In recursive directory watching ignore folders and files in node_modules starting with "."

Fixes microsoft#30004

Author: sheetalkamat

src/compiler/sys.ts

@@ -371,6 +371,8 @@ namespace ts {
             else {
                 directoryWatcher = {
                     watcher: host.watchDirectory(dirName, fileName => {
+                        if (isInNodeModulesStartingWithDot(fileName)) return;
+
                         // Call the actual callback
                         callbackCache.forEach((callbacks, rootDirName) => {
                             if (rootDirName === dirPath || (startsWith(dirPath, rootDirName) && dirPath[rootDirName.length] === directorySeparator)) {
@@ -426,7 +428,7 @@ namespace ts {
                     const childFullName = getNormalizedAbsolutePath(child, parentDir);
                     // Filter our the symbolic link directories since those arent included in recursive watch
                     // which is same behaviour when recursive: true is passed to fs.watch
-                    return filePathComparer(childFullName, normalizePath(host.realpath(childFullName))) === Comparison.EqualTo ? childFullName : undefined;
+                    return !isInNodeModulesStartingWithDot(childFullName) && filePathComparer(childFullName, normalizePath(host.realpath(childFullName))) === Comparison.EqualTo ? childFullName : undefined;
                 }) : emptyArray,
                 existingChildWatches,
                 (child, childWatcher) => filePathComparer(child, childWatcher.dirName),
@@ -452,6 +454,16 @@ namespace ts {
                 (newChildWatches || (newChildWatches = [])).push(childWatcher);
             }
         }
+
+        function isInNodeModulesStartingWithDot(path: string) {
+            return isInPath(path, "/node_modules/.");
+        }
+
+        function isInPath(path: string, searchPath: string) {
+            if (stringContains(path, searchPath)) return true;
+            if (host.useCaseSensitiveFileNames) return false;
+            return stringContains(toCanonicalFilePath(path), searchPath);
+        }
     }
 
     // TODO: GH#18217 Methods on System are often used as if they are certainly defined

src/testRunner/unittests/tsserver/watchEnvironment.ts

@@ -132,4 +132,63 @@ namespace ts.projectSystem {
             verifyRootedDirectoryWatch("c:/users/username/");
         });
     });
+
+    it(`unittests:: tsserver:: watchEnvironment:: tsserverProjectSystem recursive watch directory implementation does not watch files/directories in node_modules starting with "."`, () => {
+        const projectFolder = "/a/username/project";
+        const projectSrcFolder = `${projectFolder}/src`;
+        const configFile: File = {
+            path: `${projectFolder}/tsconfig.json`,
+            content: "{}"
+        };
+        const index: File = {
+            path: `${projectSrcFolder}/index.ts`,
+            content: `import {} from "file"`
+        };
+        const file1: File = {
+            path: `${projectSrcFolder}/file1.ts`,
+            content: ""
+        };
+        const nodeModulesExistingUnusedFile: File = {
+            path: `${projectFolder}/node_modules/someFile.d.ts`,
+            content: ""
+        };
+
+        const fileNames = [index, file1, configFile, libFile].map(file => file.path);
+        // All closed files(files other than index), project folder, project/src folder and project/node_modules/@types folder
+        const expectedWatchedFiles = arrayToMap(fileNames.slice(1), identity, () => 1);
+        const expectedWatchedDirectories = arrayToMap([projectFolder, projectSrcFolder, `${projectFolder}/${nodeModules}`, `${projectFolder}/${nodeModulesAtTypes}`], identity, () => 1);
+
+        const environmentVariables = createMap<string>();
+        environmentVariables.set("TSC_WATCHDIRECTORY", Tsc_WatchDirectory.NonRecursiveWatchDirectory);
+        const host = createServerHost([index, file1, configFile, libFile, nodeModulesExistingUnusedFile], { environmentVariables });
+        const projectService = createProjectService(host);
+        projectService.openClientFile(index.path);
+
+        const project = Debug.assertDefined(projectService.configuredProjects.get(configFile.path));
+        verifyProject();
+
+        const nodeModulesIgnoredFileFromIgnoreDirectory: File = {
+            path: `${projectFolder}/node_modules/.cache/someFile.d.ts`,
+            content: ""
+        };
+        host.ensureFileOrFolder(nodeModulesIgnoredFileFromIgnoreDirectory);
+        host.checkTimeoutQueueLength(0);
+        verifyProject();
+
+        const nodeModulesIgnoredFile: File = {
+            path: `${projectFolder}/node_modules/.cacheFile.ts`,
+            content: ""
+        };
+        host.ensureFileOrFolder(nodeModulesIgnoredFile);
+        host.checkTimeoutQueueLength(0);
+        verifyProject();
+
+        function verifyProject() {
+            checkWatchedDirectories(host, emptyArray, /*recursive*/ true);
+            checkWatchedFilesDetailed(host, expectedWatchedFiles);
+            checkWatchedDirectoriesDetailed(host, expectedWatchedDirectories, /*recursive*/ false);
+            checkProjectActualFiles(project, fileNames);
+        }
+    });
+
 }