Refactoring resolvers to make them able to be run in parallel.

pkg/code_transformers/lib/src/resolver_transformer.dart

-// 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 code_transformers.src.resolver_transformer;
-
-import 'dart:async';
-import 'package:barback/barback.dart';
-
-import 'resolver.dart';
-import 'resolver_impl.dart';
-
-/// Filter for whether the specified asset is an entry point to the Dart
-/// application.
-typedef EntryPointFilter(Asset input);
-
-/// Transformer which maintains up-to-date resolved ASTs for the specified
-/// code entry points.
-///
-/// This can used by transformers dependent on resolved ASTs which can reference
-/// this transformer to get the resolver needed.
-///
-/// This transformer must be in a phase before any dependent transformers. The
-/// resolve AST is automatically updated any time any dependent assets are
-/// changed.
-///
-/// This will only resolve the AST for code beginning from assets which are
-/// accepted by [entryPointFilter].
-///
-/// If multiple transformers rely on a resolved AST they should (ideally) share
-/// the same ResolverTransformer to avoid re-parsing the AST.
-class ResolverTransformer extends Transformer {
-  final Map<AssetId, Resolver> _resolvers = {};
-  final EntryPointFilter entryPointFilter;
-  final String dartSdkDirectory;
-
-  ResolverTransformer(this.dartSdkDirectory, this.entryPointFilter);
-
-  Future<bool> isPrimary(Asset input) =>
-      new Future.value(entryPointFilter(input));
-
-  /// Updates the resolved AST for the primary input of the transform.
-  Future apply(Transform transform) {
-    var resolver = getResolver(transform.primaryInput.id);
-
-    return resolver.updateSources(transform).then((_) {
-      transform.addOutput(transform.primaryInput);
-      return null;
-    });
-  }
-
-  /// Get a resolver for the AST starting from [id].
-  Resolver getResolver(AssetId id) =>
-      _resolvers.putIfAbsent(id, () => new ResolverImpl(id, dartSdkDirectory));
-}