Add support for transformer clusters to barback.

pkg/barback/lib/src/asset_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.asset_node;
 
 import 'dart:async';
 
 import 'asset.dart';
 import 'asset_id.dart';
 import 'errors.dart';
 import 'transform_node.dart';
 
 /// Describes the current state of an asset as part of a transformation graph.
 ///
 /// An asset node can be in one of three states (see [AssetState]). It provides
 /// an [onStateChange] stream that emits an event whenever it changes state.
 ///
 /// Asset nodes are controlled using [AssetNodeController]s.
 class AssetNode {
   /// The id of the asset that this node represents.
   final AssetId id;
 
+  /// The [AssetNode] from which [this] is forwarded.
+  ///
+  /// For nodes that aren't forwarded, this will return [this]. Otherwise, it
+  /// will return the first node in the forwarding chain.
+  ///
+  /// This is used to determine whether two nodes are forwarded from the same
+  /// source.
+  AssetNode get origin => _origin == null ? this : _origin;
+  AssetNode _origin;
+
   /// The transform that created this asset node.
   ///
   /// This is `null` for source assets. It can change if the upstream transform
   /// that created this asset changes; this change will *not* cause an
   /// [onStateChange] event.
   TransformNode get transform => _transform;
   TransformNode _transform;
 
   /// The current state of the asset node.
   AssetState get state => _state;
@@ skipping 72 matching lines @@
 
   /// Returns a Future that completes as soon as the node is in a state that
   /// matches [test].
   ///
   /// The Future completes synchronously if this is already in such a state.
   Future<AssetState> _waitForState(bool test(AssetState state)) {
     if (test(state)) return new Future.sync(() => state);
     return onStateChange.firstWhere(test);
   }
 
-  AssetNode._(this.id, this._transform)
+  AssetNode._(this.id, this._transform, this._origin)
       : _state = AssetState.DIRTY;
 
-  AssetNode._available(Asset asset, this._transform)
+  AssetNode._available(Asset asset, this._transform, this._origin)
       : id = asset.id,
         _asset = asset,
         _state = AssetState.AVAILABLE;
 }
 
 /// The controller for an [AssetNode].
 ///
 /// This controls which state the node is in.
 class AssetNodeController {
   final AssetNode node;
 
   /// Creates a controller for a dirty node.
   AssetNodeController(AssetId id, [TransformNode transform])
-      : node = new AssetNode._(id, transform);
+      : node = new AssetNode._(id, transform, null);
 
   /// Creates a controller for an available node with the given concrete
   /// [asset].
   AssetNodeController.available(Asset asset, [TransformNode transform])
-      : node = new AssetNode._available(asset, transform);
+      : node = new AssetNode._available(asset, transform, null);
 
   /// Creates a controller for a node whose initial state matches the current
   /// state of [node].
+  ///
+  /// [AssetNode.origin] of the returned node will automatically be set to
+  /// `node.origin`.
   AssetNodeController.from(AssetNode node)
-      : node = new AssetNode._(node.id, node.transform) {
+      : node = new AssetNode._(node.id, node.transform, node.origin) {
     if (node.state.isAvailable) {
       setAvailable(node.asset);
     } else if (node.state.isRemoved) {
       setRemoved();
     }
   }
 
   /// Marks the node as [AssetState.DIRTY].
   void setDirty() {
     assert(node._state != AssetState.REMOVED);
@@ skipping 19 matching lines @@
   /// marked as dirty first.
   void setAvailable(Asset asset) {
     assert(asset.id == node.id);
     assert(node._state != AssetState.REMOVED);
     assert(node._state != AssetState.AVAILABLE);
     node._state = AssetState.AVAILABLE;
     node._asset = asset;
     node._stateChangeController.add(AssetState.AVAILABLE);
   }
 
-  /// Sets the node's [AssetNode.transform] property.
-  ///
-  /// This is used when resolving collisions, where a node will stick around but
-  /// a different transform will have created it.
-  void setTransform(TransformNode transform) {
-    node._transform = transform;
+  /// Sets the origin of [node] to [origin] and the transform to
+  /// `origin.transform`.
+  void setOrigin(AssetNode origin) {
+    node._origin = origin;
+    node._transform = origin.transform;
   }
 }
 
 // TODO(nweiz): add an error state.
 /// An enum of states that an [AssetNode] can be in.
 class AssetState {
   /// The node has a concrete asset loaded, available, and up-to-date. The asset
   /// is accessible via [AssetNode.asset]. An asset can only be marked available
   /// again from the [AssetState.DIRTY] state.
   static final AVAILABLE = const AssetState._("available");
@@ skipping 14 matching lines @@
 
   /// Whether this state is [AssetState.DIRTY].
   bool get isDirty => this == AssetState.DIRTY;
 
   final String name;
 
   const AssetState._(this.name);
 
   String toString() => name;
 }