Implement ClassMirror.metadata.

dart/sdk/lib/_internal/compiler/implementation/js_backend/emitter.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 js_backend;
 
 /**
  * A function element that represents a closure call. The signature is copied
  * from the given element.
  */
@@ skipping 1539 matching lines @@
       String mixinName = namer.getName(computeMixinClass(classElement));
       superName = '$superName+$mixinName';
       needsMixinSupport = true;
     }
 
     ClassBuilder builder = new ClassBuilder();
     emitClassConstructor(classElement, builder);
     emitSuper(superName, builder);
     emitRuntimeName(runtimeName, builder);
     emitClassFields(classElement, builder, superName);
+    var metadata = buildMetadataFunction(classElement);
+    if (metadata != null) {
+      builder.addProperty("@", metadata);
+    }
     emitClassGettersSetters(classElement, builder);
     if (!classElement.isMixinApplication) {
       emitInstanceMembers(classElement, builder);
     }
     emitIsTests(classElement, builder);
 
     // TODO(ahe): This method (generateClass) should return a jsAst.Expression.
     if (!buffer.isEmpty) {
       buffer.write(',$n$n');
     }
@@ skipping 1355 matching lines @@
     buffer.write(jsAst.prettyPrint(decl, compiler).getText());
     if (compiler.enableMinification) buffer.write('\n');
   }
 
   /// The metadata function returns the metadata associated with
   /// [element] in generated code.  The metadata needs to be wrapped
   /// in a function as it refers to constants that may not have been
   /// constructed yet.  For example, a class is allowed to be
   /// annotated with itself.  The metadata function is used by
   /// mirrors_patch to implement DeclarationMirror.metadata.
-  jsAst.Expression buildMetadataFunction(Element element) {
-    if (compiler.mirrorSystemClass == null) {
-      // Since the string is not quoted, this just becomes an empty
-      // node.  Since the result is added to a list, this implicitly
-      // makes the value undefined.
-      return new jsAst.LiteralString('');
-    }
+  jsAst.Fun buildMetadataFunction(Element element) {
+    if (compiler.mirrorSystemClass == null) return null;
     var metadata = [];
     Link link = element.metadata;
     // TODO(ahe): Why is metadata sometimes null?
     if (link != null) {
       for (; !link.isEmpty; link = link.tail) {
         metadata.add(constantReference(link.head.value));
       }
     }
+    if (metadata.isEmpty) return null;
     return js.fun([], [js.return_(new jsAst.ArrayInitializer.from(metadata))]);
   }
 
   String assembleProgram() {
     measure(() {
       // Compute the required type checks to know which classes need a
       // 'is$' method.
       computeRequiredTypeChecks();
 
       computeNeededClasses();
@@ skipping 84 matching lines @@
           var buffer = buffers[0];
           var uri = library.canonicalUri;
           if (uri.scheme == 'file' && compiler.sourceMapUri != null) {
             // TODO(ahe): It is a hack to use compiler.sourceMapUri
             // here.  It should be relative to the main JavaScript
             // output file.
             uri = relativize(
                 compiler.sourceMapUri, library.canonicalUri, false);
           }
           if (buffer != null) {
+            var metadata = buildMetadataFunction(library);
             mainBuffer
                 ..write('["${library.getLibraryOrScriptName()}",$_')
                 ..write('"${uri}",$_')
-                ..write(
-                    jsAst.prettyPrint(buildMetadataFunction(library), compiler))
+                ..write(metadata == null
+                        ? "" : jsAst.prettyPrint(metadata, compiler))
                 ..write(',$_')
                 ..write('{$n')
                 ..addBuffer(buffer)
                 ..write('}],$n');
           }
           buffer = buffers[1];
           if (buffer != null) {
             deferredBuffer
                 ..write('["${library.getLibraryOrScriptName()}",$_')
                 ..write('"${uri}",$_')
@@ skipping 203 matching lines @@
 
 const String HOOKS_API_USAGE = """
 // The code supports the following hooks:
 // dartPrint(message)   - if this function is defined it is called
 //                        instead of the Dart [print] method.
 // dartMainRunner(main) - if this function is defined, the Dart [main]
 //                        method will not be invoked directly.
 //                        Instead, a closure that will invoke [main] is
 //                        passed to [dartMainRunner].
 """;