Add aggregate transformer types to barback.

pkg/barback/lib/src/transformer/transform.dart

Index: pkg/barback/lib/src/transformer/transform.dart
diff --git a/pkg/barback/lib/src/transformer/transform.dart b/pkg/barback/lib/src/transformer/transform.dart
index 809cd122683484ae84c717edd0da3e1b77b9d851..787050ee34def14c208676123465c6810ed1a981 100644
--- a/pkg/barback/lib/src/transformer/transform.dart
+++ b/pkg/barback/lib/src/transformer/transform.dart
@@ -9,11 +9,15 @@ import 'dart:convert';
 
 import '../asset/asset.dart';
 import '../asset/asset_id.dart';
-import '../asset/asset_set.dart';
 import '../errors.dart';
-import '../graph/transform_node.dart';
-import '../utils.dart';
-import 'base_transform.dart';
+import 'aggregate_transform.dart';
+import 'transform_logger.dart';
+
+/// Creates a new [Transform] wrapping an [AggregateTransform].

[Bob Nystrom, 2014/05/05 23:41:56]

It would be more helpful to document this in terms of its intent. Something
like: "provides an implementation of the more user-friendly Transformer
interface in terms of the fundamental AggregateTransform interface that barback
maps everything to."

Also, can you explain for our future selves why it doesn't have to worry about
.primaryInputs producing more than one value?

[nweiz, 2014/05/06 22:46:40]

Done.

+Future<Transform> newTransform(AggregateTransform aggregate) {
+  return aggregate.primaryInputs.first.then((primaryInput) =>
+      new Transform._(aggregate, primaryInput));
+}
 
 /// While a [Transformer] represents a *kind* of transformation, this defines
 /// one specific usage of it on a set of files.
@@ -22,10 +26,8 @@ import 'base_transform.dart';
 /// facilitate communication between the [Transformer] and the code hosting
 /// the transformation. It lets the [Transformer] access inputs and generate
 /// outputs.
-class Transform extends BaseTransform {
-  final TransformNode _node;
-
-  final _outputs = new AssetSet();
+class Transform {
+  final AggregateTransform _aggregate;

[Bob Nystrom, 2014/05/05 23:41:56]

Doc comment.

[nweiz, 2014/05/06 22:46:40]

Done.

 
   /// Gets the primary input asset.
   ///
@@ -36,31 +38,17 @@ class Transform extends BaseTransform {
   /// For example, with a dart2js transform, the primary input would be the
   /// entrypoint Dart file. All of the other Dart files that that imports
   /// would be secondary inputs.
-  ///
-  /// This method may fail at runtime with an [AssetNotFoundException] if called
-  /// asynchronously after the transform begins running. The primary input may
-  /// become unavailable while this transformer is running due to asset changes
-  /// earlier in the graph. You can ignore the error if this happens: the
-  /// transformer will be re-run automatically for you.
-  Asset get primaryInput {
-    if (!_node.primary.state.isAvailable) {
-      throw new AssetNotFoundException(_node.primary.id);
-    }
+  final Asset primaryInput;
 
-    return _node.primary.asset;
-  }
+  /// A logger so that the [Transformer] can report build details.
+  TransformLogger get logger => _aggregate.logger;
 
-  Transform._(TransformNode node)
-    : _node = node,
-      super(node);
+  Transform._(this._aggregate, this.primaryInput);
 
   /// Gets the asset for an input [id].
   ///
   /// If an input with [id] cannot be found, throws an [AssetNotFoundException].
-  Future<Asset> getInput(AssetId id) {
-    if (id == _node.primary.id) return syncFuture(() => primaryInput);
-    return _node.getInput(id);
-  }
+  Future<Asset> getInput(AssetId id) => _aggregate.getInput(id);
 
   /// A convenience method to the contents of the input with [id] as a string.
   ///
@@ -71,10 +59,8 @@ class Transform extends BaseTransform {
   /// asset is decoded using [encoding], which defaults to [UTF8].
   ///
   /// If an input with [id] cannot be found, throws an [AssetNotFoundException].
-  Future<String> readInputAsString(AssetId id, {Encoding encoding}) {
-    if (encoding == null) encoding = UTF8;
-    return getInput(id).then((input) => input.readAsString(encoding: encoding));
-  }
+  Future<String> readInputAsString(AssetId id, {Encoding encoding}) =>
+      _aggregate.readInputAsString(id, encoding: encoding);
 
   /// A convenience method to the contents of the input with [id].
   ///
@@ -83,37 +69,25 @@ class Transform extends BaseTransform {
   /// If the asset was created from a [String], this returns its UTF-8 encoding.
   ///
   /// If an input with [id] cannot be found, throws an [AssetNotFoundException].
-  Stream<List<int>> readInput(AssetId id) =>
-      futureStream(getInput(id).then((input) => input.read()));
+  Stream<List<int>> readInput(AssetId id) => _aggregate.readInput(id);
 
   /// A convenience method to return whether or not an asset exists.
   ///
   /// This is equivalent to calling [getInput] and catching an
   /// [AssetNotFoundException].
-  Future<bool> hasInput(AssetId id) {
-    return getInput(id).then((_) => true).catchError((error) {
-      if (error is AssetNotFoundException && error.id == id) return false;
-      throw error;
-    });
-  }
+  Future<bool> hasInput(AssetId id) => _aggregate.hasInput(id);
 
   /// Stores [output] as the output created by this transformation.
   ///
   /// A transformation can output as many assets as it wants.
-  void addOutput(Asset output) {
-    // TODO(rnystrom): This should immediately throw if an output with that ID
-    // has already been created by this transformer.
-    _outputs.add(output);
-  }
-}
-
-/// The controller for [Transform].
-class TransformController extends BaseTransformController {
-  Transform get transform => super.transform;
+  void addOutput(Asset output) => _aggregate.addOutput(output);
 
-  /// The set of assets that the transformer has emitted.
-  AssetSet get outputs => transform._outputs;
-
-  TransformController(TransformNode node)
-      : super(new Transform._(node));
+  /// Consume the primary input so that it doesn't get processed by future
+  /// phases or emitted once processing has finished.
+  ///
+  /// Normally the primary input will automatically be forwarded unless the
+  /// transformer overwrites it by emitting an input with the same id. This
+  /// allows the transformer to tell barback not to forward the primary input
+  /// even if it's not overwritten.
+  void consumePrimary() => _aggregate.consumePrimary(primaryInput.id);
 }