Partially replace chokidar with @parcel/watcher (#2379)

Co-authored-by: Natalie Weizenbaum <nweiz@google.com>

CHANGELOG.md

@@ -19,6 +19,13 @@
 * **Potentially breaking bug fix:** `math.unit()` now wraps multiple denominator
   units in parentheses. For example, `px/(em*em)` instead of `px/em*em`.
 
+### Command-Line Interface
+
+* Use `@parcel/watcher` to watch the filesystem when running from JavaScript and
+  not using `--poll`. This should mitigate more frequent failures users have
+  been seeing since version 4.0.0 of Chokidar, our previous watching tool, was
+  released.
+
 ### JS API
 
 * Fix `SassColor.interpolate()` to allow an undefined `options` parameter, as

lib/src/io/js.dart

@@ -16,6 +16,7 @@ import 'package:watcher/watcher.dart';
 
 import '../exception.dart';
 import '../js/chokidar.dart';
+import '../js/parcel_watcher.dart';
 
 @JS('process')
 external final Process? _nodeJsProcess; // process is null in the browser
@@ -248,39 +249,65 @@ int get exitCode => _process?.exitCode ?? 0;
 
 set exitCode(int code) => _process?.exitCode = code;
 
-Future<Stream<WatchEvent>> watchDir(String path, {bool poll = false}) {
+Future<Stream<WatchEvent>> watchDir(String path, {bool poll = false}) async {
   if (!isNodeJs) {
     throw UnsupportedError("watchDir() is only supported on Node.js");
   }
-  var watcher = chokidar.watch(path, ChokidarOptions(usePolling: poll));
 
   // Don't assign the controller until after the ready event fires. Otherwise,
   // Chokidar will give us a bunch of add events for files that already exist.
   StreamController<WatchEvent>? controller;
-  watcher
-    ..on(
-        'add',
-        allowInterop((String path, [void _]) =>
-            controller?.add(WatchEvent(ChangeType.ADD, path))))
-    ..on(
-        'change',
-        allowInterop((String path, [void _]) =>
-            controller?.add(WatchEvent(ChangeType.MODIFY, path))))
-    ..on(
-        'unlink',
-        allowInterop((String path) =>
-            controller?.add(WatchEvent(ChangeType.REMOVE, path))))
-    ..on('error', allowInterop((Object error) => controller?.addError(error)));
-
-  var completer = Completer<Stream<WatchEvent>>();
-  watcher.on('ready', allowInterop(() {
-    // dart-lang/sdk#45348
-    var stream = (controller = StreamController<WatchEvent>(onCancel: () {
-      watcher.close();
+  if (poll) {
+    var watcher = chokidar.watch(path, ChokidarOptions(usePolling: true));
+    watcher
+      ..on(
+          'add',
+          allowInterop((String path, [void _]) =>
+              controller?.add(WatchEvent(ChangeType.ADD, path))))
+      ..on(
+          'change',
+          allowInterop((String path, [void _]) =>
+              controller?.add(WatchEvent(ChangeType.MODIFY, path))))
+      ..on(
+          'unlink',
+          allowInterop((String path) =>
+              controller?.add(WatchEvent(ChangeType.REMOVE, path))))
+      ..on(
+          'error', allowInterop((Object error) => controller?.addError(error)));
+
+    var completer = Completer<Stream<WatchEvent>>();
+    watcher.on('ready', allowInterop(() {
+      // dart-lang/sdk#45348
+      var stream = (controller = StreamController<WatchEvent>(onCancel: () {
+        watcher.close();
+      }))
+          .stream;
+      completer.complete(stream);
+    }));
+
+    return completer.future;
+  } else {
+    var subscription = await ParcelWatcher.subscribeFuture(path,
+        (Object? error, List<ParcelWatcherEvent> events) {
+      if (error != null) {
+        controller?.addError(error);
+      } else {
+        for (var event in events) {
+          switch (event.type) {
+            case 'create':
+              controller?.add(WatchEvent(ChangeType.ADD, event.path));
+            case 'update':
+              controller?.add(WatchEvent(ChangeType.MODIFY, event.path));
+            case 'delete':
+              controller?.add(WatchEvent(ChangeType.REMOVE, event.path));
+          }
+        }
+      }
+    });
+
+    return (controller = StreamController<WatchEvent>(onCancel: () {
+      subscription.unsubscribe();
     }))
         .stream;
-    completer.complete(stream);
-  }));
-
-  return completer.future;
+  }
 }

lib/src/js/parcel_watcher.dart

@@ -0,0 +1,44 @@
+// Copyright 2024 Google Inc. Use of this source code is governed by an
+// MIT-style license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import 'package:js/js.dart';
+import 'package:node_interop/js.dart';
+import 'package:node_interop/util.dart';
+
+@JS()
+class ParcelWatcherSubscription {
+  external void unsubscribe();
+}
+
+@JS()
+class ParcelWatcherEvent {
+  external String get type;
+  external String get path;
+}
+
+/// The @parcel/watcher module.
+///
+/// See [the docs on npm](https://www.npmjs.com/package/@parcel/watcher).
+@JS('parcel_watcher')
+class ParcelWatcher {
+  external static Promise subscribe(String path, Function callback);
+  static Future<ParcelWatcherSubscription> subscribeFuture(String path,
+          void Function(Object? error, List<ParcelWatcherEvent>) callback) =>
+      promiseToFuture(
+          subscribe(path, allowInterop((Object? error, List<dynamic> events) {
+        callback(error, events.cast<ParcelWatcherEvent>());
+      })));
+
+  external static Promise getEventsSince(String path, String snapshotPath);
+  static Future<List<ParcelWatcherEvent>> getEventsSinceFuture(
+      String path, String snapshotPath) async {
+    List<dynamic> events =
+        await promiseToFuture(getEventsSince(path, snapshotPath));
+    return events.cast<ParcelWatcherEvent>();
+  }
+
+  external static Promise writeSnapshot(String path, String snapshotPath);
+  static Future<void> writeSnapshotFuture(String path, String snapshotPath) =>
+      promiseToFuture(writeSnapshot(path, snapshotPath));
+}

package.json

@@ -6,6 +6,7 @@
   ],
   "name": "sass",
   "devDependencies": {
+    "@parcel/watcher": "^2.4.1",
     "chokidar": "^4.0.0",
     "immutable": "^4.0.0",
     "intercept-stdout": "^0.1.2"

package/package.json

@@ -17,6 +17,7 @@
     "node": ">=14.0.0"
   },
   "dependencies": {
+    "@parcel/watcher": "^2.4.1",
     "chokidar": "^4.0.0",
     "immutable": "^4.0.0",
     "source-map-js": ">=0.6.2 <2.0.0"

tool/grind.dart

@@ -34,6 +34,7 @@ void main(List<String> args) {
   pkg.homebrewFormula.value = "Formula/sass.rb";
   pkg.homebrewEditFormula.value = _updateHomebrewLanguageRevision;
   pkg.jsRequires.value = [
+    pkg.JSRequire("@parcel/watcher", target: pkg.JSRequireTarget.cli),
     pkg.JSRequire("immutable", target: pkg.JSRequireTarget.all),
     pkg.JSRequire("chokidar", target: pkg.JSRequireTarget.cli),
     pkg.JSRequire("readline", target: pkg.JSRequireTarget.cli),