Load instances of the same transformer from the same isolate.

sdk/lib/_internal/pub/lib/src/barback/transformer_id.dart

Index: sdk/lib/_internal/pub/lib/src/barback/transformer_id.dart
diff --git a/sdk/lib/_internal/pub/lib/src/barback/transformer_id.dart b/sdk/lib/_internal/pub/lib/src/barback/transformer_id.dart
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index 0000000000000000000000000000000000000000..71bdd9c8cd4aef917b353110c21e054d708d1086
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+++ b/sdk/lib/_internal/pub/lib/src/barback/transformer_id.dart
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+// 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 pub.barback.transformer_id;
+
+import 'dart:async';
+
+import 'package:barback/barback.dart';
+import 'package:path/path.dart' as p;
+
+import '../io.dart';
+import '../utils.dart';
+
+/// A list of the names of all built-in transformers that pub exposes.
+const _BUILT_IN_TRANSFORMERS = const ['\$dart2js'];
+
+/// An identifier that indicates the library that contains a transformer.
+///
+/// It's possible that the library identified by [this] defines multiple
+/// transformers. If so, they're all always loaded in the same phase.
+class TransformerId {
+  /// The package containing the library where the transformer is defined.
+  final String package;
+
+  /// The `/`-separated path to the library that contains this transformer.
+  ///
+  /// This is relative to the `lib/` directory in [package], and doesn't end in
+  /// `.dart`.
+  ///
+  /// This can be null; if so, it indicates that the transformer(s) should be
+  /// loaded from `lib/transformer.dart` if that exists, and `lib/$package.dart`
+  /// otherwise.
+  final String path;
+
+  /// Whether this ID points to a built-in transformer exposed by pub.
+  bool get isBuiltInTransformer => package.startsWith('\$');
+
+  /// Parses a transformer identifier.
+  ///
+  /// A transformer identifier is a string of the form "package_name" or
+  /// "package_name/path/to/library". It does not have a trailing extension. If
+  /// it just has a package name, it expands to lib/transformer.dart if that
+  /// exists, or lib/${package}.dart otherwise. Otherwise, it expands to
+  /// lib/${path}.dart. In either case it's located in the given package.
+  factory TransformerId.parse(String identifier) {
+    if (identifier.isEmpty) {
+      throw new FormatException('Invalid library identifier: "".');
+    }
+
+    var parts = split1(identifier, "/");
+    if (parts.length == 1) {
+      return new TransformerId(parts.single, null);
+    }
+
+    return new TransformerId(parts.first, parts.last);
+  }
+
+  TransformerId(this.package, this.path) {
+    if (!package.startsWith('\$')) return;
+    if (_BUILT_IN_TRANSFORMERS.contains(package)) return;
+    throw new FormatException('Unsupported built-in transformer $package.');
+  }
+
+  bool operator==(other) =>
+      other is TransformerId && other.package == package && other.path == path;
+
+  int get hashCode => package.hashCode ^ path.hashCode;
+
+  String toString() => path == null ? package : '$package/$path';
+
+  /// Returns the asset id for the library identified by this transformer id.
+  ///
+  /// If `path` is null, this will determine which library to load. Unlike
+  /// [getAssetId], this doesn't take generated assets into account; it's used
+  /// to determine transformers' dependencies, which requires looking at files
+  /// on disk.
+  Future<AssetId> getAssetId(Barback barback) {
+    if (path != null) {
+      return new Future.value(new AssetId(package, 'lib/$path.dart'));
+    }
+
+    var transformerAsset = new AssetId(package, 'lib/transformer.dart');
+    return barback.getAssetById(transformerAsset).then((_) => transformerAsset)
+        .catchError((e) => new AssetId(package, 'lib/$package.dart'),
+            test: (e) => e is AssetNotFoundException);
+  }
+
+  /// Returns the path to the library identified by this transformer within
+  /// [packageDir], which should be the directory of [package].
+  ///
+  /// If `path` is null, this will determine which library to load.
+  String getFullPath(String packageDir) {
+    if (path != null) return p.join(packageDir, 'lib', p.fromUri('$path.dart'));
+
+    var transformerPath = p.join(packageDir, 'lib', 'transformer.dart');
+    if (fileExists(transformerPath)) return transformerPath;
+    return p.join(packageDir, 'lib', '$package.dart');
+  }
+}