Take a broader approach to filtering out bogus Mac OS watcher events.

pkg/watcher/lib/src/directory_watcher/mac_os.dart

 // Copyright (c) 2013, 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.
 
 library watcher.directory_watcher.mac_os;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:path/path.dart' as p;
@@ skipping 32 matching lines @@
   final String directory;
 
   Stream<WatchEvent> get events => _eventsController.stream;
   final _eventsController = new StreamController<WatchEvent>.broadcast();
 
   bool get isReady => _readyCompleter.isCompleted;
 
   Future get ready => _readyCompleter.future;
   final _readyCompleter = new Completer();
 
-  /// The number of event batches that have been received from
-  /// [Directory.watch].
-  ///
-  /// This is used to determine if the [Directory.watch] stream was falsely
-  /// closed due to issue 14849. A close caused by events in the past will only
-  /// happen before or immediately after the first batch of events.
-  int _batches = 0;
-
   /// The set of files that are known to exist recursively within the watched
   /// directory.
   ///
   /// The state of files on the filesystem is compared against this to determine
   /// the real change that occurred when working around issue 14373. This is
   /// also used to emit REMOVE events when subdirectories are moved out of the
   /// watched directory.
   final PathSet _files;
 
   /// The subscription to the stream returned by [Directory.watch].
   ///
   /// This is separate from [_subscriptions] because this stream occasionally
   /// needs to be resubscribed in order to work around issue 14849.
   StreamSubscription<FileSystemEvent> _watchSubscription;
 
-  /// A set of subscriptions that this watcher subscribes to.
-  ///
-  /// These are gathered together so that they may all be canceled when the
-  /// watcher is closed. This does not include [_watchSubscription].
-  final _subscriptions = new Set<StreamSubscription>();
+  /// The subscription to the [Directory.list] call for the initial listing of
+  /// the directory to determine its initial state.
+  StreamSubscription<FileSystemEntity> _initialListSubscription;
+
+  /// The subscription to the [Directory.list] call for listing the contents of
+  /// a subdirectory that was moved into the watched directory.
+  StreamSubscription<FileSystemEntity> _listSubscription;
+
+  /// The timer for tracking how long we wait for an initial batch of bogus
+  /// events (see issue 14373).
+  Timer _bogusEventTimer;
 
   _MacOSDirectoryWatcher(String directory, int parentId)
       : directory = directory,
         _files = new PathSet(directory),
         _id = "$parentId/${_count++}" {
     _startWatch();
 
-    _listen(Chain.track(new Directory(directory).list(recursive: true)),
-        (entity) {
-      if (entity is! Directory) _files.add(entity.path);
-    },
-        onError: _emitError,
-        onDone: () {
+    // Before we're ready to emit events, wait for [_listDir] to complete and
+    // for enough time to elapse that if bogus events (issue 14373) would be
+    // emitted, they will be.
+    //
+    // If we do receive a batch of events, [_onBatch] will ensure that these
+    // futures don't fire and that the directory is re-listed.
+    Future.wait([
+      _listDir().then((_) => print("[$_id] finished initial directory list")),

[Bob Nystrom, 2014/01/15 21:32:31]

Wrap this print in a debug check.

[nweiz, 2014/01/15 21:49:17]

Done.

+      _waitForBogusEvents()
+    ]).then((_) {
       if (MacOSDirectoryWatcher.logDebugInfo) {
         print("[$_id] watcher is ready, known files:");
         for (var file in _files.toSet()) {
           print("[$_id]   ${p.relative(file, from: directory)}");
         }
       }
       _readyCompleter.complete();
-    },
-        cancelOnError: true);
+    });
   }
 
   void close() {
     if (MacOSDirectoryWatcher.logDebugInfo) {
       print("[$_id] watcher is closed");
     }
-    for (var subscription in _subscriptions) {
-      subscription.cancel();
-    }
-    _subscriptions.clear();
     if (_watchSubscription != null) _watchSubscription.cancel();
+    if (_initialListSubscription != null) _initialListSubscription.cancel();
+    if (_listSubscription != null) _listSubscription.cancel();
     _watchSubscription = null;
+    _initialListSubscription = null;
+    _listSubscription = null;
     _eventsController.close();
   }
 
   /// The callback that's run when [Directory.watch] emits a batch of events.
   void _onBatch(List<FileSystemEvent> batch) {
     if (MacOSDirectoryWatcher.logDebugInfo) {
       print("[$_id] ======== batch:");
       for (var event in batch) {
         print("[$_id]   ${_formatEvent(event)}");
       }
 
       print("[$_id] known files:");
       for (var file in _files.toSet()) {
         print("[$_id]   ${p.relative(file, from: directory)}");
       }
     }
 
-    _batches++;
+    // If we get a batch of events before we're ready to begin emitting events,
+    // it's probable that it's a batch of pre-watcher events (see issue 14373).
+    // Ignore those events and re-list the directory.
+    if (!isReady) {
+      if (MacOSDirectoryWatcher.logDebugInfo) {
+        print("[$_id] not ready to emit events, re-listing directory");
+      }
+
+      // Cancel the timer because this batch is the only batch of bogus events

[Bob Nystrom, 2014/01/15 21:32:31]

Reword more like "because bogus events only appear in the first batch."

[nweiz, 2014/01/15 21:49:17]

Done.

+      // we'll receive.
+      _bogusEventTimer.cancel();
+      _listDir().then((_) {
+        if (MacOSDirectoryWatcher.logDebugInfo) {
+          print("[$_id] watcher is ready, known files:");
+          for (var file in _files.toSet()) {
+            print("[$_id]   ${p.relative(file, from: directory)}");
+          }
+        }
+        _readyCompleter.complete();
+      });
+      return;
+    }
 
     _sortEvents(batch).forEach((path, events) {
       var relativePath = p.relative(path, from: directory);
       if (MacOSDirectoryWatcher.logDebugInfo) {
         print("[$_id] events for $relativePath:");
         for (var event in events) {
           print("[$_id]   ${_formatEvent(event)}");
         }
       }
 
@@ skipping 15 matching lines @@
             // that happened prior to the watch beginning.
             if (_files.contains(path)) continue;
 
             _emitEvent(ChangeType.ADD, path);
             _files.add(path);
             continue;
           }
 
           if (_files.containsDir(path)) continue;
 
-          _listen(Chain.track(new Directory(path).list(recursive: true)),
-              (entity) {
+          var stream = Chain.track(new Directory(path).list(recursive: true));
+          _listSubscription = stream.listen((entity) {
             if (entity is Directory) return;
             if (_files.contains(path)) return;
 
             _emitEvent(ChangeType.ADD, entity.path);
             _files.add(entity.path);
           }, onError: (e, stackTrace) {
             if (MacOSDirectoryWatcher.logDebugInfo) {
               print("[$_id] got error listing $relativePath: $e");
             }
             _emitError(e, stackTrace);
@@ skipping 179 matching lines @@
 
     return events;
   }
 
   /// The callback that's run when the [Directory.watch] stream is closed.
   void _onDone() {
     if (MacOSDirectoryWatcher.logDebugInfo) print("[$_id] stream closed");
 
     _watchSubscription = null;
 
-    // If the directory still exists and we haven't seen more than one batch,
+    // If the directory still exists and we're still expecting bogus events,
     // this is probably issue 14849 rather than a real close event. We should
     // just restart the watcher.
-    if (_batches < 2 && new Directory(directory).existsSync()) {
+    if (!isReady && new Directory(directory).existsSync()) {
       if (MacOSDirectoryWatcher.logDebugInfo) {
         print("[$_id] fake closure (issue 14849), re-opening stream");
       }
       _startWatch();
       return;
     }
 
     // FSEvents can fail to report the contents of the directory being removed
     // when the directory itself is removed, so we need to manually mark the
     // files as removed.
     for (var file in _files.toSet()) {
       _emitEvent(ChangeType.REMOVE, file);
     }
     _files.clear();
     close();
   }
 
   /// Start or restart the underlying [Directory.watch] stream.
   void _startWatch() {
     // Batch the FSEvent changes together so that we can dedup events.
     var innerStream =
         Chain.track(new Directory(directory).watch(recursive: true))
         .transform(new BatchedStreamTransformer<FileSystemEvent>());
     _watchSubscription = innerStream.listen(_onBatch,
         onError: _eventsController.addError,
         onDone: _onDone);
   }
 
+  /// Starts or restarts listing the watched directory to get an initial picture
+  /// of its state.
+  Future _listDir() {
+    assert(!isReady);
+    if (_initialListSubscription != null) _initialListSubscription.cancel();
+
+    _files.clear();
+    var completer = new Completer();
+    var stream = Chain.track(new Directory(directory).list(recursive: true));
+    _initialListSubscription = stream.listen((entity) {
+      if (entity is! Directory) _files.add(entity.path);
+    },
+        onError: _emitError,
+        onDone: completer.complete,
+        cancelOnError: true);
+    return completer.future;
+  }
+
+  /// Wait 200ms for a batch of bogus events (issue 14373) to come in.
+  ///
+  /// 200ms is short in terms of human interaction, but longer than any Mac OS
+  /// watcher tests take on the bots, so it should be safe to assume that any
+  /// bogus events will be signaled in that time frame.
+  Future _waitForBogusEvents() {
+    var completer = new Completer();
+    _bogusEventTimer = new Timer(
+        new Duration(milliseconds: 200),
+        completer.complete);
+    return completer.future;
+  }
+
   /// Emit an event with the given [type] and [path].
   void _emitEvent(ChangeType type, String path) {
     if (!isReady) return;
 
     if (MacOSDirectoryWatcher.logDebugInfo) {
       print("[$_id] emitting $type ${p.relative(path, from: directory)}");
     }
 
     _eventsController.add(new WatchEvent(type, path));
   }
 
   /// Emit an error, then close the watcher.
   void _emitError(error, StackTrace stackTrace) {
     _eventsController.addError(error, stackTrace);
     close();
   }
 
-  /// Like [Stream.listen], but automatically adds the subscription to
-  /// [_subscriptions] so that it can be canceled when [close] is called.
-  void _listen(Stream stream, void onData(event), {Function onError,
-      void onDone(), bool cancelOnError}) {
-    var subscription;
-    subscription = stream.listen(onData, onError: onError, onDone: () {
-      _subscriptions.remove(subscription);
-      if (onDone != null) onDone();
-    }, cancelOnError: cancelOnError);
-    _subscriptions.add(subscription);
-  }
-
   // TODO(nweiz): remove this when issue 15042 is fixed.
   /// Return a human-friendly string representation of [event].
   String _formatEvent(FileSystemEvent event) {
     if (event == null) return 'null';
 
     var path = p.relative(event.path, from: directory);
     var type = event.isDirectory ? 'directory' : 'file';
     if (event is FileSystemCreateEvent) {
       return "create $type $path";
     } else if (event is FileSystemDeleteEvent) {
       return "delete $type $path";
     } else if (event is FileSystemModifyEvent) {
       return "modify $type $path";
     } else if (event is FileSystemMoveEvent) {
       return "move $type $path to "
           "${p.relative(event.destination, from: directory)}";
     }
   }
 }