Fix a barback bug that triggered when an asset was removed.

pkg/barback/lib/src/transform_node.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.transform_node;
 
 import 'dart:async';
 
 import 'asset.dart';
 import 'asset_id.dart';
@@ skipping 25 matching lines @@
   var _isDirty = true;
 
   /// The inputs read by this transform the last time it was run.
   ///
   /// Used to tell if an input was removed in a later run.
   var _inputs = new Set<AssetNode>();
 
   /// The outputs created by this transform the last time it was run.
   ///
   /// Used to tell if an output was removed in a later run.
+  Set<AssetId> get outputs => _outputs;

[Bob Nystrom, 2013/07/17 17:18:26]

Instead of making this public, how about defining:

TransformOutputs removeAllOutputs() => new TransformOutputs(new AssetSet(),
_outputs);

[nweiz, 2013/07/17 18:29:55]

I thought about that, but I couldn't come up with a name I was happy with and I
took that as a sign that that wasn't the right way to do it. For example,
[removeAllOutputs] sounds like it's a mutating operation that will remove
outputs, which isn't the case.

I'm not too worried about making [outputs] public; I think it and [inputs] will
both need to be public eventually to support more intelligence about what
transforms need to be waited for when requesting an asset.

   var _outputs = new Set<AssetId>();
 
   TransformNode(this.phase, this._transformer, this.primary);
 
   /// Marks this transform as needing to be run.
   void dirty() {
     _isDirty = true;
   }
 
   /// Applies this transform.
@@ skipping 52 matching lines @@
 class TransformOutputs {
   /// The outputs that are new or were modified since the last run.
   final AssetSet updated;
 
   /// The outputs that were created by the previous run but were not generated
   /// by the most recent run.
   final Set<AssetId> removed;
 
   TransformOutputs(this.updated, this.removed);
 }