Move isPrimary computation from PhaseInput into TransformNode.

pkg/barback/lib/src/phase_forwarder.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_forwarder;
 
 import 'dart:async';
 
 import 'asset_node.dart';
 import 'asset_node_set.dart';
 
 /// A class that takes care of forwarding assets within a phase.
 ///
-/// Each phase contains one or more channels that process its input assets. The
-/// non-grouped transformers for that phase are one such channel, and each
+/// Each phase contains one or more channels that process its input assets. Each
+/// non-grouped transformer for that phase is a channel, and each
 /// [TransformerGroup] in that phase is another. For each input asset, each
 /// channel individually decides whether to forward that asset based on whether
 /// that channel uses it. If a channel does decide to forward an asset, we call
 /// that forwarded asset an "intermediate forwarded asset" to distinguish it
 /// from the output of a [PhaseForwarder].
 ///
 /// All intermediate assets with a given origin are provided to a single
 /// [PhaseForwarder] via [addIntermediateAsset]. This forwarder then determines
 /// whether all channels in the phase produced intermediate assets. If so, that
 /// means the input asset wasn't consumed by any channel, so the
 /// [PhaseForwarder] forwards it again, producing an output which we'll call the
 /// "final forwarded asset".
 ///
 /// A final forwarded asset will be available only if all of the intermediate
 /// forwarded assets are themselves available. If any of the intermediate assets
 /// are dirty, the final asset will also be marked dirty.
 class PhaseForwarder {
   /// The number of channels through which the asset may have been forwarded.
   ///
-  /// Each group is a channel, along with one channel for the [PhaseInput] that
-  /// handles all the transformers.
+  /// Each transformer in the phase is a channel, as is each group. [value] may
+  /// be zero, indicating that this phase has no transformers or groups; if so,
+  /// the asset is always forwarded.
   set numChannels(int value) {
     _numChannels = value;
     _adjustOutput();
   }
   int _numChannels;
 
+  /// The real number of channels to forward, counting the source node.
+  ///
+  /// This is one higher than [numChannels] because the source node should get
+  /// forwarded if there are no other channels.
+  int get _realNumChannels => _numChannels + 1;

[Bob Nystrom, 2014/03/12 17:42:58]

This is pretty gross. How about we encapsulate the concept of channels within
PhaseForwarder. I'm thinking:

1. Remove numChannels and replace it with updateTransformers(int
numTransformers, int numGroups)
2. Use the same arguments for the constructor.
3. Renamed _realNumChannels -> _numChannels.

This way, Phase doesn't have any idea of "channels": it just tells
PhaseForwarder what it knows and its PhaseForwarder's job to know how to keep
track of when all of the intermediates have arrived.

WDYT?

[nweiz, 2014/03/12 21:44:47]

SGTM, done.

+
   /// The intermediate forwarded assets.
   final _intermediateAssets = new AssetNodeSet();
 
   /// The final forwarded asset.
   ///
   /// This will be null if the asset is not being forwarded.
-  AssetNode get output => _outputController.node;
+  AssetNode get output =>
+      _outputController == null ? null : _outputController.node;
   AssetNodeController _outputController;
 
   /// A stream that emits an event whenever [this] starts producing a final
   /// forwarded asset.
   ///
   /// Whenever this stream emits an event, the value will be identical to
   /// [output].
   Stream<AssetNode> get onAsset => _onAssetController.stream;
-  final _onAssetController = new StreamController<AssetNode>(sync: true);
+  final _onAssetController = new StreamController<AssetNode>.broadcast(sync: true);

[Bob Nystrom, 2014/03/12 17:42:58]

Long line.

[nweiz, 2014/03/12 21:44:47]

Done.

 
-  PhaseForwarder(this._numChannels);
+  /// Creates a phase forwarder forwarding nodes that come from [node] across
+  /// [numChannels] channels.
+  ///
+  /// [node] is passed in explicitly so that it can be forwarded if
+  /// [numChannels] becomes zero.
+  PhaseForwarder(AssetNode node, this._numChannels) {
+    addIntermediateAsset(node);
+  }
 
   /// Adds an intermediate forwarded asset to [this].
   ///
   /// [asset] must have the same origin as all other intermediate forwarded
   /// assets.
   void addIntermediateAsset(AssetNode asset) {
     if (_intermediateAssets.isNotEmpty) {
       assert(asset.origin == _intermediateAssets.first.origin);
     }
 
@@ skipping 10 matching lines @@
     if (_outputController != null) {
       _outputController.setRemoved();
       _outputController = null;
     }
     _onAssetController.close();
   }
 
   /// Adjusts [output] to ensure that it accurately reflects the current state
   /// of the intermediate forwarded assets.
   void _adjustOutput() {
-    assert(_intermediateAssets.length <= _numChannels);
+    assert(_intermediateAssets.length <= _realNumChannels);
     assert(!_intermediateAssets.any((asset) => asset.state.isRemoved));
 
     // If there are any channels that haven't forwarded an intermediate asset,
     // we shouldn't forward a final asset. If we are currently, remove
     // it.
-    if (_intermediateAssets.length < _numChannels) {
+    if (_intermediateAssets.length < _realNumChannels) {
       if (_outputController == null) return;
       _outputController.setRemoved();
       _outputController = null;
       return;
     }
 
     // If there isn't a final asset being forwarded yet, we should forward one.
     // It should be dirty iff any of the intermediate assets are dirty.
     if (_outputController == null) {
       var finalAsset = _intermediateAssets.firstWhere(
           (asset) => asset.state.isDirty,
           orElse: () => _intermediateAssets.first);
       _outputController = new AssetNodeController.from(finalAsset);
       _onAssetController.add(output);
       return;
     }
 
     // If we're already forwarding a final asset, set it dirty iff any of the
     // intermediate assets are dirty.
     if (_intermediateAssets.any((asset) => asset.state.isDirty)) {
       if (!_outputController.node.state.isDirty) _outputController.setDirty();
-    } else {
-      if (!_outputController.node.state.isAvailable) {
-        _outputController.setAvailable(_intermediateAssets.first.asset);
-      }
+    } else if (!_outputController.node.state.isAvailable) {
+      _outputController.setAvailable(_intermediateAssets.first.asset);
     }
   }
 }