Load parallel transformers in the same isolate.

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

Index: sdk/lib/_internal/pub/lib/src/barback/load_transformers.dart
diff --git a/sdk/lib/_internal/pub/lib/src/barback/load_transformers.dart b/sdk/lib/_internal/pub/lib/src/barback/load_transformers.dart
index 8b00d09816c61821282bcec57a07bff4bd0a4738..6315f5655770680642656117fc1e9dddbaf2e1b4 100644
--- a/sdk/lib/_internal/pub/lib/src/barback/load_transformers.dart
+++ b/sdk/lib/_internal/pub/lib/src/barback/load_transformers.dart
@@ -17,56 +17,71 @@ import 'asset_environment.dart';
 import 'foreign_transformer.dart';
 import 'barback_server.dart';
 
-/// Load and return all transformers and groups from the library identified by
-/// [id].
-Future<Set> loadTransformers(AssetEnvironment environment,
-    BarbackServer transformerServer, TransformerId id) {
-  return id.getAssetId(environment.barback).then((assetId) {
-    var path = assetId.path.replaceFirst('lib/', '');
-    // TODO(nweiz): load from a "package:" URI when issue 12474 is fixed.
-
+/// Load and return all transformers and groups from the libraries identified by
+/// [ids].
+///
+/// Returns a map from transformer ids to sets of transformer-like objects
+/// identified by these ids (these may be [Transformer]s,
+/// [AggregateTransformer]s, and/or [TransformerGroup]s).
+Future<Map<TransformerId, Set>> loadTransformers(AssetEnvironment environment,
+    BarbackServer transformerServer, List<TransformerId> ids) {
+  return listToMapAsync(ids, (id) => id, (id) {
+    return id.getAssetId(environment.barback);
+  }).then((idsToAssetIds) {
     var baseUrl = transformerServer.url;
-    var uri = baseUrl.resolve('packages/${id.package}/$path');
-    var code = """
-        import 'dart:isolate';
+    var idsToUrls = mapMap(idsToAssetIds, (id, _) => id, (id, assetId) {
+      var path = assetId.path.replaceFirst('lib/', '');
+      // TODO(nweiz): load from a "package:" URI when issue 12474 is fixed.
+      return baseUrl.resolve('packages/${id.package}/$path');
+    });
 
-        import '$uri';
+    var code = new StringBuffer();
+    code.writeln("import 'dart:isolate';");
 
-        import r'$baseUrl/packages/\$pub/transformer_isolate.dart';
+    for (var url in idsToUrls.values) {
+      code.writeln("import '$url';");
+    }
 
-        void main(_, SendPort replyTo) => loadTransformers(replyTo);
-        """;
-    log.fine("Loading transformers from $assetId");
+    code.writeln("import r'$baseUrl/packages/\$pub/transformer_isolate.dart';");
+    code.writeln(
+        "void main(_, SendPort replyTo) => loadTransformers(replyTo);");
+
+    log.fine("Loading transformers from $ids");
 
     var port = new ReceivePort();
-    return dart.runInIsolate(code, port.sendPort)
+    return dart.runInIsolate(code.toString(), port.sendPort)
         .then((_) => port.first)
         .then((sendPort) {
-      return call(sendPort, {
-        'library': uri.toString(),
-        'mode': environment.mode.name,
-        // TODO(nweiz): support non-JSON-encodable configuration maps.
-        'configuration': JSON.encode(id.configuration)
-      }).then((transformers) {
-        transformers = transformers.map(
-            (transformer) => deserializeTransformerLike(transformer, id))
-            .toSet();
-        log.fine("Transformers from $assetId: $transformers");
-        return transformers;
+      return mapMapAsync(idsToAssetIds, (id, _) => id, (id, assetId) {
+        return call(sendPort, {
+          'library': idsToUrls[id].toString(),
+          'mode': environment.mode.name,
+          // TODO(nweiz): support non-JSON-encodable configuration maps.
+          'configuration': JSON.encode(id.configuration)
+        }).then((transformers) {
+          transformers = transformers.map(
+              (transformer) => deserializeTransformerLike(transformer, id))
+              .toSet();
+          log.fine("Transformers from $assetId: $transformers");
+          return transformers;
+        });
       });
     }).catchError((error, stackTrace) {
       if (error is! CrossIsolateException) throw error;
       if (error.type != 'IsolateSpawnException') throw error;
+
       // TODO(nweiz): don't parse this as a string once issues 12617 and 12689
       // are fixed.
-      if (!error.message.split('\n')[1].startsWith("Failure getting $uri:")) {
-        throw error;
-      }
+      var firstErrorLine = error.message.split('\n')[1];
+      var missingTransformer = idsToUrls.keys.firstWhere((id) =>
+              firstErrorLine.startsWith("Failure getting ${idsToUrls[id]}:"),
+          orElse: () => throw error);
+      var packageUri = idToPackageUri(idsToAssetIds[missingTransformer]);
 
       // If there was an IsolateSpawnException and the import that actually
       // failed was the one we were loading transformers from, throw an
       // application exception with a more user-friendly message.
-      fail('Transformer library "package:${id.package}/$path" not found.',
+      fail('Transformer library "$packageUri" not found.',
           error, stackTrace);
     });
   });