program.ts

namespace ts {
    const ignoreDiagnosticCommentRegEx = /(^\s*$)|(^\s*\/\/\/?\s*(@ts-ignore)?)/;

    export function findConfigFile(searchPath: string, fileExists: (fileName: string) => boolean, configName = "tsconfig.json"): string | undefined {
        return forEachAncestorDirectory(searchPath, ancestor => {
            const fileName = combinePaths(ancestor, configName);
            return fileExists(fileName) ? fileName : undefined;
        });
    }

    export function resolveTripleslashReference(moduleName: string, containingFile: string): string {
        const basePath = getDirectoryPath(containingFile);
        const referencedFileName = isRootedDiskPath(moduleName) ? moduleName : combinePaths(basePath, moduleName);
        return normalizePath(referencedFileName);
    }

    /* @internal */
    export function computeCommonSourceDirectoryOfFilenames(fileNames: string[], currentDirectory: string, getCanonicalFileName: GetCanonicalFileName): string {
        let commonPathComponents: string[] | undefined;
        const failed = forEach(fileNames, sourceFile => {
            // Each file contributes into common source file path
            const sourcePathComponents = getNormalizedPathComponents(sourceFile, currentDirectory);
            sourcePathComponents.pop(); // The base file name is not part of the common directory path

            if (!commonPathComponents) {
                // first file
                commonPathComponents = sourcePathComponents;
                return;
            }

            const n = Math.min(commonPathComponents.length, sourcePathComponents.length);
            for (let i = 0; i < n; i++) {
                if (getCanonicalFileName(commonPathComponents[i]) !== getCanonicalFileName(sourcePathComponents[i])) {
                    if (i === 0) {
                        // Failed to find any common path component
                        return true;
                    }

                    // New common path found that is 0 -> i-1
                    commonPathComponents.length = i;
                    break;
                }
            }

            // If the sourcePathComponents was shorter than the commonPathComponents, truncate to the sourcePathComponents
            if (sourcePathComponents.length < commonPathComponents.length) {
                commonPathComponents.length = sourcePathComponents.length;
            }
        });

        // A common path can not be found when paths span multiple drives on windows, for example
        if (failed) {
            return "";
        }

        if (!commonPathComponents) { // Can happen when all input files are .d.ts files
            return currentDirectory;
        }

        return getPathFromPathComponents(commonPathComponents);
    }

    interface OutputFingerprint {
        hash: string;
        byteOrderMark: boolean;
        mtime: Date;
    }

    export function createCompilerHost(options: CompilerOptions, setParentNodes?: boolean): CompilerHost {
        return createCompilerHostWorker(options, setParentNodes);
    }

    /*@internal*/
    // TODO(shkamat): update this after reworking ts build API
    export function createCompilerHostWorker(options: CompilerOptions, setParentNodes?: boolean, system = sys): CompilerHost {
        const existingDirectories = createMap<boolean>();
        const getCanonicalFileName = createGetCanonicalFileName(system.useCaseSensitiveFileNames);
        function getSourceFile(fileName: string, languageVersion: ScriptTarget, onError?: (message: string) => void): SourceFile | undefined {
            let text: string | undefined;
            try {
                performance.mark("beforeIORead");
                text = compilerHost.readFile(fileName);
                performance.mark("afterIORead");
                performance.measure("I/O Read", "beforeIORead", "afterIORead");
            }
            catch (e) {
                if (onError) {
                    onError(e.message);
                }
                text = "";
            }
            return text !== undefined ? createSourceFile(fileName, text, languageVersion, setParentNodes) : undefined;
        }

        function directoryExists(directoryPath: string): boolean {
            if (existingDirectories.has(directoryPath)) {
                return true;
            }
            if (system.directoryExists(directoryPath)) {
                existingDirectories.set(directoryPath, true);
                return true;
            }
            return false;
        }

        function ensureDirectoriesExist(directoryPath: string) {
            if (directoryPath.length > getRootLength(directoryPath) && !directoryExists(directoryPath)) {
                const parentDirectory = getDirectoryPath(directoryPath);
                ensureDirectoriesExist(parentDirectory);
                if (compilerHost.createDirectory) {
                    compilerHost.createDirectory(directoryPath);
                }
                else {
                    system.createDirectory(directoryPath);
                }
            }
        }

        let outputFingerprints: Map<OutputFingerprint>;

        function writeFileIfUpdated(fileName: string, data: string, writeByteOrderMark: boolean): void {
            if (!outputFingerprints) {
                outputFingerprints = createMap<OutputFingerprint>();
            }

            const hash = system.createHash!(data); // TODO: GH#18217
            const mtimeBefore = system.getModifiedTime!(fileName); // TODO: GH#18217

            if (mtimeBefore) {
                const fingerprint = outputFingerprints.get(fileName);
                // If output has not been changed, and the file has no external modification
                if (fingerprint &&
                    fingerprint.byteOrderMark === writeByteOrderMark &&
                    fingerprint.hash === hash &&
                    fingerprint.mtime.getTime() === mtimeBefore.getTime()) {
                    return;
                }
            }

            system.writeFile(fileName, data, writeByteOrderMark);

            const mtimeAfter = system.getModifiedTime!(fileName) || missingFileModifiedTime; // TODO: GH#18217

            outputFingerprints.set(fileName, {
                hash,
                byteOrderMark: writeByteOrderMark,
                mtime: mtimeAfter
            });
        }

        function writeFile(fileName: string, data: string, writeByteOrderMark: boolean, onError?: (message: string) => void) {
            try {
                performance.mark("beforeIOWrite");
                ensureDirectoriesExist(getDirectoryPath(normalizePath(fileName)));

                if (isWatchSet(options) && system.createHash && system.getModifiedTime) {
                    writeFileIfUpdated(fileName, data, writeByteOrderMark);
                }
                else {
                    system.writeFile(fileName, data, writeByteOrderMark);
                }

                performance.mark("afterIOWrite");
                performance.measure("I/O Write", "beforeIOWrite", "afterIOWrite");
            }
            catch (e) {
                if (onError) {
                    onError(e.message);
                }
            }
        }

        function getDefaultLibLocation(): string {
            return getDirectoryPath(normalizePath(system.getExecutingFilePath()));
        }

        const newLine = getNewLineCharacter(options, () => system.newLine);
        const realpath = system.realpath && ((path: string) => system.realpath!(path));
        const compilerHost: CompilerHost = {
            getSourceFile,
            getDefaultLibLocation,
            getDefaultLibFileName: options => combinePaths(getDefaultLibLocation(), getDefaultLibFileName(options)),
            writeFile,
            getCurrentDirectory: memoize(() => system.getCurrentDirectory()),
            useCaseSensitiveFileNames: () => system.useCaseSensitiveFileNames,
            getCanonicalFileName,
            getNewLine: () => newLine,
            fileExists: fileName => system.fileExists(fileName),
            readFile: fileName => system.readFile(fileName),
            trace: (s: string) => system.write(s + newLine),
            directoryExists: directoryName => system.directoryExists(directoryName),
            getEnvironmentVariable: name => system.getEnvironmentVariable ? system.getEnvironmentVariable(name) : "",
            getDirectories: (path: string) => system.getDirectories(path),
            realpath,
            readDirectory: (path, extensions, include, exclude, depth) => system.readDirectory(path, extensions, include, exclude, depth),
            createDirectory: d => system.createDirectory(d),
            createHash: maybeBind(system, system.createHash)
        };
        return compilerHost;
    }

    /*@internal*/
    interface CompilerHostLikeForCache {
        fileExists(fileName: string): boolean;
        readFile(fileName: string, encoding?: string): string | undefined;
        directoryExists?(directory: string): boolean;
        createDirectory?(directory: string): void;
        writeFile?: WriteFileCallback;
    }

    /*@internal*/
    export function changeCompilerHostLikeToUseCache(
        host: CompilerHostLikeForCache,
        toPath: (fileName: string) => Path,
        getSourceFile?: CompilerHost["getSourceFile"]
    ) {
        const originalReadFile = host.readFile;
        const originalFileExists = host.fileExists;
        const originalDirectoryExists = host.directoryExists;
        const originalCreateDirectory = host.createDirectory;
        const originalWriteFile = host.writeFile;
        const readFileCache = createMap<string | false>();
        const fileExistsCache = createMap<boolean>();
        const directoryExistsCache = createMap<boolean>();
        const sourceFileCache = createMap<SourceFile>();

        const readFileWithCache = (fileName: string): string | undefined => {
            const key = toPath(fileName);
            const value = readFileCache.get(key);
            if (value !== undefined) return value !== false ? value : undefined;
            return setReadFileCache(key, fileName);
        };
        const setReadFileCache = (key: Path, fileName: string) => {
            const newValue = originalReadFile.call(host, fileName);
            readFileCache.set(key, newValue !== undefined ? newValue : false);
            return newValue;
        };
        host.readFile = fileName => {
            const key = toPath(fileName);
            const value = readFileCache.get(key);
            if (value !== undefined) return value !== false ? value : undefined; // could be .d.ts from output
            // Cache json or buildInfo
            if (!fileExtensionIs(fileName, Extension.Json) && !isBuildInfoFile(fileName)) {
                return originalReadFile.call(host, fileName);
            }

            return setReadFileCache(key, fileName);
        };

        const getSourceFileWithCache: CompilerHost["getSourceFile"] | undefined = getSourceFile ? (fileName, languageVersion, onError, shouldCreateNewSourceFile) => {
            const key = toPath(fileName);
            const value = sourceFileCache.get(key);
            if (value) return value;

            const sourceFile = getSourceFile(fileName, languageVersion, onError, shouldCreateNewSourceFile);
            if (sourceFile && (isDeclarationFileName(fileName) || fileExtensionIs(fileName, Extension.Json))) {
                sourceFileCache.set(key, sourceFile);
            }
            return sourceFile;
        } : undefined;

        // fileExists for any kind of extension
        host.fileExists = fileName => {
            const key = toPath(fileName);
            const value = fileExistsCache.get(key);
            if (value !== undefined) return value;
            const newValue = originalFileExists.call(host, fileName);
            fileExistsCache.set(key, !!newValue);
            return newValue;
        };
        if (originalWriteFile) {
            host.writeFile = (fileName, data, writeByteOrderMark, onError, sourceFiles) => {
                const key = toPath(fileName);
                fileExistsCache.delete(key);

                const value = readFileCache.get(key);
                if (value !== undefined && value !== data) {
                    readFileCache.delete(key);
                    sourceFileCache.delete(key);
                }
                else if (getSourceFileWithCache) {
                    const sourceFile = sourceFileCache.get(key);
                    if (sourceFile && sourceFile.text !== data) {
                        sourceFileCache.delete(key);
                    }
                }
                originalWriteFile.call(host, fileName, data, writeByteOrderMark, onError, sourceFiles);
            };
        }

        // directoryExists
        if (originalDirectoryExists && originalCreateDirectory) {
            host.directoryExists = directory => {
                const key = toPath(directory);
                const value = directoryExistsCache.get(key);
                if (value !== undefined) return value;
                const newValue = originalDirectoryExists.call(host, directory);
                directoryExistsCache.set(key, !!newValue);
                return newValue;
            };
            host.createDirectory = directory => {
                const key = toPath(directory);
                directoryExistsCache.delete(key);
                originalCreateDirectory.call(host, directory);
            };
        }

        return {
            originalReadFile,
            originalFileExists,
            originalDirectoryExists,
            originalCreateDirectory,
            originalWriteFile,
            getSourceFileWithCache,
            readFileWithCache
        };
    }

    // tslint:disable unified-signatures
    export function getPreEmitDiagnostics(program: Program, sourceFile?: SourceFile, cancellationToken?: CancellationToken): ReadonlyArray<Diagnostic>;
    /*@internal*/ export function getPreEmitDiagnostics(program: BuilderProgram, sourceFile?: SourceFile, cancellationToken?: CancellationToken): ReadonlyArray<Diagnostic>;
    export function getPreEmitDiagnostics(program: Program | BuilderProgram, sourceFile?: SourceFile, cancellationToken?: CancellationToken): ReadonlyArray<Diagnostic> {
        const diagnostics = [
            ...program.getConfigFileParsingDiagnostics(),
            ...program.getOptionsDiagnostics(cancellationToken),
            ...program.getSyntacticDiagnostics(sourceFile, cancellationToken),
            ...program.getGlobalDiagnostics(cancellationToken),
            ...program.getSemanticDiagnostics(sourceFile, cancellationToken)
        ];

        if (getEmitDeclarations(program.getCompilerOptions())) {
            addRange(diagnostics, program.getDeclarationDiagnostics(sourceFile, cancellationToken));
        }

        return sortAndDeduplicateDiagnostics(diagnostics);
    }
    // tslint:enable unified-signatures

    export interface FormatDiagnosticsHost {
        getCurrentDirectory(): string;
        getCanonicalFileName(fileName: string): string;
        getNewLine(): string;
    }

    export function formatDiagnostics(diagnostics: ReadonlyArray<Diagnostic>, host: FormatDiagnosticsHost): string {
        let output = "";

        for (const diagnostic of diagnostics) {
            output += formatDiagnostic(diagnostic, host);
        }
        return output;
    }

    export function formatDiagnostic(diagnostic: Diagnostic, host: FormatDiagnosticsHost): string {
        const errorMessage = `${diagnosticCategoryName(diagnostic)} TS${diagnostic.code}: ${flattenDiagnosticMessageText(diagnostic.messageText, host.getNewLine())}${host.getNewLine()}`;

        if (diagnostic.file) {
            const { line, character } = getLineAndCharacterOfPosition(diagnostic.file, diagnostic.start!); // TODO: GH#18217
            const fileName = diagnostic.file.fileName;
            const relativeFileName = convertToRelativePath(fileName, host.getCurrentDirectory(), fileName => host.getCanonicalFileName(fileName));
            return `${relativeFileName}(${line + 1},${character + 1}): ` + errorMessage;
        }

        return errorMessage;
    }

    /** @internal */
    export enum ForegroundColorEscapeSequences {
        Grey = "\u001b[90m",
        Red = "\u001b[91m",
        Yellow = "\u001b[93m",
        Blue = "\u001b[94m",
        Cyan = "\u001b[96m"
    }
    const gutterStyleSequence = "\u001b[7m";
    const gutterSeparator = " ";
    const resetEscapeSequence = "\u001b[0m";
    const ellipsis = "...";
    const halfIndent = "  ";
    const indent = "    ";
    function getCategoryFormat(category: DiagnosticCategory): ForegroundColorEscapeSequences {
        switch (category) {
            case DiagnosticCategory.Error: return ForegroundColorEscapeSequences.Red;
            case DiagnosticCategory.Warning: return ForegroundColorEscapeSequences.Yellow;
            case DiagnosticCategory.Suggestion: return Debug.fail("Should never get an Info diagnostic on the command line.");
            case DiagnosticCategory.Message: return ForegroundColorEscapeSequences.Blue;
        }
    }

    /** @internal */
    export function formatColorAndReset(text: string, formatStyle: string) {
        return formatStyle + text + resetEscapeSequence;
    }

    function padLeft(s: string, length: number) {
        while (s.length < length) {
            s = " " + s;
        }
        return s;
    }

    function formatCodeSpan(file: SourceFile, start: number, length: number, indent: string, squiggleColor: ForegroundColorEscapeSequences, host: FormatDiagnosticsHost) {
        const { line: firstLine, character: firstLineChar } = getLineAndCharacterOfPosition(file, start);
        const { line: lastLine, character: lastLineChar } = getLineAndCharacterOfPosition(file, start + length);
        const lastLineInFile = getLineAndCharacterOfPosition(file, file.text.length).line;

        const hasMoreThanFiveLines = (lastLine - firstLine) >= 4;
        let gutterWidth = (lastLine + 1 + "").length;
        if (hasMoreThanFiveLines) {
            gutterWidth = Math.max(ellipsis.length, gutterWidth);
        }

        let context = "";
        for (let i = firstLine; i <= lastLine; i++) {
            context += host.getNewLine();
            // If the error spans over 5 lines, we'll only show the first 2 and last 2 lines,
            // so we'll skip ahead to the second-to-last line.
            if (hasMoreThanFiveLines && firstLine + 1 < i && i < lastLine - 1) {
                context += indent + formatColorAndReset(padLeft(ellipsis, gutterWidth), gutterStyleSequence) + gutterSeparator + host.getNewLine();
                i = lastLine - 1;
            }

            const lineStart = getPositionOfLineAndCharacter(file, i, 0);
            const lineEnd = i < lastLineInFile ? getPositionOfLineAndCharacter(file, i + 1, 0) : file.text.length;
            let lineContent = file.text.slice(lineStart, lineEnd);
            lineContent = lineContent.replace(/\s+$/g, "");  // trim from end
            lineContent = lineContent.replace("\t", " ");    // convert tabs to single spaces

            // Output the gutter and the actual contents of the line.
            context += indent + formatColorAndReset(padLeft(i + 1 + "", gutterWidth), gutterStyleSequence) + gutterSeparator;
            context += lineContent + host.getNewLine();

            // Output the gutter and the error span for the line using tildes.
            context += indent + formatColorAndReset(padLeft("", gutterWidth), gutterStyleSequence) + gutterSeparator;
            context += squiggleColor;
            if (i === firstLine) {
                // If we're on the last line, then limit it to the last character of the last line.
                // Otherwise, we'll just squiggle the rest of the line, giving 'slice' no end position.
                const lastCharForLine = i === lastLine ? lastLineChar : undefined;

                context += lineContent.slice(0, firstLineChar).replace(/\S/g, " ");
                context += lineContent.slice(firstLineChar, lastCharForLine).replace(/./g, "~");
            }
            else if (i === lastLine) {
                context += lineContent.slice(0, lastLineChar).replace(/./g, "~");
            }
            else {
                // Squiggle the entire line.
                context += lineContent.replace(/./g, "~");
            }
            context += resetEscapeSequence;
        }
        return context;
    }

    /* @internal */
    export function formatLocation(file: SourceFile, start: number, host: FormatDiagnosticsHost, color = formatColorAndReset) {
        const { line: firstLine, character: firstLineChar } = getLineAndCharacterOfPosition(file, start); // TODO: GH#18217
        const relativeFileName = host ? convertToRelativePath(file.fileName, host.getCurrentDirectory(), fileName => host.getCanonicalFileName(fileName)) : file.fileName;

        let output = "";
        output += color(relativeFileName, ForegroundColorEscapeSequences.Cyan);
        output += ":";
        output += color(`${firstLine + 1}`, ForegroundColorEscapeSequences.Yellow);
        output += ":";
        output += color(`${firstLineChar + 1}`, ForegroundColorEscapeSequences.Yellow);
        return output;
    }

    export function formatDiagnosticsWithColorAndContext(diagnostics: ReadonlyArray<Diagnostic>, host: FormatDiagnosticsHost): string {
        let output = "";
        for (const diagnostic of diagnostics) {
            if (diagnostic.file) {
                const { file, start } = diagnostic;
                output += formatLocation(file, start!, host); // TODO: GH#18217
                output += " - ";
            }

            output += formatColorAndReset(diagnosticCategoryName(diagnostic), getCategoryFormat(diagnostic.category));
            output += formatColorAndReset(` TS${diagnostic.code}: `, ForegroundColorEscapeSequences.Grey);
            output += flattenDiagnosticMessageText(diagnostic.messageText, host.getNewLine());

            if (diagnostic.file) {
                output += host.getNewLine();
                output += formatCodeSpan(diagnostic.file, diagnostic.start!, diagnostic.length!, "", getCategoryFormat(diagnostic.category), host); // TODO: GH#18217
                if (diagnostic.relatedInformation) {
                    output += host.getNewLine();
                    for (const { file, start, length, messageText } of diagnostic.relatedInformation) {
                        if (file) {
                            output += host.getNewLine();
                            output += halfIndent + formatLocation(file, start!, host); // TODO: GH#18217
                            output += formatCodeSpan(file, start!, length!, indent, ForegroundColorEscapeSequences.Cyan, host); // TODO: GH#18217
                        }
                        output += host.getNewLine();
                        output += indent + flattenDiagnosticMessageText(messageText, host.getNewLine());
                    }
                }
            }

            output += host.getNewLine();
        }
        return output;
    }

    export function flattenDiagnosticMessageText(messageText: string | DiagnosticMessageChain | undefined, newLine: string): string {
        if (isString(messageText)) {
            return messageText;
        }
        else {
            let diagnosticChain = messageText;
            let result = "";

            let indent = 0;
            while (diagnosticChain) {
                if (indent) {
                    result += newLine;

                    for (let i = 0; i < indent; i++) {
                        result += "  ";
                    }
                }
                result += diagnosticChain.messageText;
                indent++;
                diagnosticChain = diagnosticChain.next;
            }

            return result;
        }
    }

    function loadWithLocalCache<T>(names: string[], containingFile: string, redirectedReference: ResolvedProjectReference | undefined, loader: (name: string, containingFile: string, redirectedReference: ResolvedProjectReference | undefined) => T): T[] {
        if (names.length === 0) {
            return [];
        }
        const resolutions: T[] = [];
        const cache = createMap<T>();
        for (const name of names) {
            let result: T;
            if (cache.has(name)) {
                result = cache.get(name)!;
            }
            else {
                cache.set(name, result = loader(name, containingFile, redirectedReference));
            }
            resolutions.push(result);
        }
        return resolutions;
    }

    interface DiagnosticCache<T extends Diagnostic> {
        perFile?: Map<T[]>;
        allDiagnostics?: Diagnostic[];
    }

    /**
     * Determines if program structure is upto date or needs to be recreated
     */
    /* @internal */
    export function isProgramUptoDate(
        program: Program | undefined,
        rootFileNames: string[],
        newOptions: CompilerOptions,
        getSourceVersion: (path: Path) => string | undefined,
        fileExists: (fileName: string) => boolean,
        hasInvalidatedResolution: HasInvalidatedResolution,
        hasChangedAutomaticTypeDirectiveNames: boolean,
        projectReferences: ReadonlyArray<ProjectReference> | undefined
    ): boolean {
        // If we haven't created a program yet or have changed automatic type directives, then it is not up-to-date
        if (!program || hasChangedAutomaticTypeDirectiveNames) {
            return false;
        }

        // If number of files in the program do not match, it is not up-to-date
        if (program.getRootFileNames().length !== rootFileNames.length) {
            return false;
        }

        let seenResolvedRefs: ResolvedProjectReference[] | undefined;

        // If project references dont match
        if (!arrayIsEqualTo(program.getProjectReferences(), projectReferences, projectReferenceUptoDate)) {
            return false;
        }

        // If any file is not up-to-date, then the whole program is not up-to-date
        if (program.getSourceFiles().some(sourceFileNotUptoDate)) {
            return false;
        }

        // If any of the missing file paths are now created
        if (program.getMissingFilePaths().some(fileExists)) {
            return false;
        }

        const currentOptions = program.getCompilerOptions();
        // If the compilation settings do no match, then the program is not up-to-date
        if (!compareDataObjects(currentOptions, newOptions)) {
            return false;
        }

        // If everything matches but the text of config file is changed,
        // error locations can change for program options, so update the program
        if (currentOptions.configFile && newOptions.configFile) {
            return currentOptions.configFile.text === newOptions.configFile.text;
        }

        return true;

        function sourceFileNotUptoDate(sourceFile: SourceFile) {
            return !sourceFileVersionUptoDate(sourceFile) ||
                hasInvalidatedResolution(sourceFile.path);
        }

        function sourceFileVersionUptoDate(sourceFile: SourceFile) {
            return sourceFile.version === getSourceVersion(sourceFile.resolvedPath);
        }

        function projectReferenceUptoDate(oldRef: ProjectReference, newRef: ProjectReference, index: number) {
            if (!projectReferenceIsEqualTo(oldRef, newRef)) {
                return false;
            }
            return resolvedProjectReferenceUptoDate(program!.getResolvedProjectReferences()![index], oldRef);
        }

        function resolvedProjectReferenceUptoDate(oldResolvedRef: ResolvedProjectReference | undefined, oldRef: ProjectReference): boolean {
            if (oldResolvedRef) {
                if (contains(seenResolvedRefs, oldResolvedRef)) {
                    // Assume true
                    return true;
                }

                // If sourceFile for the oldResolvedRef existed, check the version for uptodate
                if (!sourceFileVersionUptoDate(oldResolvedRef.sourceFile)) {
                    return false;
                }

                // Add to seen before checking the referenced paths of this config file
                (seenResolvedRefs || (seenResolvedRefs = [])).push(oldResolvedRef);

                // If child project references are upto date, this project reference is uptodate
                return !forEach(oldResolvedRef.references, (childResolvedRef, index) =>
                    !resolvedProjectReferenceUptoDate(childResolvedRef, oldResolvedRef.commandLine.projectReferences![index]));
            }

            // In old program, not able to resolve project reference path,
            // so if config file doesnt exist, it is uptodate.
            return !fileExists(resolveProjectReferencePath(oldRef));
        }
    }

    export function getConfigFileParsingDiagnostics(configFileParseResult: ParsedCommandLine): ReadonlyArray<Diagnostic> {
        return configFileParseResult.options.configFile ?
            [...configFileParseResult.options.configFile.parseDiagnostics, ...configFileParseResult.errors] :
            configFileParseResult.errors;
    }

    /**
     * Determine if source file needs to be re-created even if its text hasn't changed
     */
    function shouldProgramCreateNewSourceFiles(program: Program | undefined, newOptions: CompilerOptions): boolean {
        if (!program) return false;
        // If any compiler options change, we can't reuse old source file even if version match
        // The change in options like these could result in change in syntax tree or `sourceFile.bindDiagnostics`.
        const oldOptions = program.getCompilerOptions();
        return !!sourceFileAffectingCompilerOptions.some(option =>
            !isJsonEqual(getCompilerOptionValue(oldOptions, option), getCompilerOptionValue(newOptions, option)));
    }

    function createCreateProgramOptions(rootNames: ReadonlyArray<string>, options: CompilerOptions, host?: CompilerHost, oldProgram?: Program, configFileParsingDiagnostics?: ReadonlyArray<Diagnostic>): CreateProgramOptions {
        return {
            rootNames,
            options,
            host,
            oldProgram,
            configFileParsingDiagnostics
        };
    }

    /**
     * Create a new 'Program' instance. A Program is an immutable collection of 'SourceFile's and a 'CompilerOptions'
     * that represent a compilation unit.
     *
     * Creating a program proceeds from a set of root files, expanding the set of inputs by following imports and
     * triple-slash-reference-path directives transitively. '@types' and triple-slash-reference-types are also pulled in.
     *
     * @param createProgramOptions - The options for creating a program.
     * @returns A 'Program' object.
     */
    export function createProgram(createProgramOptions: CreateProgramOptions): Program;
    /**
     * Create a new 'Program' instance. A Program is an immutable collection of 'SourceFile's and a 'CompilerOptions'
     * that represent a compilation unit.
     *
     * Creating a program proceeds from a set of root files, expanding the set of inputs by following imports and
     * triple-slash-reference-path directives transitively. '@types' and triple-slash-reference-types are also pulled in.
     *
     * @param rootNames - A set of root files.
     * @param options - The compiler options which should be used.
     * @param host - The host interacts with the underlying file system.
     * @param oldProgram - Reuses an old program structure.
     * @param configFileParsingDiagnostics - error during config file parsing
     * @returns A 'Program' object.
     */
    export function createProgram(rootNames: ReadonlyArray<string>, options: CompilerOptions, host?: CompilerHost, oldProgram?: Program, configFileParsingDiagnostics?: ReadonlyArray<Diagnostic>): Program;
    export function createProgram(rootNamesOrOptions: ReadonlyArray<string> | CreateProgramOptions, _options?: CompilerOptions, _host?: CompilerHost, _oldProgram?: Program, _configFileParsingDiagnostics?: ReadonlyArray<Diagnostic>): Program {
        const createProgramOptions = isArray(rootNamesOrOptions) ? createCreateProgramOptions(rootNamesOrOptions, _options!, _host, _oldProgram, _configFileParsingDiagnostics) : rootNamesOrOptions; // TODO: GH#18217
        const { rootNames, options, configFileParsingDiagnostics, projectReferences } = createProgramOptions;
        let { oldProgram } = createProgramOptions;

        let program: Program;
        let processingDefaultLibFiles: SourceFile[] | undefined;
        let processingOtherFiles: SourceFile[] | undefined;
        let files: SourceFile[];
        let commonSourceDirectory: string;
        let diagnosticsProducingTypeChecker: TypeChecker;
        let noDiagnosticsTypeChecker: TypeChecker;
        let classifiableNames: UnderscoreEscapedMap<true>;
        const ambientModuleNameToUnmodifiedFileName = createMap<string>();

        const cachedSemanticDiagnosticsForFile: DiagnosticCache<Diagnostic> = {};
        const cachedDeclarationDiagnosticsForFile: DiagnosticCache<DiagnosticWithLocation> = {};

        let resolvedTypeReferenceDirectives = createMap<ResolvedTypeReferenceDirective | undefined>();
        let fileProcessingDiagnostics = createDiagnosticCollection();

        // The below settings are to track if a .js file should be add to the program if loaded via searching under node_modules.
        // This works as imported modules are discovered recursively in a depth first manner, specifically:
        // - For each root file, findSourceFile is called.
        // - This calls processImportedModules for each module imported in the source file.
        // - This calls resolveModuleNames, and then calls findSourceFile for each resolved module.
        // As all these operations happen - and are nested - within the createProgram call, they close over the below variables.
        // The current resolution depth is tracked by incrementing/decrementing as the depth first search progresses.
        const maxNodeModuleJsDepth = typeof options.maxNodeModuleJsDepth === "number" ? options.maxNodeModuleJsDepth : 0;
        let currentNodeModulesDepth = 0;

        // If a module has some of its imports skipped due to being at the depth limit under node_modules, then track
        // this, as it may be imported at a shallower depth later, and then it will need its skipped imports processed.
        const modulesWithElidedImports = createMap<boolean>();

        // Track source files that are source files found by searching under node_modules, as these shouldn't be compiled.
        const sourceFilesFoundSearchingNodeModules = createMap<boolean>();

        performance.mark("beforeProgram");

        const host = createProgramOptions.host || createCompilerHost(options);
        const configParsingHost = parseConfigHostFromCompilerHostLike(host);

        let skipDefaultLib = options.noLib;
        const getDefaultLibraryFileName = memoize(() => host.getDefaultLibFileName(options));
        const defaultLibraryPath = host.getDefaultLibLocation ? host.getDefaultLibLocation() : getDirectoryPath(getDefaultLibraryFileName());
        const programDiagnostics = createDiagnosticCollection();
        const currentDirectory = host.getCurrentDirectory();
        const supportedExtensions = getSupportedExtensions(options);
        const supportedExtensionsWithJsonIfResolveJsonModule = getSuppoertedExtensionsWithJsonIfResolveJsonModule(options, supportedExtensions);

        // Map storing if there is emit blocking diagnostics for given input
        const hasEmitBlockingDiagnostics = createMap<boolean>();
        let _compilerOptionsObjectLiteralSyntax: ObjectLiteralExpression | null | undefined;

        let moduleResolutionCache: ModuleResolutionCache | undefined;
        let resolveModuleNamesWorker: (moduleNames: string[], containingFile: string, reusedNames?: string[], redirectedReference?: ResolvedProjectReference) => ResolvedModuleFull[];
        const hasInvalidatedResolution = host.hasInvalidatedResolution || returnFalse;
        if (host.resolveModuleNames) {
            resolveModuleNamesWorker = (moduleNames, containingFile, reusedNames, redirectedReference) => host.resolveModuleNames!(Debug.assertEachDefined(moduleNames), containingFile, reusedNames, redirectedReference).map(resolved => {
                // An older host may have omitted extension, in which case we should infer it from the file extension of resolvedFileName.
                if (!resolved || (resolved as ResolvedModuleFull).extension !== undefined) {
                    return resolved as ResolvedModuleFull;
                }
                const withExtension = clone(resolved) as ResolvedModuleFull;
                withExtension.extension = extensionFromPath(resolved.resolvedFileName);
                return withExtension;
            });
        }
        else {
            moduleResolutionCache = createModuleResolutionCache(currentDirectory, x => host.getCanonicalFileName(x));
            const loader = (moduleName: string, containingFile: string, redirectedReference: ResolvedProjectReference | undefined) => resolveModuleName(moduleName, containingFile, options, host, moduleResolutionCache, redirectedReference).resolvedModule!; // TODO: GH#18217
            resolveModuleNamesWorker = (moduleNames, containingFile, _reusedNames, redirectedReference) => loadWithLocalCache<ResolvedModuleFull>(Debug.assertEachDefined(moduleNames), containingFile, redirectedReference, loader);
        }

        let resolveTypeReferenceDirectiveNamesWorker: (typeDirectiveNames: string[], containingFile: string, redirectedReference?: ResolvedProjectReference) => (ResolvedTypeReferenceDirective | undefined)[];
        if (host.resolveTypeReferenceDirectives) {
            resolveTypeReferenceDirectiveNamesWorker = (typeDirectiveNames, containingFile, redirectedReference) => host.resolveTypeReferenceDirectives!(Debug.assertEachDefined(typeDirectiveNames), containingFile, redirectedReference);
        }
        else {
            const loader = (typesRef: string, containingFile: string, redirectedReference: ResolvedProjectReference | undefined) => resolveTypeReferenceDirective(typesRef, containingFile, options, host, redirectedReference).resolvedTypeReferenceDirective!; // TODO: GH#18217
            resolveTypeReferenceDirectiveNamesWorker = (typeReferenceDirectiveNames, containingFile, redirectedReference) => loadWithLocalCache<ResolvedTypeReferenceDirective>(Debug.assertEachDefined(typeReferenceDirectiveNames), containingFile, redirectedReference, loader);
        }

        // Map from a stringified PackageId to the source file with that id.
        // Only one source file may have a given packageId. Others become redirects (see createRedirectSourceFile).
        // `packageIdToSourceFile` is only used while building the program, while `sourceFileToPackageName` and `isSourceFileTargetOfRedirect` are kept around.
        const packageIdToSourceFile = createMap<SourceFile>();
        // Maps from a SourceFile's `.path` to the name of the package it was imported with.
        let sourceFileToPackageName = createMap<string>();
        // Key is a file name. Value is the (non-empty, or undefined) list of files that redirect to it.
        let redirectTargetsMap = createMultiMap<string>();

        /**
         * map with
         * - SourceFile if present
         * - false if sourceFile missing for source of project reference redirect
         * - undefined otherwise
         */
        const filesByName = createMap<SourceFile | false | undefined>();
        let missingFilePaths: ReadonlyArray<Path> | undefined;
        // stores 'filename -> file association' ignoring case
        // used to track cases when two file names differ only in casing
        const filesByNameIgnoreCase = host.useCaseSensitiveFileNames() ? createMap<SourceFile>() : undefined;

        // A parallel array to projectReferences storing the results of reading in the referenced tsconfig files
        let resolvedProjectReferences: ReadonlyArray<ResolvedProjectReference | undefined> | undefined;
        let projectReferenceRedirects: Map<ResolvedProjectReference | false> | undefined;
        let mapFromFileToProjectReferenceRedirects: Map<Path> | undefined;

        const shouldCreateNewSourceFile = shouldProgramCreateNewSourceFiles(oldProgram, options);
        const structuralIsReused = tryReuseStructureFromOldProgram();
        if (structuralIsReused !== StructureIsReused.Completely) {
            processingDefaultLibFiles = [];
            processingOtherFiles = [];

            if (projectReferences) {
                if (!resolvedProjectReferences) {
                    resolvedProjectReferences = projectReferences.map(parseProjectReferenceConfigFile);
                }
                if (rootNames.length) {
                    for (const parsedRef of resolvedProjectReferences) {
                        if (!parsedRef) continue;
                        const out = parsedRef.commandLine.options.outFile || parsedRef.commandLine.options.out;
                        if (out) {
                            processSourceFile(changeExtension(out, ".d.ts"), /*isDefaultLib*/ false, /*ignoreNoDefaultLib*/ false, /*packageId*/ undefined);
                        }
                        else if (getEmitModuleKind(parsedRef.commandLine.options) === ModuleKind.None) {
                            for (const fileName of parsedRef.commandLine.fileNames) {
                                if (!fileExtensionIs(fileName, Extension.Dts) && hasTSFileExtension(fileName)) {
                                    processSourceFile(getOutputDeclarationFileName(fileName, parsedRef.commandLine, !host.useCaseSensitiveFileNames()), /*isDefaultLib*/ false, /*ignoreNoDefaultLib*/ false, /*packageId*/ undefined);
                                }
                            }
                        }
                    }
                }
            }

            forEach(rootNames, name => processRootFile(name, /*isDefaultLib*/ false, /*ignoreNoDefaultLib*/ false));

            // load type declarations specified via 'types' argument or implicitly from types/ and node_modules/@types folders
            const typeReferences: string[] = rootNames.length ? getAutomaticTypeDirectiveNames(options, host) : emptyArray;

            if (typeReferences.length) {
                // This containingFilename needs to match with the one used in managed-side
                const containingDirectory = options.configFilePath ? getDirectoryPath(options.configFilePath) : host.getCurrentDirectory();
                const containingFilename = combinePaths(containingDirectory, "__inferred type names__.ts");
                const resolutions = resolveTypeReferenceDirectiveNamesWorker(typeReferences, containingFilename);
                for (let i = 0; i < typeReferences.length; i++) {
                    processTypeReferenceDirective(typeReferences[i], resolutions[i]);
                }
            }

            // Do not process the default library if:
            //  - The '--noLib' flag is used.
            //  - A 'no-default-lib' reference comment is encountered in
            //      processing the root files.
            if (rootNames.length && !skipDefaultLib) {
                // If '--lib' is not specified, include default library file according to '--target'
                // otherwise, using options specified in '--lib' instead of '--target' default library file
                const defaultLibraryFileName = getDefaultLibraryFileName();
                if (!options.lib && defaultLibraryFileName) {
                    processRootFile(defaultLibraryFileName, /*isDefaultLib*/ true, /*ignoreNoDefaultLib*/ false);
                }
                else {
                    forEach(options.lib, libFileName => {
                        processRootFile(combinePaths(defaultLibraryPath, libFileName), /*isDefaultLib*/ true, /*ignoreNoDefaultLib*/ false);
                    });
                }
            }

            missingFilePaths = arrayFrom(mapDefinedIterator(filesByName.entries(), ([path, file]) => file === undefined ? path as Path : undefined));
            files = stableSort(processingDefaultLibFiles, compareDefaultLibFiles).concat(processingOtherFiles);
            processingDefaultLibFiles = undefined;
            processingOtherFiles = undefined;
        }

        Debug.assert(!!missingFilePaths);

        // Release any files we have acquired in the old program but are
        // not part of the new program.
        if (oldProgram && host.onReleaseOldSourceFile) {
            const oldSourceFiles = oldProgram.getSourceFiles();
            for (const oldSourceFile of oldSourceFiles) {
                const newFile = getSourceFileByPath(oldSourceFile.resolvedPath);
                if (shouldCreateNewSourceFile || !newFile ||
                    // old file wasnt redirect but new file is
                    (oldSourceFile.resolvedPath === oldSourceFile.path && newFile.resolvedPath !== oldSourceFile.path)) {
                    host.onReleaseOldSourceFile(oldSourceFile, oldProgram.getCompilerOptions(), !!getSourceFileByPath(oldSourceFile.path));
                }
            }
            oldProgram.forEachResolvedProjectReference((resolvedProjectReference, resolvedProjectReferencePath) => {
                if (resolvedProjectReference && !getResolvedProjectReferenceByPath(resolvedProjectReferencePath)) {
                    host.onReleaseOldSourceFile!(resolvedProjectReference.sourceFile, oldProgram!.getCompilerOptions(), /*hasSourceFileByPath*/ false);
                }
            });
        }

        // unconditionally set oldProgram to undefined to prevent it from being captured in closure
        oldProgram = undefined;

        program = {
            getRootFileNames: () => rootNames,
            getSourceFile,
            getSourceFileByPath,
            getSourceFiles: () => files,
            getMissingFilePaths: () => missingFilePaths!, // TODO: GH#18217
            getCompilerOptions: () => options,
            getSyntacticDiagnostics,
            getOptionsDiagnostics,
            getGlobalDiagnostics,
            getSemanticDiagnostics,
            getSuggestionDiagnostics,
            getDeclarationDiagnostics,
            getTypeChecker,
            getClassifiableNames,
            getDiagnosticsProducingTypeChecker,
            getCommonSourceDirectory,
            emit,
            getCurrentDirectory: () => currentDirectory,
            getNodeCount: () => getDiagnosticsProducingTypeChecker().getNodeCount(),
            getIdentifierCount: () => getDiagnosticsProducingTypeChecker().getIdentifierCount(),
            getSymbolCount: () => getDiagnosticsProducingTypeChecker().getSymbolCount(),
            getTypeCount: () => getDiagnosticsProducingTypeChecker().getTypeCount(),
            getFileProcessingDiagnostics: () => fileProcessingDiagnostics,
            getResolvedTypeReferenceDirectives: () => resolvedTypeReferenceDirectives,
            isSourceFileFromExternalLibrary,
            isSourceFileDefaultLibrary,
            dropDiagnosticsProducingTypeChecker,
            getSourceFileFromReference,
            getLibFileFromReference,
            sourceFileToPackageName,
            redirectTargetsMap,
            isEmittedFile,
            getConfigFileParsingDiagnostics,
            getResolvedModuleWithFailedLookupLocationsFromCache,
            getProjectReferences,
            getResolvedProjectReferences,
            getProjectReferenceRedirect,
            getResolvedProjectReferenceToRedirect,
            getResolvedProjectReferenceByPath,
            forEachResolvedProjectReference,
            emitBuildInfo
        };

        verifyCompilerOptions();
        performance.mark("afterProgram");
        performance.measure("Program", "beforeProgram", "afterProgram");

        return program;

        function compareDefaultLibFiles(a: SourceFile, b: SourceFile) {
            return compareValues(getDefaultLibFilePriority(a), getDefaultLibFilePriority(b));
        }

        function getDefaultLibFilePriority(a: SourceFile) {
            if (containsPath(defaultLibraryPath, a.fileName, /*ignoreCase*/ false)) {
                const basename = getBaseFileName(a.fileName);
                if (basename === "lib.d.ts" || basename === "lib.es6.d.ts") return 0;
                const name = removeSuffix(removePrefix(basename, "lib."), ".d.ts");
                const index = libs.indexOf(name);
                if (index !== -1) return index + 1;
            }
            return libs.length + 2;
        }

        function getResolvedModuleWithFailedLookupLocationsFromCache(moduleName: string, containingFile: string): ResolvedModuleWithFailedLookupLocations | undefined {
            return moduleResolutionCache && resolveModuleNameFromCache(moduleName, containingFile, moduleResolutionCache);
        }

        function toPath(fileName: string): Path {
            return ts.toPath(fileName, currentDirectory, getCanonicalFileName);
        }

        function getCommonSourceDirectory() {
            if (commonSourceDirectory === undefined) {
                const emittedFiles = filter(files, file => sourceFileMayBeEmitted(file, options, isSourceFileFromExternalLibrary, getResolvedProjectReferenceToRedirect));
                if (options.rootDir && checkSourceFilesBelongToPath(emittedFiles, options.rootDir)) {
                    // If a rootDir is specified use it as the commonSourceDirectory
                    commonSourceDirectory = getNormalizedAbsolutePath(options.rootDir, currentDirectory);
                }
                else if (options.composite && options.configFilePath) {
                    // Project compilations never infer their root from the input source paths
                    commonSourceDirectory = getDirectoryPath(normalizeSlashes(options.configFilePath));
                    checkSourceFilesBelongToPath(emittedFiles, commonSourceDirectory);
                }
                else {
                    commonSourceDirectory = computeCommonSourceDirectory(emittedFiles);
                }

                if (commonSourceDirectory && commonSourceDirectory[commonSourceDirectory.length - 1] !== directorySeparator) {
                    // Make sure directory path ends with directory separator so this string can directly
                    // used to replace with "" to get the relative path of the source file and the relative path doesn't
                    // start with / making it rooted path
                    commonSourceDirectory += directorySeparator;