Compile error Type argument of Q_PROPERTY or Q_DECLARE_METATYPE(T*) must be fully defined

[maidamai0]

I got a compile error on include/luna/controls/TreeViewAttached.hpp:

Q_PROPERTY(TreeViewTemplate* view READ view NOTIFY viewChanged)

saying:

[build] In file included from luna_autogen/EEX6FCQYDO/moc_DoubleSpinBoxTemplate.cpp:10:
[build] In file included from luna_autogen/EEX6FCQYDO/../../../include/luna/controls/DoubleSpinBoxTemplate.hpp:3:
[build] In file included from C:\Qt\6.2.0\msvc2019_64\include\QtCore/QObject:1:
[build] In file included from C:\Qt\6.2.0\msvc2019_64\include\QtCore/qobject.h:54:
[build] C:\Qt\6.2.0\msvc2019_64\include\QtCore/qmetatype.h(869,23): error: invalid application of 'sizeof' to an incomplete type 'luna::controls::TreeViewTemplate'
[build]         static_assert(sizeof(T), "Type argument of Q_PROPERTY or Q_DECLARE_METATYPE(T*) must be fully defined");
[build]                       ^~~~~~~~~
[build] C:\Qt\6.2.0\msvc2019_64\include\QtCore/qmetatype.h(1187,25): note: in instantiation of template class 'QtPrivate::IsPointerToTypeDerivedFromQObject<luna::controls::TreeViewTemplate *>' requested here
[build]                      | (IsPointerToTypeDerivedFromQObject<T>::Value ? QMetaType::PointerToQObject : 0)
[build]                         ^
[build] C:\Qt\6.2.0\msvc2019_64\include\QtCore/qmetatype.h(2330,21): note: in instantiation of template class 'QtPrivate::QMetaTypeTypeFlags<luna::controls::TreeViewTemplate *>' requested here
[build]         /*.flags=*/ QMetaTypeTypeFlags<T>::Flags,
[build]                     ^
[build] C:\Qt\6.2.0\msvc2019_64\include\QtCore/qmetatype.h(2453,48): note: in instantiation of static data member 'QtPrivate::QMetaTypeInterfaceWrapper<luna::controls::TreeViewTemplate *>::metaType' requested here
[build]         return &QMetaTypeInterfaceWrapper<Ty>::metaType;
[build]                                                ^
[build] C:\Qt\6.2.0\msvc2019_64\include\QtCore/qmetatype.h(2497,16): note: in instantiation of function template specialization 'QtPrivate::qTryMetaTypeInterfaceForType<qt_meta_stringdata_luna__controls__TreeViewAttached_t, QtPrivate::TypeAndForceComplete<luna::controls::TreeViewTemplate *, std::integral_constant<bool, true>>>' requested here
[build]     QtPrivate::qTryMetaTypeInterfaceForType<Unique, T>()...
[build]                ^
[build] luna_autogen/EEX6FCQYDO/moc_TreeViewAttached.cpp(156,1): note: in instantiation of variable template specialization 'qt_incomplete_metaTypeArray<qt_meta_stringdata_luna__controls__TreeViewAttached_t, QtPrivate::TypeAndForceComplete<luna::controls::TreeViewTemplate *, std::integral_constant<bool, true>>, QtPrivate::TypeAndForceComplete<bool, std::integral_constant<bool, true>>, QtPrivate::TypeAndForceComplete<bool, std::integral_constant<bool, true>>, QtPrivate::TypeAndForceComplete<int, std::integral_constant<bool, true>>, QtPrivate::TypeAndForceComplete<luna::controls::TreeViewAttached, std::integral_constant<bool, true>>, QtPrivate::TypeAndForceComplete<void, std::integral_constant<bool, false>>, QtPrivate::TypeAndForceComplete<void, std::integral_constant<bool, false>>, QtPrivate::TypeAndForceComplete<void, std::integral_constant<bool, false>>, QtPrivate::TypeAndForceComplete<void, std::integral_constant<bool, false>>>' requested here
[build] qt_incomplete_metaTypeArray<qt_meta_stringdata_luna__controls__TreeViewAttached_t
[build] ^
[build] luna_autogen/EEX6FCQYDO/../../../include/luna/controls/TreeViewAttached.hpp(8,7): note: forward declaration of 'luna::controls::TreeViewTemplate'
[build] class TreeViewTemplate;
[build]       ^
[build] 1 error generated.
[build] ninja: build stopped: subcommand failed.
[build] Build finished with exit code 1

I'm not sure if this is only in Qt6, but it tells me the type in Q_PROPERTY must be fully defined instead of forward declared.

[maidamai0]

Qt5 has no problem

[oclero]

I've not tried with Qt6 yet. Is it still the case now in 2022?