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..439c1d80f5c5723cb055581b14164f5c11a556b4 100644
--- a/sdk/lib/js/dart2js/js_dart2js.dart
+++ b/sdk/lib/js/dart2js/js_dart2js.dart
@@ -166,6 +166,14 @@ 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';

[justinfagnani, 2013/10/06 00:37:45]

Peter, how do I generate a unique name per-isolate? I couldn't find the example
browsing though the _internal/lib code.

+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';
+
 dynamic _convertToJS(dynamic o) {
   if (o == null) {
     return null;
@@ -178,10 +186,12 @@ dynamic _convertToJS(dynamic o) {
   } else if (o is Function) {
     return _convertToJS(new Callback(o));
   } else {
-    return JS('=Object', 'new DartProxy(#)', o);
+    return JS('=Object', 'new DartObject(#)', o);
   }
 }
 
+// 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 +200,24 @@ 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)) {
+    var dartClosure = JS('', '#[#]', o, _DART_CLOSURE_PROPERTY_NAME);

[alexandre.ardhuin, 2013/10/07 08:56:54]

Extract a method for this case and default case ?
  
  dynamic _bindDartOnJsIfAbsent(dynamic o, String propertyName, 
      JsObject createDart(o)) {
    var dartProxy = JS('', '#[#]', o, propertyName);
    if (dartProxy == null) {
      dartProxy = createDart(o);
      JS('void', 'Object.defineProperty(#, #, { value: #})', o, propertyName,
          dartProxy);
    }
    return dartProxy;
  }

[justinfagnani, 2013/10/07 17:49:13]

Good idea. Done.

+    if (dartClosure == null) {
+      dartClosure = new JsFunction._fromJs(o);
+      JS('void', 'Object.defineProperty(#, #, { value: #})', o,
+          _DART_CLOSURE_PROPERTY_NAME, dartClosure);
+    }
+    return dartClosure;
+  } else if (JS('bool', '# instanceof DartObject', o)) {
     return JS('var', '#.o', o);
   } else {
-    return new JsObject._fromJs(JS('=Object', '#', o));
+    var dartProxy = JS('', '#[#]', o, _JS_OBJECT_PROPERTY_NAME);
+    if (dartProxy == null) {
+      // check the registered proxy factories to see if we should instanciate
+      // a typed interface
+      dartProxy = new JsObject._fromJs(JS('=Object', '#', o));

[alexandre.ardhuin, 2013/10/07 08:56:54]

I don't remember why we used `JS('=Object', '#', o)` instead of `o` but having a
look now I find that really strange. The tests are passing with `o`.

[justinfagnani, 2013/10/07 17:49:13]

Peter can shed light here, but I've seen similar things in dart2js code as a way
to indicate the correct type, which in this case is not a Dart object.

I'm about to send out another CL which only changes JS() expressions for Peter
to take a closer look at.

+      JS('void', 'Object.defineProperty(#, #, { value: #})', o,
+          _JS_OBJECT_PROPERTY_NAME, dartProxy);
+    }
+    return dartProxy;
   }
 }