Transition barback's infrastructure to an aggregate-based model.

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

Index: pkg/barback/lib/src/transformer/wrapping_aggregate_transformer.dart
diff --git a/pkg/barback/lib/src/transformer/wrapping_aggregate_transformer.dart b/pkg/barback/lib/src/transformer/wrapping_aggregate_transformer.dart
new file mode 100644
index 0000000000000000000000000000000000000000..f41d07584a3fdcd742e6bfcd89c52081ad02518d
--- /dev/null
+++ b/pkg/barback/lib/src/transformer/wrapping_aggregate_transformer.dart
@@ -0,0 +1,84 @@
+// 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.transformer.wrapping_aggregate_transformer;
+
+import 'dart:async';
+
+import '../asset/asset_id.dart';
+import '../utils.dart';
+import 'aggregate_transform.dart';
+import 'aggregate_transformer.dart';
+import 'declaring_aggregate_transform.dart';
+import 'declaring_aggregate_transformer.dart';
+import 'declaring_transform.dart';
+import 'declaring_transformer.dart';
+import 'lazy_aggregate_transformer.dart';
+import 'lazy_transformer.dart';
+import 'transform.dart';
+import 'transformer.dart';
+
+/// An [AggregateTransformer] that wraps a non-aggregate [Transformer].
+///
+/// Although barback internally works in terms of [AggregateTransformer]s, most
+/// transformers only work on individual primary inputs in isolation. We want to
+/// allow those transformers to implement the more user-friendly [Transformer]
+/// interface. This class makes that possible.
+class WrappingAggregateTransformer implements AggregateTransformer {
+  /// The wrapped transformer.
+  final Transformer transformer;
+
+  factory WrappingAggregateTransformer(Transformer transformer) {
+    if (transformer is LazyTransformer) {
+      return new _LazyWrappingAggregateTransformer(
+          transformer as LazyTransformer);
+    } else if (transformer is DeclaringTransformer) {
+      return new _DeclaringWrappingAggregateTransformer(
+          transformer as DeclaringTransformer);

[Bob Nystrom, 2014/05/08 20:30:48]

Are the "as" operators needed here? Seems like a bug.

[nweiz, 2014/05/08 21:12:36]

The analyzer complained. I have no idea why, but filing bugs for this sort of
thing in the past has mostly led to heartache.

+    } else {
+      return new WrappingAggregateTransformer._(transformer);
+    }
+  }
+
+  WrappingAggregateTransformer._(this.transformer);
+
+  Future<String> classifyPrimary(AssetId id) {
+    return syncFuture(() => transformer.isPrimary(id))
+        .then((isPrimary) => isPrimary ? id.path : null);
+  }
+
+  Future apply(AggregateTransform aggregateTransform) {
+    return newTransform(aggregateTransform)
+        .then((transform) => transformer.apply(transform));
+  }
+
+  String toString() => transformer.toString();
+}
+
+/// A wrapper for [DeclaringTransformer]s that implements
+/// [DeclaringAggregateTransformer].
+class _DeclaringWrappingAggregateTransformer
+    extends WrappingAggregateTransformer
+    implements DeclaringAggregateTransformer {
+  final DeclaringTransformer _declaring;
+
+  _DeclaringWrappingAggregateTransformer(DeclaringTransformer transformer)
+      : _declaring = transformer,
+        super._(transformer as Transformer);

[Bob Nystrom, 2014/05/08 20:30:48]

Isn't this just an upcast? Why is it needed?

[nweiz, 2014/05/08 21:12:36]

DeclaringTransformer doesn't actually implement Transformer.

+
+  Future declareOutputs(DeclaringAggregateTransform aggregateTransform) {
+    return newDeclaringTransform(aggregateTransform).then((transform) {
+      return (transformer as DeclaringTransformer).declareOutputs(transform);
+    });
+  }
+}
+
+/// A wrapper for [LazyTransformer]s that implements
+/// [LazyAggregateTransformer].
+class _LazyWrappingAggregateTransformer
+    extends _DeclaringWrappingAggregateTransformer
+    implements LazyAggregateTransformer {
+  _LazyWrappingAggregateTransformer(LazyTransformer transformer)
+      : super(transformer);
+}