Optimize ExecutionEngine::metaTypeToJS()

We almost never need to construct a QVariant to do this. Constructing a
QVariant is excessively expensive if you have something simple like an
integer. This also fixes the unexpected "unwrapping" of variants when we
pass them through QJSValue.

[ChangeLog][QtQml][Important Behavior Changes] If you create a QJSValue
from a nested QVariant (that is, a QVariant containing another
QVariant), then, when retrieving its contents again, the outer variant
is not unwrapped anymore. Rather, you get exactly the value you've
passed in.

Change-Id: I8c16eed4f13e8cfdeced0756eef593b3b8e84dd1
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

1 files changed, 3 insertions, 0 deletions

diff --git a/src/qml/jsruntime/qv4engine_p.h b/src/qml/jsruntime/qv4engine_p.h
index 6c3d2d4436..0edac38d9c 100644
--- a/src/qml/jsruntime/qv4engine_p.h
+++ b/src/qml/jsruntime/qv4engine_p.h
@@ -747,6 +747,9 @@ public:
                                 QQmlRefPointer<QQmlContextData> ctxtdata, int argc, void **args, QMetaType *types);
 
 private:
+    QV4::ReturnedValue fromData(
+            const QMetaType &type, const void *ptr, const QVariant *variant = nullptr);
+
 #if QT_CONFIG(qml_debug)
     QScopedPointer<QV4::Debugging::Debugger> m_debugger;
     QScopedPointer<QV4::Profiling::Profiler> m_profiler;