pkg/59204: package upgrades can't handle python upgrades

[campbell+netbsd%mumble.net@localhost]

>Number:         59204
>Category:       pkg
>Synopsis:       package upgrades can't handle python upgrades
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Mar 22 03:45:00 +0000 2025
>Originator:     Taylor R Campbell
>Release:        netbsd-9, pkgsrc-stable
>Organization:
The NetBSD311^W312 Foundation
>Environment:
>Description:
I installed a few packages from the TNF binary package repository a while ago on a VPS.  I went to upgrade them to keep it up-to-date, but the upgrade cannot be done automatically:

# pkgin show-keep
git-2.45.2           GIT version control suite meta-package
mercurial-6.7.4      Fast, lightweight source control management system (meta package)
py311-hg-evolve-11.1.3 Experimental Mercurial extensions from Facebook
py311-hg-git-1.1.2   Push to and pull from a Git server repository using Mercurial
# pkgin up
...
# pkgin ug
calculating dependencies...done.
py312-mercurial-6.9 (to be installed) conflicts with installed package py311-mercurial-6.7.4.
proceed ? [y/N] 

In part this is because py311-hg-evolve depends on py311-mercurial and py311-mercurial installs bin/hg rather than bin/hg-3.11 with pkg_alternatives.  But in part this is also because I have no way to say `please install py3*-hg-evolve, whatever is appropriate for the default Python version'.
>How-To-Repeat:
1. install py311-foo and a non-py311 package that depends on py311-foo
2. pkgin up && pkgin ug
>Fix:
Yes, please!

Random idea: In addition to creating packages called py311-foo, py312-foo, &c., from devel/py-foo, also create a package py3x-foo which depends on whatever is the default Python version.  Then users can install py3x-foo if they don't care py311-foo vs py312-foo but just want whatever TNF picked as the default for binary packages.