Open MPI main/6.0.x fails in configury in messy way if python 3.7 or newer not available

[hppritcha]

The PMIx version needed by Open MPI main and 6.0.x requires a python 3.7 or newer be available.
The PMIx configury has a check for this and bails out if this requirement is not met.

But the Open MPI configury contains on hoping for the best as it configures prrte, which then fails if it can't find a PMIx 6 or newer installed and the resulting output is confusing (potentially)

checking if we need Python... yes
checking for a Python interpreter with version >= 3.7... none
configure: error: OpenPMIx requires Python >= 3.7 to build. Aborting.
configure: ===== done with 3rd-party/openpmix configure =====
checking for pmix pkg-config name... pmix
checking if pmix pkg-config module exists... no
checking for pmix wrapper compiler... pmixcc
checking if pmix wrapper compiler works... no
configure: Searching for pmix in default search paths
checking for pmix cppflags... 
checking for pmix ldflags... 
checking for pmix libs... -lpmix
checking for pmix static libs... -lpmix
checking pmix.h usability... no
checking pmix.h presence... no
checking for pmix.h... no
configure: error: Could not find viable pmix build.

Are we okay with this? Or maybe have a more verbose warning in our top level configury? I do not think we want to error out as there's always hope that the prrte configure will find a new enough pmix somewhere.

[rhc54]

FWIW: both PMIx and PRRTE require Python 3.6 or greater to build - configure will error out if not met. This is a consequence of the group decision to move the show-help support into memory - the processing of those files is done by Python and requires 3.6 or above (well, with Python's tendency to wiggle their support across sub-releases, it's technically more complex than that, but that's the best we can do).

[jsquyres]

Are we okay with this? Or maybe have a more verbose warning in our top level configury? I do not think we want to error out as there's always hope that the prrte configure will find a new enough pmix somewhere.

I think OMPI's configure should fail early with a decent error message.

Heck, since OMPI itself requires Python >= 3.7, we could test for that before configuring PMIx / PRTE and avoid this situation.

[rhc54]

Yeah, I was pretty sure we had coordinated to make the min Python level the same across the three projects. A little surprised you weren't already checking it, or maybe it's just a question of ordering?

If the issue is the "quality" of the error message, I'm happy to see a recommendation for improvement.