Enable cross-package transforms to see new transformers in other packages.

pkg/barback/lib/src/phase_output.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 barback.phase_output;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'asset_cascade.dart';
@@ skipping 10 matching lines @@
 /// Normally there's only a single [AssetNode] for a phase's output, but it's
 /// possible that multiple transformers in the same phase emit assets with the
 /// same id, causing collisions. This handles those collisions by forwarding the
 /// chronologically first asset.
 class PhaseOutput {
   /// The phase for which this is an output.
   final Phase _phase;
 
   /// The asset node for this output.
   AssetNode get output => _outputController.node;
-  final AssetNodeController _outputController;
+  AssetNodeController _outputController;
 
   /// The assets for this output.
   ///
   /// If there's no collision, this will only have one element. Otherwise, it
   /// will be ordered by which asset was added first.
   final _assets = new Queue<AssetNode>();
 
   /// The [AssetCollisionException] for this output, or null if there is no
   /// collision currently.
   AssetCollisionException get collisionException {
@@ skipping 10 matching lines @@
     add(output);
   }
 
   /// Adds an asset node as an output with this id.
   void add(AssetNode node) {
     assert(node.id == output.id);
     _assets.add(node);
     _watchAsset(node);
   }
 
+  /// Removes all existing listeners on [output] without actually closing
+  /// [this].
+  ///
+  /// This marks [output] as removed, but immediately replaces it with a new
+  /// [AssetNode] in the same state as the old output.

[Bob Nystrom, 2013/08/22 19:34:19]

A bit of motivation here would help.

+  void removeListeners() {
+    _outputController.setRemoved();
+    _outputController = new AssetNodeController.from(_assets.first);
+  }
+
   /// Watches [node] for state changes and adjusts [_assets] and [output]
   /// appropriately when they occur.
   void _watchAsset(AssetNode node) {
     node.onStateChange.listen((state) {
       if (state.isRemoved) {
         _removeAsset(node);
         return;
       }
       if (_assets.first != node) return;
 
@@ skipping 36 matching lines @@
     // If there's still a collision, report it. This lets the user know
     // if they've successfully resolved the collision or not.
     if (_assets.length > 1) {
       // Pump the event queue to ensure that the removal of the input triggers
       // a new build to which we can attach the error.
       // TODO(nweiz): report this through the output asset.
       newFuture(() => _phase.cascade.reportError(collisionException));
     }
   }
 }