Hello! We want to use pants to run only tests whose transitive dependents have changed. Unfortunately we’re running into a problem where if any files in a python_sources target change, any tests that depend on any of the files in that python_sources target are listed in

pants --changed-since=main --changed-dependents=transitive list

even if the files they depend on haven’t changed. Basically, it seems like the sources are being treated as a group rather than separately. I don’t particularly want to go around splitting every single python_sources target — is there anything else we can do? Is this behavior expected?

Can you make a repro repo? If I'm understanding this, you have

python_sources(*.py)
- foo.py
- bar.py

and then you change foo, and bar's tests run too?

yeah that’s exactly correct

https://www.pantsbuild.org/stable/docs/using-pants/advanced-target-selection#running-over-changed-files-with---changed-since Seems to be expected based on that hint, but I'm still a bit surprised by that.

These aren’t third-party deps

Yeah, the hint implies

target_generator

which python_sources is. I've never looked through the transitive dependency code, but this is surprising off the top of my head

Oh interesting, good catch

Just cc - someone else might already know about this

Yeah, that is mildly surprising to me, since the generated single-file target and its transitive deps should be what's in play

Hm I made the minimal foo/bar and wasn't able to reproduce, let me poke around and see if the problem isn't just that our repo has absurdly intertwined dependencies

https://www.pantsbuild.org/stable/docs/using-pants/project-introspection This page will be your friend for that search

I'm pretty sure I got to the bottom of it. In CI, we were doing

--changed-since=origin/main

to run tests affected by a PR, which isn't quite right. What we really wanted was

--changed-since="$(git merge-base HEAD origin/main)"

so that we only run the tests changed relative to the merge base, not unrelated changes to main that got merged while we were working on the PR. If you think other people might fall into this trap, I'm happy to send a PR adding this tip to the --changed-since docs. Otherwise, I'm just glad that we're not running oodles of tests anymore 🙂

Yeah, sure, doc improvements are always welcome. You could also look into pants.toml

cli.alias

to setup the ones you want, and recommend your team use those internally to make sure it’s locked down

et voila: https://github.com/pantsbuild/pants/pull/23286