Hi all. I'm trying out the (experimental) ruff backend, but pants gives an error when I invoke the lint goal. I think it's due to the fact that my ruff configuration is targeted at a different version then what pants uses. How can I (a) debug this to verify my suspicion (i.e. check which version of ruff is used by plants)?; (b) specify a specific version of ruff to use? I suspect this is covered in the documentation somewhere but I'm having trouble finding it. Many thanks for any hints!

Hi! You can change ruff version with a separate resolve for ruff. In `pants.toml`:

[python]
enable_resolves = true
default_resolve = "default"

[python.resolves]
default = "3rdparty/python/default.lock"
ruff = "3rdparty/python/ruff.lock"

[ruff]
install_from_resolve = "ruff"

Then in `BUILD`:

python_requirement(
    name="ruff",
    requirements=["ruff==0.2.0"],
    resolve="ruff",
)

Then execute

pants generate-lockfiles --resolve=ruff

That's it, then you can try

pants lint

Ah brilliant, thanks @square-psychiatrist-19087! I'll give that a try. Are you aware of an easy way to check which version of ruff (or other backends) is used in a given pants run?

You can find it here https://github.com/pantsbuild/pants/blob/release_2.19.0/src/python/pants/backend/python/lint/ruff/ruff.lock#L106

Regarding the concept of "resolves", I have seen it mentioned in several places in the documentation, but to be honest found it difficult to find an exact definition and wrap my head around deciding in which situations it is applicable/needed. The only sentence I found that comes close to defining resolves is buried deep down in the section about Python Lockfiles that you linked to. Would it make sense to dedicate a section in "Key concepts" to explaining what "resolves" are and when they should be used? It clearly seems to be something that's more general than Python Lockfiles.

resolve is just a fancy name for a collection of sources that uses a specific lockfile

@square-psychiatrist-19087 Just to report back - I tried your code and it works like a charm. I don’t think I could have come up with this on my own given my current limited experience with pants, so thanks a lot for the help and the explanations. Much appreciated.

You're welcome!