deprecated qmake build system / removed Qt5 fallback when using USE_QT6=On

[firewave]

QT 5 is now completely EOL and since we never supported Qt6 in qmake which also has various shortcomings, it is time to at least deprecate it and direct users to CMake instead.

Extracted from #4957.

[firewave]

apt.llvm.org repository is currently broken - see llvm/llvm-project#64120 (comment).

[danmar]

hmm.. I have problems with cmake.

I am working on a windows docker container that has the cppcheck build tools (visual studio, qt, wix, cmake). This container will make it possible to reproduce release builds. I do not mind to publish the container... I will do it asap..

[firewave]

Visual Studio includes CMake support: https://learn.microsoft.com/en-us/cpp/build/cmake-projects-in-visual-studio

Also if you use qmake you always need at least one other build system to be the remaining parts (like testrunner) of the project. It is also lacking several options which are only available in CMake. Also we would need to do all changes we do in qmake also in CMake so it makes sense to get rid of the less complete one. That would also require less steps in the CI.

This is also only deprecating it with no deadline. Qt6 still needs a bit of work in several parts of the CI which is what #4957 is about.

With Qt5 being EOL and phased out and no support for it in qmake on our side people need to switch anyways. Also the Qt5/qmake build is not working on several older Linux systems so you had to use CMake anyways. So this is just underlining this.

[firewave]

Also if you use qmake you always need at least one other build system to be the remaining parts (like testrunner) of the project.

You also build lib twice in that case as I just realized while looking at the Windows release job.

[danmar]

hmm.. I have problems with cmake.

I did not manage to reproduce those problems today. It seems CMake is working for me in my windows container. Well feel free to deprecate qmake.

[firewave]

I did not manage to reproduce those problems today. It seems CMake is working for me in my windows container. Well feel free to deprecate qmake.

Please file a ticket and put me in cc if you ever encounter it again.