TypeScript/src/compiler/watch.ts

/*@internal*/
namespace ts {
    const sysFormatDiagnosticsHost: FormatDiagnosticsHost | undefined = sys ? {
        getCurrentDirectory: () => sys.getCurrentDirectory(),
        getNewLine: () => sys.newLine,
        getCanonicalFileName: createGetCanonicalFileName(sys.useCaseSensitiveFileNames)
    } : undefined;

    /**
     * Create a function that reports error by writing to the system and handles the formatting of the diagnostic
     */
    export function createDiagnosticReporter(system: System, pretty?: boolean): DiagnosticReporter {
        const host: FormatDiagnosticsHost = system === sys && sysFormatDiagnosticsHost ? sysFormatDiagnosticsHost : {
            getCurrentDirectory: () => system.getCurrentDirectory(),
            getNewLine: () => system.newLine,
            getCanonicalFileName: createGetCanonicalFileName(system.useCaseSensitiveFileNames),
        };
        if (!pretty) {
            return diagnostic => system.write(formatDiagnostic(diagnostic, host));
        }

        const diagnostics: Diagnostic[] = new Array(1);
        return diagnostic => {
            diagnostics[0] = diagnostic;
            system.write(formatDiagnosticsWithColorAndContext(diagnostics, host) + host.getNewLine());
            diagnostics[0] = undefined!; // TODO: GH#18217
        };
    }

    /**
     * @returns Whether the screen was cleared.
     */
    function clearScreenIfNotWatchingForFileChanges(system: System, diagnostic: Diagnostic, options: CompilerOptions): boolean {
        if (system.clearScreen &&
            !options.preserveWatchOutput &&
            !options.extendedDiagnostics &&
            !options.diagnostics &&
            contains(screenStartingMessageCodes, diagnostic.code)) {
            system.clearScreen();
            return true;
        }

        return false;
    }

    export const screenStartingMessageCodes: number[] = [
        Diagnostics.Starting_compilation_in_watch_mode.code,
        Diagnostics.File_change_detected_Starting_incremental_compilation.code,
    ];

    function getPlainDiagnosticFollowingNewLines(diagnostic: Diagnostic, newLine: string): string {
        return contains(screenStartingMessageCodes, diagnostic.code)
            ? newLine + newLine
            : newLine;
    }

    /**
     * Get locale specific time based on whether we are in test mode
     */
    export function getLocaleTimeString(system: System) {
        return !system.now ?
            new Date().toLocaleTimeString() :
            system.now().toLocaleTimeString("en-US", { timeZone: "UTC" });
    }

    /**
     * Create a function that reports watch status by writing to the system and handles the formatting of the diagnostic
     */
    export function createWatchStatusReporter(system: System, pretty?: boolean): WatchStatusReporter {
        return pretty ?
            (diagnostic, newLine, options) => {
                clearScreenIfNotWatchingForFileChanges(system, diagnostic, options);
                let output = `[${formatColorAndReset(getLocaleTimeString(system), ForegroundColorEscapeSequences.Grey)}] `;
                output += `${flattenDiagnosticMessageText(diagnostic.messageText, system.newLine)}${newLine + newLine}`;
                system.write(output);
            } :
            (diagnostic, newLine, options) => {
                let output = "";

                if (!clearScreenIfNotWatchingForFileChanges(system, diagnostic, options)) {
                    output += newLine;
                }

                output += `${getLocaleTimeString(system)} - `;
                output += `${flattenDiagnosticMessageText(diagnostic.messageText, system.newLine)}${getPlainDiagnosticFollowingNewLines(diagnostic, newLine)}`;

                system.write(output);
            };
    }

    /** Parses config file using System interface */
    export function parseConfigFileWithSystem(configFileName: string, optionsToExtend: CompilerOptions, extendedConfigCache: Map<ExtendedConfigCacheEntry> | undefined, watchOptionsToExtend: WatchOptions | undefined, system: System, reportDiagnostic: DiagnosticReporter) {
        const host: ParseConfigFileHost = system as any;
        host.onUnRecoverableConfigFileDiagnostic = diagnostic => reportUnrecoverableDiagnostic(system, reportDiagnostic, diagnostic);
        const result = getParsedCommandLineOfConfigFile(configFileName, optionsToExtend, host, extendedConfigCache, watchOptionsToExtend);
        host.onUnRecoverableConfigFileDiagnostic = undefined!; // TODO: GH#18217
        return result;
    }

    export function getErrorCountForSummary(diagnostics: readonly Diagnostic[]) {
        return countWhere(diagnostics, diagnostic => diagnostic.category === DiagnosticCategory.Error);
    }

    export function getFilesInErrorForSummary(diagnostics: readonly Diagnostic[]): (ReportFileInError | undefined)[] {
        const filesInError =
            filter(diagnostics, diagnostic => diagnostic.category === DiagnosticCategory.Error)
            .map(
                errorDiagnostic => {
                    if(errorDiagnostic.file === undefined) return;
                    return `${errorDiagnostic.file.fileName}`;
            });
        return filesInError.map((fileName: string) => {
            const diagnosticForFileName = find(diagnostics, diagnostic =>
                diagnostic.file !== undefined && diagnostic.file.fileName === fileName
            );

            if(diagnosticForFileName !== undefined) {
                const { line } = getLineAndCharacterOfPosition(diagnosticForFileName.file!, diagnosticForFileName.start!);
                return {
                    fileName,
                    line: line + 1,
                };
            }
        });
    }

    export function getWatchErrorSummaryDiagnosticMessage(errorCount: number) {
        return errorCount === 1 ?
            Diagnostics.Found_1_error_Watching_for_file_changes :
            Diagnostics.Found_0_errors_Watching_for_file_changes;
    }

    function prettyPathForFileError(error: ReportFileInError, cwd: string) {
        const line = formatColorAndReset(":" + error.line, ForegroundColorEscapeSequences.Grey);
        if (pathIsAbsolute(error.fileName) && pathIsAbsolute(cwd)) {
            return getRelativePathFromDirectory(cwd, error.fileName, /* ignoreCase */ false) + line;
        }

        return error.fileName + line;
    }

    export function getErrorSummaryText(
        errorCount: number,
        filesInError: readonly (ReportFileInError | undefined)[],
        newLine: string,
        host: HasCurrentDirectory
    ) {
        if (errorCount === 0) return "";
        const nonNilFiles = filesInError.filter(fileInError => fileInError !== undefined);
        const distinctFileNamesWithLines = nonNilFiles.map(fileInError => `${fileInError!.fileName}:${fileInError!.line}`)
            .filter((value, index, self) => self.indexOf(value) === index);

        const firstFileReference = nonNilFiles[0] && prettyPathForFileError(nonNilFiles[0], host.getCurrentDirectory());

        const d = errorCount === 1 ?
            createCompilerDiagnostic(
                filesInError[0] !== undefined ?
                    Diagnostics.Found_1_error_in_1 :
                    Diagnostics.Found_1_error,
                errorCount,
                firstFileReference) :
            createCompilerDiagnostic(
                distinctFileNamesWithLines.length === 0 ?
                    Diagnostics.Found_0_errors :
                    distinctFileNamesWithLines.length === 1 ?
                        Diagnostics.Found_0_errors_in_the_same_file_starting_at_Colon_1 :
                        Diagnostics.Found_0_errors_in_1_files,
                errorCount,
                distinctFileNamesWithLines.length === 1 ? firstFileReference : distinctFileNamesWithLines.length);

        const suffix = distinctFileNamesWithLines.length > 1 ? createTabularErrorsDisplay(nonNilFiles, host) : "";
        return `${newLine}${flattenDiagnosticMessageText(d.messageText, newLine)}${newLine}${newLine}${suffix}`;
    }

    function createTabularErrorsDisplay(filesInError: (ReportFileInError | undefined)[], host: HasCurrentDirectory) {
        const distinctFiles = filesInError.filter((value, index, self) => index === self.findIndex(file => file?.fileName === value?.fileName));
        if (distinctFiles.length === 0) return "";

        const numberLength = (num: number) => Math.log(num) * Math.LOG10E + 1;
        const fileToErrorCount = distinctFiles.map(file => ([file, countWhere(filesInError, fileInError => fileInError!.fileName === file!.fileName)] as const));
        const maxErrors = fileToErrorCount.reduce((acc, value) => Math.max(acc, value[1] || 0), 0);

        const headerRow = Diagnostics.Errors_Files.message;
        const leftColumnHeadingLength = headerRow.split(" ")[0].length;
        const leftPaddingGoal = Math.max(leftColumnHeadingLength, numberLength(maxErrors));
        const headerPadding = Math.max(numberLength(maxErrors) - leftColumnHeadingLength, 0);

        let tabularData = "";
        tabularData += " ".repeat(headerPadding) + headerRow + "\n";
        fileToErrorCount.forEach((row) => {
            const [file, errorCount] = row;
            const errorCountDigitsLength = Math.log(errorCount) * Math.LOG10E + 1 | 0;
            const leftPadding = errorCountDigitsLength < leftPaddingGoal ?
                " ".repeat(leftPaddingGoal - errorCountDigitsLength)
                : "";

            const fileRef = prettyPathForFileError(file!, host.getCurrentDirectory());
            tabularData += `${leftPadding}${errorCount}  ${fileRef}\n`;
        });

        return tabularData;
    }

    export function isBuilderProgram(program: Program | BuilderProgram): program is BuilderProgram {
        return !!(program as BuilderProgram).getState;
    }

    export function listFiles<T extends BuilderProgram>(program: Program | T, write: (s: string) => void) {
        const options = program.getCompilerOptions();
        if (options.explainFiles) {
            explainFiles(isBuilderProgram(program) ? program.getProgram() : program, write);
        }
        else if (options.listFiles || options.listFilesOnly) {
            forEach(program.getSourceFiles(), file => {
                write(file.fileName);
            });
        }
    }

    export function explainFiles(program: Program, write: (s: string) => void) {
        const reasons = program.getFileIncludeReasons();
        const getCanonicalFileName = createGetCanonicalFileName(program.useCaseSensitiveFileNames());
        const relativeFileName = (fileName: string) => convertToRelativePath(fileName, program.getCurrentDirectory(), getCanonicalFileName);
        for (const file of program.getSourceFiles()) {
            write(`${toFileName(file, relativeFileName)}`);
            reasons.get(file.path)?.forEach(reason => write(`  ${fileIncludeReasonToDiagnostics(program, reason, relativeFileName).messageText}`));
            explainIfFileIsRedirect(file, relativeFileName)?.forEach(d => write(`  ${d.messageText}`));
        }
    }

    export function explainIfFileIsRedirect(file: SourceFile, fileNameConvertor?: (fileName: string) => string): DiagnosticMessageChain[] | undefined {
        let result: DiagnosticMessageChain[] | undefined;
        if (file.path !== file.resolvedPath) {
            (result ||= []).push(chainDiagnosticMessages(
                /*details*/ undefined,
                Diagnostics.File_is_output_of_project_reference_source_0,
                toFileName(file.originalFileName, fileNameConvertor)
            ));
        }
        if (file.redirectInfo) {
            (result ||= []).push(chainDiagnosticMessages(
                /*details*/ undefined,
                Diagnostics.File_redirects_to_file_0,
                toFileName(file.redirectInfo.redirectTarget, fileNameConvertor)
            ));
        }
        return result;
    }

    export function getMatchedFileSpec(program: Program, fileName: string) {
        const configFile = program.getCompilerOptions().configFile;
        if (!configFile?.configFileSpecs?.validatedFilesSpec) return undefined;

        const getCanonicalFileName = createGetCanonicalFileName(program.useCaseSensitiveFileNames());
        const filePath = getCanonicalFileName(fileName);
        const basePath = getDirectoryPath(getNormalizedAbsolutePath(configFile.fileName, program.getCurrentDirectory()));
        return find(configFile.configFileSpecs.validatedFilesSpec, fileSpec => getCanonicalFileName(getNormalizedAbsolutePath(fileSpec, basePath)) === filePath);
    }

    export function getMatchedIncludeSpec(program: Program, fileName: string) {
        const configFile = program.getCompilerOptions().configFile;
        if (!configFile?.configFileSpecs?.validatedIncludeSpecs) return undefined;

        const isJsonFile = fileExtensionIs(fileName, Extension.Json);
        const basePath = getDirectoryPath(getNormalizedAbsolutePath(configFile.fileName, program.getCurrentDirectory()));
        const useCaseSensitiveFileNames = program.useCaseSensitiveFileNames();
        return find(configFile?.configFileSpecs?.validatedIncludeSpecs, includeSpec => {
            if (isJsonFile && !endsWith(includeSpec, Extension.Json)) return false;
            const pattern = getPatternFromSpec(includeSpec, basePath, "files");
            return !!pattern && getRegexFromPattern(`(${pattern})$`, useCaseSensitiveFileNames).test(fileName);
        });
    }

    export function fileIncludeReasonToDiagnostics(program: Program, reason: FileIncludeReason, fileNameConvertor?: (fileName: string) => string,): DiagnosticMessageChain {
        const options = program.getCompilerOptions();
        if (isReferencedFile(reason)) {
            const referenceLocation = getReferencedFileLocation(path => program.getSourceFileByPath(path), reason);
            const referenceText = isReferenceFileLocation(referenceLocation) ? referenceLocation.file.text.substring(referenceLocation.pos, referenceLocation.end) : `"${referenceLocation.text}"`;
            let message: DiagnosticMessage;
            Debug.assert(isReferenceFileLocation(referenceLocation) || reason.kind === FileIncludeKind.Import, "Only synthetic references are imports");
            switch (reason.kind) {
                case FileIncludeKind.Import:
                    if (isReferenceFileLocation(referenceLocation)) {
                        message = referenceLocation.packageId ?
                            Diagnostics.Imported_via_0_from_file_1_with_packageId_2 :
                            Diagnostics.Imported_via_0_from_file_1;
                    }
                    else if (referenceLocation.text === externalHelpersModuleNameText) {
                        message = referenceLocation.packageId ?
                            Diagnostics.Imported_via_0_from_file_1_with_packageId_2_to_import_importHelpers_as_specified_in_compilerOptions :
                            Diagnostics.Imported_via_0_from_file_1_to_import_importHelpers_as_specified_in_compilerOptions;
                    }
                    else {
                        message = referenceLocation.packageId ?
                            Diagnostics.Imported_via_0_from_file_1_with_packageId_2_to_import_jsx_and_jsxs_factory_functions :
                            Diagnostics.Imported_via_0_from_file_1_to_import_jsx_and_jsxs_factory_functions;
                    }
                    break;
                case FileIncludeKind.ReferenceFile:
                    Debug.assert(!referenceLocation.packageId);
                    message = Diagnostics.Referenced_via_0_from_file_1;
                    break;
                case FileIncludeKind.TypeReferenceDirective:
                    message = referenceLocation.packageId ?
                        Diagnostics.Type_library_referenced_via_0_from_file_1_with_packageId_2 :
                        Diagnostics.Type_library_referenced_via_0_from_file_1;
                    break;
                case FileIncludeKind.LibReferenceDirective:
                    Debug.assert(!referenceLocation.packageId);
                    message = Diagnostics.Library_referenced_via_0_from_file_1;
                    break;
                default:
                    Debug.assertNever(reason);
            }
            return chainDiagnosticMessages(
                /*details*/ undefined,
                message,
                referenceText,
                toFileName(referenceLocation.file, fileNameConvertor),
                referenceLocation.packageId && packageIdToString(referenceLocation.packageId)
            );
        }
        switch (reason.kind) {
            case FileIncludeKind.RootFile:
                if (!options.configFile?.configFileSpecs) return chainDiagnosticMessages(/*details*/ undefined, Diagnostics.Root_file_specified_for_compilation);
                const fileName = getNormalizedAbsolutePath(program.getRootFileNames()[reason.index], program.getCurrentDirectory());
                const matchedByFiles = getMatchedFileSpec(program, fileName);
                if (matchedByFiles) return chainDiagnosticMessages(/*details*/ undefined, Diagnostics.Part_of_files_list_in_tsconfig_json);
                const matchedByInclude = getMatchedIncludeSpec(program, fileName);
                return matchedByInclude ?
                    chainDiagnosticMessages(
                        /*details*/ undefined,
                        Diagnostics.Matched_by_include_pattern_0_in_1,
                        matchedByInclude,
                        toFileName(options.configFile, fileNameConvertor)
                    ) :
                    // Could be additional files specified as roots
                    chainDiagnosticMessages(/*details*/ undefined, Diagnostics.Root_file_specified_for_compilation);
            case FileIncludeKind.SourceFromProjectReference:
            case FileIncludeKind.OutputFromProjectReference:
                const isOutput = reason.kind === FileIncludeKind.OutputFromProjectReference;
                const referencedResolvedRef = Debug.checkDefined(program.getResolvedProjectReferences()?.[reason.index]);
                return chainDiagnosticMessages(
                    /*details*/ undefined,
                    outFile(options) ?
                        isOutput ?
                            Diagnostics.Output_from_referenced_project_0_included_because_1_specified :
                            Diagnostics.Source_from_referenced_project_0_included_because_1_specified :
                        isOutput ?
                            Diagnostics.Output_from_referenced_project_0_included_because_module_is_specified_as_none :
                            Diagnostics.Source_from_referenced_project_0_included_because_module_is_specified_as_none,
                    toFileName(referencedResolvedRef.sourceFile.fileName, fileNameConvertor),
                    options.outFile ? "--outFile" : "--out",
                );
            case FileIncludeKind.AutomaticTypeDirectiveFile:
                return chainDiagnosticMessages(
                    /*details*/ undefined,
                    options.types ?
                        reason.packageId ?
                            Diagnostics.Entry_point_of_type_library_0_specified_in_compilerOptions_with_packageId_1 :
                            Diagnostics.Entry_point_of_type_library_0_specified_in_compilerOptions :
                        reason.packageId ?
                            Diagnostics.Entry_point_for_implicit_type_library_0_with_packageId_1 :
                            Diagnostics.Entry_point_for_implicit_type_library_0,
                    reason.typeReference,
                    reason.packageId && packageIdToString(reason.packageId),
                );
            case FileIncludeKind.LibFile:
                if (reason.index !== undefined) return chainDiagnosticMessages(/*details*/ undefined, Diagnostics.Library_0_specified_in_compilerOptions, options.lib![reason.index]);
                const target = forEachEntry(targetOptionDeclaration.type, (value, key) => value === getEmitScriptTarget(options) ? key : undefined);
                return chainDiagnosticMessages(
                    /*details*/ undefined,
                    target ?
                        Diagnostics.Default_library_for_target_0 :
                        Diagnostics.Default_library,
                    target,
                );
            default:
                Debug.assertNever(reason);
        }
    }

    function toFileName(file: SourceFile | string, fileNameConvertor?: (fileName: string) => string) {
        const fileName = isString(file) ? file : file.fileName;
        return fileNameConvertor ? fileNameConvertor(fileName) : fileName;
    }

    /**
     * Helper that emit files, report diagnostics and lists emitted and/or source files depending on compiler options
     */
    export function emitFilesAndReportErrors<T extends BuilderProgram>(
        program: Program | T,
        reportDiagnostic: DiagnosticReporter,
        write?: (s: string) => void,
        reportSummary?: ReportEmitErrorSummary,
        writeFile?: WriteFileCallback,
        cancellationToken?: CancellationToken,
        emitOnlyDtsFiles?: boolean,
        customTransformers?: CustomTransformers
    ) {
        const isListFilesOnly = !!program.getCompilerOptions().listFilesOnly;

        // First get and report any syntactic errors.
        const allDiagnostics = program.getConfigFileParsingDiagnostics().slice();
        const configFileParsingDiagnosticsLength = allDiagnostics.length;
        addRange(allDiagnostics, program.getSyntacticDiagnostics(/*sourceFile*/ undefined, cancellationToken));

        // If we didn't have any syntactic errors, then also try getting the global and
        // semantic errors.
        if (allDiagnostics.length === configFileParsingDiagnosticsLength) {
            addRange(allDiagnostics, program.getOptionsDiagnostics(cancellationToken));

            if (!isListFilesOnly) {
                addRange(allDiagnostics, program.getGlobalDiagnostics(cancellationToken));

                if (allDiagnostics.length === configFileParsingDiagnosticsLength) {
                    addRange(allDiagnostics, program.getSemanticDiagnostics(/*sourceFile*/ undefined, cancellationToken));
                }
            }
        }

        // Emit and report any errors we ran into.
        const emitResult = isListFilesOnly
            ? { emitSkipped: true, diagnostics: emptyArray }
            : program.emit(/*targetSourceFile*/ undefined, writeFile, cancellationToken, emitOnlyDtsFiles, customTransformers);
        const { emittedFiles, diagnostics: emitDiagnostics } = emitResult;
        addRange(allDiagnostics, emitDiagnostics);

        const diagnostics = sortAndDeduplicateDiagnostics(allDiagnostics);
        diagnostics.forEach(reportDiagnostic);
        if (write) {
            const currentDir = program.getCurrentDirectory();
            forEach(emittedFiles, file => {
                const filepath = getNormalizedAbsolutePath(file, currentDir);
                write(`TSFILE: ${filepath}`);
            });
            listFiles(program, write);
        }

        if (reportSummary) {
            reportSummary(getErrorCountForSummary(diagnostics), getFilesInErrorForSummary(diagnostics));
        }

        return {
            emitResult,
            diagnostics,
        };
    }

    export function emitFilesAndReportErrorsAndGetExitStatus<T extends BuilderProgram>(
        program: Program | T,
        reportDiagnostic: DiagnosticReporter,
        write?: (s: string) => void,
        reportSummary?: ReportEmitErrorSummary,
        writeFile?: WriteFileCallback,
        cancellationToken?: CancellationToken,
        emitOnlyDtsFiles?: boolean,
        customTransformers?: CustomTransformers
    ) {
        const { emitResult, diagnostics } = emitFilesAndReportErrors(
            program,
            reportDiagnostic,
            write,
            reportSummary,
            writeFile,
            cancellationToken,
            emitOnlyDtsFiles,
            customTransformers
        );

        if (emitResult.emitSkipped && diagnostics.length > 0) {
            // If the emitter didn't emit anything, then pass that value along.
            return ExitStatus.DiagnosticsPresent_OutputsSkipped;
        }
        else if (diagnostics.length > 0) {
            // The emitter emitted something, inform the caller if that happened in the presence
            // of diagnostics or not.
            return ExitStatus.DiagnosticsPresent_OutputsGenerated;
        }
        return ExitStatus.Success;
    }

    export const noopFileWatcher: FileWatcher = { close: noop };
    export const returnNoopFileWatcher = () => noopFileWatcher;

    export function createWatchHost(system = sys, reportWatchStatus?: WatchStatusReporter): WatchHost {
        const onWatchStatusChange = reportWatchStatus || createWatchStatusReporter(system);
        return {
            onWatchStatusChange,
            watchFile: maybeBind(system, system.watchFile) || returnNoopFileWatcher,
            watchDirectory: maybeBind(system, system.watchDirectory) || returnNoopFileWatcher,
            setTimeout: maybeBind(system, system.setTimeout) || noop,
            clearTimeout: maybeBind(system, system.clearTimeout) || noop
        };
    }

    export type WatchType = WatchTypeRegistry[keyof WatchTypeRegistry];
    export const WatchType: WatchTypeRegistry = {
        ConfigFile: "Config file",
        ExtendedConfigFile: "Extended config file",
        SourceFile: "Source file",
        MissingFile: "Missing file",
        WildcardDirectory: "Wild card directory",
        FailedLookupLocations: "Failed Lookup Locations",
        TypeRoots: "Type roots",
        ConfigFileOfReferencedProject: "Config file of referened project",
        ExtendedConfigOfReferencedProject: "Extended config file of referenced project",
        WildcardDirectoryOfReferencedProject: "Wild card directory of referenced project",
        PackageJson: "package.json file",
    };

    export interface WatchTypeRegistry {
        ConfigFile: "Config file",
        ExtendedConfigFile: "Extended config file",
        SourceFile: "Source file",
        MissingFile: "Missing file",
        WildcardDirectory: "Wild card directory",
        FailedLookupLocations: "Failed Lookup Locations",
        TypeRoots: "Type roots",
        ConfigFileOfReferencedProject: "Config file of referened project",
        ExtendedConfigOfReferencedProject: "Extended config file of referenced project",
        WildcardDirectoryOfReferencedProject: "Wild card directory of referenced project",
        PackageJson: "package.json file",
    }

    interface WatchFactory<X, Y = undefined> extends ts.WatchFactory<X, Y> {
        writeLog: (s: string) => void;
    }

    export function createWatchFactory<Y = undefined>(host: WatchFactoryHost & { trace?(s: string): void; }, options: { extendedDiagnostics?: boolean; diagnostics?: boolean; }) {
        const watchLogLevel = host.trace ? options.extendedDiagnostics ? WatchLogLevel.Verbose : options.diagnostics ? WatchLogLevel.TriggerOnly : WatchLogLevel.None : WatchLogLevel.None;
        const writeLog: (s: string) => void = watchLogLevel !== WatchLogLevel.None ? (s => host.trace!(s)) : noop;
        const result = getWatchFactory<WatchType, Y>(host, watchLogLevel, writeLog) as WatchFactory<WatchType, Y>;
        result.writeLog = writeLog;
        return result;
    }

    export function createCompilerHostFromProgramHost(host: ProgramHost<any>, getCompilerOptions: () => CompilerOptions, directoryStructureHost: DirectoryStructureHost = host): CompilerHost {
        const useCaseSensitiveFileNames = host.useCaseSensitiveFileNames();
        const hostGetNewLine = memoize(() => host.getNewLine());
        return {
            getSourceFile: (fileName, languageVersionOrOptions, onError) => {
                let text: string | undefined;
                try {
                    performance.mark("beforeIORead");
                    text = host.readFile(fileName, getCompilerOptions().charset);
                    performance.mark("afterIORead");
                    performance.measure("I/O Read", "beforeIORead", "afterIORead");
                }
                catch (e) {
                    if (onError) {
                        onError(e.message);
                    }
                    text = "";
                }

                return text !== undefined ? createSourceFile(fileName, text, languageVersionOrOptions) : undefined;
            },
            getDefaultLibLocation: maybeBind(host, host.getDefaultLibLocation),
            getDefaultLibFileName: options => host.getDefaultLibFileName(options),
            writeFile,
            getCurrentDirectory: memoize(() => host.getCurrentDirectory()),
            useCaseSensitiveFileNames: () => useCaseSensitiveFileNames,
            getCanonicalFileName: createGetCanonicalFileName(useCaseSensitiveFileNames),
            getNewLine: () => getNewLineCharacter(getCompilerOptions(), hostGetNewLine),
            fileExists: f => host.fileExists(f),
            readFile: f => host.readFile(f),
            trace: maybeBind(host, host.trace),
            directoryExists: maybeBind(directoryStructureHost, directoryStructureHost.directoryExists),
            getDirectories: maybeBind(directoryStructureHost, directoryStructureHost.getDirectories),
            realpath: maybeBind(host, host.realpath),
            getEnvironmentVariable: maybeBind(host, host.getEnvironmentVariable) || (() => ""),
            createHash: maybeBind(host, host.createHash),
            readDirectory: maybeBind(host, host.readDirectory),
            disableUseFileVersionAsSignature: host.disableUseFileVersionAsSignature,
        };

        function writeFile(fileName: string, text: string, writeByteOrderMark: boolean, onError: (message: string) => void) {
            try {
                performance.mark("beforeIOWrite");

                // NOTE: If patchWriteFileEnsuringDirectory has been called,
                // the host.writeFile will do its own directory creation and
                // the ensureDirectoriesExist call will always be redundant.
                writeFileEnsuringDirectories(
                    fileName,
                    text,
                    writeByteOrderMark,
                    (path, data, writeByteOrderMark) => host.writeFile!(path, data, writeByteOrderMark),
                    path => host.createDirectory!(path),
                    path => host.directoryExists!(path));

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

    export function setGetSourceFileAsHashVersioned(compilerHost: CompilerHost, host: { createHash?(data: string): string; }) {
        const originalGetSourceFile = compilerHost.getSourceFile;
        const computeHash = maybeBind(host, host.createHash) || generateDjb2Hash;
        compilerHost.getSourceFile = (...args) => {
            const result = originalGetSourceFile.call(compilerHost, ...args);
            if (result) {
                result.version = computeHash(result.text);
            }
            return result;
        };
    }

    /**
     * Creates the watch compiler host that can be extended with config file or root file names and options host
     */
    export function createProgramHost<T extends BuilderProgram = EmitAndSemanticDiagnosticsBuilderProgram>(system: System, createProgram: CreateProgram<T> | undefined): ProgramHost<T> {
        const getDefaultLibLocation = memoize(() => getDirectoryPath(normalizePath(system.getExecutingFilePath())));
        return {
            useCaseSensitiveFileNames: () => system.useCaseSensitiveFileNames,
            getNewLine: () => system.newLine,
            getCurrentDirectory: memoize(() => system.getCurrentDirectory()),
            getDefaultLibLocation,
            getDefaultLibFileName: options => combinePaths(getDefaultLibLocation(), getDefaultLibFileName(options)),
            fileExists: path => system.fileExists(path),
            readFile: (path, encoding) => system.readFile(path, encoding),
            directoryExists: path => system.directoryExists(path),
            getDirectories: path => system.getDirectories(path),
            readDirectory: (path, extensions, exclude, include, depth) => system.readDirectory(path, extensions, exclude, include, depth),
            realpath: maybeBind(system, system.realpath),
            getEnvironmentVariable: maybeBind(system, system.getEnvironmentVariable),
            trace: s => system.write(s + system.newLine),
            createDirectory: path => system.createDirectory(path),
            writeFile: (path, data, writeByteOrderMark) => system.writeFile(path, data, writeByteOrderMark),
            createHash: maybeBind(system, system.createHash),
            createProgram: createProgram || createEmitAndSemanticDiagnosticsBuilderProgram as any as CreateProgram<T>,
            disableUseFileVersionAsSignature: system.disableUseFileVersionAsSignature,
        };
    }

    /**
     * Creates the watch compiler host that can be extended with config file or root file names and options host
     */
    function createWatchCompilerHost<T extends BuilderProgram = EmitAndSemanticDiagnosticsBuilderProgram>(system = sys, createProgram: CreateProgram<T> | undefined, reportDiagnostic: DiagnosticReporter, reportWatchStatus?: WatchStatusReporter): WatchCompilerHost<T> {
        const write = (s: string) => system.write(s + system.newLine);
        const result = createProgramHost(system, createProgram) as WatchCompilerHost<T>;
        copyProperties(result, createWatchHost(system, reportWatchStatus));
        result.afterProgramCreate = builderProgram => {
            const compilerOptions = builderProgram.getCompilerOptions();
            const newLine = getNewLineCharacter(compilerOptions, () => system.newLine);

            emitFilesAndReportErrors(
                builderProgram,
                reportDiagnostic,
                write,
                errorCount => result.onWatchStatusChange!(
                    createCompilerDiagnostic(getWatchErrorSummaryDiagnosticMessage(errorCount), errorCount),
                    newLine,
                    compilerOptions,
                    errorCount
                )
            );
        };
        return result;
    }

    /**
     * Report error and exit
     */
    function reportUnrecoverableDiagnostic(system: System, reportDiagnostic: DiagnosticReporter, diagnostic: Diagnostic) {
        reportDiagnostic(diagnostic);
        system.exit(ExitStatus.DiagnosticsPresent_OutputsSkipped);
    }

    export interface CreateWatchCompilerHostInput<T extends BuilderProgram> {
        system: System;
        createProgram?: CreateProgram<T>;
        reportDiagnostic?: DiagnosticReporter;
        reportWatchStatus?: WatchStatusReporter;
    }

    export interface CreateWatchCompilerHostOfConfigFileInput<T extends BuilderProgram> extends CreateWatchCompilerHostInput<T> {
        configFileName: string;
        optionsToExtend?: CompilerOptions;
        watchOptionsToExtend?: WatchOptions;
        extraFileExtensions?: readonly FileExtensionInfo[];
    }
    /**
     * Creates the watch compiler host from system for config file in watch mode
     */
    export function createWatchCompilerHostOfConfigFile<T extends BuilderProgram = EmitAndSemanticDiagnosticsBuilderProgram>({
        configFileName, optionsToExtend, watchOptionsToExtend, extraFileExtensions,
        system, createProgram, reportDiagnostic, reportWatchStatus
    }: CreateWatchCompilerHostOfConfigFileInput<T>): WatchCompilerHostOfConfigFile<T> {
        const diagnosticReporter = reportDiagnostic || createDiagnosticReporter(system);
        const host = createWatchCompilerHost(system, createProgram, diagnosticReporter, reportWatchStatus) as WatchCompilerHostOfConfigFile<T>;
        host.onUnRecoverableConfigFileDiagnostic = diagnostic => reportUnrecoverableDiagnostic(system, diagnosticReporter, diagnostic);
        host.configFileName = configFileName;
        host.optionsToExtend = optionsToExtend;
        host.watchOptionsToExtend = watchOptionsToExtend;
        host.extraFileExtensions = extraFileExtensions;
        return host;
    }

    export interface CreateWatchCompilerHostOfFilesAndCompilerOptionsInput<T extends BuilderProgram> extends CreateWatchCompilerHostInput<T> {
        rootFiles: string[];
        options: CompilerOptions;
        watchOptions: WatchOptions | undefined;
        projectReferences?: readonly ProjectReference[];
    }
    /**
     * Creates the watch compiler host from system for compiling root files and options in watch mode
     */
    export function createWatchCompilerHostOfFilesAndCompilerOptions<T extends BuilderProgram = EmitAndSemanticDiagnosticsBuilderProgram>({
        rootFiles, options, watchOptions, projectReferences,
        system, createProgram, reportDiagnostic, reportWatchStatus
    }: CreateWatchCompilerHostOfFilesAndCompilerOptionsInput<T>): WatchCompilerHostOfFilesAndCompilerOptions<T> {
        const host = createWatchCompilerHost(system, createProgram, reportDiagnostic || createDiagnosticReporter(system), reportWatchStatus) as WatchCompilerHostOfFilesAndCompilerOptions<T>;
        host.rootFiles = rootFiles;
        host.options = options;
        host.watchOptions = watchOptions;
        host.projectReferences = projectReferences;
        return host;
    }

    export interface IncrementalCompilationOptions {
        rootNames: readonly string[];
        options: CompilerOptions;
        configFileParsingDiagnostics?: readonly Diagnostic[];
        projectReferences?: readonly ProjectReference[];
        host?: CompilerHost;
        reportDiagnostic?: DiagnosticReporter;
        reportErrorSummary?: ReportEmitErrorSummary;
        afterProgramEmitAndDiagnostics?(program: EmitAndSemanticDiagnosticsBuilderProgram): void;
        system?: System;
    }
    export function performIncrementalCompilation(input: IncrementalCompilationOptions) {
        const system = input.system || sys;
        const host = input.host || (input.host = createIncrementalCompilerHost(input.options, system));
        const builderProgram = createIncrementalProgram(input);
        const exitStatus = emitFilesAndReportErrorsAndGetExitStatus(
            builderProgram,
            input.reportDiagnostic || createDiagnosticReporter(system),
            s => host.trace && host.trace(s),
            input.reportErrorSummary || input.options.pretty ? (errorCount, filesInError) => system.write(getErrorSummaryText(errorCount, filesInError, system.newLine, host)) : undefined
        );
        if (input.afterProgramEmitAndDiagnostics) input.afterProgramEmitAndDiagnostics(builderProgram);
        return exitStatus;
    }
}