Support Dart core libraries in source maps.

sdk/lib/_internal/pub/lib/src/barback/dart2js_transformer.dart

Index: sdk/lib/_internal/pub/lib/src/barback/dart2js_transformer.dart
diff --git a/sdk/lib/_internal/pub/lib/src/barback/dart2js_transformer.dart b/sdk/lib/_internal/pub/lib/src/barback/dart2js_transformer.dart
index de74c749f30fcd89097d81de74c343cdcfc17c1b..83ad27cfffbf79b9c826ec8672857fb6eb4f19a9 100644
--- a/sdk/lib/_internal/pub/lib/src/barback/dart2js_transformer.dart
+++ b/sdk/lib/_internal/pub/lib/src/barback/dart2js_transformer.dart
@@ -185,8 +185,11 @@ class Dart2JSTransformer extends Transformer implements LazyTransformer {
 /// difference is that it uses barback's logging code and, more importantly, it
 /// handles missing source files more gracefully.
 class _BarbackCompilerProvider implements dart.CompilerProvider {
+  Uri get libraryRoot => Uri.parse("${path.toUri(_libraryRootPath)}/");
+
   final BuildEnvironment _environment;
   final Transform _transform;
+  String _libraryRootPath;
 
   /// The map of previously loaded files.
   ///
@@ -222,7 +225,30 @@ class _BarbackCompilerProvider implements dart.CompilerProvider {
       compiler.Diagnostic.VERBOSE_INFO.ordinal;
 
   _BarbackCompilerProvider(this._environment, this._transform,
-      {this.generateSourceMaps: true});
+      {this.generateSourceMaps: true}) {
+    // Dart2js outputs source maps that reference the Dart SDK sources. For
+    // that to work, those sources need to be inside the build environment. We
+    // do that by placing them in a special "$sdk" pseudo-package. In order for
+    // dart2js to generate the right URLs to point to that package, we give it
+    // a library root that corresponds to where that package can be found
+    // relative to the public build directory containing that entrypoint.
+    //
+    // For example, say the package being compiled is "/dev/myapp", the
+    // entrypoint is "web/sub/foo/bar.dart", and the build directory is
+    // "web/sub". This means the SDK sources will be (conceptually) at:
+    //
+    //     /dev/myapp/web/sub/packages/$sdk/lib/
+    //
+    // This implies that the asset path for a file in the SDK is:
+    //
+    //     $sdk|lib/lib/...
+    //
+    // TODO(rnystrom): Fix this if $17751 is fixed.

[nweiz, 2014/03/24 23:17:14]

"$" -> "#"

[Bob Nystrom, 2014/03/25 00:49:27]

Done.

+    var buildDir = _environment.getBuildDirectoryContaining(
+        _transform.primaryInput.id.path);
+    _libraryRootPath = path.join(_environment.rootPackage.dir,
+        buildDir, "packages", r"$sdk");
+  }
 
   /// A [CompilerInputProvider] for dart2js.
   Future<String> provideInput(Uri resourceUri) {
@@ -329,15 +355,13 @@ class _BarbackCompilerProvider implements dart.CompilerProvider {
   }
 
   Future<String> _readResource(Uri url) {
-    // See if the path is within a package. If so, use Barback so we can use
-    // generated Dart assets.
-
+    // Find the corresponding asset in barback.
     var id = _sourceUrlToId(url);
     if (id != null) return _transform.readInputAsString(id);
 
-    // If we get here, the path doesn't appear to be in a package, so we'll
-    // skip Barback and just hit the file system. This will occur at the very
-    // least for dart2js's implementations of the core libraries.
+    // If we get here, the path doesn't appear to be in any package, so we'll
+    // skip Barback and just hit the file system. This will only occur for
+    // absolute file paths in imports that don't touch a package.
     var sourcePath = path.fromUri(url);
     return Chain.track(new File(sourcePath).readAsString());
   }