Use '--source-map' and '--out' options to support source maps from non-commandline.

sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart

Index: sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart b/sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart
index d7eea273c3686935df699552d2169673ea669450..c468a92e0387cef1199d8ae4a87b016c92c75b4d 100644
--- a/sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart
@@ -1529,8 +1529,17 @@ if (typeof $printHelperName === "function") {
       } else {
         mainBuffer.add('\n');
       }
-      compiler.assembledCode = mainBuffer.getText();
-      outputSourceMap(compiler.assembledCode, '');
+      String assembledCode = mainBuffer.getText();
+      if (generateSourceMap) {
+        outputSourceMap(assembledCode, mainBuffer, '',
+            compiler.sourceMapUri, compiler.outputUri);
+        assembledCode +=

[floitsch, 2014/03/07 10:27:24]

It seems more efficient if we don't have to create a new string:

String sourceMapTags = "";
if (generateSourceMap) {
  outputSourceMap(...);
  sourceMapTags = generateSourceMapTag(...);
}
compiler.outputProvider('', 'js')
    ..add(assembledCode);
    ..add(sourceMapTags);
    ..close();

[Johnni Winther, 2014/03/07 12:38:48]

Done.

+            generateSourceMapTag(compiler.sourceMapUri, compiler.outputUri);
+      }
+      compiler.outputProvider('', 'js')
+          ..add(assembledCode)
+          ..close();
+      compiler.assembledCode = assembledCode;
 
       mainBuffer.write(
           jsAst.prettyPrint(
@@ -1547,6 +1556,25 @@ if (typeof $printHelperName === "function") {
     return compiler.assembledCode;
   }
 
+  String generateSourceMapTag(Uri sourceMapUri, Uri fileUri) {
+    if (sourceMapUri != null && fileUri != null) {
+      // Using # is the new proposed standard. @ caused problems in Internet
+      // Explorer due to "Conditional Compilation Statements" in JScript,
+      // see:
+      // http://msdn.microsoft.com/en-us/library/7kx09ct1(v=vs.80).aspx
+      // About source maps, see:
+      // https://docs.google.com/a/google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k/edit
+      // TODO(http://dartbug.com/11914): Remove @ line.

[floitsch, 2014/03/07 10:27:24]

I just tried with Chrome beta, and at least there it is already fixed. I'm not
sure of Chrome stable, but I wouldn't be surprised if we could close 11914 and
remove the line now.

[Johnni Winther, 2014/03/07 12:38:48]

Will do it in a separate CL.

+      String sourceMapFileName = relativize(fileUri, sourceMapUri, false);
+      return '''
+
+//# sourceMappingURL=$sourceMapFileName
+//@ sourceMappingURL=$sourceMapFileName
+''';
+    }
+    return '';
+  }
+
   ClassBuilder getElementDescriptorForOutputUnit(Element element,
                                                  OutputUnit outputUnit) {
     Map<OutputUnit, ClassBuilder> descriptors =
@@ -1623,7 +1651,8 @@ if (typeof $printHelperName === "function") {
       compiler.outputProvider(outputUnit.name, 'js')
         ..add(code)
         ..close();
-      outputSourceMap(compiler.assembledCode, outputUnit.name);
+
+      // TODO(johnniwinther): Support source maps for deferred code.
     }
   }
 
@@ -1633,20 +1662,24 @@ if (typeof $printHelperName === "function") {
     return '// Generated by dart2js, the Dart to JavaScript compiler$suffix.\n';
   }
 
-  String buildSourceMap(CodeBuffer buffer, SourceFile compiledFile) {
+  String buildSourceMap(CodeBuffer buffer,

[floitsch, 2014/03/07 10:27:24]

If buildSourceMap is not used anywhere else I would inline it.

[Johnni Winther, 2014/03/07 12:38:48]

Done.

+                        SourceFile compiledFile,
+                        [Uri sourceMapUri, Uri fileUri]) {
     SourceMapBuilder sourceMapBuilder =
-        new SourceMapBuilder(compiler.sourceMapUri);
+        new SourceMapBuilder(sourceMapUri, fileUri);
     buffer.forEachSourceLocation(sourceMapBuilder.addMapping);
     return sourceMapBuilder.build(compiledFile);
   }
 
-  void outputSourceMap(String code, String name) {
+  void outputSourceMap(String code, CodeBuffer buffer, String name,
+                       [Uri sourceMapUri, Uri fileUri]) {
     if (!generateSourceMap) return;
     // Create a source file for the compilation output. This allows using
     // [:getLine:] to transform offsets to line numbers in [SourceMapBuilder].
     SourceFile compiledFile =
-        new StringSourceFile(null, compiler.assembledCode);
-    String sourceMap = buildSourceMap(mainBuffer, compiledFile);
+        new StringSourceFile(null, code);
+    String sourceMap = buildSourceMap(mainBuffer, compiledFile,
+                                      sourceMapUri, fileUri);
     compiler.outputProvider(name, 'js.map')
         ..add(sourceMap)
         ..close();