session.ts

namespace ts.server {
    interface StackTraceError extends Error {
        stack?: string;
    }

    export interface ServerCancellationToken extends HostCancellationToken {
        setRequest(requestId: number): void;
        resetRequest(requestId: number): void;
    }

    export const nullCancellationToken: ServerCancellationToken = {
        isCancellationRequested: () => false,
        setRequest: () => void 0,
        resetRequest: () => void 0
    };

    function hrTimeToMilliseconds(time: number[]): number {
        const seconds = time[0];
        const nanoseconds = time[1];
        return ((1e9 * seconds) + nanoseconds) / 1000000.0;
    }

    function isDeclarationFileInJSOnlyNonConfiguredProject(project: Project, file: NormalizedPath) {
        // Checking for semantic diagnostics is an expensive process. We want to avoid it if we
        // know for sure it is not needed.
        // For instance, .d.ts files injected by ATA automatically do not produce any relevant
        // errors to a JS- only project.
        //
        // Note that configured projects can set skipLibCheck (on by default in jsconfig.json) to
        // disable checking for declaration files. We only need to verify for inferred projects (e.g.
        // miscellaneous context in VS) and external projects(e.g.VS.csproj project) with only JS
        // files.
        //
        // We still want to check .js files in a JS-only inferred or external project (e.g. if the
        // file has '// @ts-check').

        if ((project.projectKind === ProjectKind.Inferred || project.projectKind === ProjectKind.External) &&
            project.isJsOnlyProject()) {
            const scriptInfo = project.getScriptInfoForNormalizedPath(file);
            return scriptInfo && !scriptInfo.isJavaScript();
        }
        return false;
    }

    function formatDiag(fileName: NormalizedPath, project: Project, diag: Diagnostic): protocol.Diagnostic {
        const scriptInfo = project.getScriptInfoForNormalizedPath(fileName)!; // TODO: GH#18217
        return {
            start: scriptInfo.positionToLineOffset(diag.start!),
            end: scriptInfo.positionToLineOffset(diag.start! + diag.length!), // TODO: GH#18217
            text: flattenDiagnosticMessageText(diag.messageText, "\n"),
            code: diag.code,
            category: diagnosticCategoryName(diag),
            reportsUnnecessary: diag.reportsUnnecessary,
            source: diag.source,
            relatedInformation: map(diag.relatedInformation, formatRelatedInformation),
        };
    }

    function formatRelatedInformation(info: DiagnosticRelatedInformation): protocol.DiagnosticRelatedInformation {
        if (!info.file) {
            return {
                message: flattenDiagnosticMessageText(info.messageText, "\n"),
                category: diagnosticCategoryName(info),
                code: info.code
            };
        }
        return {
            span: {
                start: convertToLocation(getLineAndCharacterOfPosition(info.file, info.start!)),
                end: convertToLocation(getLineAndCharacterOfPosition(info.file, info.start! + info.length!)), // TODO: GH#18217
                file: info.file.fileName
            },
            message: flattenDiagnosticMessageText(info.messageText, "\n"),
            category: diagnosticCategoryName(info),
            code: info.code
        };
    }

    function convertToLocation(lineAndCharacter: LineAndCharacter): protocol.Location {
        return { line: lineAndCharacter.line + 1, offset: lineAndCharacter.character + 1 };
    }

    function formatConfigFileDiag(diag: Diagnostic, includeFileName: true): protocol.DiagnosticWithFileName;
    function formatConfigFileDiag(diag: Diagnostic, includeFileName: false): protocol.Diagnostic;
    function formatConfigFileDiag(diag: Diagnostic, includeFileName: boolean): protocol.Diagnostic | protocol.DiagnosticWithFileName {
        const start = (diag.file && convertToLocation(getLineAndCharacterOfPosition(diag.file, diag.start!)))!; // TODO: GH#18217
        const end = (diag.file && convertToLocation(getLineAndCharacterOfPosition(diag.file, diag.start! + diag.length!)))!; // TODO: GH#18217
        const text = flattenDiagnosticMessageText(diag.messageText, "\n");
        const { code, source } = diag;
        const category = diagnosticCategoryName(diag);
        const common = {
            start,
            end,
            text,
            code,
            category,
            reportsUnnecessary: diag.reportsUnnecessary,
            source,
            relatedInformation: map(diag.relatedInformation, formatRelatedInformation),
        };
        return includeFileName
            ? { ...common, fileName: diag.file && diag.file.fileName }
            : common;
    }

    export interface PendingErrorCheck {
        fileName: NormalizedPath;
        project: Project;
    }

    function allEditsBeforePos(edits: ReadonlyArray<TextChange>, pos: number): boolean {
        return edits.every(edit => textSpanEnd(edit.span) < pos);
    }

    // CommandNames used to be exposed before TS 2.4 as a namespace
    // In TS 2.4 we switched to an enum, keep this for backward compatibility
    // The var assignment ensures that even though CommandTypes are a const enum
    // we want to ensure the value is maintained in the out since the file is
    // built using --preseveConstEnum.
    export type CommandNames = protocol.CommandTypes;
    export const CommandNames = (<any>protocol).CommandTypes; // tslint:disable-line variable-name

    export function formatMessage<T extends protocol.Message>(msg: T, logger: Logger, byteLength: (s: string, encoding: string) => number, newLine: string): string {
        const verboseLogging = logger.hasLevel(LogLevel.verbose);

        const json = JSON.stringify(msg);
        if (verboseLogging) {
            logger.info(`${msg.type}:${indent(json)}`);
        }

        const len = byteLength(json, "utf8");
        return `Content-Length: ${1 + len}\r\n\r\n${json}${newLine}`;
    }

    /**
     * Allows to schedule next step in multistep operation
     */
    interface NextStep {
        immediate(action: () => void): void;
        delay(ms: number, action: () => void): void;
    }

    /**
     * External capabilities used by multistep operation
     */
    interface MultistepOperationHost {
        getCurrentRequestId(): number;
        sendRequestCompletedEvent(requestId: number): void;
        getServerHost(): ServerHost;
        isCancellationRequested(): boolean;
        executeWithRequestId(requestId: number, action: () => void): void;
        logError(error: Error, message: string): void;
    }

    /**
     * Represents operation that can schedule its next step to be executed later.
     * Scheduling is done via instance of NextStep. If on current step subsequent step was not scheduled - operation is assumed to be completed.
     */
    class MultistepOperation implements NextStep {
        private requestId: number | undefined;
        private timerHandle: any;
        private immediateId: number | undefined;

        constructor(private readonly operationHost: MultistepOperationHost) { }

        public startNew(action: (next: NextStep) => void) {
            this.complete();
            this.requestId = this.operationHost.getCurrentRequestId();
            this.executeAction(action);
        }

        private complete() {
            if (this.requestId !== undefined) {
                this.operationHost.sendRequestCompletedEvent(this.requestId);
                this.requestId = undefined;
            }
            this.setTimerHandle(undefined);
            this.setImmediateId(undefined);
        }

        public immediate(action: () => void) {
            const requestId = this.requestId!;
            Debug.assert(requestId === this.operationHost.getCurrentRequestId(), "immediate: incorrect request id");
            this.setImmediateId(this.operationHost.getServerHost().setImmediate(() => {
                this.immediateId = undefined;
                this.operationHost.executeWithRequestId(requestId, () => this.executeAction(action));
            }));
        }

        public delay(ms: number, action: () => void) {
            const requestId = this.requestId!;
            Debug.assert(requestId === this.operationHost.getCurrentRequestId(), "delay: incorrect request id");
            this.setTimerHandle(this.operationHost.getServerHost().setTimeout(() => {
                this.timerHandle = undefined;
                this.operationHost.executeWithRequestId(requestId, () => this.executeAction(action));
            }, ms));
        }

        private executeAction(action: (next: NextStep) => void) {
            let stop = false;
            try {
                if (this.operationHost.isCancellationRequested()) {
                    stop = true;
                }
                else {
                    action(this);
                }
            }
            catch (e) {
                stop = true;
                // ignore cancellation request
                if (!(e instanceof OperationCanceledException)) {
                    this.operationHost.logError(e, `delayed processing of request ${this.requestId}`);
                }
            }
            if (stop || !this.hasPendingWork()) {
                this.complete();
            }
        }

        private setTimerHandle(timerHandle: any) {
            if (this.timerHandle !== undefined) {
                this.operationHost.getServerHost().clearTimeout(this.timerHandle);
            }
            this.timerHandle = timerHandle;
        }

        private setImmediateId(immediateId: number | undefined) {
            if (this.immediateId !== undefined) {
                this.operationHost.getServerHost().clearImmediate(this.immediateId);
            }
            this.immediateId = immediateId;
        }

        private hasPendingWork() {
            return !!this.timerHandle || !!this.immediateId;
        }
    }

    export type Event = <T extends object>(body: T, eventName: string) => void;

    export interface EventSender {
        event: Event;
    }

    /** @internal */
    export function toEvent(eventName: string, body: object): protocol.Event {
        return {
            seq: 0,
            type: "event",
            event: eventName,
            body
        };
    }

    type Projects = ReadonlyArray<Project> | {
        readonly projects: ReadonlyArray<Project>;
        readonly symLinkedProjects: MultiMap<Project>;
    };

    /**
     * This helper function processes a list of projects and return the concatenated, sortd and deduplicated output of processing each project.
     */
    function combineProjectOutput<T, U>(
        defaultValue: T,
        getValue: (path: Path) => T,
        projects: Projects,
        action: (project: Project, value: T) => ReadonlyArray<U> | U | undefined,
    ): U[] {
        const outputs = flatMapToMutable(isArray(projects) ? projects : projects.projects, project => action(project, defaultValue));
        if (!isArray(projects) && projects.symLinkedProjects) {
            projects.symLinkedProjects.forEach((projects, path) => {
                const value = getValue(path as Path);
                outputs.push(...flatMap(projects, project => action(project, value)));
            });
        }
        return deduplicate(outputs, equateValues);
    }

    function combineProjectOutputFromEveryProject<T>(projectService: ProjectService, action: (project: Project) => ReadonlyArray<T>, areEqual: (a: T, b: T) => boolean) {
        const outputs: T[] = [];
        projectService.forEachEnabledProject(project => {
            const theseOutputs = action(project);
            outputs.push(...theseOutputs.filter(output => !outputs.some(o => areEqual(o, output))));
        });
        return outputs;
    }

    function combineProjectOutputWhileOpeningReferencedProjects<T>(
        projects: Projects,
        defaultProject: Project,
        action: (project: Project) => ReadonlyArray<T>,
        getLocation: (t: T) => sourcemaps.SourceMappableLocation,
        resultsEqual: (a: T, b: T) => boolean,
    ): T[] {
        const outputs: T[] = [];
        combineProjectOutputWorker<undefined>(
            projects,
            defaultProject,
            /*initialLocation*/ undefined,
            ({ project }, tryAddToTodo) => {
                for (const output of action(project)) {
                    if (!contains(outputs, output, resultsEqual) && !tryAddToTodo(project, getLocation(output))) {
                        outputs.push(output);
                    }
                }
            },
            /*getDefinition*/ undefined);
        return outputs;
    }

    function combineProjectOutputForRenameLocations(
        projects: Projects,
        defaultProject: Project,
        initialLocation: sourcemaps.SourceMappableLocation,
        findInStrings: boolean,
        findInComments: boolean
    ): ReadonlyArray<RenameLocation> {
        const outputs: RenameLocation[] = [];

        combineProjectOutputWorker<sourcemaps.SourceMappableLocation>(
            projects,
            defaultProject,
            initialLocation,
            ({ project, location }, tryAddToTodo) => {
                for (const output of project.getLanguageService().findRenameLocations(location.fileName, location.position, findInStrings, findInComments) || emptyArray) {
                    if (!contains(outputs, output, documentSpansEqual) && !tryAddToTodo(project, documentSpanLocation(output))) {
                        outputs.push(output);
                    }
                }
            },
            () => getDefinitionLocation(defaultProject, initialLocation)
        );

        return outputs;
    }

    function getDefinitionLocation(defaultProject: Project, initialLocation: sourcemaps.SourceMappableLocation): sourcemaps.SourceMappableLocation | undefined {
        const infos = defaultProject.getLanguageService().getDefinitionAtPosition(initialLocation.fileName, initialLocation.position);
        const info = infos && firstOrUndefined(infos);
        return info && { fileName: info.fileName, position: info.textSpan.start };
    }

    function combineProjectOutputForReferences(
        projects: Projects,
        defaultProject: Project,
        initialLocation: sourcemaps.SourceMappableLocation
    ): ReadonlyArray<ReferencedSymbol> {
        const outputs: ReferencedSymbol[] = [];

        combineProjectOutputWorker<sourcemaps.SourceMappableLocation>(
            projects,
            defaultProject,
            initialLocation,
            ({ project, location }, getMappedLocation) => {
                for (const outputReferencedSymbol of project.getLanguageService().findReferences(location.fileName, location.position) || emptyArray) {
                    const mappedDefinitionFile = getMappedLocation(project, documentSpanLocation(outputReferencedSymbol.definition));
                    const definition: ReferencedSymbolDefinitionInfo = mappedDefinitionFile === undefined ? outputReferencedSymbol.definition : {
                        ...outputReferencedSymbol.definition,
                        textSpan: createTextSpan(mappedDefinitionFile.position, outputReferencedSymbol.definition.textSpan.length),
                        fileName: mappedDefinitionFile.fileName,
                    };
                    let symbolToAddTo = find(outputs, o => documentSpansEqual(o.definition, definition));
                    if (!symbolToAddTo) {
                        symbolToAddTo = { definition, references: [] };
                        outputs.push(symbolToAddTo);
                    }

                    for (const ref of outputReferencedSymbol.references) {
                        // If it's in a mapped file, that is added to the todo list by `getMappedLocation`.
                        if (!contains(symbolToAddTo.references, ref, documentSpansEqual) && !getMappedLocation(project, documentSpanLocation(ref))) {
                            symbolToAddTo.references.push(ref);
                        }
                    }
                }
            },
            () => getDefinitionLocation(defaultProject, initialLocation)
        );

        return outputs.filter(o => o.references.length !== 0);
    }

    interface ProjectAndLocation<TLocation extends sourcemaps.SourceMappableLocation | undefined> {
        readonly project: Project;
        readonly location: TLocation;
    }

    function forEachProjectInProjects(projects: Projects, path: string | undefined, cb: (project: Project, path: string | undefined) => void): void {
        for (const project of isArray(projects) ? projects : projects.projects) {
            cb(project, path);
        }
        if (!isArray(projects) && projects.symLinkedProjects) {
            projects.symLinkedProjects.forEach((symlinkedProjects, symlinkedPath) => {
                for (const project of symlinkedProjects) {
                    cb(project, symlinkedPath);
                }
            });
        }
    }

    type CombineProjectOutputCallback<TLocation extends sourcemaps.SourceMappableLocation | undefined> = (
        where: ProjectAndLocation<TLocation>,
        getMappedLocation: (project: Project, location: sourcemaps.SourceMappableLocation) => sourcemaps.SourceMappableLocation | undefined,
    ) => void;

    function combineProjectOutputWorker<TLocation extends sourcemaps.SourceMappableLocation | undefined>(
        projects: Projects,
        defaultProject: Project,
        initialLocation: TLocation,
        cb: CombineProjectOutputCallback<TLocation>,
        getDefinition: (() => sourcemaps.SourceMappableLocation | undefined) | undefined,
    ): void {
        const projectService = defaultProject.projectService;
        let toDo: ProjectAndLocation<TLocation>[] | undefined;
        const seenProjects = createMap<true>();
        forEachProjectInProjects(projects, initialLocation && initialLocation.fileName, (project, path) => {
            // TLocation shoud be either `sourcemaps.SourceMappableLocation` or `undefined`. Since `initialLocation` is `TLocation` this cast should be valid.
            const location = (initialLocation ? { fileName: path, position: initialLocation.position } : undefined) as TLocation;
            toDo = callbackProjectAndLocation({ project, location }, projectService, toDo, seenProjects, cb);
        });

        // After initial references are collected, go over every other project and see if it has a reference for the symbol definition.
        if (getDefinition) {
            const memGetDefinition = memoize(getDefinition);
            projectService.forEachEnabledProject(project => {
                if (!addToSeen(seenProjects, project.projectName)) return;
                const definition = getDefinitionInProject(memGetDefinition(), defaultProject, project);
                if (definition) {
                    toDo = callbackProjectAndLocation<TLocation>({ project, location: definition as TLocation }, projectService, toDo, seenProjects, cb);
                }
            });
        }

        while (toDo && toDo.length) {
            toDo = callbackProjectAndLocation(Debug.assertDefined(toDo.pop()), projectService, toDo, seenProjects, cb);
        }
    }

    function getDefinitionInProject(definition: sourcemaps.SourceMappableLocation | undefined, definingProject: Project, project: Project): sourcemaps.SourceMappableLocation | undefined {
        if (!definition || project.containsFile(toNormalizedPath(definition.fileName))) return definition;
        const mappedDefinition = definingProject.getLanguageService().getSourceMapper().tryGetGeneratedLocation(definition);
        return mappedDefinition && project.containsFile(toNormalizedPath(mappedDefinition.fileName)) ? mappedDefinition : undefined;
    }

    function callbackProjectAndLocation<TLocation extends sourcemaps.SourceMappableLocation | undefined>(
        projectAndLocation: ProjectAndLocation<TLocation>,
        projectService: ProjectService,
        toDo: ProjectAndLocation<TLocation>[] | undefined,
        seenProjects: Map<true>,
        cb: CombineProjectOutputCallback<TLocation>,
    ): ProjectAndLocation<TLocation>[] | undefined {
        if (projectAndLocation.project.getCancellationToken().isCancellationRequested()) return undefined; // Skip rest of toDo if cancelled
        cb(projectAndLocation, (project, location) => {
            seenProjects.set(projectAndLocation.project.projectName, true);
            const originalLocation = projectService.getOriginalLocationEnsuringConfiguredProject(project, location);
            if (!originalLocation) return undefined;

            const originalScriptInfo = projectService.getScriptInfo(originalLocation.fileName)!;
            toDo = toDo || [];

            for (const project of originalScriptInfo.containingProjects) {
                addToTodo({ project, location: originalLocation as TLocation }, toDo, seenProjects);
            }
            const symlinkedProjectsMap = projectService.getSymlinkedProjects(originalScriptInfo);
            if (symlinkedProjectsMap) {
                symlinkedProjectsMap.forEach((symlinkedProjects) => {
                    for (const symlinkedProject of symlinkedProjects) addToTodo({ project: symlinkedProject, location: originalLocation as TLocation }, toDo!, seenProjects);
                });
            }
            return originalLocation;
        });
        return toDo;
    }

    function addToTodo<TLocation extends sourcemaps.SourceMappableLocation | undefined>(projectAndLocation: ProjectAndLocation<TLocation>, toDo: Push<ProjectAndLocation<TLocation>>, seenProjects: Map<true>): void {
        if (addToSeen(seenProjects, projectAndLocation.project.projectName)) toDo.push(projectAndLocation);
    }

    function documentSpanLocation({ fileName, textSpan }: DocumentSpan): sourcemaps.SourceMappableLocation {
        return { fileName, position: textSpan.start };
    }

    function getMappedLocation(location: sourcemaps.SourceMappableLocation, projectService: ProjectService, project: Project): sourcemaps.SourceMappableLocation | undefined {
        const mapsTo = project.getSourceMapper().tryGetOriginalLocation(location);
        return mapsTo && projectService.fileExists(toNormalizedPath(mapsTo.fileName)) ? mapsTo : undefined;
    }

    export interface SessionOptions {
        host: ServerHost;
        cancellationToken: ServerCancellationToken;
        useSingleInferredProject: boolean;
        useInferredProjectPerProjectRoot: boolean;
        typingsInstaller: ITypingsInstaller;
        byteLength: (buf: string, encoding?: string) => number;
        hrtime: (start?: number[]) => number[];
        logger: Logger;
        /**
         * If falsy, all events are suppressed.
         */
        canUseEvents: boolean;
        eventHandler?: ProjectServiceEventHandler;
        /** Has no effect if eventHandler is also specified. */
        suppressDiagnosticEvents?: boolean;
        syntaxOnly?: boolean;
        throttleWaitMilliseconds?: number;
        noGetErrOnBackgroundUpdate?: boolean;

        globalPlugins?: ReadonlyArray<string>;
        pluginProbeLocations?: ReadonlyArray<string>;
        allowLocalPluginLoads?: boolean;
        typesMapLocation?: string;
    }

    export class Session implements EventSender {
        private readonly gcTimer: GcTimer;
        protected projectService: ProjectService;
        private changeSeq = 0;

        private currentRequestId: number;
        private errorCheck: MultistepOperation;

        protected host: ServerHost;
        private readonly cancellationToken: ServerCancellationToken;
        protected readonly typingsInstaller: ITypingsInstaller;
        protected byteLength: (buf: string, encoding?: string) => number;
        private hrtime: (start?: number[]) => number[];
        protected logger: Logger;

        protected canUseEvents: boolean;
        private suppressDiagnosticEvents?: boolean;
        private eventHandler: ProjectServiceEventHandler | undefined;
        private readonly noGetErrOnBackgroundUpdate?: boolean;

        constructor(opts: SessionOptions) {
            this.host = opts.host;
            this.cancellationToken = opts.cancellationToken;
            this.typingsInstaller = opts.typingsInstaller;
            this.byteLength = opts.byteLength;
            this.hrtime = opts.hrtime;
            this.logger = opts.logger;
            this.canUseEvents = opts.canUseEvents;
            this.suppressDiagnosticEvents = opts.suppressDiagnosticEvents;
            this.noGetErrOnBackgroundUpdate = opts.noGetErrOnBackgroundUpdate;

            const { throttleWaitMilliseconds } = opts;

            this.eventHandler = this.canUseEvents
                ? opts.eventHandler || (event => this.defaultEventHandler(event))
                : undefined;
            const multistepOperationHost: MultistepOperationHost = {
                executeWithRequestId: (requestId, action) => this.executeWithRequestId(requestId, action),
                getCurrentRequestId: () => this.currentRequestId,
                getServerHost: () => this.host,
                logError: (err, cmd) => this.logError(err, cmd),
                sendRequestCompletedEvent: requestId => this.sendRequestCompletedEvent(requestId),
                isCancellationRequested: () => this.cancellationToken.isCancellationRequested()
            };
            this.errorCheck = new MultistepOperation(multistepOperationHost);
            const settings: ProjectServiceOptions = {
                host: this.host,
                logger: this.logger,
                cancellationToken: this.cancellationToken,
                useSingleInferredProject: opts.useSingleInferredProject,
                useInferredProjectPerProjectRoot: opts.useInferredProjectPerProjectRoot,
                typingsInstaller: this.typingsInstaller,
                throttleWaitMilliseconds,
                eventHandler: this.eventHandler,
                suppressDiagnosticEvents: this.suppressDiagnosticEvents,
                globalPlugins: opts.globalPlugins,
                pluginProbeLocations: opts.pluginProbeLocations,
                allowLocalPluginLoads: opts.allowLocalPluginLoads,
                typesMapLocation: opts.typesMapLocation,
                syntaxOnly: opts.syntaxOnly,
            };
            this.projectService = new ProjectService(settings);
            this.gcTimer = new GcTimer(this.host, /*delay*/ 7000, this.logger);
        }

        private sendRequestCompletedEvent(requestId: number): void {
            this.event<protocol.RequestCompletedEventBody>({ request_seq: requestId }, "requestCompleted");
        }

        private defaultEventHandler(event: ProjectServiceEvent) {
            switch (event.eventName) {
                case ProjectsUpdatedInBackgroundEvent:
                    const { openFiles } = event.data;
                    this.projectsUpdatedInBackgroundEvent(openFiles);
                    break;
                case ProjectLoadingStartEvent:
                    const { project, reason } = event.data;
                    this.event<protocol.ProjectLoadingStartEventBody>(
                        { projectName: project.getProjectName(), reason },
                        ProjectLoadingStartEvent);
                    break;
                case ProjectLoadingFinishEvent:
                    const { project: finishProject } = event.data;
                    this.event<protocol.ProjectLoadingFinishEventBody>({ projectName: finishProject.getProjectName() }, ProjectLoadingFinishEvent);
                    break;
                case LargeFileReferencedEvent:
                    const { file, fileSize, maxFileSize } = event.data;
                    this.event<protocol.LargeFileReferencedEventBody>({ file, fileSize, maxFileSize }, LargeFileReferencedEvent);
                    break;
                case ConfigFileDiagEvent:
                    const { triggerFile, configFileName: configFile, diagnostics } = event.data;
                    const bakedDiags = map(diagnostics, diagnostic => formatConfigFileDiag(diagnostic, /*includeFileName*/ true));
                    this.event<protocol.ConfigFileDiagnosticEventBody>({
                        triggerFile,
                        configFile,
                        diagnostics: bakedDiags
                    }, ConfigFileDiagEvent);
                    break;
                case SurveyReady:
                    const { surveyId } = event.data;
                    this.event<protocol.SurveyReadyEventBody>({ surveyId }, SurveyReady);
                    break;
                case ProjectLanguageServiceStateEvent: {
                    const eventName: protocol.ProjectLanguageServiceStateEventName = ProjectLanguageServiceStateEvent;
                    this.event<protocol.ProjectLanguageServiceStateEventBody>({
                        projectName: event.data.project.getProjectName(),
                        languageServiceEnabled: event.data.languageServiceEnabled
                    }, eventName);
                    break;
                }
                case ProjectInfoTelemetryEvent: {
                    const eventName: protocol.TelemetryEventName = "telemetry";
                    this.event<protocol.TelemetryEventBody>({
                        telemetryEventName: event.eventName,
                        payload: event.data,
                    }, eventName);
                    break;
                }
            }
        }

        private projectsUpdatedInBackgroundEvent(openFiles: string[]): void {
            this.projectService.logger.info(`got projects updated in background, updating diagnostics for ${openFiles}`);
            if (openFiles.length) {
                if (!this.suppressDiagnosticEvents && !this.noGetErrOnBackgroundUpdate) {
                    const checkList = this.createCheckList(openFiles);

                    // For now only queue error checking for open files. We can change this to include non open files as well
                    this.errorCheck.startNew(next => this.updateErrorCheck(next, checkList, 100, /*requireOpen*/ true));
                }

                // Send project changed event
                this.event<protocol.ProjectsUpdatedInBackgroundEventBody>({
                    openFiles
                }, ProjectsUpdatedInBackgroundEvent);
            }
        }

        public logError(err: Error, cmd: string): void {
            this.logErrorWorker(err, cmd);
        }

        private logErrorWorker(err: Error, cmd: string, fileRequest?: protocol.FileRequestArgs): void {
            let msg = "Exception on executing command " + cmd;
            if (err.message) {
                msg += ":\n" + indent(err.message);
                if ((<StackTraceError>err).stack) {
                    msg += "\n" + indent((<StackTraceError>err).stack!);
                }
            }

            if (fileRequest && this.logger.hasLevel(LogLevel.verbose)) {
                try {
                    const { file, project } = this.getFileAndProject(fileRequest);
                    const scriptInfo = project.getScriptInfoForNormalizedPath(file);
                    if (scriptInfo) {
                        const text = getSnapshotText(scriptInfo.getSnapshot());
                        msg += `\n\nFile text of ${fileRequest.file}:${indent(text)}\n`;
                    }
                }
                catch {} // tslint:disable-line no-empty
            }

            this.logger.msg(msg, Msg.Err);
        }

        public send(msg: protocol.Message) {
            if (msg.type === "event" && !this.canUseEvents) {
                if (this.logger.hasLevel(LogLevel.verbose)) {
                    this.logger.info(`Session does not support events: ignored event: ${JSON.stringify(msg)}`);
                }
                return;
            }
            this.host.write(formatMessage(msg, this.logger, this.byteLength, this.host.newLine));
        }

        public event<T extends object>(body: T, eventName: string): void {
            this.send(toEvent(eventName, body));
        }

        // For backwards-compatibility only.
        /** @deprecated */
        public output(info: any, cmdName: string, reqSeq?: number, errorMsg?: string): void {
            this.doOutput(info, cmdName, reqSeq!, /*success*/ !errorMsg, errorMsg); // TODO: GH#18217
        }

        private doOutput(info: {} | undefined, cmdName: string, reqSeq: number, success: boolean, message?: string): void {
            const res: protocol.Response = {
                seq: 0,
                type: "response",
                command: cmdName,
                request_seq: reqSeq,
                success,
            };
            if (success) {
                let metadata: unknown;
                if (isArray(info)) {
                    res.body = info;
                    metadata = (info as WithMetadata<ReadonlyArray<any>>).metadata;
                    delete (info as WithMetadata<ReadonlyArray<any>>).metadata;
                }
                else if (typeof info === "object") {
                    if ((info as WithMetadata<{}>).metadata) {
                        const { metadata: infoMetadata, ...body } = (info as WithMetadata<{}>);
                        res.body = body;
                        metadata = infoMetadata;
                    }
                    else {
                        res.body = info;
                    }
                }
                else {
                    res.body = info;
                }
                if (metadata) res.metadata = metadata;
            }
            else {
                Debug.assert(info === undefined);
            }
            if (message) {
                res.message = message;
            }
            this.send(res);
        }

        private semanticCheck(file: NormalizedPath, project: Project) {
            const diags = isDeclarationFileInJSOnlyNonConfiguredProject(project, file)
                ? emptyArray
                : project.getLanguageService().getSemanticDiagnostics(file);
            this.sendDiagnosticsEvent(file, project, diags, "semanticDiag");
        }

        private syntacticCheck(file: NormalizedPath, project: Project) {
            this.sendDiagnosticsEvent(file, project, project.getLanguageService().getSyntacticDiagnostics(file), "syntaxDiag");
        }

        private suggestionCheck(file: NormalizedPath, project: Project) {
            this.sendDiagnosticsEvent(file, project, project.getLanguageService().getSuggestionDiagnostics(file), "suggestionDiag");
        }

        private sendDiagnosticsEvent(file: NormalizedPath, project: Project, diagnostics: ReadonlyArray<Diagnostic>, kind: protocol.DiagnosticEventKind): void {
            try {
                this.event<protocol.DiagnosticEventBody>({ file, diagnostics: diagnostics.map(diag => formatDiag(file, project, diag)) }, kind);
            }
            catch (err) {
                this.logError(err, kind);
            }
        }

        /** It is the caller's responsibility to verify that `!this.suppressDiagnosticEvents`. */
        private updateErrorCheck(next: NextStep, checkList: PendingErrorCheck[], ms: number, requireOpen = true) {
            Debug.assert(!this.suppressDiagnosticEvents); // Caller's responsibility

            const seq = this.changeSeq;
            const followMs = Math.min(ms, 200);

            let index = 0;
            const checkOne = () => {
                if (this.changeSeq !== seq) {
                    return;
                }

                const { fileName, project } = checkList[index];
                index++;
                // Ensure the project is upto date before checking if this file is present in the project
                updateProjectIfDirty(project);
                if (!project.containsFile(fileName, requireOpen)) {
                    return;
                }

                this.syntacticCheck(fileName, project);
                if (this.changeSeq !== seq) {
                    return;
                }

                next.immediate(() => {
                    this.semanticCheck(fileName, project);
                    if (this.changeSeq !== seq) {
                        return;
                    }

                    const goNext = () => {
                        if (checkList.length > index) {
                            next.delay(followMs, checkOne);
                        }
                    };
                    if (this.getPreferences(fileName).disableSuggestions) {
                        goNext();
                    }
                    else {
                        next.immediate(() => {
                            this.suggestionCheck(fileName, project);
                            goNext();
                        });
                    }
                });
            };

            if (checkList.length > index && this.changeSeq === seq) {
                next.delay(ms, checkOne);
            }
        }

        private cleanProjects(caption: string, projects: Project[]) {
            if (!projects) {
                return;
            }
            this.logger.info(`cleaning ${caption}`);
            for (const p of projects) {
                p.getLanguageService(/*ensureSynchronized*/ false).cleanupSemanticCache();
            }
        }

        private cleanup() {
            this.cleanProjects("inferred projects", this.projectService.inferredProjects);
            this.cleanProjects("configured projects", arrayFrom(this.projectService.configuredProjects.values()));
            this.cleanProjects("external projects", this.projectService.externalProjects);
            if (this.host.gc) {
                this.logger.info(`host.gc()`);
                this.host.gc();
            }
        }

        private getEncodedSemanticClassifications(args: protocol.EncodedSemanticClassificationsRequestArgs) {
            const { file, project } = this.getFileAndProject(args);
            return project.getLanguageService().getEncodedSemanticClassifications(file, args);
        }

        private getProject(projectFileName: string | undefined): Project | undefined {
            return projectFileName === undefined ? undefined : this.projectService.findProject(projectFileName);
        }

        private getConfigFileAndProject(args: protocol.FileRequestArgs): { configFile: NormalizedPath | undefined, project: Project | undefined } {
            const project = this.getProject(args.projectFileName);
            const file = toNormalizedPath(args.file);

            return {
                configFile: project && project.hasConfigFile(file) ? file : undefined,
                project
            };
        }

        private getConfigFileDiagnostics(configFile: NormalizedPath, project: Project, includeLinePosition: boolean) {
            const projectErrors = project.getAllProjectErrors();
            const optionsErrors = project.getLanguageService().getCompilerOptionsDiagnostics();
            const diagnosticsForConfigFile = filter(
                concatenate(projectErrors, optionsErrors),
                diagnostic => !!diagnostic.file && diagnostic.file.fileName === configFile
            );
            return includeLinePosition ?
                this.convertToDiagnosticsWithLinePositionFromDiagnosticFile(diagnosticsForConfigFile) :
                map(
                    diagnosticsForConfigFile,
                    diagnostic => formatConfigFileDiag(diagnostic, /*includeFileName*/ false)
                );
        }

        private convertToDiagnosticsWithLinePositionFromDiagnosticFile(diagnostics: ReadonlyArray<Diagnostic>): protocol.DiagnosticWithLinePosition[] {
            return diagnostics.map<protocol.DiagnosticWithLinePosition>(d => ({
                message: flattenDiagnosticMessageText(d.messageText, this.host.newLine),
                start: d.start!, // TODO: GH#18217
                length: d.length!, // TODO: GH#18217
                category: diagnosticCategoryName(d),
                code: d.code,
                startLocation: (d.file && convertToLocation(getLineAndCharacterOfPosition(d.file, d.start!)))!, // TODO: GH#18217
                endLocation: (d.file && convertToLocation(getLineAndCharacterOfPosition(d.file, d.start! + d.length!)))!, // TODO: GH#18217
                relatedInformation: map(d.relatedInformation, formatRelatedInformation)
            }));
        }

        private getCompilerOptionsDiagnostics(args: protocol.CompilerOptionsDiagnosticsRequestArgs) {
            const project = this.getProject(args.projectFileName)!;
            // Get diagnostics that dont have associated file with them
            // The diagnostics which have file would be in config file and
            // would be reported as part of configFileDiagnostics
            return this.convertToDiagnosticsWithLinePosition(
                filter(
                    project.getLanguageService().getCompilerOptionsDiagnostics(),
                    diagnostic => !diagnostic.file
                ),
                /*scriptInfo*/ undefined
            );
        }

        private convertToDiagnosticsWithLinePosition(diagnostics: ReadonlyArray<Diagnostic>, scriptInfo: ScriptInfo | undefined): protocol.DiagnosticWithLinePosition[] {
            return diagnostics.map(d => <protocol.DiagnosticWithLinePosition>{
                message: flattenDiagnosticMessageText(d.messageText, this.host.newLine),
                start: d.start,
                length: d.length,
                category: diagnosticCategoryName(d),
                code: d.code,
                source: d.source,
                startLocation: scriptInfo && scriptInfo.positionToLineOffset(d.start!), // TODO: GH#18217
                endLocation: scriptInfo && scriptInfo.positionToLineOffset(d.start! + d.length!),
                reportsUnnecessary: d.reportsUnnecessary,
                relatedInformation: map(d.relatedInformation, formatRelatedInformation),
            });
        }

        private getDiagnosticsWorker(
            args: protocol.FileRequestArgs, isSemantic: boolean, selector: (project: Project, file: string) => ReadonlyArray<Diagnostic>, includeLinePosition: boolean
        ): ReadonlyArray<protocol.DiagnosticWithLinePosition> | ReadonlyArray<protocol.Diagnostic> {
            const { project, file } = this.getFileAndProject(args);
            if (isSemantic && isDeclarationFileInJSOnlyNonConfiguredProject(project, file)) {
                return emptyArray;
            }
            const scriptInfo = project.getScriptInfoForNormalizedPath(file);
            const diagnostics = selector(project, file);
            return includeLinePosition
                ? this.convertToDiagnosticsWithLinePosition(diagnostics, scriptInfo)
                : diagnostics.map(d => formatDiag(file, project, d));
        }

        private getDefinition(args: protocol.FileLocationRequestArgs, simplifiedResult: boolean): ReadonlyArray<protocol.FileSpan> | ReadonlyArray<DefinitionInfo> {
            const { file, project } = this.getFileAndProject(args);
            const position = this.getPositionInFile(args, file);
            const definitions = this.mapDefinitionInfoLocations(project.getLanguageService().getDefinitionAtPosition(file, position) || emptyArray, project);
            return simplifiedResult ? this.mapDefinitionInfo(definitions, project) : definitions.map(Session.mapToOriginalLocation);
        }

        private mapDefinitionInfoLocations(definitions: ReadonlyArray<DefinitionInfo>, project: Project): ReadonlyArray<DefinitionInfo> {
            return definitions.map((info): DefinitionInfo => {
                const newLoc = getMappedLocation(documentSpanLocation(info), this.projectService, project);
                return !newLoc ? info : {
                    containerKind: info.containerKind,
                    containerName: info.containerName,
                    fileName: newLoc.fileName,
                    kind: info.kind,
                    name: info.name,
                    textSpan: {
                        start: newLoc.position,
                        length: info.textSpan.length
                    },
                    originalFileName: info.fileName,
                    originalTextSpan: info.textSpan,
                };
            });
        }

        private getDefinitionAndBoundSpan(args: protocol.FileLocationRequestArgs, simplifiedResult: boolean): protocol.DefinitionInfoAndBoundSpan | DefinitionInfoAndBoundSpan {
            const { file, project } = this.getFileAndProject(args);
            const position = this.getPositionInFile(args, file);
            const scriptInfo = Debug.assertDefined(project.getScriptInfo(file));

            const unmappedDefinitionAndBoundSpan = project.getLanguageService().getDefinitionAndBoundSpan(file, position);

            if (!unmappedDefinitionAndBoundSpan || !unmappedDefinitionAndBoundSpan.definitions) {
                return {
                    definitions: emptyArray,
                    textSpan: undefined! // TODO: GH#18217
                };
            }

            const definitions = this.mapDefinitionInfoLocations(unmappedDefinitionAndBoundSpan.definitions, project);
            const { textSpan } = unmappedDefinitionAndBoundSpan;

            if (simplifiedResult) {
                return {
                    definitions: this.mapDefinitionInfo(definitions, project),
                    textSpan: this.toLocationTextSpan(textSpan, scriptInfo)
                };
            }

            return {
                definitions: definitions.map(Session.mapToOriginalLocation),
                textSpan,
            };
        }

        private getEmitOutput(args: protocol.FileRequestArgs): EmitOutput {
            const { file, project } = this.getFileAndProject(args);
            return project.getLanguageService().getEmitOutput(file);
        }

        private mapDefinitionInfo(definitions: ReadonlyArray<DefinitionInfo>, project: Project): ReadonlyArray<protocol.FileSpan> {
            return definitions.map(def => this.toFileSpan(def.fileName, def.textSpan, project));
        }

        /*
         * When we map a .d.ts location to .ts, Visual Studio gets confused because there's no associated Roslyn Document in
         * the same project which corresponds to the file. VS Code has no problem with this, and luckily we have two protocols.
         * This retains the existing behavior for the "simplified" (VS Code) protocol but stores the .d.ts location in a
         * set of additional fields, and does the reverse for VS (store the .d.ts location where
         * it used to be and stores the .ts location in the additional fields).
        */
        private static mapToOriginalLocation<T extends DocumentSpan>(def: T): T {
            if (def.originalFileName) {