This patch fixes the QMetaObject::superClass hierarchy for Q_GADGETs
that inherit from a template which in turn inherits another Q_GADGET.
One common scenario where this is applied is for the CRTP. Without this
patch, moc would stop at the template and then sets the superClass
QMetaObject to a nullptr. For QObjects this works, since there moc knows
that every child must by definition inherit QObject. In order to support
this for Q_GADGETs too, we defer the judgment about the availability
of a staticMetaObject in the base class to compile time through the
existing QtPrivate::MetaObjectForType<Base>::value() helper.
[ChangeLog][QtCore][moc] Moc now correctly sets a non-null
QMetaObject::superClass for Q_GADGETs that inherit from a template which
inherits another Q_GADGET.
Change-Id: I103b5efd74ed24172dffce477ca2ed6d0f374d44
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>
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