Add a new magic element type for annotating types that have Javascript array behavior.

lib/compiler/implementation/compiler.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.
 
 class WorkItem {
   final Element element;
   TreeElements resolutionTree;
   bool allowSpeculativeOptimization = true;
   List<HTypeGuard> guards = const <HTypeGuard>[];
 
@@ skipping 90 matching lines @@
   ClassElement dynamicClass;
   ClassElement boolClass;
   ClassElement numClass;
   ClassElement intClass;
   ClassElement doubleClass;
   ClassElement stringClass;
   ClassElement functionClass;
   ClassElement nullClass;
   ClassElement listClass;
 
+  /**
+   * Interface used to determine if an object has the JavaScript
+   * indexing behavior. The interface is only visible to specific
+   * libraries.
+   */
+  ClassElement javaScriptIndexingBehaviorInterface;

[ahe, 2012/06/12 18:30:04]

How about jsIndexingBehaviorInterface?

[ngeoffray, 2012/06/13 13:02:42]

Done.

+
   Element get currentElement() => _currentElement;
   withCurrentElement(Element element, f()) {
     Element old = currentElement;
     _currentElement = element;
     try {
       return f();
     } catch (CompilerCancelledException ex) {
       throw;
     } catch (var ex) {
       unhandledExceptionOnElement(element);
@@ skipping 201 matching lines @@
     scanner.importLibrary(coreImplLibrary, coreLibrary, null);
     scanner.importLibrary(jsHelperLibrary, coreLibrary, null);
     scanner.importLibrary(interceptorsLibrary, coreLibrary, null);
     addForeignFunctions(jsHelperLibrary);
     addForeignFunctions(interceptorsLibrary);
 
     libraries['dart:core'] = coreLibrary;
     libraries['dart:coreimpl'] = coreImplLibrary;
 
     initializeSpecialClasses();
+
+    javaScriptIndexingBehaviorInterface =
+        findHelper(const SourceString('JavaScriptIndexingBehavior'));
   }
 
   /** Define the JS helper functions in the given library. */
   void addForeignFunctions(LibraryElement library) {
     library.define(new ForeignElement(
         const SourceString('JS'), library), this);
     library.define(new ForeignElement(
         const SourceString('UNINTERCEPTED'), library), this);
     library.define(new ForeignElement(
         const SourceString('JS_HAS_EQUALS'), library), this);
@@ skipping 252 matching lines @@
     // invariant that endOffset > beginOffset, but for EOF the
     // charoffset of the next token may be [beginOffset]. This can
     // also happen for synthetized tokens that are produced during
     // error handling.
     final endOffset =
       Math.max((end.next !== null) ? end.next.charOffset : 0, beginOffset + 1);
     assert(endOffset > beginOffset);
     return f(beginOffset, endOffset);
   }
 }