(perf) Optimize fallback watcher (#955)

* ignore initial in fallback watcher

* debounce fallback watcher event

* simplify

Author: jasonlyu123

packages/language-server/src/lib/FallbackWatcher.ts

@@ -1,14 +1,19 @@
 import { FSWatcher, watch } from 'chokidar';
+import { debounce } from 'lodash';
 import { join } from 'path';
 import { DidChangeWatchedFilesParams, FileChangeType, FileEvent } from 'vscode-languageserver';
 import { pathToUrl } from '../utils';
 
 type DidChangeHandler = (para: DidChangeWatchedFilesParams) => void;
 
+const DELAY = 50;
+
 export class FallbackWatcher {
     private readonly watcher: FSWatcher;
     private readonly callbacks: DidChangeHandler[] = [];
 
+    private undeliveredFileEvents: FileEvent[] = [];
+
     constructor(glob: string, workspacePaths: string[]) {
         const gitOrNodeModules = /\.git|node_modules/;
         this.watcher = watch(
@@ -18,31 +23,43 @@ export class FallbackWatcher {
                     gitOrNodeModules.test(path) &&
                     // Handle Sapper's alias mapping
                     !path.includes('src/node_modules') &&
-                    !path.includes('src\\node_modules')
+                    !path.includes('src\\node_modules'),
+
+                // typescript would scan the project files on init.
+                // We only need to know what got updated.
+                ignoreInitial: true,
+                ignorePermissionErrors: true
             }
         );
 
         this.watcher
-            .on('add', (path) => this.callback(path, FileChangeType.Created))
-            .on('unlink', (path) => this.callback(path, FileChangeType.Deleted))
-            .on('change', (path) => this.callback(path, FileChangeType.Changed));
+            .on('add', (path) => this.onFSEvent(path, FileChangeType.Created))
+            .on('unlink', (path) => this.onFSEvent(path, FileChangeType.Deleted))
+            .on('change', (path) => this.onFSEvent(path, FileChangeType.Changed));
     }
 
-    private convert(path: string, type: FileChangeType): DidChangeWatchedFilesParams {
-        const event: FileEvent = {
+    private convert(path: string, type: FileChangeType): FileEvent {
+        return {
             type,
             uri: pathToUrl(path)
         };
+    }
 
-        return {
-            changes: [event]
-        };
+    private onFSEvent(path: string, type: FileChangeType) {
+        const fileEvent = this.convert(path, type);
+
+        this.undeliveredFileEvents.push(fileEvent);
+        this.scheduleTrigger();
     }
 
-    private callback(path: string, type: FileChangeType) {
-        const para = this.convert(path, type);
+    private readonly scheduleTrigger = debounce(() => {
+        const para: DidChangeWatchedFilesParams = {
+            changes: this.undeliveredFileEvents
+        };
+        this.undeliveredFileEvents = [];
+
         this.callbacks.forEach((callback) => callback(para));
-    }
+    }, DELAY);
 
     onDidChangeWatchedFiles(callback: DidChangeHandler) {
         this.callbacks.push(callback);