Cache snapshots of (mostly) immutable transformer phases.

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
new file mode 100644
index 0000000000000000000000000000000000000000..5ce8cb0de348f15a88f7cca7fa7b0a506e4b6249
--- /dev/null
+++ b/sdk/lib/_internal/pub_generated/lib/src/barback/transformer_cache.dart
@@ -0,0 +1,75 @@
+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 '../source/cached.dart';
+import '../utils.dart';
+import 'asset_environment.dart';
+import 'transformer_id.dart';
+class TransformerCache {
+  final PackageGraph _graph;
+  Set<TransformerId> _oldTransformers;
+  Set<TransformerId> _newTransformers;
+  String _dir;
+  String get _manifestPath => p.join(_dir, "manifest.txt");
+  TransformerCache.load(PackageGraph graph)
+      : _graph = graph,
+        _dir = p.join(graph.entrypoint.root.dir, ".pub/transformers") {
+    _oldTransformers = _parseManifest();
+  }
+  void clearIfOutdated(Set<String> changedPackages) {
+    var snapshotDependencies = unionAll(_oldTransformers.map((id) {
+      return _graph.transitiveDependencies(
+          id.package).map((package) => package.name).toSet();
+    }));
+    if (!changedPackages.any(snapshotDependencies.contains)) return;
+    deleteEntry(_dir);
+    _oldTransformers = new Set();
+  }
+  String snapshotPath(Set<TransformerId> transformers) {
+    var usesMutableTransformer = transformers.any((id) {
+      var package = _graph.lockFile.packages[id.package];
+      if (package == null) return true;
+      var source = _graph.entrypoint.cache.sources[package.source];
+      return source is! CachedSource;
+    });
+    var path = p.join(_dir, "transformers.snapshot");
+    if (usesMutableTransformer) {
+      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+      log.fine("Cached transformer snapshot is out-of-date, deleting.");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;
+  }
+  void save() {
+    if (_newTransformers == null) {
+      if (_dir != null) deleteEntry(_dir);
+      return;
+    }
+    if (_oldTransformers.containsAll(_newTransformers)) return;
+    ensureDir(_dir);
+    writeTextFile(
+        _manifestPath,
+        "${sdk.version}\n" +
+            ordered(_newTransformers.map((id) => id.serialize())).join(","));
+  }
+  Set<TransformerId> _parseManifest() {
+    if (!fileExists(_manifestPath)) return new Set();
+    var manifest = readTextFile(_manifestPath).split("\n");
+    if (manifest.removeAt(0) != sdk.version.toString()) {
+      deleteEntry(_dir);
+      return new Set();
+    }
+    return manifest.single.split(
+        ",").map((id) => new TransformerId.parse(id, null)).toSet();
+  }
+}