After the "Modernize cmake build" patch (97df448e) an ImporrtError showed up on Windows.
This was fixed by "Fix pyi generation on Windows" (8689054d).
The script generate_pyi.py was drastically rewritten and simplefied, and all imports of the script are now mandatory.
When trying to check this new version in, this error showed up:
This happens when the script tries to import QtCore. It has most probably a similar reason to happen as the Windows problem before: some path must be missing in CMake.