Fix QMetaObject::newInstance on non-QObject meta object

QMetaObject::newInstance returns a QObject, thus it's not possible to
create a new instance of a Q_GADGET using this function. Previously, we
returned a non-null QObject pointer for such scenarios, which then
leads to crashes when one tries to use it. Now, we check whether the
meta object inherits QObject's meta object, and error out early
otherwise.

Change-Id: I7b1fb6c8d48b3e98161894be2f281a491963345e
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/tests/auto/corelib/kernel/qmetaobject/tst_qmetaobject.cpp b/tests/auto/corelib/kernel/qmetaobject/tst_qmetaobject.cpp
index 9855bec520..cfe1443fd3 100644
--- a/tests/auto/corelib/kernel/qmetaobject/tst_qmetaobject.cpp
+++ b/tests/auto/corelib/kernel/qmetaobject/tst_qmetaobject.cpp
@@ -40,6 +40,13 @@ struct MyStruct
     int i;
 };
 
+class MyGadget
+{
+    Q_GADGET
+public:
+    Q_INVOKABLE MyGadget() {}
+};
+
 namespace MyNamespace {
     // Used in tst_QMetaObject::checkScope
     class MyClass : public QObject
@@ -1207,6 +1214,12 @@ void tst_QMetaObject::invokeMetaConstructor()
         QCOMPARE(obj2->parent(), (QObject*)&obj);
         QVERIFY(qobject_cast<NamespaceWithConstructibleClass::ConstructibleClass*>(obj2) != 0);
     }
+    // gadget shouldn't return a valid pointer
+    {
+        QCOMPARE(MyGadget::staticMetaObject.constructorCount(), 1);
+        QTest::ignoreMessage(QtWarningMsg, "QMetaObject::newInstance: type MyGadget does not inherit QObject");
+        QVERIFY(!MyGadget::staticMetaObject.newInstance());
+    }
 }
 
 void tst_QMetaObject::invokeTypedefTypes()