waf PortGroup: make the python version configurable

[yan12125 (Chih-Hsuan Yen)]

Currently in _resources/port1.0/group/waf-1.0.tcl, Python 2.7 is hard-coded. It would be great to get the Python version configurable, so that ports using waf (e.g. mpv) can gradually move from Python 2.7 to Python 3.x.

For now the mpv port still uses Python 2.7 to build even with variant +python37. See ​https://github.com/macports/macports-ports/pull/3431 for some related discussions.

[mf2k (Frank Schima)]

Don't forget to assign to the maintainer(s).

[ryandesign (Ryan Carsten Schmidt)]

Cc'ing Rainer who made the waf portgroup.

[raimue (Rainer Müller)]

Looking at the port group, the waf.python option is already configurable. Maybe the automatic build dependency on the chosen python version could be handled better. But what else would be required here?

[i0ntempest]

Ran in to this while trying to fix #61042. I couldn't find a way to change waf.python, nor did I find any documentation about it.

[ryandesign (Ryan Carsten Schmidt)]

Rainer, it isn't configurable. That is, a maintainer could certainly change the value of waf.python in their portfile but that would have no effect on the configure.cmd and build.cmd that the portgroup already sets (the portgroup would need to use defaults for configure.cmd and build.cmd instead), and as you say the python dependency is not handled in a configurable way either. I'll see what I can do to improve the situation. I'll try to introduce a python version variable.

[ryandesign (Ryan Carsten Schmidt)]

proposal 1

[ryandesign (Ryan Carsten Schmidt)]

Try this patch. I haven't fully tested it. Let me know if the interface seems reasonable.

[i0ntempest]

Thanks, seems good. I've modified mpv based on this, will push after you push this.

[ryandesign (Ryan Carsten Schmidt)]

In dbfd0d5394af692cbae759a31d1520634db3ab28/macports-ports (master):

waf-1.0.tcl: Make python version configurable

Closes: #57927