Gracefully handle transformers rejecting their configuration.

R=rnystrom@google.com
BUG=16008

Review URL: https://codereview.chromium.org//352923002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@37752 260f80e4-7a28-3924-810f-c04153c831b5

lib/src/barback/transformer_isolate.dart

@@ -9,9 +9,12 @@ import 'dart:convert';
 import 'dart:isolate';
 
 import 'package:barback/barback.dart';
+import 'package:source_maps/source_maps.dart';
+import 'package:stack_trace/stack_trace.dart';
 
 import '../../../asset/dart/serialize.dart';
 import '../barback.dart';
+import '../exceptions.dart';
 import '../dart.dart' as dart;
 import '../log.dart' as log;
 import '../utils.dart';
@@ -112,6 +115,18 @@ class TransformerIsolate {
           .toSet();
       log.fine("Transformers from $config: $transformers");
       return transformers;
+    }).catchError((error, stackTrace) {
+      throw new TransformerLoadError(error, config.span);
     });
   }
 }
+
+/// An error thrown when a transformer fails to load.
+class TransformerLoadError extends SpanException implements WrappedException {
+  final CrossIsolateException innerError;
+  Chain get innerChain => innerError.stackTrace;
+
+  TransformerLoadError(CrossIsolateException error, Span span)
+      : innerError = error,
+        super("Error loading transformer: ${error.message}", span);
+}

test/transformer/a_transformer_rejects_its_config_test.dart

+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS d.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_tests;
+
+import 'package:scheduled_test/scheduled_test.dart';
+
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+import '../serve/utils.dart';
+
+const REJECT_CONFIG_TRANSFORMER = """
+import 'dart:async';
+
+import 'package:barback/barback.dart';
+
+class RejectConfigTransformer extends Transformer {
+  RejectConfigTransformer.asPlugin(BarbackSettings settings) {
+    throw "I hate these settings!";
+  }
+
+  Future<bool> isPrimary(_) => new Future.value(true);
+  Future apply(Transform transform) {}
+}
+""";
+
+main() {
+  initConfig();
+
+  withBarbackVersions("any", () {
+     integration("a transformer can reject is configuration", () {
+       d.dir(appPath, [
+         d.pubspec({
+           "name": "myapp",
+           "transformers": [{"myapp/src/transformer": {'foo': 'bar'}}]
+         }),
+         d.dir("lib", [d.dir("src", [
+           d.file("transformer.dart", REJECT_CONFIG_TRANSFORMER)
+         ])])
+       ]).create();
+
+       createLockFile('myapp', pkg: ['barback']);
+
+       var pub = startPubServe();
+       pub.stderr.expect(endsWith('Error loading transformer: I hate these '
+           'settings!'));
+       pub.shouldExit(1);
+     });
+  });
+}
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