkSpans ? value : undefined;
                    case "start":
                    case "length":
                        // Never omit the values in a span, even if they are 0.
                        return value;
                    case "childItems":
                        return !value || value.length === 0 ? undefined : value;
                    default:
                        // Omit falsy values, those are presumed to be the default.
                        return value || undefined;
                }
            }
        }

        public printNavigationItems(searchValue: string) {
            const items = this.languageService.getNavigateToItems(searchValue);
            Harness.IO.log(`NavigationItems list (${items.length} items)`);
            for (const item of items) {
                Harness.IO.log(`name: ${item.name}, kind: ${item.kind}, parentName: ${item.containerName}, fileName: ${item.fileName}`);
            }
        }

        public printNavigationBar() {
            const items = this.languageService.getNavigationBarItems(this.activeFile.fileName);
            Harness.IO.log(`Navigation bar (${items.length} items)`);
            for (const item of items) {
                Harness.IO.log(`${ts.repeatString(" ", item.indent)}name: ${item.text}, kind: ${item.kind}, childItems: ${item.childItems.map(child => child.text)}`);
            }
        }

        private getOccurrencesAtCurrentPosition() {
            return this.languageService.getOccurrencesAtPosition(this.activeFile.fileName, this.currentCaretPosition);
        }

        public verifyOccurrencesAtPositionListContains(fileName: string, start: number, end: number, isWriteAccess?: boolean) {
            const occurrences = this.getOccurrencesAtCurrentPosition();

            if (!occurrences || occurrences.length === 0) {
                return this.raiseError("verifyOccurrencesAtPositionListContains failed - found 0 references, expected at least one.");
            }

            for (const occurrence of occurrences) {
                if (occurrence && occurrence.fileName === fileName && occurrence.textSpan.start === start && ts.textSpanEnd(occurrence.textSpan) === end) {
                    if (typeof isWriteAccess !== "undefined" && occurrence.isWriteAccess !== isWriteAccess) {
                        this.raiseError(`verifyOccurrencesAtPositionListContains failed - item isWriteAccess value does not match, actual: ${occurrence.isWriteAccess}, expected: ${isWriteAccess}.`);
                    }
                    return;
                }
            }

            const missingItem = { fileName, start, end, isWriteAccess };
            this.raiseError(`verifyOccurrencesAtPositionListContains failed - could not find the item: ${stringify(missingItem)} in the returned list: (${stringify(occurrences)})`);
        }

        public verifyOccurrencesAtPositionListCount(expectedCount: number) {
            const occurrences = this.getOccurrencesAtCurrentPosition();
            const actualCount = occurrences ? occurrences.length : 0;
            if (expectedCount !== actualCount) {
                this.raiseError(`verifyOccurrencesAtPositionListCount failed - actual: ${actualCount}, expected:${expectedCount}`);
            }
        }

        private getDocumentHighlightsAtCurrentPosition(fileNamesToSearch: readonly string[]) {
            const filesToSearch = fileNamesToSearch.map(name => ts.combinePaths(this.basePath, name));
            return this.languageService.getDocumentHighlights(this.activeFile.fileName, this.currentCaretPosition, filesToSearch);
        }

        public verifyRangesAreOccurrences(isWriteAccess?: boolean, ranges?: Range[]) {
            ranges = ranges || this.getRanges();
            assert(ranges.length);
            for (const r of ranges) {
                this.goToRangeStart(r);
                this.verifyOccurrencesAtPositionListCount(ranges.length);
                for (const range of ranges) {
                    this.verifyOccurrencesAtPositionListContains(range.fileName, range.pos, range.end, isWriteAccess);
                }
            }
        }

        public verifyRangesWithSameTextAreRenameLocations(...texts: string[]) {
            if (texts.length) {
                texts.forEach(text => this.verifyRangesAreRenameLocations(this.rangesByText().get(text)));
            }
            else {
                this.rangesByText().forEach(ranges => this.verifyRangesAreRenameLocations(ranges));
            }
        }

        public verifyRangesWithSameTextAreDocumentHighlights() {
            this.rangesByText().forEach(ranges => this.verifyRangesAreDocumentHighlights(ranges, /*options*/ undefined));
        }

        public verifyDocumentHighlightsOf(startRange: Range, ranges: Range[], options: FourSlashInterface.VerifyDocumentHighlightsOptions | undefined) {
            const fileNames = options && options.filesToSearch || unique(ranges, range => range.fileName);
            this.goToRangeStart(startRange);
            this.verifyDocumentHighlights(ranges, fileNames);
        }

        public verifyRangesAreDocumentHighlights(ranges: Range[] | undefined, options: FourSlashInterface.VerifyDocumentHighlightsOptions | undefined) {
            ranges = ranges || this.getRanges();
            assert(ranges.length);
            const fileNames = options && options.filesToSearch || unique(ranges, range => range.fileName);
            for (const range of ranges) {
                this.goToRangeStart(range);
                this.verifyDocumentHighlights(ranges, fileNames);
            }
        }

        public verifyNoDocumentHighlights(startRange: Range) {
            this.goToRangeStart(startRange);
            const documentHighlights = this.getDocumentHighlightsAtCurrentPosition([this.activeFile.fileName]);
            const numHighlights = ts.length(documentHighlights);
            if (numHighlights > 0) {
                this.raiseError(`verifyNoDocumentHighlights failed - unexpectedly got ${numHighlights} highlights`);
            }
        }

        private verifyDocumentHighlights(expectedRanges: Range[], fileNames: readonly string[] = [this.activeFile.fileName]) {
            fileNames = ts.map(fileNames, ts.normalizePath);
            const documentHighlights = this.getDocumentHighlightsAtCurrentPosition(fileNames) || [];

            for (const dh of documentHighlights) {
                if (fileNames.indexOf(dh.fileName) === -1) {
                    this.raiseError(`verifyDocumentHighlights failed - got highlights in unexpected file name ${dh.fileName}`);
                }
            }

            for (const fileName of fileNames) {
                const expectedRangesInFile = expectedRanges.filter(r => ts.normalizePath(r.fileName) === fileName);
                const highlights = ts.find(documentHighlights, dh => dh.fileName === fileName);
                const spansInFile = highlights ? highlights.highlightSpans.sort((s1, s2) => s1.textSpan.start - s2.textSpan.start) : [];

                if (expectedRangesInFile.length !== spansInFile.length) {
                    this.raiseError(`verifyDocumentHighlights failed - In ${fileName}, expected ${expectedRangesInFile.length} highlights, got ${spansInFile.length}`);
                }

                ts.zipWith(expectedRangesInFile, spansInFile, (expectedRange, span) => {
                    if (span.textSpan.start !== expectedRange.pos || ts.textSpanEnd(span.textSpan) !== expectedRange.end) {
                        this.raiseError(`verifyDocumentHighlights failed - span does not match, actual: ${stringify(span.textSpan)}, expected: ${expectedRange.pos}--${expectedRange.end}`);
                    }
                });
            }
        }

        public verifyCodeFixAvailable(negative: boolean, expected: FourSlashInterface.VerifyCodeFixAvailableOptions[] | string | undefined): void {
            const codeFixes = this.getCodeFixes(this.activeFile.fileName);
            if (negative) {
                if (typeof expected === "undefined") {
                    this.assertObjectsEqual(codeFixes, ts.emptyArray);
                }
                else if (typeof expected === "string") {
                    if (codeFixes.some(fix => fix.fixName === expected)) {
                        this.raiseError(`Expected not to find a fix with the name '${expected}', but one exists.`);
                    }
                }
                else {
                    assert(typeof expected === "undefined" || typeof expected === "string", "With a negated assertion, 'expected' must be undefined or a string value of a codefix name.");
                }
            }
            else if (typeof expected === "string") {
                this.assertObjectsEqual(codeFixes.map(fix => fix.fixName), [expected]);
            }
            else {
                const actuals = codeFixes.map((fix): FourSlashInterface.VerifyCodeFixAvailableOptions => ({ description: fix.description, commands: fix.commands }));
                this.assertObjectsEqual(actuals, negative ? ts.emptyArray : expected);
            }
        }

        public verifyCodeFixAllAvailable(negative: boolean, fixName: string) {
            const availableFixes = this.getCodeFixes(this.activeFile.fileName);
            const hasFix = availableFixes.some(fix => fix.fixName === fixName && fix.fixId);
            if (negative && hasFix) {
                this.raiseError(`Expected not to find a fix with the name '${fixName}', but one exists.`);
            }
            else if (!negative && !hasFix) {
                if (availableFixes.some(fix => fix.fixName === fixName)) {
                    this.raiseError(`Found a fix with the name '${fixName}', but fix-all is not available.`);
                }

                this.raiseError(
                    `Expected to find a fix with the name '${fixName}', but none exists.` +
                        availableFixes.length
                        ? ` Available fixes: ${availableFixes.map(fix => `${fix.fixName} (${fix.fixId ? "with" : "without"} fix-all)`).join(", ")}`
                        : ""
                );
            }
        }

        public verifyApplicableRefactorAvailableAtMarker(negative: boolean, markerName: string) {
            const isAvailable = this.getApplicableRefactors(this.getMarkerByName(markerName)).length > 0;
            if (negative && isAvailable) {
                this.raiseError(`verifyApplicableRefactorAvailableAtMarker failed - expected no refactor at marker ${markerName} but found some.`);
            }
            if (!negative && !isAvailable) {
                this.raiseError(`verifyApplicableRefactorAvailableAtMarker failed - expected a refactor at marker ${markerName} but found none.`);
            }
        }

        private getSelection(): ts.TextRange {
            return {
                pos: this.currentCaretPosition,
                end: this.selectionEnd === -1 ? this.currentCaretPosition : this.selectionEnd
            };
        }

        public verifyRefactorAvailable(negative: boolean, triggerReason: ts.RefactorTriggerReason, name: string, actionName?: string, actionDescription?: string) {
            let refactors = this.getApplicableRefactorsAtSelection(triggerReason);
            refactors = refactors.filter(r => r.name === name);

            if (actionName !== undefined) {
                refactors.forEach(r => r.actions = r.actions.filter(a => a.name === actionName));
            }

            if (actionDescription !== undefined) {
                refactors.forEach(r => r.actions = r.actions.filter(a => a.description === actionDescription));
            }

            refactors = refactors.filter(r => r.actions.length > 0);

            const isAvailable = refactors.length > 0;

            if (negative) {
                if (isAvailable) {
                    this.raiseError(`verifyApplicableRefactorAvailableForRange failed - expected no refactor but found: ${refactors.map(r => r.name).join(", ")}`);
                }
            }
            else {
                if (!isAvailable) {
                    this.raiseError(`verifyApplicableRefactorAvailableForRange failed - expected a refactor but found none.`);
                }
                if (refactors.length > 1) {
                    this.raiseError(`${refactors.length} available refactors both have name ${name} and action ${actionName}`);
                }
            }
        }

        public verifyRefactorKindsAvailable(kind: string, expected: string[], preferences = ts.emptyOptions) {
            const refactors = this.getApplicableRefactorsAtSelection("invoked", kind, preferences);
            const availableKinds = ts.flatMap(refactors, refactor => refactor.actions).map(action => action.kind);
            assert.deepEqual(availableKinds.sort(), expected.sort(), `Expected kinds to be equal`);
        }

        public verifyRefactorsAvailable(names: readonly string[]): void {
            assert.deepEqual(unique(this.getApplicableRefactorsAtSelection(), r => r.name), names);
        }

        public verifyApplicableRefactorAvailableForRange(negative: boolean) {
            const ranges = this.getRanges();
            if (!(ranges && ranges.length === 1)) {
                throw new Error("Exactly one refactor range is allowed per test.");
            }

            const isAvailable = this.getApplicableRefactors(ts.first(ranges)).length > 0;
            if (negative && isAvailable) {
                this.raiseError(`verifyApplicableRefactorAvailableForRange failed - expected no refactor but found some.`);
            }
            if (!negative && !isAvailable) {
                this.raiseError(`verifyApplicableRefactorAvailableForRange failed - expected a refactor but found none.`);
            }
        }

        public applyRefactor({ refactorName, actionName, actionDescription, newContent: newContentWithRenameMarker, triggerReason }: FourSlashInterface.ApplyRefactorOptions) {
            const range = this.getSelection();
            const refactors = this.getApplicableRefactorsAtSelection(triggerReason);
            const refactorsWithName = refactors.filter(r => r.name === refactorName);
            if (refactorsWithName.length === 0) {
                this.raiseError(`The expected refactor: ${refactorName} is not available at the marker location.\nAvailable refactors: ${refactors.map(r => r.name)}`);
            }

            const action = ts.firstDefined(refactorsWithName, refactor => refactor.actions.find(a => a.name === actionName));
            if (!action) {
                throw this.raiseError(`The expected action: ${actionName} is not included in: ${ts.flatMap(refactorsWithName, r => r.actions.map(a => a.name))}`);
            }
            if (action.description !== actionDescription) {
                this.raiseError(`Expected action description to be ${JSON.stringify(actionDescription)}, got: ${JSON.stringify(action.description)}`);
            }

            const editInfo = this.languageService.getEditsForRefactor(this.activeFile.fileName, this.formatCodeSettings, range, refactorName, actionName, ts.emptyOptions)!;
            for (const edit of editInfo.edits) {
                this.applyEdits(edit.fileName, edit.textChanges);
            }

            let renameFilename: string | undefined;
            let renamePosition: number | undefined;

            const newFileContents = typeof newContentWithRenameMarker === "string" ? { [this.activeFile.fileName]: newContentWithRenameMarker } : newContentWithRenameMarker;
            for (const fileName in newFileContents) {
                const { renamePosition: rp, newContent } = TestState.parseNewContent(newFileContents[fileName]);
                if (renamePosition === undefined) {
                    renameFilename = fileName;
                    renamePosition = rp;
                }
                else {
                    ts.Debug.assert(rp === undefined);
                }
                this.verifyFileContent(fileName, newContent);

            }

            if (renamePosition === undefined) {
                if (editInfo.renameLocation !== undefined) {
                    this.raiseError(`Did not expect a rename location, got ${editInfo.renameLocation}`);
                }
            }
            else {
                this.assertObjectsEqual(editInfo.renameFilename, renameFilename);
                if (renamePosition !== editInfo.renameLocation) {
                    this.raiseError(`Expected rename position of ${renamePosition}, but got ${editInfo.renameLocation}`);
                }
            }
        }

        private static parseNewContent(newContentWithRenameMarker: string): { readonly renamePosition: number | undefined, readonly newContent: string } {
            const renamePosition = newContentWithRenameMarker.indexOf("/*RENAME*/");
            if (renamePosition === -1) {
                return { renamePosition: undefined, newContent: newContentWithRenameMarker };
            }
            else {
                const newContent = newContentWithRenameMarker.slice(0, renamePosition) + newContentWithRenameMarker.slice(renamePosition + "/*RENAME*/".length);
                return { renamePosition, newContent };
            }
        }

        public noMoveToNewFile() {
            const ranges = this.getRanges();
            assert(ranges.length);
            for (const range of ranges) {
                for (const refactor of this.getApplicableRefactors(range, { allowTextChangesInNewFiles: true })) {
                    if (refactor.name === "Move to a new file") {
                        ts.Debug.fail("Did not expect to get 'move to a new file' refactor");
                    }
                }
            }
        }

        public moveToNewFile(options: FourSlashInterface.MoveToNewFileOptions): void {
            assert(this.getRanges().length === 1, "Must have exactly one fourslash range (source enclosed between '[|' and '|]' delimiters) in the source file");
            const range = this.getRanges()[0];
            const refactor = ts.find(this.getApplicableRefactors(range, { allowTextChangesInNewFiles: true }), r => r.name === "Move to a new file")!;
            assert(refactor.actions.length === 1);
            const action = ts.first(refactor.actions);
            assert(action.name === "Move to a new file" && action.description === "Move to a new file");

            const editInfo = this.languageService.getEditsForRefactor(range.fileName, this.formatCodeSettings, range, refactor.name, action.name, options.preferences || ts.emptyOptions)!;
            this.verifyNewContent({ newFileContent: options.newFileContents }, editInfo.edits);
        }

        private testNewFileContents(edits: readonly ts.FileTextChanges[], newFileContents: { [fileName: string]: string }, description: string): void {
            for (const { fileName, textChanges } of edits) {
                const newContent = newFileContents[fileName];
                if (newContent === undefined) {
                    this.raiseError(`${description} - There was an edit in ${fileName} but new content was not specified.`);
                }

                const fileContent = this.tryGetFileContent(fileName);
                if (fileContent !== undefined) {
                    const actualNewContent = ts.textChanges.applyChanges(fileContent, textChanges);
                    assert.equal(actualNewContent, newContent, `new content for ${fileName}`);
                }
                else {
                    // Creates a new file.
                    assert(textChanges.length === 1);
                    const change = ts.first(textChanges);
                    assert.deepEqual(change.span, ts.createTextSpan(0, 0));
                    assert.equal(change.newText, newContent, `${description} - Content for ${fileName}`);
                }
            }

            for (const fileName in newFileContents) {
                if (!edits.some(e => e.fileName === fileName)) {
                    ts.Debug.fail(`${description} - Asserted new contents of ${fileName} but there were no edits`);
                }
            }
        }

        public verifyFileAfterApplyingRefactorAtMarker(
            markerName: string,
            expectedContent: string,
            refactorNameToApply: string,
            actionName: string,
            formattingOptions?: ts.FormatCodeSettings) {

            formattingOptions = formattingOptions || this.formatCodeSettings;
            const marker = this.getMarkerByName(markerName);

            const applicableRefactors = this.languageService.getApplicableRefactors(this.activeFile.fileName, marker.position, ts.emptyOptions);
            const applicableRefactorToApply = ts.find(applicableRefactors, refactor => refactor.name === refactorNameToApply);

            if (!applicableRefactorToApply) {
                this.raiseError(`The expected refactor: ${refactorNameToApply} is not available at the marker location.`);
            }

            const editInfo = this.languageService.getEditsForRefactor(marker.fileName, formattingOptions, marker.position, refactorNameToApply, actionName, ts.emptyOptions)!;

            for (const edit of editInfo.edits) {
                this.applyEdits(edit.fileName, edit.textChanges);
            }
            const actualContent = this.getFileContent(marker.fileName);

            if (actualContent !== expectedContent) {
                this.raiseError(`verifyFileAfterApplyingRefactors failed:\n${showTextDiff(expectedContent, actualContent)}`);
            }
        }

        public printAvailableCodeFixes() {
            const codeFixes = this.getCodeFixes(this.activeFile.fileName);
            Harness.IO.log(stringify(codeFixes));
        }

        private formatCallHierarchyItemSpan(file: FourSlashFile, span: ts.TextSpan, prefix: string, trailingPrefix = prefix) {
            const startLc = this.languageServiceAdapterHost.positionToLineAndCharacter(file.fileName, span.start);
            const endLc = this.languageServiceAdapterHost.positionToLineAndCharacter(file.fileName, ts.textSpanEnd(span));
            const lines = this.spanLines(file, span, { fullLines: true, lineNumbers: true, selection: true });
            let text = "";
            text += `${prefix}╭ ${file.fileName}:${startLc.line + 1}:${startLc.character + 1}-${endLc.line + 1}:${endLc.character + 1}\n`;
            for (const line of lines) {
                text += `${prefix}│ ${line.trimRight()}\n`;
            }
            text += `${trailingPrefix}╰\n`;
            return text;
        }

        private formatCallHierarchyItemSpans(file: FourSlashFile, spans: ts.TextSpan[], prefix: string, trailingPrefix = prefix) {
            let text = "";
            for (let i = 0; i < spans.length; i++) {
                text += this.formatCallHierarchyItemSpan(file, spans[i], prefix, i < spans.length - 1 ? prefix : trailingPrefix);
            }
            return text;
        }

        private formatCallHierarchyItem(file: FourSlashFile, callHierarchyItem: ts.CallHierarchyItem, direction: CallHierarchyItemDirection, seen: ts.ESMap<string, boolean>, prefix: string, trailingPrefix: string = prefix) {
            const key = `${callHierarchyItem.file}|${JSON.stringify(callHierarchyItem.span)}|${direction}`;
            const alreadySeen = seen.has(key);
            seen.set(key, true);

            const incomingCalls =
                direction === CallHierarchyItemDirection.Outgoing ? { result: "skip" } as const :
                    alreadySeen ? { result: "seen" } as const :
                        { result: "show", values: this.languageService.provideCallHierarchyIncomingCalls(callHierarchyItem.file, callHierarchyItem.selectionSpan.start) } as const;

            const outgoingCalls =
                direction === CallHierarchyItemDirection.Incoming ? { result: "skip" } as const :
                    alreadySeen ? { result: "seen" } as const :
                        { result: "show", values: this.languageService.provideCallHierarchyOutgoingCalls(callHierarchyItem.file, callHierarchyItem.selectionSpan.start) } as const;

            let text = "";
            text += `${prefix}╭ name: ${callHierarchyItem.name}\n`;
            text += `${prefix}├ kind: ${callHierarchyItem.kind}\n`;
            if (callHierarchyItem.containerName) {
                text += `${prefix}├ containerName: ${callHierarchyItem.containerName}\n`;
            }
            text += `${prefix}├ file: ${callHierarchyItem.file}\n`;
            text += `${prefix}├ span:\n`;
            text += this.formatCallHierarchyItemSpan(file, callHierarchyItem.span, `${prefix}│ `);
            text += `${prefix}├ selectionSpan:\n`;
            text += this.formatCallHierarchyItemSpan(file, callHierarchyItem.selectionSpan, `${prefix}│ `,
                incomingCalls.result !== "skip" || outgoingCalls.result !== "skip" ? `${prefix}│ ` :
                    `${trailingPrefix}╰ `);

            if (incomingCalls.result === "seen") {
                if (outgoingCalls.result === "skip") {
                    text += `${trailingPrefix}╰ incoming: ...\n`;
                }
                else {
                    text += `${prefix}├ incoming: ...\n`;
                }
            }
            else if (incomingCalls.result === "show") {
                if (!ts.some(incomingCalls.values)) {
                    if (outgoingCalls.result === "skip") {
                        text += `${trailingPrefix}╰ incoming: none\n`;
                    }
                    else {
                        text += `${prefix}├ incoming: none\n`;
                    }
                }
                else {
                    text += `${prefix}├ incoming:\n`;
                    for (let i = 0; i < incomingCalls.values.length; i++) {
                        const incomingCall = incomingCalls.values[i];
                        const file = this.findFile(incomingCall.from.file);
                        text += `${prefix}│ ╭ from:\n`;
                        text += this.formatCallHierarchyItem(file, incomingCall.from, CallHierarchyItemDirection.Incoming, seen, `${prefix}│ │ `);
                        text += `${prefix}│ ├ fromSpans:\n`;
                        text += this.formatCallHierarchyItemSpans(file, incomingCall.fromSpans, `${prefix}│ │ `,
                            i < incomingCalls.values.length - 1 ? `${prefix}│ ╰ ` :
                                outgoingCalls.result !== "skip" ? `${prefix}│ ╰ ` :
                                    `${trailingPrefix}╰ ╰ `);
                    }
                }
            }

            if (outgoingCalls.result === "seen") {
                text += `${trailingPrefix}╰ outgoing: ...\n`;
            }
            else if (outgoingCalls.result === "show") {
                if (!ts.some(outgoingCalls.values)) {
                    text += `${trailingPrefix}╰ outgoing: none\n`;
                }
                else {
                    text += `${prefix}├ outgoing:\n`;
                    for (let i = 0; i < outgoingCalls.values.length; i++) {
                        const outgoingCall = outgoingCalls.values[i];
                        text += `${prefix}│ ╭ to:\n`;
                        text += this.formatCallHierarchyItem(this.findFile(outgoingCall.to.file), outgoingCall.to, CallHierarchyItemDirection.Outgoing, seen, `${prefix}│ │ `);
                        text += `${prefix}│ ├ fromSpans:\n`;
                        text += this.formatCallHierarchyItemSpans(file, outgoingCall.fromSpans, `${prefix}│ │ `,
                            i < outgoingCalls.values.length - 1 ? `${prefix}│ ╰ ` :
                                `${trailingPrefix}╰ ╰ `);
                    }
                }
            }
            return text;
        }

        private formatCallHierarchy(callHierarchyItem: ts.CallHierarchyItem | undefined) {
            let text = "";
            if (callHierarchyItem) {
                const file = this.findFile(callHierarchyItem.file);
                text += this.formatCallHierarchyItem(file, callHierarchyItem, CallHierarchyItemDirection.Root, new ts.Map(), "");
            }
            return text;
        }

        public baselineCallHierarchy() {
            const baselineFile = this.getBaselineFileNameForContainingTestFile(".callHierarchy.txt");
            const callHierarchyItem = this.languageService.prepareCallHierarchy(this.activeFile.fileName, this.currentCaretPosition);
            const text = callHierarchyItem ? ts.mapOneOrMany(callHierarchyItem, item => this.formatCallHierarchy(item), result => result.join("")) : "none";
            Harness.Baseline.runBaseline(baselineFile, text);
        }

        private assertTextSpanEqualsRange(span: ts.TextSpan, range: Range, message?: string) {
            if (!textSpanEqualsRange(span, range)) {
                this.raiseError(`${prefixMessage(message)}Expected to find TextSpan ${JSON.stringify({ start: range.pos, length: range.end - range.pos })} but got ${JSON.stringify(span)} instead.`);
            }
        }

        private getLineContent(index: number) {
            const text = this.getFileContent(this.activeFile.fileName);
            const pos = this.languageServiceAdapterHost.lineAndCharacterToPosition(this.activeFile.fileName, { line: index, character: 0 });
            let startPos = pos, endPos = pos;

            while (startPos > 0) {
                const ch = text.charCodeAt(startPos - 1);
                if (ch === ts.CharacterCodes.carriageReturn || ch === ts.CharacterCodes.lineFeed) {
                    break;
                }

                startPos--;
            }

            while (endPos < text.length) {
                const ch = text.charCodeAt(endPos);

                if (ch === ts.CharacterCodes.carriageReturn || ch === ts.CharacterCodes.lineFeed) {
                    break;
                }

                endPos++;
            }

            return text.substring(startPos, endPos);
        }

        // Get the text of the entire line the caret is currently at
        private getCurrentLineContent() {
            return this.getLineContent(this.languageServiceAdapterHost.positionToLineAndCharacter(
                this.activeFile.fileName,
                this.currentCaretPosition,
            ).line);
        }

        private findFile(indexOrName: string | number): FourSlashFile {
            if (typeof indexOrName === "number") {
                const index = indexOrName;
                if (index >= this.testData.files.length) {
                    throw new Error(`File index (${index}) in openFile was out of range. There are only ${this.testData.files.length} files in this test.`);
                }
                else {
                    return this.testData.files[index];
                }
            }
            else if (ts.isString(indexOrName)) {
                const { file, availableNames } = this.tryFindFileWorker(indexOrName);
                if (!file) {
                    throw new Error(`No test file named "${indexOrName}" exists. Available file names are: ${availableNames.join(", ")}`);
                }
                return file;
            }
            else {
                return ts.Debug.assertNever(indexOrName);
            }
        }

        private tryFindFileWorker(name: string): { readonly file: FourSlashFile | undefined; readonly availableNames: readonly string[]; } {
            name = ts.normalizePath(name);
            // names are stored in the compiler with this relative path, this allows people to use goTo.file on just the fileName
            name = name.indexOf("/") === -1 ? (this.basePath + "/" + name) : name;

            const availableNames: string[] = [];
            const file = ts.forEach(this.testData.files, file => {
                const fn = ts.normalizePath(file.fileName);
                if (fn) {
                    if (fn === name) {
                        return file;
                    }
                    availableNames.push(fn);
                }
            });
            return { file, availableNames };
        }

        private hasFile(name: string): boolean {
            return this.tryFindFileWorker(name).file !== undefined;
        }

        private getLineColStringAtPosition(position: number, file: FourSlashFile = this.activeFile) {
            const pos = this.languageServiceAdapterHost.positionToLineAndCharacter(file.fileName, position);
            return `line ${(pos.line + 1)}, col ${pos.character}`;
        }

        public getMarkerByName(markerName: string) {
            const markerPos = this.testData.markerPositions.get(markerName);
            if (markerPos === undefined) {
                throw new Error(`Unknown marker "${markerName}" Available markers: ${this.getMarkerNames().map(m => "\"" + m + "\"").join(", ")}`);
            }
            else {
                return markerPos;
            }
        }

        public setCancelled(numberOfCalls: number): void {
            this.cancellationToken.setCancelled(numberOfCalls);
        }

        public resetCancelled(): void {
            this.cancellationToken.resetCancelled();
        }

        public getEditsForFileRename({ oldPath, newPath, newFileContents, preferences }: FourSlashInterface.GetEditsForFileRenameOptions): void {
            const test = (fileContents: { readonly [fileName: string]: string }, description: string): void => {
                const changes = this.languageService.getEditsForFileRename(oldPath, newPath, this.formatCodeSettings, preferences);
                this.testNewFileContents(changes, fileContents, description);
            };

            ts.Debug.assert(!this.hasFile(newPath), "initially, newPath should not exist");

            test(newFileContents, "with file not yet moved");

            this.languageServiceAdapterHost.renameFileOrDirectory(oldPath, newPath);
            this.languageService.cleanupSemanticCache();
            const pathUpdater = ts.getPathUpdater(oldPath, newPath, ts.createGetCanonicalFileName(/*useCaseSensitiveFileNames*/ false), /*sourceMapper*/ undefined);
            test(renameKeys(newFileContents, key => pathUpdater(key) || key), "with file moved");
        }

        private getApplicableRefactorsAtSelection(triggerReason: ts.RefactorTriggerReason = "implicit", kind?: string, preferences = ts.emptyOptions) {
            return this.getApplicableRefactorsWorker(this.getSelection(), this.activeFile.fileName, preferences, triggerReason, kind);
        }
        private getApplicableRefactors(rangeOrMarker: Range | Marker, preferences = ts.emptyOptions, triggerReason: ts.RefactorTriggerReason = "implicit", kind?: string): readonly ts.ApplicableRefactorInfo[] {
            return this.getApplicableRefactorsWorker("position" in rangeOrMarker ? rangeOrMarker.position : rangeOrMarker, rangeOrMarker.fileName, preferences, triggerReason, kind); // eslint-disable-line local/no-in-operator
        }
        private getApplicableRefactorsWorker(positionOrRange: number | ts.TextRange, fileName: string, preferences = ts.emptyOptions, triggerReason: ts.RefactorTriggerReason, kind?: string): readonly ts.ApplicableRefactorInfo[] {
            return this.languageService.getApplicableRefactors(fileName, positionOrRange, preferences, triggerReason, kind) || ts.emptyArray;
        }

        public configurePlugin(pluginName: string, configuration: any): void {
            (this.languageService as ts.server.SessionClient).configurePlugin(pluginName, configuration);
        }

        public setCompilerOptionsForInferredProjects(options: ts.server.protocol.CompilerOptions) {
            ts.Debug.assert(this.testType === FourSlashTestType.Server);
            (this.languageService as ts.server.SessionClient).setCompilerOptionsForInferredProjects(options);
        }

        public toggleLineComment(newFileContent: string): void {
            const changes: ts.TextChange[] = [];
            for (const range of this.getRanges()) {
                changes.push.apply(changes, this.languageService.toggleLineComment(this.activeFile.fileName, range));
            }

            this.applyEdits(this.activeFile.fileName, changes);

            this.verifyCurrentFileContent(newFileContent);
        }

        public toggleMultilineComment(newFileContent: string): void {
            const changes: ts.TextChange[] = [];
            for (const range of this.getRanges()) {
                changes.push.apply(changes, this.languageService.toggleMultilineComment(this.activeFile.fileName, range));
            }

            this.applyEdits(this.activeFile.fileName, changes);

            this.verifyCurrentFileContent(newFileContent);
        }

        public commentSelection(newFileContent: string): void {
            const changes: ts.TextChange[] = [];
            for (const range of this.getRanges()) {
                changes.push.apply(changes, this.languageService.commentSelection(this.activeFile.fileName, range));
            }

            this.applyEdits(this.activeFile.fileName, changes);

            this.verifyCurrentFileContent(newFileContent);
        }

        public uncommentSelection(newFileContent: string): void {
            const changes: ts.TextChange[] = [];
            for (const range of this.getRanges()) {
                changes.push.apply(changes, this.languageService.uncommentSelection(this.activeFile.fileName, range));
            }

            this.applyEdits(this.activeFile.fileName, changes);

            this.verifyCurrentFileContent(newFileContent);
        }
    }

    function prefixMessage(message: string | undefined) {
        return message ? `${message} - ` : "";
    }

    function textSpanEqualsRange(span: ts.TextSpan, range: Range) {
        return span.start === range.pos && span.length === range.end - range.pos;
    }

    function updateTextRangeForTextChanges({ pos, end }: ts.TextRange, textChanges: readonly ts.TextChange[]): ts.TextRange {
        forEachTextChange(textChanges, change => {
            const update = (p: number): number => updatePosition(p, change.span.start, ts.textSpanEnd(change.span), change.newText);
            pos = update(pos);
            end = update(end);
        });
        return { pos, end };
    }

    /** Apply each textChange in order, updating future changes to account for the text offset of previous changes. */
    function forEachTextChange(changes: readonly ts.TextChange[], cb: (change: ts.TextChange) => void): void {
        // Copy this so we don't ruin someone else's copy
        changes = JSON.parse(JSON.stringify(changes));
        for (let i = 0; i < changes.length; i++) {
            const change = changes[i];
            cb(change);
            const changeDelta = change.newText.length - change.span.length;
            for (let j = i + 1; j < changes.length; j++) {
                if (changes[j].span.start >= change.span.start) {
                    changes[j].span.start += changeDelta;
                }
            }
        }
    }

    function updatePosition(position: number, editStart: number, editEnd: number, { length }: string): number {
        // If inside the edit, return -1 to mark as invalid
        return position <= editStart ? position : position < editEnd ? -1 : position + length - + (editEnd - editStart);
    }

    function renameKeys<T>(obj: { readonly [key: string]: T }, renameKey: (key: string) => string): { readonly [key: string]: T } {
        const res: { [key: string]: T } = {};
        for (const key in obj) {
            res[renameKey(key)] = obj[key];
        }
        return res;
    }

    export function runFourSlashTest(basePath: string, testType: FourSlashTestType, fileName: string) {
        const content = Harness.IO.readFile(fileName)!;
        runFourSlashTestContent(basePath, testType, content, fileName);
    }

    export function runFourSlashTestContent(basePath: string, testType: FourSlashTestType, content: string, fileName: string): void {
        // Give file paths an absolute path for the virtual file system
        const absoluteBasePath = ts.combinePaths(Harness.virtualFileSystemRoot, basePath);
        const absoluteFileName = ts.combinePaths(Harness.virtualFileSystemRoot, fileName);

        // Parse out the files and their metadata
        const testData = parseTestData(absoluteBasePath, content, absoluteFileName);
        const state = new TestState(absoluteFileName, absoluteBasePath, testType, testData);
        const actualFileName = Harness.IO.resolvePath(fileName) || absoluteFileName;
        const compilerOptions: ts.CompilerOptions = { target: ts.ScriptTarget.ES2015, inlineSourceMap: true, inlineSources: true, packageManagerType: testType === FourSlashTestType.OH ? "ohpm" : "npm" };
        const output = ts.transpileModule(content, { reportDiagnostics: true, fileName: actualFileName, compilerOptions });
        if (output.diagnostics!.length > 0) {
            throw new Error(`Syntax error in ${absoluteBasePath}: ${output.diagnostics![0].messageText}`);
        }
        runCode(output.outputText, state, actualFileName);
    }

    function runCode(code: string, state: TestState, fileName: string): void {
        // Compile and execute the test
        const generatedFile = ts.changeExtension(fileName, ".js");
        const wrappedCode = `(function(test, goTo, plugins, verify, edit, debug, format, cancellation, classification, completion, verifyOperationIsCancelled) {${code}\n//# sourceURL=${ts.getBaseFileName(generatedFile)}\n})`;

        type SourceMapSupportModule = typeof import("source-map-support") & {
            // TODO(rbuckton): This is missing from the DT definitions and needs to be added.
            resetRetrieveHandlers(): void
        };

        // Provide the content of the current test to 'source-map-support' so that it can give us the correct source positions
        // for test failures.
        let sourceMapSupportModule: SourceMapSupportModule | undefined;
        try {
            sourceMapSupportModule = require("source-map-support");
        }
        catch {
            // do nothing
        }

        sourceMapSupportModule?.install({
            retrieveFile: path => {
                return path === generatedFile ? wrappedCode :
                    undefined!;
            }
        });

        try {
            const test = new FourSlashInterface.Test(state);
            const goTo = new FourSlashInterface.GoTo(state);
            const config = new FourSlashInterface.Config(state);
            const verify = new FourSlashInterface.Verify(state);
            const edit = new FourSlashInterface.Edit(state);
            const debug = new FourSlashInterface.Debug(state);
            const format = new FourSlashInterface.Format(state);
            const cancellation = new FourSlashInterface.Cancellation(state);
            // eslint-disable-next-line no-eval
            const f = eval(wrappedCode);
            f(test, goTo, config, verify, edit, debug, format, cancellation, FourSlashInterface.classification, FourSlashInterface.Completion, verifyOperationIsCancelled);
        }
        catch (err) {
            // ensure 'source-map-support' is triggered while we still have the handler attached by accessing `error.stack`.
            err.stack?.toString();
            throw err;
        }
        finally {
            sourceMapSupportModule?.resetRetrieveHandlers();
        }
    }

    function chompLeadingSpace(content: string) {
        const lines = content.split("\n");
        for (const line of lines) {
            if ((line.length !== 0) && (line.charAt(0) !== " ")) {
                return content;
            }
        }

        return lines.map(s => s.substr(1)).join("\n");
    }

    function parseTestData(basePath: string, contents: string, fileName: string): FourSlashData {
        // Regex for parsing options in the format "@Alpha: Value of any sort"
        const optionRegex = /^\s*@(\w+):\s*(.*)\s*/;

        // List of all the subfiles we've parsed out
        const files: FourSlashFile[] = [];
        // Global options
        const globalOptions: { [s: string]: string; } = {};
        let symlinks: vfs.FileSet | undefined;
        // Marker positions

        // Split up the input file by 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 lines = contents.split("\n");
        let i = 0;

        const markerPositions = new ts.Map<string, Marker>();
        const markers: Marker[] = [];
        const ranges: Range[] = [];

        // Stuff related to the subfile we're parsing
        let currentFileContent: string | undefined;
        let currentFileName = fileName;
        let currentFileSymlinks: string[] | undefined;
        let currentFileOptions: { [s: string]: string } = {};

        function nextFile() {
            if (currentFileContent === undefined) return;

            const file = parseFileContent(currentFileContent, currentFileName, markerPositions, markers, ranges);
            file.fileOptions = currentFileOptions;
            file.symlinks = currentFileSymlinks;

            // Store result file
            files.push(file);

            currentFileContent = undefined;
            currentFileOptions = {};
            currentFileName = fileName;
            currentFileSymlinks = undefined;
        }

        for (let line of lines) {
            i++;
            if (line.length > 0 && line.charAt(line.length - 1) === "\r") {
                line = line.substr(0, line.length - 1);
            }

            if (line.substr(0, 4) === "////") {
                const text = line.substr(4);
                currentFileContent = currentFileContent === undefined ? text : currentFileContent + "\n" + text;
            }
            else if (line.substr(0, 3) === "///" && currentFileContent !== undefined) {
                throw new Error("Three-slash line in the middle of four-slash region at line " + i);
            }
            else if (line.substr(0, 2) === "//") {
                const possiblySymlinks = Harness.TestCaseParser.parseSymlinkFromTest(line, symlinks);
                if (possiblySymlinks) {
                    symlinks = possiblySymlinks;
                }
                else {
                    // Comment line, check for global/file @options and record them
                    const match = optionRegex.exec(line.substr(2));
                    if (match) {
                        const key = match[1].toLowerCase();
                        const value = match[2];
                        if (!ts.contains(fileMetadataNames, key)) {
                            // Check if the match is already existed in the global options
                            if (globalOptions[key] !== undefined) {
                                throw new Error(`Global option '${key}' already exists`);
                            }
                            globalOptions[key] = value;
                        }
                        else {
                            switch (key) {
                                case MetadataOptionNames.fileName:
                                    // Found an @FileName directive, if this is not the first then create a new subfile
                                    nextFile();
                                    currentFileName = ts.isRootedDiskPath(value) ? value : basePath + "/" + value;
                                    currentFileOptions[key] = value;
                                    break;
                                case MetadataOptionNames.symlink:
                                    currentFileSymlinks = ts.append(currentFileSymlinks, value);
                                    break;
                                default:
                                    // Add other fileMetadata flag
                                    currentFileOptions[key] = value;
                            }
                        }
                    }
                }
            }
            // Previously blank lines between fourslash content caused it to be considered as 2 files,
            // Remove this behavior since it just causes errors now
            else if (line !== "") {
                // Code line, terminate current subfile if there is one
                nextFile();
            }
        }

        // @Filename is the only directive that can be used in a test that contains tsconfig.json file.
        const config = ts.find(files, isConfig);
        if (config) {
            let directive = getNonFileNameOptionInFileList(files);
            if (!directive) {
                directive = getNonFileNameOptionInObject(globalOptions);
            }
            if (directive) {
                throw Error(`It is not allowed to use ${config.fileName} along with directive '${directive}'`);
            }
        }

        return {
            markerPositions,
            markers,
            globalOptions,
            files,
            symlinks,
            ranges
        };
    }

    function isConfig(file: FourSlashFile): boolean {
        return Harness.getConfigNameFromFileName(file.fileName) !== undefined;
    }

    function getNonFileNameOptionInFileList(files: FourSlashFile[]): string | undefined {
        return ts.forEach(files, f => getNonFileNameOptionInObject(f.fileOptions));
    }

    function getNonFileNameOptionInObject(optionObject: { [s: string]: string }): string | undefined {
        for (const option in optionObject) {
            switch (option) {
                case MetadataOptionNames.fileName:
                case MetadataOptionNames.baselineFile:
                case MetadataOptionNames.emitThisFile:
                    break;
                default:
                    return option;
            }
        }
        return undefined;
    }

    const enum State {
        none,
        inSlashStarMarker,
        inObjectMarker
    }

    function reportError(fileName: string, line: number, col: number, message: string) {
        const errorMessage = fileName + "(" + line + "," + col + "): " + message;
        throw new Error(errorMessage);
    }

    function recordObjectMarker(fileName: string, location: LocationInformation, text: string, markerMap: ts.ESMap<string, Marker>, markers: Marker[]): Marker | undefined {
        let markerValue: any;
        try {
            // Attempt to parse the marker value as JSON
            markerValue = JSON.parse("{ " + text + " }");
        }
        catch (e) {
            reportError(fileName, location.sourceLine, location.sourceColumn, "Unable to parse marker text " + e.message);
        }

        if (markerValue === undefined) {
            reportError(fileName, location.sourceLine, location.sourceColumn, "Object markers can not be empty");
            return undefined;
        }

        const marker: Marker = {
            fileName,
            position: location.position,
            data: markerValue
        };

        // Object markers can be anonymous
        if (markerValue.name) {
            markerMap.set(markerValue.name, marker);
        }

        markers.push(marker);

        return marker;
    }

    function recordMarker(fileName: string, location: LocationInformation, name: string, markerMap: ts.ESMap<string, Marker>, markers: Marker[]): Marker | undefined {
        const marker: Marker = {
            fileName,
            position: location.position
        };

        // Verify markers for uniqueness
        if (markerMap.has(name)) {
            const message = "Marker '" + name + "' is duplicated in the source file contents.";
            reportError(marker.fileName, location.sourceLine, location.sourceColumn, message);
            return undefined;
        }
        else {
            markerMap.set(name, marker);
            markers.push(marker);
            return marker;
        }
    }

    function parseFileContent(content: string, fileName: string, markerMap: ts.ESMap<string, Marker>, markers: Marker[], ranges: Range[]): FourSlashFile {
        content = chompLeadingSpace(content);

        // Any slash-star comment with a character not in this string is not a marker.
        const validMarkerChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz$1234567890_";

        /// The file content (minus metacharacters) so far
        let output = "";

        /// The current marker (or maybe multi-line comment?) we're parsing, possibly
        let openMarker: LocationInformation | undefined;

        /// A stack of the open range markers that are still unclosed
        const openRanges: RangeLocationInformation[] = [];

        /// A list of ranges we've collected so far */
        let localRanges: Range[] = [];

        /// The latest position of the start of an unflushed plain text area
        let lastNormalCharPosition = 0;

        /// The total number of metacharacters removed from the file (so far)
        let difference = 0;

        /// The fourslash file state object we are generating
        let state: State = State.none;

        /// Current position data
        let line = 1;
        let column = 1;

        const flush = (lastSafeCharIndex: number | undefined) => {
            output = output + content.substr(lastNormalCharPosition, lastSafeCharIndex === undefined ? undefined : lastSafeCharIndex - lastNormalCharPosition);
        };

        if (content.length > 0) {
            let previousChar = content.charAt(0);
            for (let i = 1; i < content.length; i++) {
                const currentChar = content.charAt(i);
                switch (state) {
                    case State.none:
                        if (previousChar === "[" && currentChar === "|") {
                            // found a range start
                            openRanges.push({
                                position: (i - 1) - difference,
                                sourcePosition: i - 1,
                                sourceLine: line,
                                sourceColumn: column,
                            });
                            // copy all text up to marker position
                            flush(i - 1);
                            lastNormalCharPosition = i + 1;
                            difference += 2;
                        }
                        else if (previousChar === "|" && currentChar === "]") {
                            // found a range end
                            const rangeStart = openRanges.pop();
                            if (!rangeStart) {
                                throw reportError(fileName, line, column, "Found range end with no matching start.");
                            }

                            const range: Range = {
                                fileName,
                                pos: rangeStart.position,
                                end: (i - 1) - difference,
                                marker: rangeStart.marker
                            };
                            localRanges.push(range);

                            // copy all text up to range marker position
                            flush(i - 1);
                            lastNormalCharPosition = i + 1;
                            difference += 2;
                        }
                        else if (previousChar === "/" && currentChar === "*") {
                            // found a possible marker start
                            state = State.inSlashStarMarker;
                            openMarker = {
                                position: (i - 1) - difference,
                                sourcePosition: i - 1,
                                sourceLine: line,
                                sourceColumn: column,
                            };
                        }
                        else if (previousChar === "{" && currentChar === "|") {
                            // found an object marker start
                            state = State.inObjectMarker;
                            openMarker = {
                                position: (i - 1) - difference,
                                sourcePosition: i - 1,
                                sourceLine: line,
                                sourceColumn: column,
                            };
                            flush(i - 1);
                        }
                        break;

                    case State.inObjectMarker:
                        // Object markers are only ever terminated by |} and have no content restrictions
                        if (previousChar === "|" && currentChar === "}") {
                            // Record the marker
                            const objectMarkerNameText = content.substring(openMarker!.sourcePosition + 2, i - 1).trim();
                            const marker = recordObjectMarker(fileName, openMarker!, objectMarkerNameText, markerMap, markers);

                            if (openRanges.length > 0) {
                                openRanges[openRanges.length - 1].marker = marker;
                            }

                            // Set the current start to point to the end of the current marker to ignore its text
                            lastNormalCharPosition = i + 1;
                            difference += i + 1 - openMarker!.sourcePosition;

                            // Reset the state
                            openMarker = undefined;
                            state = State.none;
                        }
                        break;

                    case State.inSlashStarMarker:
                        if (previousChar === "*" && currentChar === "/") {
                            // Record the marker
                            // start + 2 to ignore the */, -1 on the end to ignore the * (/ is next)
                            const markerNameText = content.substring(openMarker!.sourcePosition + 2, i - 1).trim();
                            const marker = recordMarker(fileName, openMarker!, markerNameText, markerMap, markers);

                            if (openRanges.length > 0) {
                                openRanges[openRanges.length - 1].marker = marker;
                            }

                            // Set the current start to point to the end of the current marker to ignore its text
                            flush(openMarker!.sourcePosition);
                            lastNormalCharPosition = i + 1;
                            difference += i + 1 - openMarker!.sourcePosition;

                            // Reset the state
                            openMarker = undefined;
                            state = State.none;
                        }
                        else if (validMarkerChars.indexOf(currentChar) < 0) {
                            if (currentChar === "*" && i < content.length - 1 && content.charAt(i + 1) === "/") {
                                // The marker is about to be closed, ignore the 'invalid' char
                            }
                            else {
                                // We've hit a non-valid marker character, so we were actually in a block comment
                                // Bail out the text we've gathered so far back into the output
                                flush(i);
                                lastNormalCharPosition = i;
                                openMarker = undefined;

                                state = State.none;
                            }
                        }
                        break;
                }

                if (currentChar === "\n" && previousChar === "\r") {
                    // Ignore trailing \n after a \r
                    continue;
                }
                else if (currentChar === "\n" || currentChar === "\r") {
                    line++;
                    column = 1;
                    continue;
                }

                column++;
                previousChar = currentChar;
            }
        }

        // Add the remaining text
        flush(/*lastSafeCharIndex*/ undefined);

        if (openRanges.length > 0) {
            const openRange = openRanges[0];
            reportError(fileName, openRange.sourceLine, openRange.sourceColumn, "Unterminated range.");
        }

        if (openMarker) {
            reportError(fileName, openMarker.sourceLine, openMarker.sourceColumn, "Unterminated marker.");
        }

        // put ranges in the correct order
        localRanges = localRanges.sort((a, b) => a.pos < b.pos ? -1 : a.pos === b.pos && a.end > b.end ? -1 : 1);
        localRanges.forEach(r => ranges.push(r));

        return {
            content: output,
            fileOptions: {},
            version: 0,
            fileName,
        };
    }

    function stringify(data: any, replacer?: (key: string, value: any) => any): string {
        return JSON.stringify(data, replacer, 2);
    }

    /** Collects an array of unique outputs. */
    function unique<T>(inputs: readonly T[], getOutput: (t: T) => string): string[] {
        const set = new ts.Map<string, true>();
        for (const input of inputs) {
            const out = getOutput(input);
            set.set(out, true);
        }
        return ts.arrayFrom(set.keys());
    }

    function toArray<T>(x: ArrayOrSingle<T>): readonly T[] {
        return ts.isArray(x) ? x : [x];
    }

    function makeWhitespaceVisible(text: string) {
        return text.replace(/ /g, "\u00B7").replace(/\r/g, "\u00B6").replace(/\n/g, "\u2193\n").replace(/\t/g, "\u2192\   ");
    }

    function showTextDiff(expected: string, actual: string): string {
        // Only show whitespace if the difference is whitespace-only.
        if (differOnlyByWhitespace(expected, actual)) {
            expected = makeWhitespaceVisible(expected);
            actual = makeWhitespaceVisible(actual);
        }
        return displayExpectedAndActualString(expected, actual);
    }

    function differOnlyByWhitespace(a: string, b: string) {
        return stripWhitespace(a) === stripWhitespace(b);
    }

    function stripWhitespace(s: string): string {
        return s.replace(/\s/g, "");
    }

    function findDuplicatedElement<T>(a: readonly T[], equal: (a: T, b: T) => boolean): T | undefined {
        for (let i = 0; i < a.length; i++) {
            for (let j = i + 1; j < a.length; j++) {
                if (equal(a[i], a[j])) {
                    return a[i];
                }
            }
        }
    }

    function displayExpectedAndActualString(expected: string, actual: string, quoted = false) {
        const expectMsg = "\x1b[1mExpected\x1b[0m\x1b[31m";
        const actualMsg = "\x1b[1mActual\x1b[0m\x1b[31m";
        const expectedString = quoted ? "\"" + expected + "\"" : expected;
        const actualString = quoted ? "\"" + actual + "\"" : actual;
        return `\n${expectMsg}:\n${expectedString}\n\n${actualMsg}:\n${highlightDifferenceBetweenStrings(expected, actualString)}`;
    }

    function templateToRegExp(template: string) {
        return new RegExp(`^${ts.regExpEscape(template).replace(/\\\{\d+\\\}/g, ".*?")}$`);
    }

    function rangesOfDiffBetweenTwoStrings(source: string, target: string) {
        const ranges = [] as { start: number; length: number }[];

        const addToIndex = (index: number) => {
            const closestIndex = ranges[ranges.length - 1];
            if (closestIndex) {
                const doesAddToIndex = closestIndex.start + closestIndex.length === index - 1;
                if (doesAddToIndex) {
                    closestIndex.length = closestIndex.length + 1;
                }
            else {
                ranges.push({ start: index - 1, length: 1 });
            }
          }
          else {
                ranges.push({ start: index - 1, length: 1 });
          }
        };

        for (let index = 0; index < Math.max(source.length, target.length); index++) {
            const srcChar = source[index];
            const targetChar = target[index];
            if (srcChar !== targetChar) addToIndex(index);
        }

        return ranges;
      }

      // Adds an _ when the source string and the target string have a whitespace difference
      function highlightDifferenceBetweenStrings(source: string, target: string) {
        const ranges = rangesOfDiffBetweenTwoStrings(source, target);
        let emTarget = target;
        ranges.forEach((range, index) => {
            const lhs = `\x1b[4m`;
            const rhs = `\x1b[0m\x1b[31m`;
            const additionalOffset = index * lhs.length + index * rhs.length;
            const before = emTarget.slice(0, range.start + 1 + additionalOffset);
            const between = emTarget.slice(
                range.start + 1 + additionalOffset,
                range.start + range.length + 1 + additionalOffset
            );
             const after = emTarget.slice(range.start + range.length + 1 + additionalOffset, emTarget.length);
            emTarget = before + lhs + between + rhs + after;
        });
        return emTarget;
      }
}