lib/src/directory_watcher/mac_os.dart - watcher - Git at Google

 // 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.

 import 'dart:async';
 import 'dart:io';

 import '../directory_watcher.dart';
 import '../constructable_file_system_event.dart';
 import '../path_set.dart';
 import '../resubscribable.dart';
 import '../utils.dart';
 import '../watch_event.dart';

 /// Uses the FSEvents subsystem to watch for filesystem events.
 ///
 /// FSEvents has two main idiosyncrasies that this class works around. First, it
 /// will occasionally report events that occurred before the filesystem watch
 /// was initiated. Second, if multiple events happen to the same file in close
 /// succession, it won't report them in the order they occurred. See issue
 /// 14373.
 ///
 /// This also works around issues 16003 and 14849 in the implementation of
 /// [Directory.watch].
 class MacOSDirectoryWatcher extends ResubscribableWatcher
     implements DirectoryWatcher {
   @override
   String get directory => path;

   MacOSDirectoryWatcher(String directory)
       : super(directory, () => _MacOSDirectoryWatcher(directory));
 }

 class _MacOSDirectoryWatcher
     implements DirectoryWatcher, ManuallyClosedWatcher {
   @override
   String get directory => path;
   @override
   final String path;

   @override
   Stream<WatchEvent> get events => _eventsController.stream;
   final _eventsController = StreamController<WatchEvent>.broadcast();

   @override
   bool get isReady => _readyCompleter.isCompleted;

   @override
   Future get ready => _readyCompleter.future;
   final _readyCompleter = Completer();

   /// 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 [_listSubscriptions] because this stream
   /// occasionally needs to be resubscribed in order to work around issue 14849.
   StreamSubscription<List<FileSystemEvent>> _watchSubscription;

   /// The subscription to the [Directory.list] call for the initial listing of
   /// the directory to determine its initial state.
   StreamSubscription<FileSystemEntity> _initialListSubscription;

   /// The subscriptions to [Directory.list] calls for listing the contents of a
   /// subdirectory that was moved into the watched directory.
   final _listSubscriptions = <StreamSubscription<FileSystemEntity>>{};

   /// The timer for tracking how long we wait for an initial batch of bogus
   /// events (see issue 14373).
   Timer _bogusEventTimer;

   _MacOSDirectoryWatcher(String path)
       : path = path,
         _files = PathSet(path) {
     _startWatch();

     // 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(), _waitForBogusEvents()])
         .then((_) => _readyCompleter.complete());
   }

   @override
   void close() {
     if (_watchSubscription != null) _watchSubscription.cancel();
     if (_initialListSubscription != null) _initialListSubscription.cancel();
     _watchSubscription = null;
     _initialListSubscription = null;

     for (var subscription in _listSubscriptions) {
       subscription.cancel();
     }
     _listSubscriptions.clear();

     _eventsController.close();
   }

   /// The callback that's run when [Directory.watch] emits a batch of events.
   void _onBatch(List<FileSystemEvent> batch) {
     // 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) {
       // Cancel the timer because bogus events only occur in the first batch, so
       // we can fire [ready] as soon as we're done listing the directory.
       _bogusEventTimer.cancel();
       _listDir().then((_) => _readyCompleter.complete());
       return;
     }

     _sortEvents(batch).forEach((path, eventSet) {
       var canonicalEvent = _canonicalEvent(eventSet);
       var events = canonicalEvent == null
           ? _eventsBasedOnFileSystem(path)
           : [canonicalEvent];

       for (var event in events) {
         if (event is FileSystemCreateEvent) {
           if (!event.isDirectory) {
             // If we already know about the file, treat it like a modification.
             // This can happen if a file is copied on top of an existing one.
             // We'll see an ADD event for the latter file when from the user's
             // perspective, the file's contents just changed.
             var type =
                 _files.contains(path) ? ChangeType.MODIFY : ChangeType.ADD;

             _emitEvent(type, path);
             _files.add(path);
             continue;
           }

           if (_files.containsDir(path)) continue;

           StreamSubscription<FileSystemEntity> subscription;
           subscription = Directory(path).list(recursive: true).listen((entity) {
             if (entity is Directory) return;
             if (_files.contains(path)) return;

             _emitEvent(ChangeType.ADD, entity.path);
             _files.add(entity.path);
           }, onError: (e, StackTrace stackTrace) {
             _emitError(e, stackTrace);
           }, onDone: () {
             _listSubscriptions.remove(subscription);
           }, cancelOnError: true);
           _listSubscriptions.add(subscription);
         } else if (event is FileSystemModifyEvent) {
           assert(!event.isDirectory);
           _emitEvent(ChangeType.MODIFY, path);
         } else {
           assert(event is FileSystemDeleteEvent);
           for (var removedPath in _files.remove(path)) {
             _emitEvent(ChangeType.REMOVE, removedPath);
           }
         }
       }
     });
   }

   /// Sort all the events in a batch into sets based on their path.
   ///
   /// A single input event may result in multiple events in the returned map;
   /// for example, a MOVE event becomes a DELETE event for the source and a
   /// CREATE event for the destination.
   ///
   /// The returned events won't contain any [FileSystemMoveEvent]s, nor will it
   /// contain any events relating to [path].
   Map<String, Set<FileSystemEvent>> _sortEvents(List<FileSystemEvent> batch) {
     var eventsForPaths = <String, Set<FileSystemEvent>>{};

     // FSEvents can report past events, including events on the root directory
     // such as it being created. We want to ignore these. If the directory is
     // really deleted, that's handled by [_onDone].
     batch = batch.where((event) => event.path != path).toList();

     // Events within directories that already have events are superfluous; the
     // directory's full contents will be examined anyway, so we ignore such
     // events. Emitting them could cause useless or out-of-order events.
     var directories = unionAll(batch.map((event) {
       if (!event.isDirectory) return <String>{};
       if (event is FileSystemMoveEvent) {
         return {event.path, event.destination};
       }
       return {event.path};
     }));

     bool isInModifiedDirectory(String path) =>
         directories.any((dir) => path != dir && path.startsWith(dir));

     void addEvent(String path, FileSystemEvent event) {
       if (isInModifiedDirectory(path)) return;
       eventsForPaths.putIfAbsent(path, () => <FileSystemEvent>{}).add(event);
     }

     for (var event in batch) {
       // The Mac OS watcher doesn't emit move events. See issue 14806.
       assert(event is! FileSystemMoveEvent);
       addEvent(event.path, event);
     }

     return eventsForPaths;
   }

   /// Returns the canonical event from a batch of events on the same path, if
   /// one exists.
   ///
   /// If [batch] doesn't contain any contradictory events (e.g. DELETE and
   /// CREATE, or events with different values for `isDirectory`), this returns a
   /// single event that describes what happened to the path in question.
   ///
   /// If [batch] does contain contradictory events, this returns `null` to
   /// indicate that the state of the path on the filesystem should be checked to
   /// determine what occurred.
   FileSystemEvent _canonicalEvent(Set<FileSystemEvent> batch) {
     // An empty batch indicates that we've learned earlier that the batch is
     // contradictory (e.g. because of a move).
     if (batch.isEmpty) return null;

     var type = batch.first.type;
     var isDir = batch.first.isDirectory;
     var hadModifyEvent = false;

     for (var event in batch.skip(1)) {
       // If one event reports that the file is a directory and another event
       // doesn't, that's a contradiction.
       if (isDir != event.isDirectory) return null;

       // Modify events don't contradict either CREATE or REMOVE events. We can
       // safely assume the file was modified after a CREATE or before the
       // REMOVE; otherwise there will also be a REMOVE or CREATE event
       // (respectively) that will be contradictory.
       if (event is FileSystemModifyEvent) {
         hadModifyEvent = true;
         continue;
       }
       assert(event is FileSystemCreateEvent || event is FileSystemDeleteEvent);

       // If we previously thought this was a MODIFY, we now consider it to be a
       // CREATE or REMOVE event. This is safe for the same reason as above.
       if (type == FileSystemEvent.modify) {
         type = event.type;
         continue;
       }

       // A CREATE event contradicts a REMOVE event and vice versa.
       assert(type == FileSystemEvent.create || type == FileSystemEvent.delete);
       if (type != event.type) return null;
     }

     // If we got a CREATE event for a file we already knew about, that comes
     // from FSEvents reporting an add that happened prior to the watch
     // beginning. If we also received a MODIFY event, we want to report that,
     // but not the CREATE.
     if (type == FileSystemEvent.create &&
         hadModifyEvent &&
         _files.contains(batch.first.path)) {
       type = FileSystemEvent.modify;
     }

     switch (type) {
       case FileSystemEvent.create:
         // Issue 16003 means that a CREATE event for a directory can indicate
         // that the directory was moved and then re-created.
         // [_eventsBasedOnFileSystem] will handle this correctly by producing a
         // DELETE event followed by a CREATE event if the directory exists.
         if (isDir) return null;
         return ConstructableFileSystemCreateEvent(batch.first.path, false);
       case FileSystemEvent.delete:
         return ConstructableFileSystemDeleteEvent(batch.first.path, isDir);
       case FileSystemEvent.modify:
         return ConstructableFileSystemModifyEvent(
             batch.first.path, isDir, false);
       default:
         throw 'unreachable';
     }
   }

   /// Returns one or more events that describe the change between the last known
   /// state of [path] and its current state on the filesystem.
   ///
   /// This returns a list whose order should be reflected in the events emitted
   /// to the user, unlike the batched events from [Directory.watch]. The
   /// returned list may be empty, indicating that no changes occurred to [path]
   /// (probably indicating that it was created and then immediately deleted).
   List<FileSystemEvent> _eventsBasedOnFileSystem(String path) {
     var fileExisted = _files.contains(path);
     var dirExisted = _files.containsDir(path);
     var fileExists = File(path).existsSync();
     var dirExists = Directory(path).existsSync();

     var events = <FileSystemEvent>[];
     if (fileExisted) {
       if (fileExists) {
         events.add(ConstructableFileSystemModifyEvent(path, false, false));
       } else {
         events.add(ConstructableFileSystemDeleteEvent(path, false));
       }
     } else if (dirExisted) {
       if (dirExists) {
         // If we got contradictory events for a directory that used to exist and
         // still exists, we need to rescan the whole thing in case it was
         // replaced with a different directory.
         events.add(ConstructableFileSystemDeleteEvent(path, true));
         events.add(ConstructableFileSystemCreateEvent(path, true));
       } else {
         events.add(ConstructableFileSystemDeleteEvent(path, true));
       }
     }

     if (!fileExisted && fileExists) {
       events.add(ConstructableFileSystemCreateEvent(path, false));
     } else if (!dirExisted && dirExists) {
       events.add(ConstructableFileSystemCreateEvent(path, true));
     }

     return events;
   }

   /// The callback that's run when the [Directory.watch] stream is closed.
   void _onDone() {
     _watchSubscription = null;

     // 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 (!isReady && Directory(path).existsSync()) {
       _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.paths) {
       _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 = Directory(path)
         .watch(recursive: true)
         .transform(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 = Completer();
     var stream = Directory(path).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 = Completer();
     _bogusEventTimer = Timer(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;
     _eventsController.add(WatchEvent(type, path));
   }

   /// Emit an error, then close the watcher.
   void _emitError(error, StackTrace stackTrace) {
     _eventsController.addError(error, stackTrace);
     close();
   }
 }
	// 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.

	import 'dart:async';
	import 'dart:io';

	import '../directory_watcher.dart';
	import '../constructable_file_system_event.dart';
	import '../path_set.dart';
	import '../resubscribable.dart';
	import '../utils.dart';
	import '../watch_event.dart';

	/// Uses the FSEvents subsystem to watch for filesystem events.
	///
	/// FSEvents has two main idiosyncrasies that this class works around. First, it
	/// will occasionally report events that occurred before the filesystem watch
	/// was initiated. Second, if multiple events happen to the same file in close
	/// succession, it won't report them in the order they occurred. See issue
	/// 14373.
	///
	/// This also works around issues 16003 and 14849 in the implementation of
	/// [Directory.watch].
	class MacOSDirectoryWatcher extends ResubscribableWatcher
	implements DirectoryWatcher {
	@override
	String get directory => path;

	MacOSDirectoryWatcher(String directory)
	: super(directory, () => _MacOSDirectoryWatcher(directory));
	}

	class _MacOSDirectoryWatcher
	implements DirectoryWatcher, ManuallyClosedWatcher {
	@override
	String get directory => path;
	@override
	final String path;

	@override
	Stream<WatchEvent> get events => _eventsController.stream;
	final _eventsController = StreamController<WatchEvent>.broadcast();

	@override
	bool get isReady => _readyCompleter.isCompleted;

	@override
	Future get ready => _readyCompleter.future;
	final _readyCompleter = Completer();

	/// 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 [_listSubscriptions] because this stream
	/// occasionally needs to be resubscribed in order to work around issue 14849.
	StreamSubscription<List<FileSystemEvent>> _watchSubscription;

	/// The subscription to the [Directory.list] call for the initial listing of
	/// the directory to determine its initial state.
	StreamSubscription<FileSystemEntity> _initialListSubscription;

	/// The subscriptions to [Directory.list] calls for listing the contents of a
	/// subdirectory that was moved into the watched directory.
	final _listSubscriptions = <StreamSubscription<FileSystemEntity>>{};

	/// The timer for tracking how long we wait for an initial batch of bogus
	/// events (see issue 14373).
	Timer _bogusEventTimer;

	_MacOSDirectoryWatcher(String path)
	: path = path,
	_files = PathSet(path) {
	_startWatch();

	// 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(), _waitForBogusEvents()])
	.then((_) => _readyCompleter.complete());
	}

	@override
	void close() {
	if (_watchSubscription != null) _watchSubscription.cancel();
	if (_initialListSubscription != null) _initialListSubscription.cancel();
	_watchSubscription = null;
	_initialListSubscription = null;

	for (var subscription in _listSubscriptions) {
	subscription.cancel();
	}
	_listSubscriptions.clear();

	_eventsController.close();
	}

	/// The callback that's run when [Directory.watch] emits a batch of events.
	void _onBatch(List<FileSystemEvent> batch) {
	// 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) {
	// Cancel the timer because bogus events only occur in the first batch, so
	// we can fire [ready] as soon as we're done listing the directory.
	_bogusEventTimer.cancel();
	_listDir().then((_) => _readyCompleter.complete());
	return;
	}

	_sortEvents(batch).forEach((path, eventSet) {
	var canonicalEvent = _canonicalEvent(eventSet);
	var events = canonicalEvent == null
	? _eventsBasedOnFileSystem(path)
	: [canonicalEvent];

	for (var event in events) {
	if (event is FileSystemCreateEvent) {
	if (!event.isDirectory) {
	// If we already know about the file, treat it like a modification.
	// This can happen if a file is copied on top of an existing one.
	// We'll see an ADD event for the latter file when from the user's
	// perspective, the file's contents just changed.
	var type =
	_files.contains(path) ? ChangeType.MODIFY : ChangeType.ADD;

	_emitEvent(type, path);
	_files.add(path);
	continue;
	}

	if (_files.containsDir(path)) continue;

	StreamSubscription<FileSystemEntity> subscription;
	subscription = Directory(path).list(recursive: true).listen((entity) {
	if (entity is Directory) return;
	if (_files.contains(path)) return;

	_emitEvent(ChangeType.ADD, entity.path);
	_files.add(entity.path);
	}, onError: (e, StackTrace stackTrace) {
	_emitError(e, stackTrace);
	}, onDone: () {
	_listSubscriptions.remove(subscription);
	}, cancelOnError: true);
	_listSubscriptions.add(subscription);
	} else if (event is FileSystemModifyEvent) {
	assert(!event.isDirectory);
	_emitEvent(ChangeType.MODIFY, path);
	} else {
	assert(event is FileSystemDeleteEvent);
	for (var removedPath in _files.remove(path)) {
	_emitEvent(ChangeType.REMOVE, removedPath);
	}
	}
	}
	});
	}

	/// Sort all the events in a batch into sets based on their path.
	///
	/// A single input event may result in multiple events in the returned map;
	/// for example, a MOVE event becomes a DELETE event for the source and a
	/// CREATE event for the destination.
	///
	/// The returned events won't contain any [FileSystemMoveEvent]s, nor will it
	/// contain any events relating to [path].
	Map<String, Set<FileSystemEvent>> _sortEvents(List<FileSystemEvent> batch) {
	var eventsForPaths = <String, Set<FileSystemEvent>>{};

	// FSEvents can report past events, including events on the root directory
	// such as it being created. We want to ignore these. If the directory is
	// really deleted, that's handled by [_onDone].
	batch = batch.where((event) => event.path != path).toList();

	// Events within directories that already have events are superfluous; the
	// directory's full contents will be examined anyway, so we ignore such
	// events. Emitting them could cause useless or out-of-order events.
	var directories = unionAll(batch.map((event) {
	if (!event.isDirectory) return <String>{};
	if (event is FileSystemMoveEvent) {
	return {event.path, event.destination};
	}
	return {event.path};
	}));

	bool isInModifiedDirectory(String path) =>
	directories.any((dir) => path != dir && path.startsWith(dir));

	void addEvent(String path, FileSystemEvent event) {
	if (isInModifiedDirectory(path)) return;
	eventsForPaths.putIfAbsent(path, () => <FileSystemEvent>{}).add(event);
	}

	for (var event in batch) {
	// The Mac OS watcher doesn't emit move events. See issue 14806.
	assert(event is! FileSystemMoveEvent);
	addEvent(event.path, event);
	}

	return eventsForPaths;
	}

	/// Returns the canonical event from a batch of events on the same path, if
	/// one exists.
	///
	/// If [batch] doesn't contain any contradictory events (e.g. DELETE and
	/// CREATE, or events with different values for `isDirectory`), this returns a
	/// single event that describes what happened to the path in question.
	///
	/// If [batch] does contain contradictory events, this returns `null` to
	/// indicate that the state of the path on the filesystem should be checked to
	/// determine what occurred.
	FileSystemEvent _canonicalEvent(Set<FileSystemEvent> batch) {
	// An empty batch indicates that we've learned earlier that the batch is
	// contradictory (e.g. because of a move).
	if (batch.isEmpty) return null;

	var type = batch.first.type;
	var isDir = batch.first.isDirectory;
	var hadModifyEvent = false;

	for (var event in batch.skip(1)) {
	// If one event reports that the file is a directory and another event
	// doesn't, that's a contradiction.
	if (isDir != event.isDirectory) return null;

	// Modify events don't contradict either CREATE or REMOVE events. We can
	// safely assume the file was modified after a CREATE or before the
	// REMOVE; otherwise there will also be a REMOVE or CREATE event
	// (respectively) that will be contradictory.
	if (event is FileSystemModifyEvent) {
	hadModifyEvent = true;
	continue;
	}
	assert(event is FileSystemCreateEvent \|\| event is FileSystemDeleteEvent);

	// If we previously thought this was a MODIFY, we now consider it to be a
	// CREATE or REMOVE event. This is safe for the same reason as above.
	if (type == FileSystemEvent.modify) {
	type = event.type;
	continue;
	}

	// A CREATE event contradicts a REMOVE event and vice versa.
	assert(type == FileSystemEvent.create \|\| type == FileSystemEvent.delete);
	if (type != event.type) return null;
	}

	// If we got a CREATE event for a file we already knew about, that comes
	// from FSEvents reporting an add that happened prior to the watch
	// beginning. If we also received a MODIFY event, we want to report that,
	// but not the CREATE.
	if (type == FileSystemEvent.create &&
	hadModifyEvent &&
	_files.contains(batch.first.path)) {
	type = FileSystemEvent.modify;
	}

	switch (type) {
	case FileSystemEvent.create:
	// Issue 16003 means that a CREATE event for a directory can indicate
	// that the directory was moved and then re-created.
	// [_eventsBasedOnFileSystem] will handle this correctly by producing a
	// DELETE event followed by a CREATE event if the directory exists.
	if (isDir) return null;
	return ConstructableFileSystemCreateEvent(batch.first.path, false);
	case FileSystemEvent.delete:
	return ConstructableFileSystemDeleteEvent(batch.first.path, isDir);
	case FileSystemEvent.modify:
	return ConstructableFileSystemModifyEvent(
	batch.first.path, isDir, false);
	default:
	throw 'unreachable';
	}
	}

	/// Returns one or more events that describe the change between the last known
	/// state of [path] and its current state on the filesystem.
	///
	/// This returns a list whose order should be reflected in the events emitted
	/// to the user, unlike the batched events from [Directory.watch]. The
	/// returned list may be empty, indicating that no changes occurred to [path]
	/// (probably indicating that it was created and then immediately deleted).
	List<FileSystemEvent> _eventsBasedOnFileSystem(String path) {
	var fileExisted = _files.contains(path);
	var dirExisted = _files.containsDir(path);
	var fileExists = File(path).existsSync();
	var dirExists = Directory(path).existsSync();

	var events = <FileSystemEvent>[];
	if (fileExisted) {
	if (fileExists) {
	events.add(ConstructableFileSystemModifyEvent(path, false, false));
	} else {
	events.add(ConstructableFileSystemDeleteEvent(path, false));
	}
	} else if (dirExisted) {
	if (dirExists) {
	// If we got contradictory events for a directory that used to exist and
	// still exists, we need to rescan the whole thing in case it was
	// replaced with a different directory.
	events.add(ConstructableFileSystemDeleteEvent(path, true));
	events.add(ConstructableFileSystemCreateEvent(path, true));
	} else {
	events.add(ConstructableFileSystemDeleteEvent(path, true));
	}
	}

	if (!fileExisted && fileExists) {
	events.add(ConstructableFileSystemCreateEvent(path, false));
	} else if (!dirExisted && dirExists) {
	events.add(ConstructableFileSystemCreateEvent(path, true));
	}

	return events;
	}

	/// The callback that's run when the [Directory.watch] stream is closed.
	void _onDone() {
	_watchSubscription = null;

	// 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 (!isReady && Directory(path).existsSync()) {
	_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.paths) {
	_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 = Directory(path)
	.watch(recursive: true)
	.transform(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 = Completer();
	var stream = Directory(path).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 = Completer();
	_bogusEventTimer = Timer(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;
	_eventsController.add(WatchEvent(type, path));
	}

	/// Emit an error, then close the watcher.
	void _emitError(error, StackTrace stackTrace) {
	_eventsController.addError(error, stackTrace);
	close();
	}
	}