Cache snapshots of (mostly) immutable transformer phases.

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

Index: sdk/lib/_internal/pub/lib/src/barback/load_all_transformers.dart
diff --git a/sdk/lib/_internal/pub/lib/src/barback/load_all_transformers.dart b/sdk/lib/_internal/pub/lib/src/barback/load_all_transformers.dart
index 18bf853d4262d8f5e6644cfd32df034ab2f914b1..51b8dbf43b3a030b90244a9bc421160e08f6832d 100644
--- a/sdk/lib/_internal/pub/lib/src/barback/load_all_transformers.dart
+++ b/sdk/lib/_internal/pub/lib/src/barback/load_all_transformers.dart
@@ -6,19 +6,15 @@ library pub.load_all_transformers;
 
 import 'dart:async';
 
-import 'package:barback/barback.dart';
-
 import '../log.dart' as log;
 import '../package_graph.dart';
 import '../utils.dart';
 import 'asset_environment.dart';
 import 'barback_server.dart';
-import 'dart2js_transformer.dart';
-import 'excluding_transformer.dart';
 import 'rewrite_import_transformer.dart';
-import 'transformer_config.dart';
+import 'transformer_cache.dart';
 import 'transformer_id.dart';
-import 'transformer_isolate.dart';
+import 'transformer_loader.dart';
 import 'transformers_needed_by_transformers.dart';
 
 /// Loads all transformers depended on by packages in [environment].
@@ -50,7 +46,7 @@ Future loadAllTransformers(AssetEnvironment environment,
   var packagesThatUseTransformers =
       _packagesThatUseTransformers(environment.graph);
 
-  var loader = new _TransformerLoader(environment, transformerServer);
+  var loader = new TransformerLoader(environment, transformerServer);
 
   // Add a rewrite transformer for each package, so that we can resolve
   // "package:" imports while loading transformers.
@@ -60,10 +56,17 @@ Future loadAllTransformers(AssetEnvironment environment,
   }
   environment.barback.updateTransformers(r'$pub', [[rewrite]]);
 
+  var cache = new TransformerCache.load(environment);
+
+  var i = 0;
   return Future.forEach(phasedTransformers, (phase) {
+    i++;
+
+    var snapshotPath = cache.snapshotPath(phase, i);
+
     /// Load all the transformers in [phase], then add them to the appropriate
     /// locations in the transformer graphs of the packages that use them.
-    return loader.load(phase).then((_) {
+    return loader.load(phase, snapshot: snapshotPath).then((_) {
       // Only update packages that use transformers in [phase].
       var packagesToUpdate = unionAll(phase.map((id) =>
           packagesThatUseTransformers[id]));
@@ -80,6 +83,8 @@ Future loadAllTransformers(AssetEnvironment environment,
       }));
     });
   }).then((_) {
+    cache.save();
+
     /// Reset the transformers for each package to get rid of [rewrite], which
     /// is no longer needed.
     return Future.wait(environment.graph.packages.values.map((package) {
@@ -146,111 +151,3 @@ Map<TransformerId, Set<String>> _packagesThatUseTransformers(
   }
   return results;
 }
-
-/// A class that loads transformers defined in specific files.
-class _TransformerLoader {
-  final AssetEnvironment _environment;
-
-  final BarbackServer _transformerServer;
-
-  final _isolates = new Map<TransformerId, TransformerIsolate>();
-
-  final _transformers = new Map<TransformerConfig, Set<Transformer>>();
-
-  /// The packages that use each transformer id.
-  ///
-  /// Used for error reporting.
-  final _transformerUsers = new Map<TransformerId, Set<String>>();
-
-  _TransformerLoader(this._environment, this._transformerServer) {
-    for (var package in _environment.graph.packages.values) {
-      for (var config in unionAll(package.pubspec.transformers)) {
-        _transformerUsers.putIfAbsent(config.id, () => new Set<String>())
-            .add(package.name);
-      }
-    }
-  }
-
-  /// Loads a transformer plugin isolate that imports the transformer libraries
-  /// indicated by [ids].
-  ///
-  /// Once the returned future completes, transformer instances from this
-  /// isolate can be created using [transformersFor] or [transformersForPhase].
-  ///
-  /// This will skip any ids that have already been loaded.
-  Future load(Iterable<TransformerId> ids) {
-    ids = ids.where((id) => !_isolates.containsKey(id)).toList();
-    if (ids.isEmpty) return new Future.value();
-
-    return log.progress("Loading ${toSentence(ids)} transformers", () {
-      return TransformerIsolate.spawn(_environment, _transformerServer, ids);
-    }).then((isolate) {
-      for (var id in ids) {
-        _isolates[id] = isolate;
-      }
-    });
-  }
-
-  /// Instantiates and returns all transformers in the library indicated by
-  /// [config] with the given configuration.
-  ///
-  /// If this is called before the library has been loaded into an isolate via
-  /// [load], it will return an empty set.
-  Future<Set<Transformer>> transformersFor(TransformerConfig config) {
-    if (_transformers.containsKey(config)) {
-      return new Future.value(_transformers[config]);
-    } else if (_isolates.containsKey(config.id)) {
-      return _isolates[config.id].create(config).then((transformers) {
-        if (transformers.isNotEmpty) {
-          _transformers[config] = transformers;
-          return transformers;
-        }
-
-        var message = "No transformers";
-        if (config.configuration.isNotEmpty) {
-          message += " that accept configuration";
-        }
-
-        var location;
-        if (config.id.path == null) {
-          location = 'package:${config.id.package}/transformer.dart or '
-            'package:${config.id.package}/${config.id.package}.dart';
-        } else {
-          location = 'package:$config.dart';
-        }
-
-        var users = toSentence(ordered(_transformerUsers[config.id]));
-        fail("$message were defined in $location,\n"
-            "required by $users.");
-      });
-    } else if (config.id.package != '\$dart2js') {
-      return new Future.value(new Set());
-    }
-
-    var transformer;
-    try {
-      transformer = new Dart2JSTransformer.withSettings(_environment,
-          new BarbackSettings(config.configuration, _environment.mode));
-    } on FormatException catch (error, stackTrace) {
-      fail(error.message, error, stackTrace);
-    }
-
-    // Handle any exclusions.
-    _transformers[config] = new Set.from(
-        [ExcludingTransformer.wrap(transformer, config)]);
-    return new Future.value(_transformers[config]);
-  }
-
-  /// Loads all transformers defined in each phase of [phases].
-  ///
-  /// If any library hasn't yet been loaded via [load], it will be ignored.
-  Future<List<Set<Transformer>>> transformersForPhases(
-      Iterable<Set<TransformerConfig>> phases) {
-    return Future.wait(phases.map((phase) {
-      return waitAndPrintErrors(phase.map(transformersFor)).then(unionAll);
-    })).then((phases) {
-      // Return a growable list so that callers can add phases.
-      return phases.toList();
-    });
-  }
-}