Add Proxy support for prototype handling

Cleanup get/setPrototypeOf and fix some smaller incompatibilities
in the default implementation for Object.

Add the methods to the vtable and reimplement them according to
spec for ProxyObjects.

Clean up the Object.prototype.get/setPrototypeOf/__proto__ methods
and fix a smaller bug in the Reflect API for those methods.

Change-Id: I6e438753332ec4db963d6cdcf86f340ff212777a
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

22 files changed, 205 insertions, 106 deletions

diff --git a/src/imports/localstorage/plugin.cpp b/src/imports/localstorage/plugin.cpp
index fb20a1c457..60c1f89c9b 100644
--- a/src/imports/localstorage/plugin.cpp
+++ b/src/imports/localstorage/plugin.cpp
@@ -323,7 +323,7 @@ static ReturnedValue qmlsqldatabase_executeSql(const FunctionObject *b, const Va
         if (query.exec()) {
             QV4::Scoped<QQmlSqlDatabaseWrapper> rows(scope, QQmlSqlDatabaseWrapper::create(scope.engine));
             QV4::ScopedObject p(scope, databaseData(scope.engine)->rowsProto.value());
-            rows->setPrototype(p.getPointer());
+            rows->setPrototypeUnchecked(p.getPointer());
             rows->d()->type = Heap::QQmlSqlDatabaseWrapper::Rows;
             *rows->d()->database = db;
             *rows->d()->sqlQuery = query;
@@ -397,7 +397,7 @@ static ReturnedValue qmlsqldatabase_changeVersion(const FunctionObject *b, const
 
     Scoped<QQmlSqlDatabaseWrapper> w(scope, QQmlSqlDatabaseWrapper::create(scope.engine));
     ScopedObject p(scope, databaseData(scope.engine)->queryProto.value());
-    w->setPrototype(p.getPointer());
+    w->setPrototypeUnchecked(p.getPointer());
     w->d()->type = Heap::QQmlSqlDatabaseWrapper::Query;
     *w->d()->database = db;
     *w->d()->version = *r->d()->version;
@@ -449,7 +449,7 @@ static ReturnedValue qmlsqldatabase_transaction_shared(const FunctionObject *b,
 
     Scoped<QQmlSqlDatabaseWrapper> w(scope, QQmlSqlDatabaseWrapper::create(scope.engine));
     QV4::ScopedObject p(scope, databaseData(scope.engine)->queryProto.value());
-    w->setPrototype(p.getPointer());
+    w->setPrototypeUnchecked(p.getPointer());
     w->d()->type = Heap::QQmlSqlDatabaseWrapper::Query;
     *w->d()->database = db;
     *w->d()->version = *r->d()->version;
@@ -773,7 +773,7 @@ void QQuickLocalStorage::openDatabaseSync(QQmlV4Function *args)
 
     QV4::Scoped<QQmlSqlDatabaseWrapper> db(scope, QQmlSqlDatabaseWrapper::create(scope.engine));
     QV4::ScopedObject p(scope, databaseData(scope.engine)->databaseProto.value());
-    db->setPrototype(p.getPointer());
+    db->setPrototypeUnchecked(p.getPointer());
     *db->d()->database = database;
     *db->d()->version = version;
 
diff --git a/src/particles/qquickv4particledata.cpp b/src/particles/qquickv4particledata.cpp
index cf05245f5b..6d43b3880b 100644
--- a/src/particles/qquickv4particledata.cpp
+++ b/src/particles/qquickv4particledata.cpp
@@ -520,7 +520,7 @@ QQuickV4ParticleData::QQuickV4ParticleData(QV4::ExecutionEngine* v4, QQuickParti
     QV4ParticleDataDeletable *d = particleV4Data(scope.engine);
     QV4::ScopedObject o(scope, v4->memoryManager->allocate<QV4ParticleData>(datum, system));
     QV4::ScopedObject p(scope, d->proto.value());
-    o->setPrototype(p);
+    o->setPrototypeUnchecked(p);
     m_v4Value = o;
 }
 
diff --git a/src/qml/jsapi/qjsvalue.cpp b/src/qml/jsapi/qjsvalue.cpp
index aaac4e0a9a..01ec44e250 100644
--- a/src/qml/jsapi/qjsvalue.cpp
+++ b/src/qml/jsapi/qjsvalue.cpp
@@ -852,7 +852,7 @@ QJSValue QJSValue::prototype() const
     ScopedObject o(scope, QJSValuePrivate::getValue(this)->as<QV4::Object>());
     if (!o)
         return QJSValue();
-    ScopedObject p(scope, o->prototype());
+    ScopedObject p(scope, o->getPrototypeOf());
     if (!p)
         return QJSValue(NullValue);
     return QJSValue(o->internalClass()->engine, p.asReturnedValue());
@@ -884,7 +884,7 @@ void QJSValue::setPrototype(const QJSValue& prototype)
     if (!val)
         return;
     if (val->isNull()) {
-        o->setPrototype(nullptr);
+        o->setPrototypeOf(nullptr);
         return;
     }
 
@@ -895,7 +895,7 @@ void QJSValue::setPrototype(const QJSValue& prototype)
         qWarning("QJSValue::setPrototype() failed: cannot set a prototype created in a different engine");
         return;
     }
-    if (!o->setPrototype(p))
+    if (!o->setPrototypeOf(p))
         qWarning("QJSValue::setPrototype() failed: cyclic prototype value");
 }
 
diff --git a/src/qml/jsruntime/qv4engine.cpp b/src/qml/jsruntime/qv4engine.cpp
index 7cef7c8039..5f202b8a24 100644
--- a/src/qml/jsruntime/qv4engine.cpp
+++ b/src/qml/jsruntime/qv4engine.cpp
@@ -402,7 +402,7 @@ ExecutionEngine::ExecutionEngine(QJSEngine *jsEngine)
     jsObjects[URIErrorProto] = memoryManager->allocObject<URIErrorPrototype>(ic->d());
 
     jsObjects[VariantProto] = memoryManager->allocate<VariantPrototype>();
-    Q_ASSERT(variantPrototype()->prototype() == objectPrototype()->d());
+    Q_ASSERT(variantPrototype()->getPrototypeOf() == objectPrototype()->d());
 
 #if QT_CONFIG(qml_sequence_object)
     ic = newInternalClass(SequencePrototype::staticVTable(), SequencePrototype::defaultPrototype(this));
@@ -1849,7 +1849,7 @@ bool ExecutionEngine::metaTypeFromJS(const Value *value, int type, void *data)
         } else if (Object *o = value->objectValue()) {
             // Look in the prototype chain.
             QV4::Scope scope(this);
-            QV4::ScopedObject proto(scope, o->prototype());
+            QV4::ScopedObject proto(scope, o->getPrototypeOf());
             while (proto) {
                 bool canCast = false;
                 if (QV4::VariantObject *vo = proto->as<QV4::VariantObject>()) {
@@ -1870,7 +1870,7 @@ bool ExecutionEngine::metaTypeFromJS(const Value *value, int type, void *data)
                         *reinterpret_cast<void* *>(data) = var.data();
                     return true;
                 }
-                proto = proto->prototype();
+                proto = proto->getPrototypeOf();
             }
         }
     } else if (value->isNull() && name.endsWith('*')) {
diff --git a/src/qml/jsruntime/qv4generatorobject.cpp b/src/qml/jsruntime/qv4generatorobject.cpp
index a29eef513c..1c4c970c2e 100644
--- a/src/qml/jsruntime/qv4generatorobject.cpp
+++ b/src/qml/jsruntime/qv4generatorobject.cpp
@@ -78,9 +78,9 @@ Heap::FunctionObject *GeneratorFunction::create(ExecutionContext *context, Funct
     Scope scope(context);
     Scoped<GeneratorFunction> g(scope, context->engine()->memoryManager->allocate<GeneratorFunction>(context, function));
     ScopedObject proto(scope, scope.engine->newObject());
-    proto->setPrototype(scope.engine->generatorPrototype());
+    proto->setPrototypeOf(scope.engine->generatorPrototype());
     g->defineDefaultProperty(scope.engine->id_prototype(), proto, Attr_NotConfigurable|Attr_NotEnumerable);
-    g->setPrototype(ScopedObject(scope, scope.engine->generatorFunctionCtor()->get(scope.engine->id_prototype())));
+    g->setPrototypeOf(ScopedObject(scope, scope.engine->generatorFunctionCtor()->get(scope.engine->id_prototype())));
     return g->d();
 }
 
@@ -104,7 +104,7 @@ ReturnedValue GeneratorFunction::call(const FunctionObject *f, const Value *this
 
     Scope scope(gf);
     Scoped<GeneratorObject> g(scope, scope.engine->memoryManager->allocManaged<GeneratorObject>(requiredMemory, scope.engine->classes[EngineBase::Class_GeneratorObject]));
-    g->setPrototype(ScopedObject(scope, gf->get(scope.engine->id_prototype())));
+    g->setPrototypeOf(ScopedObject(scope, gf->get(scope.engine->id_prototype())));
 
     Heap::GeneratorObject *gp = g->d();
     gp->stack.size = stackSize;
@@ -160,7 +160,7 @@ void GeneratorPrototype::init(ExecutionEngine *engine, Object *ctor)
     ctorProto->defineDefaultProperty(engine->symbol_toStringTag(), (v = engine->newIdentifier(QStringLiteral("GeneratorFunction"))), Attr_ReadOnly_ButConfigurable);
     ctorProto->defineDefaultProperty(engine->id_prototype(), (v = this), Attr_ReadOnly_ButConfigurable);
 
-    setPrototype(engine->iteratorPrototype());
+    setPrototypeOf(engine->iteratorPrototype());
     defineDefaultProperty(QStringLiteral("constructor"), ctorProto, Attr_ReadOnly_ButConfigurable);
     defineDefaultProperty(QStringLiteral("next"), method_next, 1);
     defineDefaultProperty(QStringLiteral("return"), method_return, 1);
diff --git a/src/qml/jsruntime/qv4object.cpp b/src/qml/jsruntime/qv4object.cpp
index 02acc1a5e0..d1f71b18ae 100644
--- a/src/qml/jsruntime/qv4object.cpp
+++ b/src/qml/jsruntime/qv4object.cpp
@@ -93,19 +93,6 @@ void Heap::Object::setUsedAsProto()
     internalClass.set(internalClass->engine, internalClass->asProtoClass());
 }
 
-bool Object::setPrototype(Object *proto)
-{
-    Heap::Object *p = proto ? proto->d() : nullptr;
-    Heap::Object *pp = p;
-    while (pp) {
-        if (pp == d())
-            return false;
-        pp = pp->prototype();
-    }
-    setInternalClass(internalClass()->changePrototype(p));
-    return true;
-}
-
 ReturnedValue Object::getValue(const Value &thisObject, const Value &v, PropertyAttributes attrs)
 {
     if (!attrs.isAccessor())
@@ -278,6 +265,11 @@ void Object::insertMember(StringOrSymbol *s, const Property *p, PropertyAttribut
     }
 }
 
+void Object::setPrototypeUnchecked(const Object *p)
+{
+    setInternalClass(internalClass()->changePrototype(p ? p->d() : nullptr));
+}
+
 // Section 8.12.2
 PropertyIndex Object::getValueOrSetter(StringOrSymbol *name, PropertyAttributes *attrs)
 {
@@ -484,7 +476,7 @@ ReturnedValue Object::internalGetIndexed(uint index, bool *hasProperty) const
                 return str.asReturnedValue();
             }
         }
-        o = o->prototype();
+        o = o->getPrototypeOf();
     }
 
     if (exists) {
@@ -543,13 +535,13 @@ bool Object::internalPut(StringOrSymbol *name, const Value &value)
             memberIndex.set(engine, value);
         }
         return true;
-    } else if (!prototype()) {
+    } else if (!getPrototypeOf()) {
         if (!isExtensible())
             return false;
     } else {
         // clause 4
         Scope scope(engine);
-        memberIndex = ScopedObject(scope, prototype())->getValueOrSetter(name, &attrs);
+        memberIndex = ScopedObject(scope, getPrototypeOf())->getValueOrSetter(name, &attrs);
         if (!memberIndex.isNull()) {
             if (attrs.isAccessor()) {
                 if (!memberIndex->as<FunctionObject>())
@@ -608,13 +600,13 @@ bool Object::internalPutIndexed(uint index, const Value &value)
 
         arrayIndex.set(engine, value);
         return true;
-    } else if (!prototype()) {
+    } else if (!getPrototypeOf()) {
         if (!isExtensible())
             return false;
     } else {
         // clause 4
         Scope scope(engine);
-        arrayIndex = ScopedObject(scope, prototype())->getValueOrSetter(index, &attrs);
+        arrayIndex = ScopedObject(scope, getPrototypeOf())->getValueOrSetter(index, &attrs);
         if (!arrayIndex.isNull()) {
             if (attrs.isAccessor()) {
                 if (!arrayIndex->as<FunctionObject>())
@@ -978,7 +970,7 @@ bool Object::hasProperty(const Managed *m, Identifier id)
         if (o->getOwnProperty(id, p) != Attr_Invalid)
             return true;
 
-        o = o->prototype();
+        o = o->getPrototypeOf();
     }
 
     return false;
@@ -1033,6 +1025,34 @@ bool Object::preventExtensions(Managed *m)
     return true;
 }
 
+Heap::Object *Object::getPrototypeOf(const Managed *m)
+{
+    return m->internalClass()->prototype;
+}
+
+bool Object::setPrototypeOf(Managed *m, const Object *proto)
+{
+    Q_ASSERT(m->isObject());
+    Object *o = static_cast<Object *>(m);
+    Heap::Object *current = o->internalClass()->prototype;
+    Heap::Object *protod = proto ? proto->d() : nullptr;
+    if (current == protod)
+        return true;
+    if (!o->internalClass()->extensible)
+        return false;
+    Heap::Object *p = protod;
+    while (p) {
+        if (p == o->d())
+            return false;
+        if (reinterpret_cast<const ObjectVTable *>(p->vtable())->getPrototypeOf !=
+                reinterpret_cast<const ObjectVTable *>(Object::staticVTable())->getPrototypeOf)
+            break;
+        p = p->prototype();
+    }
+    o->setInternalClass(o->internalClass()->changePrototype(protod));
+    return true;
+}
+
 bool Object::setArrayLength(uint newLen)
 {
     Q_ASSERT(isArrayObject());
diff --git a/src/qml/jsruntime/qv4object_p.h b/src/qml/jsruntime/qv4object_p.h
index b55e8f25e2..6ec7452ca6 100644
--- a/src/qml/jsruntime/qv4object_p.h
+++ b/src/qml/jsruntime/qv4object_p.h
@@ -179,6 +179,8 @@ struct ObjectVTable
     PropertyAttributes (*getOwnProperty)(Managed *m, Identifier id, Property *p);
     bool (*isExtensible)(const Managed *);
     bool (*preventExtensions)(Managed *);
+    Heap::Object *(*getPrototypeOf)(const Managed *);
+    bool (*setPrototypeOf)(Managed *, const Object *);
     qint64 (*getLength)(const Managed *m);
     void (*advanceIterator)(Managed *m, ObjectIterator *it, Value *name, uint *index, Property *p, PropertyAttributes *attributes);
     ReturnedValue (*instanceOf)(const Object *typeObject, const Value &var);
@@ -200,6 +202,8 @@ const QV4::ObjectVTable classname::static_vtbl =    \
     getOwnProperty,                             \
     isExtensible,                               \
     preventExtensions,                          \
+    getPrototypeOf,                             \
+    setPrototypeOf,                             \
     getLength,                                  \
     advanceIterator,                            \
     instanceOf                                  \
@@ -244,8 +248,6 @@ struct Q_QML_EXPORT Object: Managed {
     void setProperty(ExecutionEngine *engine, uint index, Heap::Base *b) const { d()->setProperty(engine, index, b); }
 
     const ObjectVTable *vtable() const { return reinterpret_cast<const ObjectVTable *>(d()->vtable()); }
-    Heap::Object *prototype() const { return d()->prototype(); }
-    bool setPrototype(Object *proto);
 
     PropertyAttributes getOwnProperty(Identifier id, Property *p = nullptr) {
         return vtable()->getOwnProperty(this, id, p);
@@ -307,6 +309,9 @@ struct Q_QML_EXPORT Object: Managed {
 
     bool isExtensible() const { return vtable()->isExtensible(this); }
     bool preventExtensions() { return vtable()->preventExtensions(this); }
+    Heap::Object *getPrototypeOf() const { return vtable()->getPrototypeOf(this); }
+    bool setPrototypeOf(const Object *p) { return vtable()->setPrototypeOf(this, p); }
+    void setPrototypeUnchecked(const Object *p);
 
     // Array handling
 
@@ -366,7 +371,7 @@ public:
         Scope scope(engine());
         ScopedObject p(scope, this);
 
-        while ((p = p->prototype()))
+        while ((p = p->getPrototypeOf()))
             if (p->arrayData())
                 return true;
 
@@ -445,6 +450,8 @@ protected:
     static PropertyAttributes getOwnProperty(Managed *m, Identifier id, Property *p);
     static bool isExtensible(const Managed *m);
     static bool preventExtensions(Managed *);
+    static Heap::Object *getPrototypeOf(const Managed *);
+    static bool setPrototypeOf(Managed *, const Object *);
     static void advanceIterator(Managed *m, ObjectIterator *it, Value *name, uint *index, Property *p, PropertyAttributes *attributes);
     static qint64 getLength(const Managed *m);
     static ReturnedValue instanceOf(const Object *typeObject, const Value &var);
diff --git a/src/qml/jsruntime/qv4objectiterator.cpp b/src/qml/jsruntime/qv4objectiterator.cpp
index 109e189ede..fc4a06747f 100644
--- a/src/qml/jsruntime/qv4objectiterator.cpp
+++ b/src/qml/jsruntime/qv4objectiterator.cpp
@@ -109,7 +109,7 @@ void ObjectIterator::next(Value *name, uint *index, Property *pd, PropertyAttrib
                         shadowed = true;
                         break;
                     }
-                    o = o->prototype();
+                    o = o->getPrototypeOf();
                 }
                 if (shadowed)
                     continue;
@@ -118,7 +118,7 @@ void ObjectIterator::next(Value *name, uint *index, Property *pd, PropertyAttrib
         }
 
         if (flags & WithProtoChain)
-            current->setM(co->prototype());
+            current->setM(co->getPrototypeOf());
         else
             current->setM(nullptr);
 
diff --git a/src/qml/jsruntime/qv4objectproto.cpp b/src/qml/jsruntime/qv4objectproto.cpp
index 84238477fd..9d52ab1980 100644
--- a/src/qml/jsruntime/qv4objectproto.cpp
+++ b/src/qml/jsruntime/qv4objectproto.cpp
@@ -71,7 +71,7 @@ ReturnedValue ObjectCtor::callAsConstructor(const FunctionObject *f, const Value
         ScopedObject obj(scope, scope.engine->newObject());
         ScopedObject proto(scope, ctor->get(scope.engine->id_prototype()));
         if (!!proto)
-            obj->setPrototype(proto);
+            obj->setPrototypeOf(proto);
         return obj.asReturnedValue();
     } else {
         return argv[0].toObject(v4)->asReturnedValue();
@@ -136,7 +136,7 @@ ReturnedValue ObjectPrototype::method_getPrototypeOf(const FunctionObject *b, co
     if (scope.engine->hasException)
         return QV4::Encode::undefined();
 
-    ScopedObject p(scope, o->prototype());
+    ScopedObject p(scope, o->getPrototypeOf());
     return (!!p ? p->asReturnedValue() : Encode::null());
 }
 
@@ -264,7 +264,7 @@ ReturnedValue ObjectPrototype::method_create(const FunctionObject *builtin, cons
     ScopedObject O(scope, argv[0]);
 
     ScopedObject newObject(scope, scope.engine->newObject());
-    newObject->setPrototype(O);
+    newObject->setPrototypeOf(O);
 
 
     if (argc > 1 && !argv[1].isUndefined()) {
@@ -516,17 +516,10 @@ ReturnedValue ObjectPrototype::method_setPrototypeOf(const FunctionObject *f, co
         return argv[0].asReturnedValue();
 
     ScopedObject o(scope, argv[0]);
-    ScopedObject p(scope, argv[1]);
-    Q_ASSERT(!!o);
-
-    if (o->prototype() != p->d()) {
-        bool ok = false;
-        if (o->isExtensible()) {
-            ok = o->setPrototype(p);
-        }
-        if (!ok)
-            return scope.engine->throwTypeError(QStringLiteral("Object.setPrototypeOf: Could not change prototype"));
-    }
+    const Object *p = argv[1].isNull() ? nullptr : static_cast<const Object *>(argv + 1);
+    bool ok = o->setPrototypeOf(p);
+    if (!ok)
+        return scope.engine->throwTypeError(QStringLiteral("Could not change prototype."));
     return o->asReturnedValue();
 }
 
@@ -604,11 +597,11 @@ ReturnedValue ObjectPrototype::method_isPrototypeOf(const FunctionObject *b, con
     ScopedObject O(scope, thisObject->toObject(scope.engine));
     if (scope.engine->hasException)
         return QV4::Encode::undefined();
-    ScopedObject proto(scope, V->prototype());
+    ScopedObject proto(scope, V->getPrototypeOf());
     while (proto) {
         if (O->d() == proto->d())
             return Encode(true);
-        proto = proto->prototype();
+        proto = proto->getPrototypeOf();
     }
     return Encode(false);
 }
@@ -694,32 +687,21 @@ ReturnedValue ObjectPrototype::method_get_proto(const FunctionObject *b, const V
     if (!o)
         THROW_TYPE_ERROR();
 
-    return Encode(o->prototype());
+    return Encode(o->getPrototypeOf());
 }
 
 ReturnedValue ObjectPrototype::method_set_proto(const FunctionObject *b, const Value *thisObject, const Value *argv, int argc)
 {
     Scope scope(b);
     ScopedObject o(scope, thisObject);
-    if (!o || !argc)
+    if (!o || !argc || (!argv[0].isObject() && !argv[0].isNull()))
         THROW_TYPE_ERROR();
 
-    if (argv[0].isNull()) {
-        o->setPrototype(nullptr);
-        RETURN_UNDEFINED();
-    }
-
-    ScopedObject p(scope, argv[0]);
-    bool ok = false;
-    if (!!p) {
-        if (o->prototype() == p->d()) {
-            ok = true;
-        } else if (o->isExtensible()) {
-            ok = o->setPrototype(p);
-        }
-    }
+    const Object *p = argv[0].isNull() ? nullptr : static_cast<const Object *>(argv);
+    bool ok = o->setPrototypeOf(p);
     if (!ok)
-        return scope.engine->throwTypeError(QStringLiteral("Cyclic __proto__ value"));
+        return scope.engine->throwTypeError(QStringLiteral("Could not change prototype."));
+    return Encode::undefined();
     RETURN_UNDEFINED();
 }
 
diff --git a/src/qml/jsruntime/qv4proxy.cpp b/src/qml/jsruntime/qv4proxy.cpp
index e499dfbcf1..80e1b70a1a 100644
--- a/src/qml/jsruntime/qv4proxy.cpp
+++ b/src/qml/jsruntime/qv4proxy.cpp
@@ -361,6 +361,89 @@ bool ProxyObject::preventExtensions(Managed *m)
     return result;
 }
 
+Heap::Object *ProxyObject::getPrototypeOf(const Managed *m)
+{
+    Scope scope(m);
+    const ProxyObject *o = static_cast<const ProxyObject *>(m);
+    if (!o->d()->handler) {
+        scope.engine->throwTypeError();
+        return nullptr;
+    }
+
+    ScopedObject target(scope, o->d()->target);
+    Q_ASSERT(target);
+    ScopedObject handler(scope, o->d()->handler);
+    ScopedString name(scope, scope.engine->newString(QStringLiteral("getPrototypeOf")));
+    ScopedValue trap(scope, handler->get(name));
+    if (scope.hasException())
+        return nullptr;
+    if (trap->isNullOrUndefined())
+        return target->getPrototypeOf();
+    if (!trap->isFunctionObject()) {
+        scope.engine->throwTypeError();
+        return nullptr;
+    }
+
+    JSCallData cdata(scope, 1, nullptr, handler);
+    cdata.args[0] = target;
+
+    ScopedValue trapResult(scope, static_cast<const FunctionObject *>(trap.ptr)->call(cdata));
+    if (!trapResult->isNull() && !trapResult->isObject()) {
+        scope.engine->throwTypeError();
+        return nullptr;
+    }
+    Heap::Object *proto = trapResult->isNull() ? nullptr : static_cast<Heap::Object *>(trapResult->heapObject());
+    if (!target->isExtensible()) {
+        Heap::Object *targetProto = target->getPrototypeOf();
+        if (proto != targetProto) {
+            scope.engine->throwTypeError();
+            return nullptr;
+        }
+    }
+    return proto;
+}
+
+bool ProxyObject::setPrototypeOf(Managed *m, const Object *p)
+{
+    Scope scope(m);
+    const ProxyObject *o = static_cast<const ProxyObject *>(m);
+    if (!o->d()->handler) {
+        scope.engine->throwTypeError();
+        return false;
+    }
+
+    ScopedObject target(scope, o->d()->target);
+    Q_ASSERT(target);
+    ScopedObject handler(scope, o->d()->handler);
+    ScopedString name(scope, scope.engine->newString(QStringLiteral("setPrototypeOf")));
+    ScopedValue trap(scope, handler->get(name));
+    if (scope.hasException())
+        return false;
+    if (trap->isNullOrUndefined())
+        return target->setPrototypeOf(p);
+    if (!trap->isFunctionObject()) {
+        scope.engine->throwTypeError();
+        return false;
+    }
+
+    JSCallData cdata(scope, 2, nullptr, handler);
+    cdata.args[0] = target;
+    cdata.args[1] = p ? p->asReturnedValue() : Encode::null();
+
+    ScopedValue trapResult(scope, static_cast<const FunctionObject *>(trap.ptr)->call(cdata));
+    bool result = trapResult->toBoolean();
+    if (!result)
+        return false;
+    if (!target->isExtensible()) {
+        Heap::Object *targetProto = target->getPrototypeOf();
+        if (p->d() != targetProto) {
+            scope.engine->throwTypeError();
+            return false;
+        }
+    }
+    return true;
+}
+
 //ReturnedValue ProxyObject::callAsConstructor(const FunctionObject *f, const Value *argv, int argc)
 //{
 
diff --git a/src/qml/jsruntime/qv4proxy_p.h b/src/qml/jsruntime/qv4proxy_p.h
index a8b5b63a6c..cbabc7e5d9 100644
--- a/src/qml/jsruntime/qv4proxy_p.h
+++ b/src/qml/jsruntime/qv4proxy_p.h
@@ -95,6 +95,8 @@ struct ProxyObject: Object {
     static PropertyAttributes getOwnProperty(Managed *m, Identifier id, Property *p);
     static bool isExtensible(const Managed *m);
     static bool preventExtensions(Managed *);
+    static Heap::Object *getPrototypeOf(const Managed *);
+    static bool setPrototypeOf(Managed *, const Object *);
 
     // those might require a second proxy object that derives from FunctionObject...
 //    static ReturnedValue callAsConstructor(const FunctionObject *f, const Value *argv, int argc);
diff --git a/src/qml/jsruntime/qv4qobjectwrapper.cpp b/src/qml/jsruntime/qv4qobjectwrapper.cpp
index 2ab77502d6..94d645ac2b 100644
--- a/src/qml/jsruntime/qv4qobjectwrapper.cpp
+++ b/src/qml/jsruntime/qv4qobjectwrapper.cpp
@@ -2093,7 +2093,7 @@ ReturnedValue QMetaObjectWrapper::constructInternal(const Value *argv, int argc)
     }
     Scoped<QMetaObjectWrapper> metaObject(scope, this);
     object->defineDefaultProperty(v4->id_constructor(), metaObject);
-    object->setPrototype(const_cast<QMetaObjectWrapper*>(this));
+    object->setPrototypeOf(const_cast<QMetaObjectWrapper*>(this));
     return object.asReturnedValue();
 
 }
diff --git a/src/qml/jsruntime/qv4reflect.cpp b/src/qml/jsruntime/qv4reflect.cpp
index 219e28b6e7..9b4a5a2375 100644
--- a/src/qml/jsruntime/qv4reflect.cpp
+++ b/src/qml/jsruntime/qv4reflect.cpp
@@ -175,12 +175,14 @@ ReturnedValue Reflect::method_getOwnPropertyDescriptor(const FunctionObject *f,
     return ObjectPrototype::method_getOwnPropertyDescriptor(f, thisObject, argv, argc);
 }
 
-ReturnedValue Reflect::method_getPrototypeOf(const FunctionObject *f, const Value *thisObject, const Value *argv, int argc)
+ReturnedValue Reflect::method_getPrototypeOf(const FunctionObject *f, const Value *, const Value *argv, int argc)
 {
     if (!argc || !argv[0].isObject())
         return f->engine()->throwTypeError();
 
-    return ObjectPrototype::method_getPrototypeOf(f, thisObject, argv, argc);
+    const Object *o = static_cast<const Object *>(argv);
+    Heap::Object *p = o->getPrototypeOf();
+    return (p ? p->asReturnedValue() : Encode::null());
 }
 
 ReturnedValue Reflect::method_has(const FunctionObject *f, const Value *, const Value *argv, int argc)
@@ -260,10 +262,13 @@ ReturnedValue Reflect::method_set(const FunctionObject *f, const Value *, const
     return Encode(result);
 }
 
-ReturnedValue Reflect::method_setPrototypeOf(const FunctionObject *f, const Value *thisObject, const Value *argv, int argc)
+ReturnedValue Reflect::method_setPrototypeOf(const FunctionObject *f, const Value *, const Value *argv, int argc)
 {
-    if (argc < 2 || !argv[0].isObject())
+    if (argc < 2 || !argv[0].isObject() || (!argv[1].isNull() && !argv[1].isObject()))
         return f->engine()->throwTypeError();
 
-    return ObjectPrototype::method_setPrototypeOf(f, thisObject, argv, argc);
+    Scope scope(f);
+    ScopedObject o(scope, static_cast<const Object *>(argv));
+    const Object *proto = argv[1].isNull() ? nullptr : static_cast<const Object *>(argv + 1);
+    return Encode(o->setPrototypeOf(proto));
 }
diff --git a/src/qml/jsruntime/qv4reflect_p.h b/src/qml/jsruntime/qv4reflect_p.h
index 73d257e006..d480e1d914 100644
--- a/src/qml/jsruntime/qv4reflect_p.h
+++ b/src/qml/jsruntime/qv4reflect_p.h
@@ -73,7 +73,7 @@ struct Reflect : Object {
     static ReturnedValue method_deleteProperty(const FunctionObject *, const Value *thisObject, const Value *argv, int argc);
     static ReturnedValue method_get(const FunctionObject *, const Value *thisObject, const Value *argv, int argc);
     static ReturnedValue method_getOwnPropertyDescriptor(const FunctionObject *, const Value *thisObject, const Value *argv, int argc);
-    static ReturnedValue method_getPrototypeOf(const FunctionObject *, const Value *thisObject, const Value *argv, int argc);
+    static ReturnedValue method_getPrototypeOf(const FunctionObject *, const Value *, const Value *argv, int argc);
     static ReturnedValue method_has(const FunctionObject *, const Value *thisObject, const Value *argv, int argc);
     static ReturnedValue method_isExtensible(const FunctionObject *, const Value *thisObject, const Value *argv, int argc);
     static ReturnedValue method_ownKeys(const FunctionObject *, const Value *thisObject, const Value *argv, int argc);
diff --git a/src/qml/jsruntime/qv4typedarray.cpp b/src/qml/jsruntime/qv4typedarray.cpp
index 3eadfe04a6..86aa18c3a4 100644
--- a/src/qml/jsruntime/qv4typedarray.cpp
+++ b/src/qml/jsruntime/qv4typedarray.cpp
@@ -410,9 +410,9 @@ void TypedArrayPrototype::init(ExecutionEngine *engine, TypedArrayCtor *ctor)
     ctor->defineReadonlyConfigurableProperty(engine->id_length(), Primitive::fromInt32(3));
     ctor->defineReadonlyProperty(engine->id_prototype(), *this);
     ctor->defineReadonlyProperty(QStringLiteral("BYTES_PER_ELEMENT"), Primitive::fromInt32(operations[ctor->d()->type].bytesPerElement));
-    ctor->setPrototype(engine->intrinsicTypedArrayCtor());
+    ctor->setPrototypeOf(engine->intrinsicTypedArrayCtor());
 
-    setPrototype(engine->intrinsicTypedArrayPrototype());
+    setPrototypeOf(engine->intrinsicTypedArrayPrototype());
     defineDefaultProperty(engine->id_constructor(), (o = ctor));
     defineReadonlyProperty(QStringLiteral("BYTES_PER_ELEMENT"), Primitive::fromInt32(operations[ctor->d()->type].bytesPerElement));
 }
diff --git a/src/qml/qml/qqmlcomponent.cpp b/src/qml/qml/qqmlcomponent.cpp
index 22e20de8d7..9986d3577a 100644
--- a/src/qml/qml/qqmlcomponent.cpp
+++ b/src/qml/qml/qqmlcomponent.cpp
@@ -1409,7 +1409,7 @@ void QQmlComponent::incubateObject(QQmlV4Function *args)
 
     QV4::Scoped<QV4::QmlIncubatorObject> r(scope, v4->memoryManager->allocate<QV4::QmlIncubatorObject>(mode));
     QV4::ScopedObject p(scope, e->incubationProto.value());
-    r->setPrototype(p);
+    r->setPrototypeOf(p);
 
     if (!valuemap->isUndefined())
         r->d()->valuemap.set(scope.engine, valuemap);
diff --git a/src/qml/qml/qqmllocale.cpp b/src/qml/qml/qqmllocale.cpp
index f17f0fb77a..cdca4f794c 100644
--- a/src/qml/qml/qqmllocale.cpp
+++ b/src/qml/qml/qqmllocale.cpp
@@ -828,7 +828,7 @@ QV4::ReturnedValue QQmlLocale::wrap(ExecutionEngine *v4, const QLocale &locale)
     QV4::Scoped<QQmlLocaleData> wrapper(scope, v4->memoryManager->allocate<QQmlLocaleData>());
     *wrapper->d()->locale = locale;
     QV4::ScopedObject p(scope, d->prototype.value());
-    wrapper->setPrototype(p);
+    wrapper->setPrototypeOf(p);
     return wrapper.asReturnedValue();
 }
 
diff --git a/src/qml/qml/qqmlxmlhttprequest.cpp b/src/qml/qml/qqmlxmlhttprequest.cpp
index 41531c1df3..a8faac4b0d 100644
--- a/src/qml/qml/qqmlxmlhttprequest.cpp
+++ b/src/qml/qml/qqmlxmlhttprequest.cpp
@@ -611,7 +611,7 @@ ReturnedValue Node::create(ExecutionEngine *v4, NodeImpl *data)
 
     switch (data->type) {
     case NodeImpl::Attr:
-        instance->setPrototype((p = Attr::prototype(v4)));
+        instance->setPrototypeUnchecked((p = Attr::prototype(v4)));
         break;
     case NodeImpl::Comment:
     case NodeImpl::Document:
@@ -623,13 +623,13 @@ ReturnedValue Node::create(ExecutionEngine *v4, NodeImpl *data)
     case NodeImpl::ProcessingInstruction:
         return Encode::undefined();
     case NodeImpl::CDATA:
-        instance->setPrototype((p = CDATA::prototype(v4)));
+        instance->setPrototypeUnchecked((p = CDATA::prototype(v4)));
         break;
     case NodeImpl::Text:
-        instance->setPrototype((p = Text::prototype(v4)));
+        instance->setPrototypeUnchecked((p = Text::prototype(v4)));
         break;
     case NodeImpl::Element:
-        instance->setPrototype((p = Element::prototype(v4)));
+        instance->setPrototypeUnchecked((p = Element::prototype(v4)));
         break;
     }
 
@@ -643,7 +643,7 @@ ReturnedValue Element::prototype(ExecutionEngine *engine)
         Scope scope(engine);
         ScopedObject p(scope, engine->newObject());
         ScopedObject pp(scope);
-        p->setPrototype((pp = NodePrototype::getProto(engine)));
+        p->setPrototypeUnchecked((pp = NodePrototype::getProto(engine)));
         p->defineAccessorProperty(QStringLiteral("tagName"), NodePrototype::method_get_nodeName, nullptr);
         d->elementPrototype.set(engine, p);
         engine->v8Engine->freezeObject(p);
@@ -658,7 +658,7 @@ ReturnedValue Attr::prototype(ExecutionEngine *engine)
         Scope scope(engine);
         ScopedObject p(scope, engine->newObject());
         ScopedObject pp(scope);
-        p->setPrototype((pp = NodePrototype::getProto(engine)));
+        p->setPrototypeUnchecked((pp = NodePrototype::getProto(engine)));
         p->defineAccessorProperty(QStringLiteral("name"), method_name, nullptr);
         p->defineAccessorProperty(QStringLiteral("value"), method_value, nullptr);
         p->defineAccessorProperty(QStringLiteral("ownerElement"), method_ownerElement, nullptr);
@@ -715,7 +715,7 @@ ReturnedValue CharacterData::prototype(ExecutionEngine *v4)
         Scope scope(v4);
         ScopedObject p(scope, v4->newObject());
         ScopedObject pp(scope);
-        p->setPrototype((pp = NodePrototype::getProto(v4)));
+        p->setPrototypeUnchecked((pp = NodePrototype::getProto(v4)));
         p->defineAccessorProperty(QStringLiteral("data"), NodePrototype::method_get_nodeValue, nullptr);
         p->defineAccessorProperty(QStringLiteral("length"), method_length, nullptr);
         d->characterDataPrototype.set(v4, p);
@@ -751,7 +751,7 @@ ReturnedValue Text::prototype(ExecutionEngine *v4)
         Scope scope(v4);
         ScopedObject p(scope, v4->newObject());
         ScopedObject pp(scope);
-        p->setPrototype((pp = CharacterData::prototype(v4)));
+        p->setPrototypeUnchecked((pp = CharacterData::prototype(v4)));
         p->defineAccessorProperty(QStringLiteral("isElementContentWhitespace"), method_isElementContentWhitespace, nullptr);
         p->defineAccessorProperty(QStringLiteral("wholeText"), method_wholeText, nullptr);
         d->textPrototype.set(v4, p);
@@ -768,7 +768,7 @@ ReturnedValue CDATA::prototype(ExecutionEngine *v4)
         Scope scope(v4);
         ScopedObject p(scope, v4->newObject());
         ScopedObject pp(scope);
-        p->setPrototype((pp = Text::prototype(v4)));
+        p->setPrototypeUnchecked((pp = Text::prototype(v4)));
         d->cdataPrototype.set(v4, p);
         v4->v8Engine->freezeObject(p);
     }
@@ -782,7 +782,7 @@ ReturnedValue Document::prototype(ExecutionEngine *v4)
         Scope scope(v4);
         ScopedObject p(scope, v4->newObject());
         ScopedObject pp(scope);
-        p->setPrototype((pp = NodePrototype::getProto(v4)));
+        p->setPrototypeUnchecked((pp = NodePrototype::getProto(v4)));
         p->defineAccessorProperty(QStringLiteral("xmlVersion"), method_xmlVersion, nullptr);
         p->defineAccessorProperty(QStringLiteral("xmlEncoding"), method_xmlEncoding, nullptr);
         p->defineAccessorProperty(QStringLiteral("xmlStandalone"), method_xmlStandalone, nullptr);
@@ -879,7 +879,7 @@ ReturnedValue Document::load(ExecutionEngine *v4, const QByteArray &data)
     ScopedObject instance(scope, v4->memoryManager->allocate<Node>(document));
     document->release(); // the GC should own the NodeImpl via Node now
     ScopedObject p(scope);
-    instance->setPrototype((p = Document::prototype(v4)));
+    instance->setPrototypeUnchecked((p = Document::prototype(v4)));
     return instance.asReturnedValue();
 }
 
@@ -1650,7 +1650,7 @@ struct QQmlXMLHttpRequestCtor : public FunctionObject
         QQmlXMLHttpRequest *r = new QQmlXMLHttpRequest(scope.engine->v8Engine->networkAccessManager(), scope.engine);
         Scoped<QQmlXMLHttpRequestWrapper> w(scope, scope.engine->memoryManager->allocate<QQmlXMLHttpRequestWrapper>(r));
         ScopedObject proto(scope, ctor->d()->proto);
-        w->setPrototype(proto);
+        w->setPrototypeUnchecked(proto);
         return w.asReturnedValue();
     }
 
diff --git a/src/qml/qml/v8/qv8engine.cpp b/src/qml/qml/v8/qv8engine.cpp
index b5e25fb6d4..f99c4def45 100644
--- a/src/qml/qml/v8/qv8engine.cpp
+++ b/src/qml/qml/v8/qv8engine.cpp
@@ -223,13 +223,13 @@ static void freeze_recursive(QV4::ExecutionEngine *v4, QV4::Object *object)
     QV4::Scope scope(v4);
 
     bool instanceOfObject = false;
-    QV4::ScopedObject p(scope, object->prototype());
+    QV4::ScopedObject p(scope, object->getPrototypeOf());
     while (p) {
         if (p->d() == v4->objectPrototype()->d()) {
             instanceOfObject = true;
             break;
         }
-        p = p->prototype();
+        p = p->getPrototypeOf();
     }
     if (!instanceOfObject)
         return;
diff --git a/src/qml/types/qqmldelegatemodel.cpp b/src/qml/types/qqmldelegatemodel.cpp
index 33fe5f3438..98b90af5c3 100644
--- a/src/qml/types/qqmldelegatemodel.cpp
+++ b/src/qml/types/qqmldelegatemodel.cpp
@@ -2563,7 +2563,7 @@ QQmlV4Handle QQmlDelegateModelGroup::get(int index)
     QV4::Scope scope(v4);
     QV4::ScopedObject o(scope, v4->memoryManager->allocate<QQmlDelegateModelItemObject>(cacheItem));
     QV4::ScopedObject p(scope, model->m_cacheMetaType->modelItemProto.value());
-    o->setPrototype(p);
+    o->setPrototypeOf(p);
     ++cacheItem->scriptRef;
 
     return QQmlV4Handle(o);
@@ -3395,7 +3395,7 @@ public:
 
         QV4::ScopedObject changeProto(scope, engineData(v4)->changeProto.value());
         QV4::Scoped<QQmlDelegateModelGroupChange> object(scope, QQmlDelegateModelGroupChange::create(v4));
-        object->setPrototype(changeProto);
+        object->setPrototypeOf(changeProto);
         object->d()->change = change;
 
         if (hasProperty)
diff --git a/src/qml/util/qqmladaptormodel.cpp b/src/qml/util/qqmladaptormodel.cpp
index 3016316e57..4130eff33a 100644
--- a/src/qml/util/qqmladaptormodel.cpp
+++ b/src/qml/util/qqmladaptormodel.cpp
@@ -439,7 +439,7 @@ public:
         QV4::Scope scope(v4);
         QV4::ScopedObject proto(scope, type->prototype.value());
         QV4::ScopedObject o(scope, proto->engine()->memoryManager->allocate<QQmlDelegateModelItemObject>(this));
-        o->setPrototype(proto);
+        o->setPrototypeOf(proto);
         ++scriptRef;
         return o.asReturnedValue();
     }
@@ -620,7 +620,7 @@ public:
         QV4::Scope scope(v4);
         QV4::ScopedObject o(scope, v4->memoryManager->allocate<QQmlDelegateModelItemObject>(this));
         QV4::ScopedObject p(scope, data->listItemProto.value());
-        o->setPrototype(p);
+        o->setPrototypeOf(p);
         ++scriptRef;
         return o.asReturnedValue();
     }
diff --git a/src/quick/items/context2d/qquickcontext2d.cpp b/src/quick/items/context2d/qquickcontext2d.cpp
index 07d5f6d39b..314b7904b4 100644
--- a/src/quick/items/context2d/qquickcontext2d.cpp
+++ b/src/quick/items/context2d/qquickcontext2d.cpp
@@ -956,7 +956,7 @@ static QV4::ReturnedValue qt_create_image_data(qreal w, qreal h, QV4::ExecutionE
     QQuickContext2DEngineData *ed = engineData(scope.engine);
     QV4::Scoped<QQuickJSContext2DPixelData> pixelData(scope, scope.engine->memoryManager->allocate<QQuickJSContext2DPixelData>());
     QV4::ScopedObject p(scope, ed->pixelArrayProto.value());
-    pixelData->setPrototype(p);
+    pixelData->setPrototypeOf(p);
 
     if (image.isNull()) {
         *pixelData->d()->image = QImage(w, h, QImage::Format_ARGB32);
@@ -1584,7 +1584,7 @@ QV4::ReturnedValue QQuickJSContext2DPrototype::method_createLinearGradient(const
 
         QV4::Scoped<QQuickContext2DStyle> gradient(scope, scope.engine->memoryManager->allocate<QQuickContext2DStyle>());
         QV4::ScopedObject p(scope, ed->gradientProto.value());
-        gradient->setPrototype(p);
+        gradient->setPrototypeOf(p);
         *gradient->d()->brush = QLinearGradient(x0, y0, x1, y1);
         RETURN_RESULT(*gradient);
     }
@@ -1636,7 +1636,7 @@ QV4::ReturnedValue QQuickJSContext2DPrototype::method_createRadialGradient(const
 
         QV4::Scoped<QQuickContext2DStyle> gradient(scope, scope.engine->memoryManager->allocate<QQuickContext2DStyle>());
         QV4::ScopedObject p(scope, ed->gradientProto.value());
-        gradient->setPrototype(p);
+        gradient->setPrototypeOf(p);
         *gradient->d()->brush = QRadialGradient(QPointF(x1, y1), r1, QPointF(x0, y0), r0);
         RETURN_RESULT(*gradient);
     }
@@ -1680,7 +1680,7 @@ QV4::ReturnedValue QQuickJSContext2DPrototype::method_createConicalGradient(cons
 
         QV4::Scoped<QQuickContext2DStyle> gradient(scope, scope.engine->memoryManager->allocate<QQuickContext2DStyle>());
         QV4::ScopedObject p(scope, ed->gradientProto.value());
-        gradient->setPrototype(p);
+        gradient->setPrototypeOf(p);
         *gradient->d()->brush = QConicalGradient(x, y, angle);
         RETURN_RESULT(*gradient);
     }
@@ -4401,7 +4401,7 @@ void QQuickContext2D::setV4Engine(QV4::ExecutionEngine *engine)
         QV4::Scope scope(engine);
         QV4::Scoped<QQuickJSContext2D> wrapper(scope, engine->memoryManager->allocate<QQuickJSContext2D>());
         QV4::ScopedObject p(scope, ed->contextPrototype.value());
-        wrapper->setPrototype(p);
+        wrapper->setPrototypeOf(p);
         wrapper->d()->context = this;
         m_v4value = wrapper;
     }