Don't include source maps in release mode.

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 176d4908d15f398fa0a80618d5b1ba486f967482..8e000571b53ab47e6ecbce27b9b2e5ed55293fb4 100644
--- a/sdk/lib/_internal/pub/lib/src/barback/dart2js_transformer.dart
+++ b/sdk/lib/_internal/pub/lib/src/barback/dart2js_transformer.dart
@@ -93,7 +93,8 @@ class Dart2JSTransformer extends Transformer implements LazyTransformer {
           return null;
         }
 
-        var provider = new _BarbackCompilerProvider(_environment, transform);
+        var provider = new _BarbackCompilerProvider(_environment, transform,
+            generateSourceMaps: _settings.mode != BarbackMode.RELEASE);

[nweiz, 2014/03/11 20:10:30]

It might be nice to add a "sourceMaps" configuration flag so this can be
configured independently from the mode (or a TODO to do so).

[Bob Nystrom, 2014/03/11 20:43:31]

I'm a little worried that we have too many flags right now, so I'm not inclined
to add another unless we get users specifically asking for it. Since source maps
are strictly a debugging tool, I think it would be weird to configure them in
your pubspec. At the same time, I think using the mode here is a good fit.

 
         // Create a "path" to the entrypoint script. The entrypoint may not
         // actually be on disk, but this gives dart2js a root to resolve
@@ -122,7 +123,9 @@ class Dart2JSTransformer extends Transformer implements LazyTransformer {
             suppressHints: _configBool('suppressHints'),
             suppressPackageWarnings: _configBool(
                 'suppressPackageWarnings', defaultsTo: true),
-            terse: _configBool('terse'))).then((_) {
+            terse: _configBool('terse'),
+            includeSourceMapUrls: _settings.mode != BarbackMode.RELEASE))
+            .then((_) {
           stopwatch.stop();
           transform.logger.info("Took ${stopwatch.elapsed} to compile $id.");
         });
@@ -211,6 +214,8 @@ class _BarbackCompilerProvider implements dart.CompilerProvider {
   /// errors.
   var _isAborting = false;
 
+  final bool generateSourceMaps;
+
   compiler.Diagnostic _lastKind = null;
 
   static final int _FATAL =
@@ -220,7 +225,8 @@ class _BarbackCompilerProvider implements dart.CompilerProvider {
       compiler.Diagnostic.INFO.ordinal |
       compiler.Diagnostic.VERBOSE_INFO.ordinal;
 
-  _BarbackCompilerProvider(this._environment, this._transform);
+  _BarbackCompilerProvider(this._environment, this._transform,
+      {this.generateSourceMaps: true});
 
   /// A [CompilerInputProvider] for dart2js.
   Future<String> provideInput(Uri resourceUri) {
@@ -244,6 +250,11 @@ class _BarbackCompilerProvider implements dart.CompilerProvider {
     // for it.
     assert(name == "");
 
+    // TODO(rnystrom): Do this more cleanly. See: #17403.
+    if (!generateSourceMaps && extension.endsWith(".map")) {
+      return new NullSink<String>();
+    }
+
     var primaryId = _transform.primaryInput.id;
     var id = new AssetId(primaryId.package, "${primaryId.path}.$extension");
 
@@ -356,3 +367,11 @@ class _BarbackCompilerProvider implements dart.CompilerProvider {
     return null;
   }
 }
+
+/// 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() {}
+}