Fix URI for packages: make them self contained within the domain served by pub-serve

lib/src/barback/dart2js_transformer.dart

 // Copyright (c) 2013, 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.
 
 import 'dart:async';
 import 'dart:convert';
 
 import 'package:analyzer/analyzer.dart';
 import 'package:barback/barback.dart';
 import 'package:collection/collection.dart';
@@ skipping 107 matching lines @@
     var provider = new _BarbackCompilerProvider(_environment, transform,
         generateSourceMaps: _generateSourceMaps);
 
     // Create a "path" to the entrypoint script. The entrypoint may not actually
     // be on disk, but this gives dart2js a root to resolve relative paths
     // against.
     var id = transform.primaryInput.id;
 
     var entrypoint = _environment.graph.packages[id.package].path(id.path);
 
+    // We define the packageRoot in terms of the entrypoint directory, and not
+    // the rootPackage, to ensure that the generated source-maps are valid.
+    // Source-maps contain relative URLs to package sources and these relative
+    // URLs should be self-contained within the paths served by pub-serve.
+    // See #1511 for details.
+    var buildDir = _environment.getSourceDirectoryContaining(id.path);
+    var packageRoot = _environment.rootPackage.path(buildDir, "packages");
+
     // TODO(rnystrom): Should have more sophisticated error-handling here. Need
     // to report compile errors to the user in an easily visible way. Need to
     // make sure paths in errors are mapped to the original source path so they
     // can understand them.
     return dart.compile(
         entrypoint, provider,
         commandLineOptions: _configCommandLineOptions,
         csp: _configBool('csp'),
         checked: _configBool('checked'),
         minify: _configBool(
             'minify', defaultsTo: _settings.mode == BarbackMode.RELEASE),
         verbose: _configBool('verbose'),
         environment: _configEnvironment,
-        packageRoot: _environment.rootPackage.path("packages"),
+        packageRoot: packageRoot,
         analyzeAll: _configBool('analyzeAll'),
         preserveUris: _configBool('preserveUris'),
         suppressWarnings: _configBool('suppressWarnings'),
         suppressHints: _configBool('suppressHints'),
         suppressPackageWarnings: _configBool(
             'suppressPackageWarnings', defaultsTo: true),
         terse: _configBool('terse'),
         includeSourceMapUrls: _generateSourceMaps);
   }
 
@@ skipping 260 matching lines @@
   }
 }
 
 /// An [EventSink] that discards all data. Provided to dart2js when we don't
 /// want an actual output.
 class NullSink<T> implements EventSink<T> {
   void add(T event) {}
   void addError(errorEvent, [StackTrace stackTrace]) {}
   void close() {}
 }