Expose aggregate transformers in barback.

pkg/barback/test/transformer/aggregate_many_to_many.dart

Index: pkg/barback/test/transformer/aggregate_many_to_many.dart
diff --git a/pkg/barback/test/transformer/aggregate_many_to_many.dart b/pkg/barback/test/transformer/aggregate_many_to_many.dart
new file mode 100644
index 0000000000000000000000000000000000000000..620e81c085b26a636f6cc98f5b6b199378374bf5
--- /dev/null
+++ b/pkg/barback/test/transformer/aggregate_many_to_many.dart
@@ -0,0 +1,37 @@
+// Copyright (c) 2014, 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.test.transformer.aggregate_many_to_many;
+
+import 'dart:async';
+
+import 'package:barback/barback.dart';
+import 'package:path/path.dart' as path;
+
+import 'mock_aggregate.dart';
+
+/// An [AggregateTransformer] that takes all assets in each directory with a
+/// given extension and adds to their contents.

[Bob Nystrom, 2014/05/27 17:20:18]

This is ambiguous. How about "all assets with a given extension, grouped by
directory".

[nweiz, 2014/05/27 21:03:10]

Done.

+class AggregateManyToManyTransformer extends MockAggregateTransformer {
+  /// The extension of assets to combine.
+  final String extension;
+
+  AggregateManyToManyTransformer(this.extension);
+
+  String doClassifyPrimary(AssetId id) {
+    if (id.extension != ".$extension") return null;
+    return path.url.dirname(id.path);
+  }
+
+  Future doApply(AggregateTransform transform) {
+    return getPrimaryInputs(transform).asyncMap((asset) {
+      return asset.readAsString().then((contents) {
+        transform.addOutput(new Asset.fromString(
+            asset.id, "modified $contents"));
+      });
+    }).toList();
+  }
+
+  String toString() => "aggregate $extension->many";
+}