Merge pull request #16684 from amcasey/Vsts434619

Watch for the creation of missing files

Jakefile.js

@@ -138,6 +138,7 @@ var harnessSources = harnessCoreSources.concat([
     "telemetry.ts",
     "transform.ts",
     "customTransforms.ts",
+    "programMissingFiles.ts",
 ].map(function (f) {
     return path.join(unittestsDirectory, f);
 })).concat([

src/compiler/core.ts

@@ -1098,6 +1098,15 @@ namespace ts {
         return result;
     }
 
+    /**
+     * Creates a set from the elements of an array.
+     *
+     * @param array the array of input elements.
+     */
+    export function arrayToSet<T>(array: T[], makeKey: (value: T) => string): Map<true> {
+        return arrayToMap<T, true>(array, makeKey, () => true);
+    }
+
     export function cloneMap<T>(map: Map<T>) {
         const clone = createMap<T>();
         copyEntries(map, clone);

src/compiler/program.ts

@@ -472,7 +472,7 @@ namespace ts {
             resolveTypeReferenceDirectiveNamesWorker = (typeReferenceDirectiveNames, containingFile) => loadWithLocalCache(typeReferenceDirectiveNames, containingFile, loader);
         }
 
-        const filesByName = createMap<SourceFile>();
+        const filesByName = createMap<SourceFile | undefined>();
         // stores 'filename -> file association' ignoring case
         // used to track cases when two file names differ only in casing
         const filesByNameIgnoreCase = host.useCaseSensitiveFileNames() ? createFileMap<SourceFile>(fileName => fileName.toLowerCase()) : undefined;
@@ -513,6 +513,8 @@ namespace ts {
             }
         }
 
+        const missingFilePaths = arrayFrom(filesByName.keys(), p => <Path>p).filter(p => !filesByName.get(p));
+
         // unconditionally set moduleResolutionCache to undefined to avoid unnecessary leaks
         moduleResolutionCache = undefined;
 
@@ -524,6 +526,7 @@ namespace ts {
             getSourceFile,
             getSourceFileByPath,
             getSourceFiles: () => files,
+            getMissingFilePaths: () => missingFilePaths,
             getCompilerOptions: () => options,
             getSyntacticDiagnostics,
             getOptionsDiagnostics,
@@ -862,6 +865,21 @@ namespace ts {
                 return oldProgram.structureIsReused;
             }
 
+            // If a file has ceased to be missing, then we need to discard some of the old
+            // structure in order to pick it up.
+            // Caution: if the file has created and then deleted between since it was discovered to
+            // be missing, then the corresponding file watcher will have been closed and no new one
+            // will be created until we encounter a change that prevents complete structure reuse.
+            // During this interval, creation of the file will go unnoticed.  We expect this to be
+            // both rare and low-impact.
+            if (oldProgram.getMissingFilePaths().some(missingFilePath => host.fileExists(missingFilePath))) {
+                return oldProgram.structureIsReused = StructureIsReused.SafeModules;
+            }
+
+            for (const p of oldProgram.getMissingFilePaths()) {
+                filesByName.set(p, undefined);
+            }
+
             // update fileName -> file mapping
             for (let i = 0; i < newSourceFiles.length; i++) {
                 filesByName.set(filePaths[i], newSourceFiles[i]);

src/compiler/sys.ts

@@ -4,7 +4,13 @@ declare function setTimeout(handler: (...args: any[]) => void, timeout: number):
 declare function clearTimeout(handle: any): void;
 
 namespace ts {
-    export type FileWatcherCallback = (fileName: string, removed?: boolean) => void;
+    export enum FileWatcherEventKind {
+        Created,
+        Changed,
+        Deleted
+    }
+
+    export type FileWatcherCallback = (fileName: string, eventKind: FileWatcherEventKind) => void;
     export type DirectoryWatcherCallback = (fileName: string) => void;
     export interface WatchedFile {
         fileName: string;
@@ -174,7 +180,7 @@ namespace ts {
                         const callbacks = fileWatcherCallbacks.get(fileName);
                         if (callbacks) {
                             for (const fileCallback of callbacks) {
-                                fileCallback(fileName);
+                                fileCallback(fileName, FileWatcherEventKind.Changed);
                             }
                         }
                     }
@@ -340,11 +346,22 @@ namespace ts {
                     }
 
                     function fileChanged(curr: any, prev: any) {
-                        if (+curr.mtime <= +prev.mtime) {
+                        const isCurrZero = +curr.mtime === 0;
+                        const isPrevZero = +prev.mtime === 0;
+                        const created = !isCurrZero && isPrevZero;
+                        const deleted = isCurrZero && !isPrevZero;
+
+                        const eventKind = created
+                            ? FileWatcherEventKind.Created
+                            : deleted
+                                ? FileWatcherEventKind.Deleted
+                                : FileWatcherEventKind.Changed;
+
+                        if (eventKind === FileWatcherEventKind.Changed && +curr.mtime <= +prev.mtime) {
                             return;
                         }
 
-                        callback(fileName);
+                        callback(fileName, eventKind);
                     }
                 },
                 watchDirectory: (directoryName, callback, recursive) => {

src/compiler/tsc.ts

@@ -285,6 +285,16 @@ namespace ts {
 
             setCachedProgram(compileResult.program);
             reportWatchDiagnostic(createCompilerDiagnostic(Diagnostics.Compilation_complete_Watching_for_file_changes));
+
+            const missingPaths = compileResult.program.getMissingFilePaths();
+            missingPaths.forEach(path => {
+                const fileWatcher = sys.watchFile(path, (_fileName, eventKind) => {
+                    if (eventKind === FileWatcherEventKind.Created) {
+                        fileWatcher.close();
+                        startTimerForRecompilation();
+                    }
+                });
+            });
         }
 
         function cachedFileExists(fileName: string): boolean {
@@ -308,7 +318,7 @@ namespace ts {
             const sourceFile = hostGetSourceFile(fileName, languageVersion, onError);
             if (sourceFile && isWatchSet(compilerOptions) && sys.watchFile) {
                 // Attach a file watcher
-                sourceFile.fileWatcher = sys.watchFile(sourceFile.fileName, (_fileName: string, removed?: boolean) => sourceFileChanged(sourceFile, removed));
+                sourceFile.fileWatcher = sys.watchFile(sourceFile.fileName, (_fileName, eventKind) => sourceFileChanged(sourceFile, eventKind));
             }
             return sourceFile;
         }
@@ -330,10 +340,10 @@ namespace ts {
         }
 
         // If a source file changes, mark it as unwatched and start the recompilation timer
-        function sourceFileChanged(sourceFile: SourceFile, removed?: boolean) {
+        function sourceFileChanged(sourceFile: SourceFile, eventKind: FileWatcherEventKind) {
             sourceFile.fileWatcher.close();
             sourceFile.fileWatcher = undefined;
-            if (removed) {
+            if (eventKind === FileWatcherEventKind.Deleted) {
                 unorderedRemoveItem(rootFileNames, sourceFile.fileName);
             }
             startTimerForRecompilation();

src/compiler/types.ts

@@ -2426,6 +2426,13 @@ namespace ts {
          */
         getSourceFiles(): SourceFile[];
 
+        /**
+         * Get a list of file names that were passed to 'createProgram' or referenced in a
+         * program source file but could not be located.
+         */
+        /* @internal */
+        getMissingFilePaths(): Path[];
+
         /**
          * Emits the JavaScript and declaration files.  If targetSourceFile is not specified, then
          * the JavaScript and declaration files will be produced for all the files in this program.

src/harness/tsconfig.json

@@ -129,6 +129,7 @@
         "./unittests/transform.ts",
         "./unittests/customTransforms.ts",
         "./unittests/textChanges.ts",
-        "./unittests/telemetry.ts"
+        "./unittests/telemetry.ts",
+        "./unittests/programMissingFiles.ts"
     ]
 }

src/harness/unittests/cachingInServerLSHost.ts

@@ -75,7 +75,7 @@ namespace ts {
         const rootScriptInfo = projectService.getOrCreateScriptInfo(rootFile, /* openedByClient */ true, /*containingProject*/ undefined);
 
         const project = projectService.createInferredProjectWithRootFileIfNecessary(rootScriptInfo);
-        project.setCompilerOptions({ module: ts.ModuleKind.AMD } );
+        project.setCompilerOptions({ module: ts.ModuleKind.AMD, noLib: true } );
         return {
             project,
             rootScriptInfo

src/harness/unittests/compileOnSave.ts

@@ -208,7 +208,7 @@ namespace ts.projectSystem {
 
                 file1Consumer1.content = `let y = 10;`;
                 host.reloadFS([moduleFile1, file1Consumer1, file1Consumer2, configFile, libFile]);
-                host.triggerFileWatcherCallback(file1Consumer1.path, /*removed*/ false);
+                host.triggerFileWatcherCallback(file1Consumer1.path, FileWatcherEventKind.Changed);
 
                 session.executeCommand(changeModuleFile1ShapeRequest1);
                 sendAffectedFileRequestAndCheckResult(session, moduleFile1FileListRequest, [{ projectFileName: configFile.path, files: [moduleFile1, file1Consumer2] }]);
@@ -225,7 +225,7 @@ namespace ts.projectSystem {
                 session.executeCommand(changeModuleFile1ShapeRequest1);
                 // Delete file1Consumer2
                 host.reloadFS([moduleFile1, file1Consumer1, configFile, libFile]);
-                host.triggerFileWatcherCallback(file1Consumer2.path, /*removed*/ true);
+                host.triggerFileWatcherCallback(file1Consumer2.path, FileWatcherEventKind.Deleted);
                 sendAffectedFileRequestAndCheckResult(session, moduleFile1FileListRequest, [{ projectFileName: configFile.path, files: [moduleFile1, file1Consumer1] }]);
             });
 
@@ -475,7 +475,7 @@ namespace ts.projectSystem {
 
                 openFilesForSession([referenceFile1], session);
                 host.reloadFS([referenceFile1, configFile]);
-                host.triggerFileWatcherCallback(moduleFile1.path, /*removed*/ true);
+                host.triggerFileWatcherCallback(moduleFile1.path, FileWatcherEventKind.Deleted);
 
                 const request = makeSessionRequest<server.protocol.FileRequestArgs>(CommandNames.CompileOnSaveAffectedFileList, { file: referenceFile1.path });
                 sendAffectedFileRequestAndCheckResult(session, request, [

src/harness/unittests/programMissingFiles.ts

@@ -0,0 +1,103 @@
+/// <reference path="..\harness.ts" />
+
+namespace ts {
+    describe("Program.getMissingFilePaths", () => {
+
+        const options: CompilerOptions = {
+            noLib: true,
+        };
+
+        const emptyFileName = "empty.ts";
+        const emptyFileRelativePath = "./" + emptyFileName;
+
+        const emptyFile: Harness.Compiler.TestFile = {
+            unitName: emptyFileName,
+            content: ""
+        };
+
+        const referenceFileName = "reference.ts";
+        const referenceFileRelativePath = "./" + referenceFileName;
+
+        const referenceFile: Harness.Compiler.TestFile = {
+            unitName: referenceFileName,
+            content:
+                "/// <reference path=\"d:/imaginary/nonexistent1.ts\"/>\n" + // Absolute
+                "/// <reference path=\"./nonexistent2.ts\"/>\n" + // Relative
+                "/// <reference path=\"nonexistent3.ts\"/>\n" + // Unqualified
+                "/// <reference path=\"nonexistent4\"/>\n"   // No extension
+        };
+
+        const testCompilerHost = Harness.Compiler.createCompilerHost(
+            /*inputFiles*/ [emptyFile, referenceFile],
+            /*writeFile*/ undefined,
+            /*scriptTarget*/ undefined,
+            /*useCaseSensitiveFileNames*/ false,
+            /*currentDirectory*/ "d:\\pretend\\",
+            /*newLineKind*/ NewLineKind.LineFeed,
+            /*libFiles*/ undefined
+        );
+
+        it("handles no missing root files", () => {
+            const program = createProgram([emptyFileRelativePath], options, testCompilerHost);
+            const missing = program.getMissingFilePaths();
+            assert.isDefined(missing);
+            assert.deepEqual(missing, []);
+        });
+
+        it("handles missing root file", () => {
+            const program = createProgram(["./nonexistent.ts"], options, testCompilerHost);
+            const missing = program.getMissingFilePaths();
+            assert.isDefined(missing);
+            assert.deepEqual(missing, ["d:/pretend/nonexistent.ts"]); // Absolute path
+        });
+
+        it("handles multiple missing root files", () => {
+            const program = createProgram(["./nonexistent0.ts", "./nonexistent1.ts"], options, testCompilerHost);
+            const missing = program.getMissingFilePaths().sort();
+            assert.deepEqual(missing, ["d:/pretend/nonexistent0.ts", "d:/pretend/nonexistent1.ts"]);
+        });
+
+        it("handles a mix of present and missing root files", () => {
+            const program = createProgram(["./nonexistent0.ts", emptyFileRelativePath, "./nonexistent1.ts"], options, testCompilerHost);
+            const missing = program.getMissingFilePaths().sort();
+            assert.deepEqual(missing, ["d:/pretend/nonexistent0.ts", "d:/pretend/nonexistent1.ts"]);
+        });
+
+        it("handles repeatedly specified root files", () => {
+            const program = createProgram(["./nonexistent.ts", "./nonexistent.ts"], options, testCompilerHost);
+            const missing = program.getMissingFilePaths();
+            assert.isDefined(missing);
+            assert.deepEqual(missing, ["d:/pretend/nonexistent.ts"]);
+        });
+
+        it("normalizes file paths", () => {
+            const program0 = createProgram(["./nonexistent.ts", "./NONEXISTENT.ts"], options, testCompilerHost);
+            const program1 = createProgram(["./NONEXISTENT.ts", "./nonexistent.ts"], options, testCompilerHost);
+            const missing0 = program0.getMissingFilePaths();
+            const missing1 = program1.getMissingFilePaths();
+            assert.equal(missing0.length, 1);
+            assert.deepEqual(missing0, missing1);
+        });
+
+        it("handles missing triple slash references", () => {
+            const program = createProgram([referenceFileRelativePath], options, testCompilerHost);
+            const missing = program.getMissingFilePaths().sort();
+            assert.isDefined(missing);
+            assert.deepEqual(missing, [
+                // From absolute reference
+                "d:/imaginary/nonexistent1.ts",
+
+                // From relative reference
+                "d:/pretend/nonexistent2.ts",
+
+                // From unqualified reference
+                "d:/pretend/nonexistent3.ts",
+
+                // From no-extension reference
+                "d:/pretend/nonexistent4.d.ts",
+                "d:/pretend/nonexistent4.ts",
+                "d:/pretend/nonexistent4.tsx"
+            ]);
+        });
+    });
+}

src/harness/unittests/projectErrors.ts

@@ -135,7 +135,7 @@ namespace ts.projectSystem {
             }
             // fix config and trigger watcher
             host.reloadFS([file1, file2, correctConfig]);
-            host.triggerFileWatcherCallback(correctConfig.path, /*false*/);
+            host.triggerFileWatcherCallback(correctConfig.path, FileWatcherEventKind.Changed);
             {
                 projectService.checkNumberOfProjects({ configuredProjects: 1 });
                 const configuredProject = forEach(projectService.synchronizeProjectList([]), f => f.info.projectName === corruptedConfig.path && f);
@@ -177,7 +177,7 @@ namespace ts.projectSystem {
             }
             // break config and trigger watcher
             host.reloadFS([file1, file2, corruptedConfig]);
-            host.triggerFileWatcherCallback(corruptedConfig.path, /*false*/);
+            host.triggerFileWatcherCallback(corruptedConfig.path, FileWatcherEventKind.Changed);
             {
                 projectService.checkNumberOfProjects({ configuredProjects: 1 });
                 const configuredProject = forEach(projectService.synchronizeProjectList([]), f => f.info.projectName === corruptedConfig.path && f);

src/harness/unittests/reuseProgramStructure.ts

@@ -316,6 +316,31 @@ namespace ts {
             assert.isTrue(program_1.structureIsReused === StructureIsReused.Not);
         });
 
+        it("succeeds if missing files remain missing", () => {
+            const options: CompilerOptions = { target, noLib: true };
+
+            const program_1 = newProgram(files, ["a.ts"], options);
+            assert.notDeepEqual(emptyArray, program_1.getMissingFilePaths());
+
+            const program_2 = updateProgram(program_1, ["a.ts"], options, noop);
+            assert.deepEqual(program_1.getMissingFilePaths(), program_2.getMissingFilePaths());
+
+            assert.equal(StructureIsReused.Completely, program_1.structureIsReused);
+        });
+
+        it("fails if missing file is created", () => {
+            const options: CompilerOptions = { target, noLib: true };
+
+            const program_1 = newProgram(files, ["a.ts"], options);
+            assert.notDeepEqual(emptyArray, program_1.getMissingFilePaths());
+
+            const newTexts: NamedSourceText[] = files.concat([{ name: "non-existing-file.ts", text: SourceText.New("", "", `var x = 1`) }]);
+            const program_2 = updateProgram(program_1, ["a.ts"], options, noop, newTexts);
+            assert.deepEqual(emptyArray, program_2.getMissingFilePaths());
+
+            assert.equal(StructureIsReused.SafeModules, program_1.structureIsReused);
+        });
+
         it("resolution cache follows imports", () => {
             (<any>Error).stackTraceLimit = Infinity;
 

src/harness/unittests/tsserverProjectSystem.ts

@@ -484,12 +484,12 @@ namespace ts.projectSystem {
             }
         }
 
-        triggerFileWatcherCallback(fileName: string, removed?: boolean): void {
+        triggerFileWatcherCallback(fileName: string, eventKind: FileWatcherEventKind): void {
             const path = this.toPath(fileName);
             const callbacks = this.watchedFiles.get(path);
             if (callbacks) {
                 for (const callback of callbacks) {
-                    callback(path, removed);
+                    callback(path, eventKind);
                 }
             }
         }
@@ -770,7 +770,7 @@ namespace ts.projectSystem {
 
             // remove the tsconfig file
             host.reloadFS(filesWithoutConfig);
-            host.triggerFileWatcherCallback(configFile.path);
+            host.triggerFileWatcherCallback(configFile.path, FileWatcherEventKind.Changed);
 
             checkNumberOfInferredProjects(projectService, 2);
             checkNumberOfConfiguredProjects(projectService, 0);
@@ -927,7 +927,7 @@ namespace ts.projectSystem {
                 "files": ["${commonFile1.path}"]
             }`;
             host.reloadFS(files);
-            host.triggerFileWatcherCallback(configFile.path);
+            host.triggerFileWatcherCallback(configFile.path, FileWatcherEventKind.Changed);
 
             checkNumberOfConfiguredProjects(projectService, 1);
             checkProjectRootFiles(project, [commonFile1.path]);
@@ -1001,7 +1001,7 @@ namespace ts.projectSystem {
                 "files": ["${file1.path}"]
             }`;
             host.reloadFS(files);
-            host.triggerFileWatcherCallback(configFile.path);
+            host.triggerFileWatcherCallback(configFile.path, FileWatcherEventKind.Changed);
             checkProjectActualFiles(project, [file1.path, classicModuleFile.path, configFile.path]);
             checkNumberOfInferredProjects(projectService, 1);
         });
@@ -1432,7 +1432,7 @@ namespace ts.projectSystem {
             };
 
             host.reloadFS([file1, modifiedFile2, file3]);
-            host.triggerFileWatcherCallback(modifiedFile2.path, /*removed*/ false);
+            host.triggerFileWatcherCallback(modifiedFile2.path, FileWatcherEventKind.Changed);
 
             checkNumberOfInferredProjects(projectService, 1);
             checkProjectActualFiles(projectService.inferredProjects[0], [file1.path, modifiedFile2.path, file3.path]);
@@ -1464,7 +1464,7 @@ namespace ts.projectSystem {
             checkNumberOfProjects(projectService, { inferredProjects: 1 });
 
             host.reloadFS([file1, file3]);
-            host.triggerFileWatcherCallback(file2.path, /*removed*/ true);
+            host.triggerFileWatcherCallback(file2.path, FileWatcherEventKind.Deleted);
 
             checkNumberOfProjects(projectService, { inferredProjects: 2 });
 
@@ -1662,7 +1662,7 @@ namespace ts.projectSystem {
             };
 
             host.reloadFS([file1, file2, modifiedConfigFile]);
-            host.triggerFileWatcherCallback(configFile.path, /*removed*/ false);
+            host.triggerFileWatcherCallback(configFile.path, FileWatcherEventKind.Changed);
 
             checkNumberOfProjects(projectService, { configuredProjects: 1 });
             checkProjectRootFiles(projectService.configuredProjects[0], [file1.path, file2.path]);
@@ -1695,7 +1695,7 @@ namespace ts.projectSystem {
             };
 
             host.reloadFS([file1, file2, modifiedConfigFile]);
-            host.triggerFileWatcherCallback(configFile.path, /*removed*/ false);
+            host.triggerFileWatcherCallback(configFile.path, FileWatcherEventKind.Changed);
 
             checkNumberOfProjects(projectService, { configuredProjects: 1 });
             checkProjectRootFiles(projectService.configuredProjects[0], [file1.path, file2.path]);
@@ -1775,7 +1775,7 @@ namespace ts.projectSystem {
             checkProjectActualFiles(projectService.configuredProjects[0], [file1.path, file2.path, config.path]);
 
             host.reloadFS([file1, file2]);
-            host.triggerFileWatcherCallback(config.path, /*removed*/ true);
+            host.triggerFileWatcherCallback(config.path, FileWatcherEventKind.Deleted);
 
             checkNumberOfProjects(projectService, { inferredProjects: 2 });
             checkProjectActualFiles(projectService.inferredProjects[0], [file1.path]);
@@ -2027,7 +2027,7 @@ namespace ts.projectSystem {
             projectService.openExternalProject({ projectFileName, options: {}, rootFiles: [{ fileName: file1.path, scriptKind: ScriptKind.JS, hasMixedContent: true }] });
 
             checkNumberOfProjects(projectService, { externalProjects: 1 });
-            checkWatchedFiles(host, []);
+            checkWatchedFiles(host, [libFile.path]); // watching the "missing" lib file
 
             const project = projectService.externalProjects[0];
 
@@ -2257,7 +2257,7 @@ namespace ts.projectSystem {
             assert.isFalse(lastEvent.data.languageServiceEnabled, "Language service state");
 
             host.reloadFS([f1, f2, configWithExclude]);
-            host.triggerFileWatcherCallback(config.path, /*removed*/ false);
+            host.triggerFileWatcherCallback(config.path, FileWatcherEventKind.Changed);
 
             checkNumberOfProjects(projectService, { configuredProjects: 1 });
             assert.isTrue(project.languageServiceEnabled, "Language service enabled");
@@ -2491,7 +2491,7 @@ namespace ts.projectSystem {
 
             // rename tsconfig.json back to lib.ts
             host.reloadFS([f1, f2]);
-            host.triggerFileWatcherCallback(tsconfig.path, /*removed*/ true);
+            host.triggerFileWatcherCallback(tsconfig.path, FileWatcherEventKind.Deleted);
             projectService.openExternalProject({
                 projectFileName: projectName,
                 rootFiles: toExternalFiles([f1.path, f2.path]),
@@ -2636,7 +2636,7 @@ namespace ts.projectSystem {
             checkProjectActualFiles(projectService.configuredProjects[0], [libES5.path, app.path, config1.path]);
 
             host.reloadFS([libES5, libES2015Promise, app, config2]);
-            host.triggerFileWatcherCallback(config1.path);
+            host.triggerFileWatcherCallback(config1.path, FileWatcherEventKind.Changed);
 
             projectService.checkNumberOfProjects({ configuredProjects: 1 });
             checkProjectActualFiles(projectService.configuredProjects[0], [libES5.path, libES2015Promise.path, app.path, config2.path]);
@@ -2859,7 +2859,7 @@ namespace ts.projectSystem {
             const moduleFileNewPath = "/a/b/moduleFile1.ts";
             moduleFile.path = moduleFileNewPath;
             host.reloadFS([moduleFile, file1]);
-            host.triggerFileWatcherCallback(moduleFileOldPath);
+            host.triggerFileWatcherCallback(moduleFileOldPath, FileWatcherEventKind.Changed);
             host.triggerDirectoryWatcherCallback("/a/b", moduleFile.path);
             host.runQueuedTimeoutCallbacks();
             diags = <server.protocol.Diagnostic[]>session.executeCommand(getErrRequest).response;
@@ -2867,7 +2867,7 @@ namespace ts.projectSystem {
 
             moduleFile.path = moduleFileOldPath;
             host.reloadFS([moduleFile, file1]);
-            host.triggerFileWatcherCallback(moduleFileNewPath);
+            host.triggerFileWatcherCallback(moduleFileNewPath, FileWatcherEventKind.Changed);
             host.triggerDirectoryWatcherCallback("/a/b", moduleFile.path);
             host.runQueuedTimeoutCallbacks();
 
@@ -2911,7 +2911,7 @@ namespace ts.projectSystem {
             const moduleFileNewPath = "/a/b/moduleFile1.ts";
             moduleFile.path = moduleFileNewPath;
             host.reloadFS([moduleFile, file1, configFile]);
-            host.triggerFileWatcherCallback(moduleFileOldPath);
+            host.triggerFileWatcherCallback(moduleFileOldPath, FileWatcherEventKind.Changed);
             host.triggerDirectoryWatcherCallback("/a/b", moduleFile.path);
             host.runQueuedTimeoutCallbacks();
             diags = <server.protocol.Diagnostic[]>session.executeCommand(getErrRequest).response;
@@ -2919,7 +2919,7 @@ namespace ts.projectSystem {
 
             moduleFile.path = moduleFileOldPath;
             host.reloadFS([moduleFile, file1, configFile]);
-            host.triggerFileWatcherCallback(moduleFileNewPath);
+            host.triggerFileWatcherCallback(moduleFileNewPath, FileWatcherEventKind.Changed);
             host.triggerDirectoryWatcherCallback("/a/b", moduleFile.path);
             host.runQueuedTimeoutCallbacks();
             diags = <server.protocol.Diagnostic[]>session.executeCommand(getErrRequest).response;
@@ -3084,7 +3084,7 @@ namespace ts.projectSystem {
                 }
             }`;
             host.reloadFS([file, configFile]);
-            host.triggerFileWatcherCallback(configFile.path);
+            host.triggerFileWatcherCallback(configFile.path, FileWatcherEventKind.Changed);
             host.runQueuedTimeoutCallbacks();
             serverEventManager.checkEventCountOfType("configFileDiag", 2);
 
@@ -3092,7 +3092,7 @@ namespace ts.projectSystem {
                 "compilerOptions": {}
             }`;
             host.reloadFS([file, configFile]);
-            host.triggerFileWatcherCallback(configFile.path);
+            host.triggerFileWatcherCallback(configFile.path, FileWatcherEventKind.Changed);
             host.runQueuedTimeoutCallbacks();
             serverEventManager.checkEventCountOfType("configFileDiag", 3);
         });
@@ -4020,7 +4020,7 @@ namespace ts.projectSystem {
 
             configFile.content = configFileContentWithoutCommentLine;
             host.reloadFS([file, configFile]);
-            host.triggerFileWatcherCallback(configFile.path);
+            host.triggerFileWatcherCallback(configFile.path, FileWatcherEventKind.Changed);
 
             const diagsAfterEdit = session.executeCommand(<server.protocol.SemanticDiagnosticsSyncRequest>{
                 type: "request",

src/harness/unittests/typingsInstaller.ts

@@ -737,7 +737,7 @@ namespace ts.projectSystem {
             checkNumberOfProjects(projectService, { configuredProjects: 1 });
             const p = projectService.configuredProjects[0];
             checkProjectActualFiles(p, [app.path, jsconfig.path]);
-            checkWatchedFiles(host, [jsconfig.path, "/bower_components", "/node_modules"]);
+            checkWatchedFiles(host, [jsconfig.path, "/bower_components", "/node_modules", libFile.path]);
 
             installer.installAll(/*expectedCount*/ 1);
 
@@ -826,7 +826,7 @@ namespace ts.projectSystem {
             installer.checkPendingCommands(/*expectedCount*/ 0);
 
             host.reloadFS([f, fixedPackageJson]);
-            host.triggerFileWatcherCallback(fixedPackageJson.path, /*removed*/ false);
+            host.triggerFileWatcherCallback(fixedPackageJson.path, FileWatcherEventKind.Changed);
             // expected install request
             installer.installAll(/*expectedCount*/ 1);
 

src/server/lsHost.ts

@@ -210,8 +210,11 @@ namespace ts.server {
             return this.host.resolvePath(path);
         }
 
-        fileExists(path: string): boolean {
-            return this.host.fileExists(path);
+        fileExists(file: string): boolean {
+            // As an optimization, don't hit the disks for files we already know don't exist
+            // (because we're watching for their creation).
+            const path = toPath(file, this.host.getCurrentDirectory(), this.getCanonicalFileName);
+            return !this.project.isWatchedMissingFile(path) && this.host.fileExists(file);
         }
 
         readFile(fileName: string): string {

src/server/project.ts

@@ -107,6 +107,7 @@ namespace ts.server {
         private rootFilesMap: Map<ScriptInfo> = createMap<ScriptInfo>();
         private program: ts.Program;
         private externalFiles: SortedReadonlyArray<string>;
+        private missingFilesMap: Map<FileWatcher> = createMap<FileWatcher>();
 
         private cachedUnresolvedImportsPerFile = new UnresolvedImportsMap();
         private lastCachedUnresolvedImportsList: SortedReadonlyArray<string>;
@@ -310,6 +311,10 @@ namespace ts.server {
             this.lsHost.dispose();
             this.lsHost = undefined;
 
+            // Clean up file watchers waiting for missing files
+            this.missingFilesMap.forEach(fileWatcher => fileWatcher.close());
+            this.missingFilesMap = undefined;
+
             // signal language service to release source files acquired from document registry
             this.languageService.dispose();
             this.languageService = undefined;
@@ -586,12 +591,12 @@ namespace ts.server {
             const oldProgram = this.program;
             this.program = this.languageService.getProgram();
 
-            let hasChanges = false;
             // bump up the version if
             // - oldProgram is not set - this is a first time updateGraph is called
             // - newProgram is different from the old program and structure of the old program was not reused.
-            if (!oldProgram || (this.program !== oldProgram && !(oldProgram.structureIsReused & StructureIsReused.Completely))) {
-                hasChanges = true;
+            const hasChanges = !oldProgram || (this.program !== oldProgram && !(oldProgram.structureIsReused & StructureIsReused.Completely));
+
+            if (hasChanges) {
                 if (oldProgram) {
                     for (const f of oldProgram.getSourceFiles()) {
                         if (this.program.getSourceFileByPath(f.path)) {
@@ -604,6 +609,35 @@ namespace ts.server {
                         }
                     }
                 }
+
+                const missingFilePaths = this.program.getMissingFilePaths();
+                const missingFilePathsSet = arrayToSet(missingFilePaths, p => p);
+
+                // Files that are no longer missing (e.g. because they are no longer required)
+                // should no longer be watched.
+                this.missingFilesMap.forEach((fileWatcher, missingFilePath) => {
+                    if (!missingFilePathsSet.has(missingFilePath)) {
+                        this.missingFilesMap.delete(missingFilePath);
+                        fileWatcher.close();
+                    }
+                });
+
+                // Missing files that are not yet watched should be added to the map.
+                for (const missingFilePath of missingFilePaths) {
+                    if (!this.missingFilesMap.has(missingFilePath)) {
+                        const fileWatcher = this.projectService.host.watchFile(missingFilePath, (_filename: string, eventKind: FileWatcherEventKind) => {
+                            if (eventKind === FileWatcherEventKind.Created && this.missingFilesMap.has(missingFilePath)) {
+                                fileWatcher.close();
+                                this.missingFilesMap.delete(missingFilePath);
+
+                                // When a missing file is created, we should update the graph.
+                                this.markAsDirty();
+                                this.updateGraph();
+                            }
+                        });
+                        this.missingFilesMap.set(missingFilePath, fileWatcher);
+                    }
+                }
             }
 
             const oldExternalFiles = this.externalFiles || emptyArray as SortedReadonlyArray<string>;
@@ -626,6 +660,10 @@ namespace ts.server {
             return hasChanges;
         }
 
+        isWatchedMissingFile(path: Path) {
+            return this.missingFilesMap.has(path);
+        }
+
         getScriptInfoLSHost(fileName: string) {
             const scriptInfo = this.projectService.getOrCreateScriptInfo(fileName, /*openedByClient*/ false);
             if (scriptInfo) {

src/server/server.ts

@@ -523,11 +523,14 @@ namespace ts.server {
 
             fs.stat(watchedFile.fileName, (err: any, stats: any) => {
                 if (err) {
-                    watchedFile.callback(watchedFile.fileName);
+                    watchedFile.callback(watchedFile.fileName, FileWatcherEventKind.Changed);
                 }
                 else if (watchedFile.mtime.getTime() !== stats.mtime.getTime()) {
                     watchedFile.mtime = stats.mtime;
-                    watchedFile.callback(watchedFile.fileName, watchedFile.mtime.getTime() === 0);
+                    const eventKind = watchedFile.mtime.getTime() === 0
+                        ? FileWatcherEventKind.Deleted
+                        : FileWatcherEventKind.Changed;
+                    watchedFile.callback(watchedFile.fileName, eventKind);
                 }
             });
         }
@@ -559,7 +562,9 @@ namespace ts.server {
             const file: WatchedFile = {
                 fileName,
                 callback,
-                mtime: getModifiedTime(fileName)
+                mtime: sys.fileExists(fileName)
+                    ? getModifiedTime(fileName)
+                    : new Date(0) // Any subsequent modification will occur after this time
             };
 
             watchedFiles.push(file);

src/services/documentHighlights.ts

@@ -2,7 +2,10 @@
 namespace ts.DocumentHighlights {
     export function getDocumentHighlights(program: Program, cancellationToken: CancellationToken, sourceFile: SourceFile, position: number, sourceFilesToSearch: SourceFile[]): DocumentHighlights[] | undefined {
         const node = getTouchingWord(sourceFile, position, /*includeJsDocComment*/ true);
-        if (!node) return undefined;
+        // Note that getTouchingWord indicates failure by returning the sourceFile node.
+        if (node === sourceFile) return undefined;
+
+        Debug.assert(node.parent !== undefined);
 
         if (isJsxOpeningElement(node.parent) && node.parent.tagName === node || isJsxClosingElement(node.parent)) {
             // For a JSX element, just highlight the matching tag, not all references.