Handle watching a non-existent directory.

pkg/watcher/lib/src/directory_watcher.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;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:crypto/crypto.dart';
@@ skipping 100 matching lines @@
 
     _ready = new Completer();
   }
 
   /// Scans the contents of the directory once to see which files have been
   /// added, removed, and modified.
   void _poll() {
     _filesToProcess.clear();
     _polledFiles.clear();
 
+    endListing() {
+      assert(_state != _WatchState.UNSUBSCRIBED);
+      _listSubscription = null;
+
+      // Null tells the queue consumer that we're done listing.
+      _filesToProcess.add(null);
+    }
+
     var stream = new Directory(directory).list(recursive: true);
     _listSubscription = stream.listen((entity) {
       assert(_state != _WatchState.UNSUBSCRIBED);
 
       if (entity is! File) return;
       _filesToProcess.add(entity.path);
-    }, onDone: () {
-      assert(_state != _WatchState.UNSUBSCRIBED);
-      _listSubscription = null;
-
-      // Null tells the queue consumer that we're done listing.
-      _filesToProcess.add(null);
-    });
+    }, onError: (error) {
+      // If an error occurred during the listing, it usually means the

[nweiz, 2013/08/14 19:43:11]

Check if the error is the error we expect from the directory getting deleted,
and print an error message describing what it actually is if not.

[Bob Nystrom, 2013/08/16 21:40:19]

Done. Instead of printing it, I pipe the error to the event stream's error
channel.

+      // directory doesn't exist. We end the listing normally, which has the
+      // desired effect of marking all files that were in the directory as
+      // being removed.
+      endListing();
+    }, onDone: endListing);
   }
 
   /// Processes [file] to determine if it has been modified since the last
   /// time it was scanned.
   Future _processFile(String file) {
     assert(_state != _WatchState.UNSUBSCRIBED);
 
     // `null` is the sentinel which means the directory listing is complete.
     if (file == null) return _completePoll();
 
@@ skipping 114 matching lines @@
 
 class _FileStatus {
   /// The last time the file was modified.
   DateTime modified;
 
   /// The SHA-1 hash of the contents of the file.
   List<int> hash;
 
   _FileStatus(this.modified, this.hash);
 }