maintainer-feedback requested: [Bug 272745] www/qt6-webengine cmake find python routines no longer respect python.mk, highest python version install always found

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Bugzilla Automation <bugzilla at FreeBSD.org> has asked freebsd-kde (Team)
<kde at FreeBSD.org> for maintainer-feedback:
Bug 272745: www/qt6-webengine cmake find python routines no longer respect
python.mk, highest python version install always found
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=272745



--- Description ---
ran into this recently with graphics/qgis , and now with qt6-webengine. The
cmake routines for FindPython, and its variants seemingly for finding python3
or python2 do not care to check what python.mk has defined for the python
version to build for. They would return the greatest version installed by
default. After installing blender this started happening as it requires python
3.10, so now python 3.9 used for everything else is causing issues finding the
python executable. In this port some items like py-boost were properly detected
for python 3.9, but the general Python3_EXECUTABLE is returned as python3.10,
and this caused py39-html5lib from not being found. Had to explicitly pass a
hint to CMake to override the default behavior of the ports installed
cmake-core system. Those find python routines in
/usr/local/share/cmake/Modules/ do not look at PYTHON_VER defined in python.mk
any longer, nor force the hint for Python_EXECUTABLE, Python3_EXECUTABLE in
this case, nor Python2_EXECUTABLE to use default or as overridden in make.conf
to use other system version. As such they default to returning the highest
version of python installed, unless an alternate selection strategy is set by
the port using python in their call to FindPython.  see PR 168159

patch forces the version returned by python.mk to be used, in my case the ports
default version.

AMD64; 13.2-p1 release, live system building