cola used designer and .ui files early in its history, but
compatibility across versions and flexibility in widget construction
led to removal of .ui files back in 2009.
See
https://github.com/git-cola/git-cola/issues/24 for more details.
These days most of the GUI code is in cola/widgets/*.py and cola/qt*.py
Qt Designer is a good tool, and you can always use pyuic{4,5} to
generate code from .ui files, but we'd still prefer an expanded
version in the repo for maximum flexibility if you're looking to
submit patches. For example, we use QtPy now, and pyuic5 doesn't
generate qtpy code, or python2+3 compatible code, etc.
We also have rather strict requirements that most projects might not
need to take on. For example, we maintain PyQt4 + PyQt5
compatibility. If you don't care about that then pyuic5 might be just
the right tool for the job. SInce QtPy is PyQt5-ish, it should also
be possible to use pyuic5 and run it through sed to qtpy-ify it, but
we'd probably still avoid pyuic in general (in the build system) for
the same reasons as #24.
I hope that that helps!
cheers,
--
David