Handle watching a non-existent directory.

pkg/watcher/lib/src/directory_watcher.dart

Index: pkg/watcher/lib/src/directory_watcher.dart
diff --git a/pkg/watcher/lib/src/directory_watcher.dart b/pkg/watcher/lib/src/directory_watcher.dart
index c5dd9db606bb589bd69fc411a16d428a0de7c6aa..6fa49a9aad0e9a12e1703b7f5f2a45e5bc17d456 100644
--- a/pkg/watcher/lib/src/directory_watcher.dart
+++ b/pkg/watcher/lib/src/directory_watcher.dart
@@ -118,19 +118,27 @@ class DirectoryWatcher {
     _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