Add package-private extension type Event on FileSystemEvent. (#2200)

Author: davidmorgan

.github/workflows/watcher.yaml

@@ -54,7 +54,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
-        sdk: [3.1, dev]
+        sdk: [3.3, dev]
     steps:
       - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8
       - uses: dart-lang/setup-dart@e51d8e571e22473a2ddebf0ef8a2123f0ab2c02c

pkgs/watcher/lib/src/directory_watcher/linux.dart

@@ -8,6 +8,7 @@ import 'dart:io';
 import 'package:async/async.dart';
 
 import '../directory_watcher.dart';
+import '../event.dart';
 import '../path_set.dart';
 import '../resubscribable.dart';
 import '../utils.dart';
@@ -81,7 +82,7 @@ class _LinuxDirectoryWatcher
     })));
 
     // Batch the inotify changes together so that we can dedup events.
-    var innerStream = _nativeEvents.stream.batchEvents();
+    var innerStream = _nativeEvents.stream.map(Event.new).batchEvents();
     _listen(innerStream, _onBatch,
         onError: (Object error, StackTrace stackTrace) {
       // Guarantee that ready always completes.
@@ -145,7 +146,7 @@ class _LinuxDirectoryWatcher
   }
 
   /// The callback that's run when a batch of changes comes in.
-  void _onBatch(List<FileSystemEvent> batch) {
+  void _onBatch(List<Event> batch) {
     var files = <String>{};
     var dirs = <String>{};
     var changed = <String>{};
@@ -162,30 +163,40 @@ class _LinuxDirectoryWatcher
 
       changed.add(event.path);
 
-      if (event is FileSystemMoveEvent) {
-        files.remove(event.path);
-        dirs.remove(event.path);
-
-        var destination = event.destination;
-        if (destination == null) continue;
-
-        changed.add(destination);
-        if (event.isDirectory) {
-          files.remove(destination);
-          dirs.add(destination);
-        } else {
-          files.add(destination);
-          dirs.remove(destination);
-        }
-      } else if (event is FileSystemDeleteEvent) {
-        files.remove(event.path);
-        dirs.remove(event.path);
-      } else if (event.isDirectory) {
-        files.remove(event.path);
-        dirs.add(event.path);
-      } else {
-        files.add(event.path);
-        dirs.remove(event.path);
+      switch (event.type) {
+        case EventType.moveFile:
+          files.remove(event.path);
+          dirs.remove(event.path);
+          var destination = event.destination;
+          if (destination != null) {
+            changed.add(destination);
+            files.add(destination);
+            dirs.remove(destination);
+          }
+
+        case EventType.moveDirectory:
+          files.remove(event.path);
+          dirs.remove(event.path);
+          var destination = event.destination;
+          if (destination != null) {
+            changed.add(destination);
+            files.remove(destination);
+            dirs.add(destination);
+          }
+
+        case EventType.delete:
+          files.remove(event.path);
+          dirs.remove(event.path);
+
+        case EventType.createDirectory:
+        case EventType.modifyDirectory:
+          files.remove(event.path);
+          dirs.add(event.path);
+
+        case EventType.createFile:
+        case EventType.modifyFile:
+          files.add(event.path);
+          dirs.remove(event.path);
       }
     }
 

pkgs/watcher/lib/src/event.dart

@@ -0,0 +1,59 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:io';
+
+/// Extension type replacing [FileSystemEvent] for `package:watcher` internal
+/// use.
+///
+/// The [FileSystemDeleteEvent] subclass of [FileSystemEvent] does something
+/// surprising for `isDirectory`: it always returns `false`. The constructor
+/// accepts a boolean called `isDirectory` but discards it.
+///
+/// So, this extension type hides `isDirectory` and instead provides an
+/// [EventType] enum with the seven types of event actually used.
+extension type Event(FileSystemEvent event) {
+  /// See [FileSystemEvent.path].
+  String get path => event.path;
+
+  EventType get type {
+    switch (event.type) {
+      case FileSystemEvent.create:
+        return event.isDirectory
+            ? EventType.createDirectory
+            : EventType.createFile;
+      case FileSystemEvent.delete:
+        return EventType.delete;
+      case FileSystemEvent.modify:
+        return event.isDirectory
+            ? EventType.modifyDirectory
+            : EventType.modifyFile;
+      case FileSystemEvent.move:
+        return event.isDirectory ? EventType.moveDirectory : EventType.moveFile;
+      default:
+        throw StateError('Invalid event type ${event.type}.');
+    }
+  }
+
+  /// See [FileSystemMoveEvent.destination].
+  ///
+  /// For other types of event, always `null`.
+  String? get destination => event.type == FileSystemEvent.move
+      ? (event as FileSystemMoveEvent).destination
+      : null;
+}
+
+/// See [FileSystemEvent.type].
+///
+/// This additionally encodes [FileSystemEvent.isDirectory], which is specified
+/// for all event types except deletes.
+enum EventType {
+  delete,
+  createFile,
+  createDirectory,
+  modifyFile,
+  modifyDirectory,
+  moveFile,
+  moveDirectory;
+}

pkgs/watcher/lib/src/file_watcher/native.dart

@@ -5,6 +5,7 @@
 import 'dart:async';
 import 'dart:io';
 
+import '../event.dart';
 import '../file_watcher.dart';
 import '../resubscribable.dart';
 import '../utils.dart';
@@ -33,7 +34,7 @@ class _NativeFileWatcher implements FileWatcher, ManuallyClosedWatcher {
   Future<void> get ready => _readyCompleter.future;
   final _readyCompleter = Completer<void>();
 
-  StreamSubscription<List<FileSystemEvent>>? _subscription;
+  StreamSubscription<List<Event>>? _subscription;
 
   /// On MacOS only, whether the file existed on startup.
   bool? _existedAtStartup;
@@ -50,7 +51,7 @@ class _NativeFileWatcher implements FileWatcher, ManuallyClosedWatcher {
     var file = File(path);
 
     // Batch the events together so that we can dedupe them.
-    var stream = file.watch().batchEvents();
+    var stream = file.watch().map(Event.new).batchEvents();
 
     if (Platform.isMacOS) {
       var existedAtStartupFuture = file.exists();
@@ -65,8 +66,8 @@ class _NativeFileWatcher implements FileWatcher, ManuallyClosedWatcher {
         onError: _eventsController.addError, onDone: _onDone);
   }
 
-  void _onBatch(List<FileSystemEvent> batch) {
-    if (batch.any((event) => event.type == FileSystemEvent.delete)) {
+  void _onBatch(List<Event> batch) {
+    if (batch.any((event) => event.type == EventType.delete)) {
       // If the file is deleted, the underlying stream will close. We handle
       // emitting our own REMOVE event in [_onDone].
       return;
@@ -77,7 +78,7 @@ class _NativeFileWatcher implements FileWatcher, ManuallyClosedWatcher {
       // created just before the `watch`. If the file existed at startup then it
       // should be ignored.
       if (_existedAtStartup! &&
-          batch.every((event) => event.type == FileSystemEvent.create)) {
+          batch.every((event) => event.type == EventType.createFile)) {
         return;
       }
     }

pkgs/watcher/pubspec.yaml

@@ -7,7 +7,7 @@ repository: https://github.com/dart-lang/tools/tree/main/pkgs/watcher
 issue_tracker: https://github.com/dart-lang/tools/labels/package%3Awatcher
 
 environment:
-  sdk: ^3.1.0
+  sdk: ^3.3.0
 
 dependencies:
   async: ^2.5.0