Canonicalize closures passed to native functions.

frog/leg/lib/js_helper.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.
 
 #library('js_helper');
 
 #import('coreimpl.dart');
 
 #source('date_helper.dart');
 #source('regexp_helper.dart');
@@ skipping 1315 matching lines @@
     result[key] = value;
   }
   return result;
 }
 
 /**
  * Called by generated code to convert a Dart closure to a JS
  * closure when the Dart closure is passed to the DOM.
  */
 convertDartClosureToJS(closure) {
-  return JS("var", @"""function() {
+  if (JS('bool', @'"$identity" in $0', closure)) {

[kasperl, 2012/03/08 15:06:08]

The 'in' construct is probably not going to perform very well. How about
something like this:

   var function = JS('var', @'$0.$identity', closure);
   if (JS('bool', @'!!$0', function)) return function;

[ngeoffray, 2012/03/08 15:11:36]

OK, I copied the test from line 1276, I'll change it there too (unfortunately
the code cannot be shared because of how we analyze JS).

[ngeoffray, 2012/03/08 15:24:01]

There is actually a good reason why the code line 1276 uses 'in'. The exception
thrown may have been null. I have added a comment there.

+    return JS('var', @'$0.$identity', closure);
+  }
+  var function = JS("var", @"""function() {
     var dartClosure = $0;
     switch (arguments.length) {
       case 0: return $1(dartClosure);
       case 1: return $2(dartClosure, arguments[0]);
       case 2: return $3(dartClosure, arguments[0], arguments[1]);
       default:
         throw new Error('Unsupported number of arguments for wrapped closure');
     }
   }""",
   closure,
   callClosure0,
   callClosure1,
   callClosure2);
+  JS('void', @'$0.$identity = $1', closure, function);
+  return function;
 }
 
 /**
  * Helper methods when converting a Dart closure to a JS closure.
  */
 callClosure0(closure) => closure();
 callClosure1(closure, arg1) => closure(arg1);
 callClosure2(closure, arg1, arg2) => closure(arg1, arg2);
 
 class StackTrace {
   var stack;
   StackTrace(this.stack);
   String toString() => stack != null ? stack : '';
 }