src/configure gets confused by multiple pythons

[SebKuzminsky]

If there are multiple versions of python installed, src/configure can get confused about which one to use, leading to failure to configure.

The configure script first looks for python interpreters, and selects the python version with the highest version number. It then looks for the python libraries for that version only.

Currently on Bookworm, python3 is python3.10, and python3-dev is python3.10-dev. So if somehow python3.11 gets installed, LinuxCNC will fail to configure (unless the developer also installs python3.11-dev, or uninstalls python3.11).

This is problematic because building & installing linuxcnc-uspace.deb on Bookworm currently installs python3.11, which breaks building of linuxcnc.

So the workaround is to make sure that you have installed the python${VERSION}-dev package matching the highest-numbered python${VERSION} package on your system.

I'm not sure what the best way to actually fix this is.

[allistar]

This happens on Gentoo Linux too. If I have Python 3.9, 3.10 and 3.11 installed but 3.10 is the currently active version, the configure script assumes 3.11 is the correct version to use. My solution for now is to set 3.11 as the active version.

It would be better if the configure script just ran "python" with a default path and ask it what its version is, and use that version.

This is controlled in src/m4/ax_python.m4 in the first few non comment lines in this file.