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

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

 // Copyright (c) 2012, 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.
 
 part of dart2js.js_emitter;
 
 /**
  * Generates the code for all used classes in the program. Static fields (even
  * in classes) are ignored, since they can be treated as non-class elements.
  *
@@ skipping 1511 matching lines @@
 
       emitMain(mainBuffer);
       jsAst.FunctionDeclaration precompiledFunctionAst =
           buildPrecompiledFunction();
       emitInitFunction(mainBuffer);
       if (!compiler.deferredLoadTask.splitProgram) {
         mainBuffer.add('})()\n');
       } 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(
               precompiledFunctionAst, compiler,
               allowVariableMinification: false).getText());
 
       compiler.outputProvider('', 'precompiled.js')
           ..add(mainBuffer.getText())
           ..close();
 
       emitDeferredCode();
 
     });
     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 =
         elementDescriptors.putIfAbsent(
             element, () => new Map<OutputUnit, ClassBuilder>());
     return descriptors.putIfAbsent(outputUnit,
         () => new ClassBuilder(namer));
   }
 
   ClassBuilder getElementDecriptor(Element element) {
@@ skipping 56 matching lines @@
       classesCollector = oldClassesCollector;
 
       typeTestEmitter.emitRuntimeTypeSupport(buffer, outputUnit);
 
       emitCompileTimeConstants(buffer, outputUnit);
 
       String code = buffer.getText();
       compiler.outputProvider(outputUnit.name, 'js')
         ..add(code)
         ..close();
-      outputSourceMap(compiler.assembledCode, outputUnit.name);
+
+      // TODO(johnniwinther): Support source maps for deferred code.
     }
   }
 
   String buildGeneratedBy() {
     var suffix = '';
     if (compiler.hasBuildId) suffix = ' version: ${compiler.buildId}';
     return '// Generated by dart2js, the Dart to JavaScript compiler$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();
   }
 
   void registerReadTypeVariable(TypeVariableElement element) {
     readTypeVariables.add(element);
   }
 }