Build script tags.

dart/frog/leg/universe.dart

 // Copyright (c) 2011, 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.
 
 class Universe {
   final Element scope;
 
   Map<SourceString, Element> elements;
   Map<Element, String> generatedCode;
   Map<Element, String> generatedBailoutCode;
   final Set<ClassElement> instantiatedClasses;
   // TODO(floitsch): we want more information than just the method name. For
   // example the number of arguments, etc.
   final Map<SourceString, Set<int>> invokedNames;
   final Set<SourceString> invokedGetters;
   final Set<SourceString> invokedSetters;
 
   Universe() : elements = {}, generatedCode = {}, generatedBailoutCode = {},
                instantiatedClasses = new Set<ClassElement>(),
                invokedNames = new Map<SourceString, Set<int>>(),
                invokedGetters = new Set<SourceString>(),
                invokedSetters = new Set<SourceString>(),
                scope = new Element(const SourceString('global scope'),
                                    null, null);
 
   Element find(SourceString name) {
     return elements[name];
   }
 
-  void define(Element element) {
-    assert(elements[element.name] == null);
-    elements[element.name] = element;
+  void define(Element element, Compiler compiler) {
+    Element existing = elements.putIfAbsent(element.name, () => element);
+    if (existing !== element) {
+      compiler.cancel('duplicate definition', token: element.position());
+      compiler.cancel('existing definition', token: existing.position());
+    }
   }
 
   void addGeneratedCode(WorkItem work, String code) {
     if (work.isBailoutVersion()) {
       generatedBailoutCode[work.element] = code;
     } else {
       generatedCode[work.element] = code;
     }
   }
 }