Maintain referential integrity of proxy instances in dart:js

sdk/lib/js/dart2js/js_dart2js.dart

Index: sdk/lib/js/dart2js/js_dart2js.dart
diff --git a/sdk/lib/js/dart2js/js_dart2js.dart b/sdk/lib/js/dart2js/js_dart2js.dart
index 64b4af0b4771972ac4ac9b773480ece956d914b8..35968a9f5926ba74928f79402dd0425553e5d7c9 100644
--- a/sdk/lib/js/dart2js/js_dart2js.dart
+++ b/sdk/lib/js/dart2js/js_dart2js.dart
@@ -4,7 +4,7 @@
 
 library dart.js;
 
-import 'dart:_foreign_helper' show JS;
+import 'dart:_foreign_helper' show JS, DART_CLOSURE_TO_JS;
 import 'dart:_js_helper' show Primitives, convertDartClosureToJS;
 
 final JsObject context = new JsObject._fromJs(Primitives.computeGlobalThis());
@@ -39,10 +39,41 @@ class Callback implements Serializable<JsFunction> {
   JsFunction toJs() => new JsFunction._fromJs(_jsFunction);
 }
 
+/*
+ * TODO(justinfagnani): add tests and make public when we remove Callback.
+ *
+ * Returns a [JsFunction] that captures its 'this' binding and calls [f]
+ * with the value of this passed as the first argument.
+ */
+JsFunction _captureThis(Function f) => 
+  new JsFunction._fromJs(_convertDartFunction(f, captureThis: true));
+
+_convertDartFunction(Function f, {bool captureThis: false}) {
+  return JS('',
+    'function(_call, f, captureThis) {'
+      'return function() {'
+        'return _call(f, captureThis, this, '
+            'Array.prototype.slice.apply(arguments));'
+      '}'
+    '}(#, #, #)', DART_CLOSURE_TO_JS(_callDartFunction), f, captureThis);
+}
+
+_callDartFunction(callback, bool captureThis, self, List arguments) {
+  if (captureThis) {
+    arguments = [self]..addAll(arguments);
+  }
+  var dartArgs = arguments.map(_convertToDart).toList();
+  return _convertToJS(Function.apply(callback, dartArgs));
+}
+
+
 class JsObject implements Serializable<JsObject> {
   final dynamic _jsObject;
 
-  JsObject._fromJs(this._jsObject);
+  JsObject._fromJs(this._jsObject) {
+    // remember this proxy for the JS object
+    _getDartProxy(_jsObject, _DART_OBJECT_PROPERTY_NAME, (o) => this);
+  }
 
   // TODO(vsm): Type constructor as Serializable<JsFunction> when
   // dartbug.com/11854 is fixed.
@@ -120,6 +151,7 @@ return ret;
 
   operator[](key) =>
       _convertToDart(JS('=Object', '#[#]', _convertToJS(this), key));
+
   operator[]=(key, value) => JS('void', '#[#]=#', _convertToJS(this), key,
       _convertToJS(value));
 
@@ -166,6 +198,27 @@ abstract class Serializable<T> {
   T toJs();
 }
 
+// property added to a Dart object referencing its JS-side DartObject proxy
+const _DART_OBJECT_PROPERTY_NAME = r'_$dart_dartObject';
+const _DART_CLOSURE_PROPERTY_NAME = r'_$dart_dartClosure';
+
+// property added to a JS object referencing its Dart-side JsObject proxy
+const _JS_OBJECT_PROPERTY_NAME = r'_$dart_jsObject';
+const _JS_FUNCTION_PROPERTY_NAME = r'$dart_jsFunction';
+
+bool _defineProperty(o, String name, value) {
+  if (JS('bool', 'Object.isExtensible(#)', o)) {
+    try {
+      JS('void', 'Object.defineProperty(#, #, { value: #})', o, name, value);
+      return true;
+    } catch(e) {
+      // object is native and lies about being extensible
+      // see https://bugzilla.mozilla.org/show_bug.cgi?id=775185
+    }
+  }
+  return false;
+}
+
 dynamic _convertToJS(dynamic o) {
   if (o == null) {
     return null;
@@ -176,12 +229,29 @@ dynamic _convertToJS(dynamic o) {
   } else if (o is Serializable) {
     return _convertToJS(o.toJs());
   } else if (o is Function) {
-    return _convertToJS(new Callback(o));
+    return _getJsProxy(o, _JS_FUNCTION_PROPERTY_NAME, (o) {
+      var jsFunction = _convertDartFunction(o);
+      // set a property on the JS closure referencing the Dart closure
+      _defineProperty(jsFunction, _DART_CLOSURE_PROPERTY_NAME, o);
+      return jsFunction;
+    });
   } else {
-    return JS('=Object', 'new DartProxy(#)', o);
+    return _getJsProxy(o, _JS_OBJECT_PROPERTY_NAME,
+        (o) => JS('', 'new DartObject(#)', o));
+  }
+}
+
+dynamic _getJsProxy(o, String propertyName, createProxy(o)) {
+  var jsProxy = JS('', '#[#]', o, propertyName);
+  if (jsProxy == null) {
+    jsProxy = createProxy(o);
+    _defineProperty(o, propertyName, jsProxy);
   }
+  return jsProxy;
 }
 
+// converts a Dart object to a reference to a native JS object
+// which might be a DartObject JS->Dart proxy
 dynamic _convertToDart(dynamic o) {
   if (JS('bool', '# == null', o)) {
     return null;
@@ -190,10 +260,21 @@ dynamic _convertToDart(dynamic o) {
       JS('bool', 'typeof # == "boolean" || # instanceof Boolean', o, o)) {
     return o;
   } else if (JS('bool', '# instanceof Function', o)) {
-    return new JsFunction._fromJs(JS('=Object', '#', o));
-  } else if (JS('bool', '# instanceof DartProxy', o)) {
+    return _getDartProxy(o, _DART_CLOSURE_PROPERTY_NAME,
+        (o) => new JsFunction._fromJs(o));
+  } else if (JS('bool', '# instanceof DartObject', o)) {
     return JS('var', '#.o', o);
   } else {
-    return new JsObject._fromJs(JS('=Object', '#', o));
+    return _getDartProxy(o, _DART_OBJECT_PROPERTY_NAME,
+        (o) => new JsObject._fromJs(o));
+  }
+}
+
+dynamic _getDartProxy(o, String propertyName, createProxy(o)) {
+  var dartProxy = JS('', '#[#]', o, propertyName);
+  if (dartProxy == null) {
+    dartProxy = createProxy(o);
+    _defineProperty(o, propertyName, dartProxy);
   }
-}
+  return dartProxy;
+}