Add observatory_pub_packages snapshot to third_party

observatory_pub_packages/barback/src/transformer/transform.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 barback.transformer.transform;
+
+import 'dart:async';
+import 'dart:convert';
+
+import '../asset/asset.dart';
+import '../asset/asset_id.dart';
+import '../errors.dart';
+import 'aggregate_transform.dart';
+import 'transform_logger.dart';
+
+/// Creates a new [Transform] wrapping an [AggregateTransform].
+///
+/// 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 which takes the more user-friendly [Transform] object. This method
+/// wraps the more general [AggregateTransform] to return a [Transform] instead.
+Future<Transform> newTransform(AggregateTransform aggregate) {
+  // A wrapped [Transformer] will assign each primary input a unique transform
+  // key, so we can safely get the first asset emitted. We don't want to wait
+  // for the stream to close, since that requires barback to prove that no more
+  // new assets will be generated.
+  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.
+///
+/// This ephemeral object exists only during an actual transform application to
+/// facilitate communication between the [Transformer] and the code hosting
+/// the transformation. It lets the [Transformer] access inputs and generate
+/// outputs.
+class Transform {
+  /// The underlying aggregate transform.
+  final AggregateTransform _aggregate;
+
+  /// Gets the primary input asset.
+  ///
+  /// While a transformation can use multiple input assets, one must be a
+  /// special "primary" asset. This will be the "entrypoint" or "main" input
+  /// file for a transformation.
+  ///
+  /// 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.
+  final Asset primaryInput;
+
+  /// A logger so that the [Transformer] can report build details.
+  TransformLogger get logger => _aggregate.logger;
+
+  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) => _aggregate.getInput(id);
+
+  /// A convenience method to the contents of the input with [id] as a string.
+  ///
+  /// This is equivalent to calling [getInput] followed by [Asset.readAsString].
+  ///
+  /// If the asset was created from a [String] the original string is always
+  /// returned and [encoding] is ignored. Otherwise, the binary data of the
+  /// 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}) =>
+      _aggregate.readInputAsString(id, encoding: encoding);
+
+  /// A convenience method to the contents of the input with [id].
+  ///
+  /// This is equivalent to calling [getInput] followed by [Asset.read].
+  ///
+  /// 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) => _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) => _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) => _aggregate.addOutput(output);
+
+  /// 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);
+}