Remove barback from the repo.

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

-// 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 barback.transformer.transformer;
-
-import 'dart:async';
-
-import '../asset/asset_id.dart';
-import '../utils.dart';
-import 'transform.dart';
-
-/// A [Transformer] represents a processor that takes in one or more input
-/// assets and uses them to generate one or more output assets.
-///
-/// Dart2js, a SASS->CSS processor, a CSS spriter, and a tool to concatenate
-/// files are all examples of transformers. To define your own transformation
-/// step, extend (or implement) this class.
-///
-/// If possible, transformers should implement [DeclaringTransformer] as well to
-/// help barback optimize the package graph.
-abstract class Transformer {
-  /// Override this to return a space-separated list of file extensions that are
-  /// allowed for the primary inputs to this transformer.
-  ///
-  /// Each extension must begin with a leading `.`.
-  ///
-  /// If you don't override [isPrimary] yourself, it defaults to allowing any
-  /// asset whose extension matches one of the ones returned by this. If you
-  /// don't override [isPrimary] *or* this, it allows all files.
-  String get allowedExtensions => null;
-
-  Transformer() {
-    if (allowedExtensions == null) return;
-
-    var invalidExtensions = allowedExtensions.split(" ")
-        .where((extension) => !extension.startsWith("."))
-        .map((extension) => '"$extension"');
-    if (invalidExtensions.isEmpty) return;
-
-    throw new FormatException('Each extension in $this.allowedExtensions '
-        'must begin with a ".", but ${toSentence(invalidExtensions)} '
-        '${pluralize("doesn't", invalidExtensions.length, plural: "don't")}.');
-  }
-
-  /// Returns `true` if [id] can be a primary input for this transformer.
-  ///
-  /// While a transformer can read from multiple input files, one must be the
-  /// "primary" input. This asset determines whether the transformation should
-  /// be run at all. If the primary input is removed, the transformer will no
-  /// longer be run.
-  ///
-  /// A concrete example is dart2js. When you run dart2js, it will traverse
-  /// all of the imports in your Dart source files and use the contents of all
-  /// of those to generate the final JS. However you still run dart2js "on" a
-  /// single file: the entrypoint Dart file that has your `main()` method.
-  /// This entrypoint file would be the primary input.
-  ///
-  /// If this is not overridden, defaults to allow any asset whose extension
-  /// matches one of the ones returned by [allowedExtensions]. If *that* is
-  /// not overridden, allows all assets.
-  ///
-  /// This may return a `Future<bool>` or, if it's entirely synchronous, a
-  /// `bool`.
-  isPrimary(AssetId id) {
-    // Allow all files if [primaryExtensions] is not overridden.
-    if (allowedExtensions == null) return true;
-
-    for (var extension in allowedExtensions.split(" ")) {
-      if (id.path.endsWith(extension)) return true;
-    }
-
-    return false;
-  }
-
-  /// Run this transformer on the primary input specified by [transform].
-  ///
-  /// The [transform] is used by the [Transformer] for two purposes (in
-  /// addition to accessing the primary input). It can call `getInput()` to
-  /// request additional input assets. It also calls `addOutput()` to provide
-  /// generated assets back to the system. Either can be called multiple times,
-  /// in any order.
-  ///
-  /// In other words, a Transformer's job is to find all inputs for a
-  /// transform, starting at the primary input, then generate all output assets
-  /// and yield them back to the transform.
-  ///
-  /// If this does asynchronous work, it should return a [Future] that completes
-  /// once it's finished.
-  apply(Transform transform);
-
-  String toString() => runtimeType.toString().replaceAll("Transformer", "");
-}