Do not crash on non-QVariant return types

Patch e354bdc5 introduced a regression that triggers a crash
in Qt 5.9 when returning a type that is not implicitly convertible
to QVariant, such as a QJsonValue, from an invoked method/slot.

This patch fixes this situation and adds proper unit test coverage.

Change-Id: Ib8cb0c96e7496bc8dc9a628245d7a44e4234aff0
Task-number: QTBUG-62045
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@qt.io>
Reviewed-by: Kai Dohmen <psykai1993@googlemail.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/src/webchannel/qmetaobjectpublisher.cpp b/src/webchannel/qmetaobjectpublisher.cpp
index dcc589c..cfc6ad2 100644
--- a/src/webchannel/qmetaobjectpublisher.cpp
+++ b/src/webchannel/qmetaobjectpublisher.cpp
@@ -383,12 +383,12 @@ QVariant QMetaObjectPublisher::invokeMethod(QObject *const object, const int met
                   arguments[0], arguments[1], arguments[2], arguments[3], arguments[4],
                   arguments[5], arguments[6], arguments[7], arguments[8], arguments[9]);
     } else {
-        QGenericReturnArgument returnArgument(method.typeName(), returnValue.data());
-
         // Only init variant with return type if its not a variant itself, which would
         // lead to nested variants which is not what we want.
         if (method.returnType() != QMetaType::QVariant)
             returnValue = QVariant(method.returnType(), 0);
+
+        QGenericReturnArgument returnArgument(method.typeName(), returnValue.data());
         method.invoke(object, returnArgument,
                   arguments[0], arguments[1], arguments[2], arguments[3], arguments[4],
                   arguments[5], arguments[6], arguments[7], arguments[8], arguments[9]);