Revert "Revert "Use native async/await support in pub.""

sdk/lib/_internal/pub_generated/lib/src/barback/transformer_cache.dart

Index: sdk/lib/_internal/pub_generated/lib/src/barback/transformer_cache.dart
diff --git a/sdk/lib/_internal/pub_generated/lib/src/barback/transformer_cache.dart b/sdk/lib/_internal/pub_generated/lib/src/barback/transformer_cache.dart
deleted file mode 100644
index 7e8a61d90c76b2c53a97bc1bd1c39600fd89d147..0000000000000000000000000000000000000000
--- a/sdk/lib/_internal/pub_generated/lib/src/barback/transformer_cache.dart
+++ /dev/null
@@ -1,144 +0,0 @@
-// 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 pub.barback.transformer_cache;
-
-import 'package:path/path.dart' as p;
-
-import '../io.dart';
-import '../log.dart' as log;
-import '../package_graph.dart';
-import '../sdk.dart' as sdk;
-import '../utils.dart';
-import 'transformer_id.dart';
-
-/// A cache for managing a snapshot of the first "stage" of transformers to
-/// load.
-///
-/// This uses the [_stageTransformers] notion of a stage. Transformers are
-/// divided into stages for loading based on which transformers are needed to
-/// load one another. For example, if a transformer T1 produces a file that's
-/// imported by another transformer T2, T2 must be put in a stage after T1.
-///
-/// We only cache the first stage because it's the only stage whose contents are
-/// independent of any configuration. Since most transformers don't import the
-/// output of other transformers, many packages will only have one stage.
-class TransformerCache {
-  final PackageGraph _graph;
-
-  /// The set of transformer ids that were previously cached.
-  ///
-  /// If there was no previous cache, this will be empty.
-  Set<TransformerId> _oldTransformers;
-
-  /// The set of transformer ids that are newly cached or re-used from the
-  /// previous cache.
-  Set<TransformerId> _newTransformers;
-
-  /// The directory in which transformers are cached.
-  ///
-  /// This may be `null` if there's no physical entrypoint directory.
-  String _dir;
-
-  /// The directory of the manifest listing which transformers were cached.
-  String get _manifestPath => p.join(_dir, "manifest.txt");
-
-  /// Loads the transformer cache for [environment].
-  ///
-  /// This may modify the cache.
-  TransformerCache.load(PackageGraph graph)
-      : _graph = graph,
-        _dir = graph.entrypoint.root.path(".pub/transformers") {
-    _oldTransformers = _parseManifest();
-  }
-
-  /// Clear the cache if it depends on any package in [changedPackages].
-  void clearIfOutdated(Set<String> changedPackages) {
-    var snapshotDependencies = unionAll(_oldTransformers.map((id) {
-      // If the transformer cache contains transformers we don't know about,
-      // that's fine; we just won't load them.
-      if (!_graph.packages.containsKey(id.package)) return new Set();
-
-      return _graph.transitiveDependencies(
-          id.package).map((package) => package.name).toSet();
-    }));
-
-    // If none of the snapshot's dependencies have changed, then we can reuse
-    // it.
-    if (!overlaps(changedPackages, snapshotDependencies)) return;
-
-    // Otherwise, delete it.
-    deleteEntry(_dir);
-    _oldTransformers = new Set();
-  }
-
-  /// Returns the path for the transformer snapshot for [transformers], or
-  /// `null` if the transformers shouldn't be cached.
-  ///
-  /// There may or may not exist a file at the returned path. If one does exist,
-  /// it can safely be used to load the stage. Otherwise, a snapshot of the
-  /// stage should be written there.
-  String snapshotPath(Set<TransformerId> transformers) {
-    var path = p.join(_dir, "transformers.snapshot");
-    if (_newTransformers != null) return path;
-
-    if (transformers.any((id) => _graph.isPackageMutable(id.package))) {
-      log.fine("Not caching mutable transformers.");
-      deleteEntry(_dir);
-      return null;
-    }
-
-    if (!_oldTransformers.containsAll(transformers)) {
-      log.fine("Cached transformer snapshot is out-of-date, deleting.");
-      deleteEntry(path);
-    } else {
-      log.fine("Using cached transformer snapshot.");
-    }
-
-    _newTransformers = transformers;
-    return path;
-  }
-
-  /// Saves the manifest to the transformer cache.
-  void save() {
-    // If we didn't write any snapshots, there's no need to write a manifest.
-    if (_newTransformers == null) {
-      if (_dir != null) deleteEntry(_dir);
-      return;
-    }
-
-    // We only need to rewrite the manifest if we created a new snapshot.
-    if (_oldTransformers.containsAll(_newTransformers)) return;
-
-    ensureDir(_dir);
-    writeTextFile(
-        _manifestPath,
-        "${sdk.version}\n" +
-            ordered(_newTransformers.map((id) => id.serialize())).join(","));
-  }
-
-  /// Parses the cache manifest and returns the set of previously-cached
-  /// transformers.
-  ///
-  /// If the manifest indicates that the SDK version is out-of-date, this
-  /// deletes the existing cache. Otherwise,
-  Set<TransformerId> _parseManifest() {
-    if (!fileExists(_manifestPath)) return new Set();
-
-    var manifest = readTextFile(_manifestPath).split("\n");
-
-    // The first line of the manifest is the SDK version. We want to clear out
-    // the snapshots even if they're VM-compatible, since pub's transformer
-    // isolate scaffolding may have changed.
-    if (manifest.removeAt(0) != sdk.version.toString()) {
-      deleteEntry(_dir);
-      return new Set();
-    }
-
-    /// The second line of the manifest is a list of transformer ids used to
-    /// create the existing snapshot.
-    return manifest.single.split(
-        ",").map((id) => new TransformerId.parse(id, null)).toSet();
-  }
-}