I've been running buildbot using Python 3 for nearly a year (see: lopsided98/nixpkgs@7db611f...8853014), but I never submitted the code upstream because I couldn't get tests to pass and also I wrote it when I wasn't very experienced with Nix and never got around to cleaning it up.

Yesterday I submitted #45763, which updates sphinx-jinja and adds Python 3 support (mostly the same as your commit).

I also updated tempita to use a fork that fixes the tests with Python 3 (see #39692), because tempita is seemingly abandoned. This fork is also used by the official Arch Linux package.

Switching to Python 3 has the potential to break deployments because buildbot's configuration files are written in Python. That was why I tried to make the Python version configurable.

Switching to Python 3 has the potential to break deployments because buildbot's configuration files are written in Python. That was why I tried to make the Python version configurable.

These configuration files are typically quite small and trivial, I suppose?

Not necessarily, they can get pretty long and complicated.
These examples are some of the simplest: https://github.com/buildbot/buildbot/tree/master/master/docs/examples
This is the configuration I use: https://github.com/lopsided98/aur-buildbot/blob/master/master/master.cfg
This is one of the most complicated I've found, used by buildbot themselves: https://github.com/buildbot/metabbotcfg

In that case we may need to provide version for 2 and 3. Do our maintainers want that? If so, we might want to pull it into python-packages.nix. Regardless, this is going to require a mention in the changelog.

I can move the package to pythonPackages. Does that mean we want to support both versions and make it configurable in the module?

Yes, we can make it configurable using the usual package option found in many modules.

Citing from #45782 (comment)

I think we should provide indeed provide pylint 1.9 as python2Packages.pylint until support ends. I also think we should move buildbot to pythonPackages as @FRidh suggested.
@lopsided98 Do you want to continue my work?

See #45890

#45890 was merged a while ago, so this can be closed