Bug 760109 - Add an API to lookup proto key via standard prototype objects and vice-versa.

js/src/jsapi.cpp

@@ -2226,6 +2226,30 @@ JS_GetClassObject(JSContext *cx, JSObject *obj_, JSProtoKey key, JSObject **objp
     return result;
 }
 
+JS_PUBLIC_API(JSBool)
+JS_GetClassPrototype(JSContext *cx, JSProtoKey key, JSObject **objp_)
+{
+    AssertHeapIsIdle(cx);
+    CHECK_REQUEST(cx);
+    RootedObject global(cx, cx->compartment->maybeGlobal());
+    if (!global)
+        return false;
+    RootedObject objp(cx);
+    bool result = js_GetClassPrototype(cx, global, key, &objp);
+    *objp_ = objp;
+    return result;
+}
+
+JS_PUBLIC_API(JSProtoKey)
+JS_IdentifyClassPrototype(JSContext *cx, JSObject *obj)
+{
+    AssertHeapIsIdle(cx);
+    CHECK_REQUEST(cx);
+    assertSameCompartment(cx, obj);
+    JS_ASSERT(!IsCrossCompartmentWrapper(obj));
+    return js_IdentifyClassPrototype(obj);
+}
+
 JS_PUBLIC_API(JSObject *)
 JS_GetObjectPrototype(JSContext *cx, JSObject *forObj)
 {

js/src/jsapi.h

@@ -3284,6 +3284,12 @@ extern JS_PUBLIC_API(JSBool)
 JS_GetClassObject(JSContext *cx, JSObject *obj, JSProtoKey key,
                   JSObject **objp);
 
+extern JS_PUBLIC_API(JSBool)
+JS_GetClassPrototype(JSContext *cx, JSProtoKey key, JSObject **objp);
+
+extern JS_PUBLIC_API(JSProtoKey)
+JS_IdentifyClassPrototype(JSContext *cx, JSObject *obj);
+
 /*
  * Returns the original value of |Function.prototype| from the global object in
  * which |forObj| was created.

js/src/jsobj.cpp

@@ -3829,6 +3829,29 @@ js_GetClassObject(JSContext *cx, HandleObject obj, JSProtoKey key,
     return true;
 }
 
+JSProtoKey
+js_IdentifyClassPrototype(JSObject *obj)
+{
+    // First, get the key off the JSClass. This tells us which prototype we
+    // _might_ be. But we still don't know for sure, since the prototype shares
+    // its JSClass with instances.
+    JSProtoKey key = JSCLASS_CACHED_PROTO_KEY(obj->getClass());
+    if (key == JSProto_Null)
+        return JSProto_Null;
+
+    // Now, see if the cached object matches |obj|.
+    //
+    // Note that standard class objects are cached in the range [0, JSProto_LIMIT),
+    // and the prototypes are cached in [JSProto_LIMIT, 2*JSProto_LIMIT).
+    JSObject &global = obj->global();
+    Value v = global.getReservedSlot(JSProto_LIMIT + key);
+    if (v.isObject() && obj == &v.toObject())
+        return key;
+
+    // False alarm - just an instance.
+    return JSProto_Null;
+}
+
 bool
 js_FindClassObject(JSContext *cx, HandleObject start, JSProtoKey protoKey,
                    MutableHandleValue vp, Class *clasp)

js/src/jsobj.h

@@ -1110,6 +1110,13 @@ extern bool
 js_GetClassObject(JSContext *cx, js::HandleObject obj, JSProtoKey key,
                   js::MutableHandleObject objp);
 
+/*
+ * Determine if the given object is a prototype for a standard class. If so,
+ * return the associated JSProtoKey. If not, return JSProto_Null.
+ */
+extern JSProtoKey
+js_IdentifyClassPrototype(JSObject *obj);
+
 /*
  * If protoKey is not JSProto_Null, then clasp is ignored. If protoKey is
  * JSProto_Null, clasp must non-null.