Store a QV4::ReturnedValue in QJSValue

Being careful, we can now save primitive values inline. We use the heap
pointer of QV4::Value as either QString* or QV4::Value* for complex
types. We cannot store persistent managed QV4::Value without the double
indirection as those need to be allocated in a special place.

The generic QVariant case is not supported anymore. The only place where
it was actually needed were the stream operators for QJSValue. Those
were fundamentally broken:

* A managed QJSValue saved and loaded from a stream was converted to a
  QVariant-type QJSValue
* QVariant-type QJSValues were not callable, could not be objects or
  arrays, or any of the special types.
* Cyclic references were forcibly broken when saving to a data stream.

In general the support for saving and loading of managed types to/from
a data stream was so abysmally bad that we don't lose much by dropping
it.

[ChangeLog][QML][Important Behavior Changes] When saving a QJSValue to a
QDataStream only primitive values or strings will be retained. Support
for objects and arrays was incomplete and unreliable already before. It
cannot work correctly as we don't necessarily have a JavaScript heap
when loading a QJSValue from a stream. Therefore, we don't have a proper
place to keep any managed values. Using QVariant to keep them instead is
a bad idea because QVariant cannot represent everything a QJSValue can
contain.

Fixes: QTBUG-75174
Change-Id: I75697670639bca8d4b1668763d7020c4cf871bda
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

1 files changed, 3 insertions, 3 deletions

diff --git a/src/qml/jsapi/qjsvalueiterator.cpp b/src/qml/jsapi/qjsvalueiterator.cpp
index 076b90c5f2..360a39aea3 100644
--- a/src/qml/jsapi/qjsvalueiterator.cpp
+++ b/src/qml/jsapi/qjsvalueiterator.cpp
@@ -58,12 +58,12 @@ void QJSValueIteratorPrivate::init(const QJSValue &v)
     QV4::ExecutionEngine *e = QJSValuePrivate::engine(&v);
     if (!e)
         return;
-    QV4::Object *o = QJSValuePrivate::getValue(&v)->objectValue();
+    const QV4::Object *o = QJSValuePrivate::asManagedType<QV4::Object>(&v);
     if (!o)
         return;
 
     engine = e;
-    object = o;
+    object.set(e, o->asReturnedValue());
     iterator.reset(o->ownPropertyKeys(object.valueRef()));
     next();
 }
@@ -209,7 +209,7 @@ QJSValue QJSValueIterator::value() const
         scope.engine->catchException();
         return QJSValue();
     }
-    return QJSValue(scope.engine, val->asReturnedValue());
+    return QJSValuePrivate::fromReturnedValue(val->asReturnedValue());
 }