moc-generated code error at Qt6 when not at Qt5

[JonB]

@Axel-Spoerl
I have now changed over to cmake (project mocerror2). FWIW my CMakeLists.txt:

cmake_minimum_required(VERSION 3.14)

project(mocerror2 LANGUAGES CXX)

set(CMAKE_AUTOUIC ON)
set(CMAKE_AUTOMOC ON)
set(CMAKE_AUTORCC ON)

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

find_package(QT NAMES Qt6 Qt5 REQUIRED COMPONENTS Core)
find_package(Qt${QT_VERSION_MAJOR} REQUIRED COMPONENTS Core)

add_executable(mocerror2
  main.cpp
  bar.cpp bar.h foo.cpp foo.h
)
target_link_libraries(mocerror2 Qt${QT_VERSION_MAJOR}::Core)

include(GNUInstallDirs)
install(TARGETS mocerror2
    LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
    RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
)

As I expected it makes no difference and I get same error:

[ 14%] Automatic MOC and UIC for target mocerror2
[ 14%] Built target mocerror2_autogen
[ 28%] Building CXX object CMakeFiles/mocerror2.dir/mocerror2_autogen/mocs_compilation.cpp.o
In file included from /usr/include/x86_64-linux-gnu/qt6/QtCore/qobject.h:18,
                 from /usr/include/x86_64-linux-gnu/qt6/QtCore/QObject:1,
                 from /home/jon/QtTests/mocerror2/build/Desktop-Debug/mocerror2_autogen/EWIEGA46WW/../../../../foo.h:5,
                 from /home/jon/QtTests/mocerror2/build/Desktop-Debug/mocerror2_autogen/EWIEGA46WW/moc_foo.cpp:10,
                 from /home/jon/QtTests/mocerror2/build/Desktop-Debug/mocerror2_autogen/mocs_compilation.cpp:2:
/usr/include/x86_64-linux-gnu/qt6/QtCore/qmetatype.h: In instantiation of ‘struct QtPrivate::IsPointerToTypeDerivedFromQObject<Bar*>’:
/usr/include/x86_64-linux-gnu/qt6/QtCore/qmetatype.h:1102:60:   required from ‘struct QMetaTypeId<Bar*>’
/usr/include/x86_64-linux-gnu/qt6/QtCore/qmetatype.h:1122:38:   required from ‘struct QMetaTypeId2<Bar*>’
/usr/include/x86_64-linux-gnu/qt6/QtCore/qmetatype.h:1585:1:   required from ‘struct QMetaTypeId<QList<Bar*> >’
/usr/include/x86_64-linux-gnu/qt6/QtCore/qmetatype.h:2364:42:   recursively required by substitution of ‘template<class T> struct QtPrivate::BuiltinMetaType<T, typename std::enable_if<QMetaTypeId2<T>::IsBuiltIn, void>::type> [with T = QList<Bar*>]’
/usr/include/x86_64-linux-gnu/qt6/QtCore/qmetatype.h:2364:42:   required from ‘constexpr const QtPrivate::QMetaTypeInterface QtPrivate::QMetaTypeInterfaceWrapper<QList<Bar*> >::metaType’
/usr/include/x86_64-linux-gnu/qt6/QtCore/qmetatype.h:2486:16:   required from ‘constexpr const QtPrivate::QMetaTypeInterface* QtPrivate::qTryMetaTypeInterfaceForType() [with Unique = {anonymous}::qt_meta_stringdata_Foo_t; TypeCompletePair = TypeAndForceComplete<QList<Bar*>, std::integral_constant<bool, false> >]’
/usr/include/x86_64-linux-gnu/qt6/QtCore/qmetatype.h:2537:55:   required from ‘constexpr const QtPrivate::QMetaTypeInterface* const qt_incomplete_metaTypeArray [5]<{anonymous}::qt_meta_stringdata_Foo_t, QtPrivate::TypeAndForceComplete<Foo, std::integral_constant<bool, true> >, QtPrivate::TypeAndForceComplete<void, std::integral_constant<bool, false> >, QtPrivate::TypeAndForceComplete<Bar*, std::integral_constant<bool, false> >, QtPrivate::TypeAndForceComplete<void, std::integral_constant<bool, false> >, QtPrivate::TypeAndForceComplete<QList<Bar*>, std::integral_constant<bool, false> > >’
/home/jon/QtTests/mocerror2/build/Desktop-Debug/mocerror2_autogen/EWIEGA46WW/moc_foo.cpp:95:5:   required from here
/usr/include/x86_64-linux-gnu/qt6/QtCore/qmetatype.h:842:23: error: invalid application of ‘sizeof’ to incomplete type ‘Bar’
  842 |         static_assert(sizeof(T), "Type argument of Q_PROPERTY or Q_DECLARE_METATYPE(T*) must be fully defined");
      |                       ^~~~~~~~~
gmake[2]: *** [CMakeFiles/mocerror2.dir/build.make:82: CMakeFiles/mocerror2.dir/mocerror2_autogen/mocs_compilation.cpp.o] Error 1
gmake[1]: *** [CMakeFiles/Makefile2:86: CMakeFiles/mocerror2.dir/all] Error 2
gmake: *** [Makefile:136: all] Error 2
10:38:41: The process "/usr/bin/cmake" exited with code 2.

I do not understand why you do not get same error as I do.

My gcc is 13.2.0. My moc is 6.4.2 as is my Qt6.

[Axel Spoerl]

I am using gcc 13.3.0, moc 6.9.0.
The only difference in our CMake files is that I require 3.16, you require 3.14.

[JonB]

@Axel-Spoerl
Thank you. So what would you like me to do about our difference in behaviour? :)
[I fetch all my Qt stuff from apt as supplied with Ubuntu 24.04 distro.]

[J.Hilk]

I actually remember something similar, early when QVector was nuked for QList to prosper.

I think if you change it from QList<Bar *>bars to QList<Bar *> *bars it actually works. Axel is using a way later Qt6 version ( 6.8 vs 6.4.2) QList was probably touched again in between those versions, to fix this :D

[JonB]

@J-Hilk said in moc-generated code error at Qt6 when not at Qt5:

I think if you change it from QList<Bar *>bars to QList<Bar *> *bars it actually works.

But those are quite different types! :) Are you just showing me that to say what it could cope with?

Axel is using a way later Qt6 version ( 6.8 vs 6.4.2) QList was probably touched again in between those versions, to fix this :D

Ah! Well in that case it's obviously not to be reported. Thanks for the heads-up.

With Qt5 I always had Qt 5.15 (or maybe 5.12) via apt under various Ubuntu releases over the years. And I have to say that was just great, I didn't encounter problems and I didn't need later versions. I suspected Qt6 would be problematic, looks like I get a quite older version and am going to have issues which really need a later version from TQtC :( Ho-hum....

[J.Hilk]

@JonB what was the reason again, why you don't fetch the latest version from the installer or the repo (to compile yourself) ?

[JonB]

@J-Hilk

• I have never even attempted to download from TQtC, having seen the endless problems with downloads/mirrors. Fills me with dread....
• ...As does when I see people who for whatever reason (e.g. maybe to do with configuration, whatever it happens) get an error during compilation of the whole of Qt....
• I don't have the disk space in VM for Qt sources + compilation outputs.
• I don't have the memory in VM to compile it. Not to mention the requirements for QWebEngine.
• I share (development) with other people using Qt from Ubuntu distro. They are not going to want to fetch/compile/install or take from me.

Am I being difficult? ;-) It was all so simple with Qt5, everything worked. Now beginning to think of backing out of the whole of Qt6 and reverting to Qt5. But that would be a shame for my answering questions on this forum.

[J.Hilk]

@JonB I Understand, I myself are still on 5.15.17 and I stay with 5 as long as possible.

But Android support is apparently already dropped for Qt5. So I have at most a year until I have to switch over :(

[JonB]

@J-Hilk said in moc-generated code error at Qt6 when not at Qt5:

@JonB I Understand, I myself are still on 5.15.17 and I stay with 5 as long as possible.

OMG! What platform/OS version are you on?

[J.Hilk]

@JonB windows, macOS, iOS, iPadOS & Android. Still so far all the latest available (not betas)

[JonB]

@J-Hilk Right, but not my Ubuntu 24.04 which I am moving to, and doing Qt as part of it.

[J.Hilk]

@JonB non of our customers use Linux, only reason why we support macOS is because its my development environment and its only a few steps more to deploy for it as well ;)