In trying to see if my ye olde issue is still happening (see #34953), I decided to try on my newer laptop to force everything to be gcc 13 and then figure out what might be the cause of the oddity.

So, the only compiler in compilers.yaml? GCC 13. The only compiler in packages.yaml? GCC 13. But when I tried that I got:

❯ spack spec -I pfunit +mpi %gcc@13.2.0
==> Error: concretization failed for the following reasons:

   1. python: CPython does not compile with GCC on macOS yet, use clang. See: https://github.com/python/cpython/pull/13306
   2. python: CPython does not compile with GCC on macOS yet, use clang. See: https://github.com/python/cpython/pull/13306
        required because conflict is triggered when %gcc arch=darwin-None-None
        required because conflict constraint

Hmm. So I went to that PR URL on python/cpython which is closed now but points to a new PR (python/cpython#20176) which is merged.

So I did the usual rash thing, spack edit python, commented out the conflict, and then spack install python and...it worked.

I'm not sure of how to make a PR to add a when to the conflict a la libuv. I'm guessing there is some version of python where this started working. Does anyone know enough python development dates of release to help bracket it so I could do some test builds to see when things fail?