Track missing files

1. Expose missing files from the `Program`.
2. In `tsc --watch` and `tsserver`, add file watchers to missing files.
3. When missing files are created, schedule compilation (tsc) or refresh
the containing projects (tsserver).

src/compiler/program.ts

@@ -513,6 +513,8 @@ namespace ts {
             }
         }
 
+        const missingFilePaths = filesByName.getKeys().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,
@@ -862,11 +865,31 @@ 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) {
+                const missingFilePaths: Path[] = oldProgram.getMissingFilePaths() || emptyArray;
+                for (const missingFilePath of missingFilePaths) {
+                    if (host.fileExists(missingFilePath)) {
+                        return oldProgram.structureIsReused = StructureIsReused.SafeModules;
+                    }
+                }
+            }
+
             // update fileName -> file mapping
             for (let i = 0; i < newSourceFiles.length; i++) {
                 filesByName.set(filePaths[i], newSourceFiles[i]);
             }
 
+            for (const p of oldProgram.getMissingFilePaths()) {
+                filesByName.set(p, undefined);
+            }
+
             files = newSourceFiles;
             fileProcessingDiagnostics = oldProgram.getFileProcessingDiagnostics();
 

src/compiler/sys.ts

@@ -340,11 +340,20 @@ namespace ts {
                     }
 
                     function fileChanged(curr: any, prev: any) {
-                        if (+curr.mtime <= +prev.mtime) {
+                        const isCurrZero = +curr.mtime === 0;
+                        const isPrevZero = +prev.mtime === 0;
+                        const added = !isCurrZero && isPrevZero;
+                        const deleted = isCurrZero && !isPrevZero;
+
+                        // This value is consistent with poll() in createPollingWatchedFileSet()
+                        // and depended upon by the file watchers created in Project.updateGraphWorker.
+                        const removed = deleted ? true : (added ? false : undefined);
+
+                        if (!added && !deleted && +curr.mtime <= +prev.mtime) {
                             return;
                         }
 
-                        callback(fileName);
+                        callback(fileName, removed);
                     }
                 },
                 watchDirectory: (directoryName, callback, recursive) => {

src/compiler/tsc.ts

@@ -285,6 +285,19 @@ namespace ts {
 
             setCachedProgram(compileResult.program);
             reportWatchDiagnostic(createCompilerDiagnostic(Diagnostics.Compilation_complete_Watching_for_file_changes));
+
+            if (compileResult.program.getMissingFilePaths) {
+                const missingPaths = compileResult.program.getMissingFilePaths() || [];
+                missingPaths.forEach((path: Path): void => {
+                    const fileWatcher = sys.watchFile(path, (_fileName: string, removed?: boolean) => {
+                        // removed = deleted ? true : (added ? false : undefined)
+                        if (removed === false) {
+                            fileWatcher.close();
+                            startTimerForRecompilation();
+                        }
+                    });
+                });
+            }
         }
 
         function cachedFileExists(fileName: string): boolean {

src/compiler/types.ts

@@ -2426,6 +2426,12 @@ 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.
+         */
+        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/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: FileMap<FileWatcher> = createFileMap<FileWatcher>();
 
         private cachedUnresolvedImportsPerFile = new UnresolvedImportsMap();
         private lastCachedUnresolvedImportsList: SortedReadonlyArray<string>;
@@ -606,6 +607,39 @@ namespace ts.server {
                 }
             }
 
+            if (hasChanges && this.program.getMissingFilePaths) {
+                const missingFilePaths = this.program.getMissingFilePaths() || emptyArray;
+                const missingFilePathsSet = createMap<true>();
+                missingFilePaths.forEach(p => missingFilePathsSet.set(p, true));
+
+                // Files that are no longer missing (e.g. because they are no longer required)
+                // should no longer be watched.
+                this.missingFilesMap.getKeys().forEach(p => {
+                    if (!missingFilePathsSet.has(p)) {
+                        this.missingFilesMap.get(p).close();
+                        this.missingFilesMap.remove(p);
+                    }
+                });
+
+                // Missing files that are not yet watched should be added to the map.
+                missingFilePaths.forEach(p => {
+                    if (!this.missingFilesMap.contains(p)) {
+                        const fileWatcher = ts.sys.watchFile(p, (_filename: string, removed?: boolean) => {
+                            // removed = deleted ? true : (added ? false : undefined)
+                            if (removed === false && this.missingFilesMap.contains(p)) {
+                                fileWatcher.close();
+                                this.missingFilesMap.remove(p);
+
+                                // When a missing file is created, we should update the graph.
+                                this.markAsDirty();
+                                this.updateGraph();
+                            }
+                        });
+                        this.missingFilesMap.set(p, fileWatcher);
+                    }
+                });
+            }
+
             const oldExternalFiles = this.externalFiles || emptyArray as SortedReadonlyArray<string>;
             this.externalFiles = this.getExternalFiles();
             enumerateInsertsAndDeletes(this.externalFiles, oldExternalFiles,
@@ -626,6 +660,10 @@ namespace ts.server {
             return hasChanges;
         }
 
+        isWatchedMissingFile(path: Path) {
+            return this.missingFilesMap.contains(path);
+        }
+
         getScriptInfoLSHost(fileName: string) {
             const scriptInfo = this.projectService.getOrCreateScriptInfo(fileName, /*openedByClient*/ false);
             if (scriptInfo) {

src/server/server.ts

@@ -522,6 +522,9 @@ namespace ts.server {
                 return;
             }
 
+            // removed = deleted ? true : (added ? false : undefined)
+            // This value is consistent with sys.watchFile()
+            // and depended upon by the file watchers created in performCompilation() in tsc's executeCommandLine().
             fs.stat(watchedFile.fileName, (err: any, stats: any) => {
                 if (err) {
                     watchedFile.callback(watchedFile.fileName);
@@ -560,7 +563,9 @@ 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);