I have started looking into linting BUILD files using

flake8

. The use case is https://github.com/pantsbuild/pants/issues/19486 - I want to error on duplicate keys in a dict, e.g.

python_sources(
    name="lib",
    overrides={
        "main.py": {"dependencies": ["//:reqs#pytest"]},
        "main.py": {"dependencies": []},
        },
)

we currently only run formatter on BUILD files, so this would be new. I've experimented in a local branch and this would require making changes to the flake8 rules. Before I proceed, are we okay with the new feature? Anything that is worth taking into account?

One challenge will be undefined symbols. BUILD files have a bunch of magic symbols Flake8 will be mad about since there are no imports

I was hoping to pick rules only selectively if that helps...

Yeah, I think you'll want to do that. But that means for example ignoring the Flake8 config the user has. So it's maybe a little weird to open source to Pants because users wouldn't be able to control the chosen lints You'd probably want it a dedicated backend for lint and build files and Flake8

right. So just as we have

src/python/pants/backend/python/lint/flake8/rules.py

for Python sources, I thought to have an independent function/rule in

src/python/pants/backend/build_files/lint/flake8/rules.py

that would only be used by the

pants lint src/files/BUILD

do you know which lints you'd use? And is it worth using Ruff instead since it's so much faster?

I hope Pants will route the requests accordingly to the relevant rules when run

pants lint src/files/BUILD src/files/module.py

will route the requests accordingly to the relevant rules when run pants lint src/files/BUILD

I thinkkkkk I fixed this but am not certain. What happens when you run

pants lint

on a BUILD file today? In the past, it would run on all targets defined in that BUILD file. But I think I changed that. (sorry, don't have Pants handy)

pants lint src/python/pants/backend/python/lint/flake8/BUILD

doesn't lint Python files from the BUILD file targets

I'd be a +1 for a Ruff-based linter for BUILD files, where Pants chooses the rules for you and it intentionally ignores config files etc. I think the only thing we'd need to consider is how to indicate if certain BUILD files should be ignored. But maybe you could ignore that. If you don't want a BUILD file reviewed, then use

build_ignore

or

pants_ignore

, or inline comments to disable Ruff for each violation The last thing I'd suggest is: where would you document this? An issue with Pants is discoverability. How do users find out about this?

thanks for the input, Eric, let me explore and think about these bits

A ruff based linter for BUILD files would be awesome.