First shot at source maps generation in dart2js.

lib/compiler/implementation/emitter.dart

Index: lib/compiler/implementation/emitter.dart
diff --git a/lib/compiler/implementation/emitter.dart b/lib/compiler/implementation/emitter.dart
index f6afda53dc2eaaf8e7ec13c099be1dbf5e167999..e00e960182a8a7afe5049ee0d2f222cdfe961b00 100644
--- a/lib/compiler/implementation/emitter.dart
+++ b/lib/compiler/implementation/emitter.dart
@@ -34,11 +34,16 @@ class CodeEmitterTask extends CompilerTask {
   String classesCollector;
   final Map<int, String> boundClosureCache;
 
-  CodeEmitterTask(Compiler compiler)
+  final bool generateSourceMap;
+  final List<SourceMappingEntry> sourceMappings;
+
+  CodeEmitterTask(Compiler compiler, [bool generateSourceMap = false])
       : namer = compiler.namer,
         boundClosureBuffer = new StringBuffer(),
         mainBuffer = new StringBuffer(),
         boundClosureCache = new Map<int, String>(),
+        generateSourceMap = generateSourceMap,
+        sourceMappings = new List<SourceMappingEntry>(),
         super(compiler) {
     nativeEmitter = new NativeEmitter(this);
   }
@@ -616,7 +621,14 @@ function(collectedClasses) {
     generatedCode.forEach((Element element, String codeBlock) {
       if (!element.isInstanceMember()) {
         String functionName = functionNamer(element);
-        buffer.add('$isolateProperties.$functionName = $codeBlock;\n\n');
+        buffer.add('$isolateProperties.$functionName = ');
+        int beginPosition = buffer.length;
+        buffer.add(codeBlock);
+        int endPosition = buffer.length;
+        buffer.add(';\n\n');
+        if (generateSourceMap) {
+          addSourceMapping(element, beginPosition, endPosition);
+        }
       }
     });
   }
@@ -1032,7 +1044,29 @@ if (typeof window != 'undefined' && typeof document != 'undefined' &&
       emitFinishIsolateConstructor(mainBuffer);
       mainBuffer.add('}\n');
       compiler.assembledCode = mainBuffer.toString();
+
+      if (generateSourceMap) {
+        SourceFile compiledFile = new SourceFile(null, compiler.assembledCode);
+        String sourceMap = new SourceMapBuilder().build(sourceMappings,
+                                                        compiledFile);
+        // TODO(podivilov): We should find a better way to return source maps to
+        // compiler. Using diagnostic handler for that purpose is a temporary
+        // hack.
+        compiler.reportDiagnostic(
+            null, sourceMap, new api.Diagnostic(-1, 'source map'));
+      }
     });
     return compiler.assembledCode;
   }
+
+  void addSourceMapping(FunctionElement element,
+                        int beginPosition,
+                        int endPosition) {
+    SourceFile sourceFile = element.getCompilationUnit().script.file;
+    FunctionExpression expression = element.cachedNode;
+    sourceMappings.add(new SourceMappingEntry(
+        sourceFile, expression.getBeginToken().charOffset, beginPosition));
+    sourceMappings.add(new SourceMappingEntry(
+        sourceFile, expression.getEndToken().charOffset, endPosition));
+  }
 }