F821 not recognizing `requires-python` in `pyproject.toml`

[CNSeniorious000]

I tried to use anext and aiter in a project configured with requires-python = "~=3.10", but Ruff still complaining

F821 Undefined name `anext`. Consider specifying `requires-python = ">= 3.10"` or `tool.ruff.target-version = "py310"` in your `pyproject.toml` file.
  |
8 | async def main():
9 |     print(anext(g()))
  |           ^^^^^ F821
  |

Here is a reproduction repository:

https://github.com/CNSeniorious000/ruff-F821-repro

See these workflow logs:

https://github.com/CNSeniorious000/ruff-F821-repro/actions/runs/12198261365/job/34029609880#step:5:13

[charliermarsh]

If you add [tool.ruff] (even followed by nothing else) to your pyproject.toml, then we'll read the requires-python.

[CNSeniorious000]

Thank you! I'm surprised this workaround is needed.

[MichaReiser]

So am I! I'd expect Ruff to pick up the pyproject.toml as the root even if it has no tool.ruff section and there's no other configuration in any ancestor directory. However, that's probably a breaking change

[looztra]

Does not work for me.

# in pyproject.toml
[tool.ruff]
# DO NOT PUT ANYTHING HERE, use the ruff.toml file, this is a fix for https://github.com/astral-sh/ruff/issues/14813

• a ruff.toml file with all the config

target-version is still py39

╰─»  uv run ruff check --show-settings | grep target
linter.target_version = Py39
formatter.target_version = Py39
analyze.target_version = Py39

using ruff 0.9.2

[looztra]

when I run uv run check --show-settings --verbose there's multiple lines saying

[2025-01-17][11:45:48][ruff_workspace::pyproject][DEBUG] `project.requires_python` in `pyproject.toml` will not be used to set `target_version` when using `ruff.toml`

[dhruvmanila]

@looztra Ruff has to pickup one configuration if there are multiple files present. The precedence is documented at https://docs.astral.sh/ruff/configuration/#config-file-discovery:

If Ruff detects multiple configuration files in the same directory, the .ruff.toml file will take precedence over the ruff.toml file, and the ruff.toml file will take precedence over the pyproject.toml file.

Related #3470. Maybe we could use a separate logic for target-version specifically where the precedence is different i.e., pyproject.toml, ruff.toml, .ruff.toml.

[MichaReiser]

I think the solution here is to implement a configuration discovery similar to uv (and, in the future, red knot) where a ruff.toml takes precedence, but Ruff respects the projects pyproject.toml's project table (if any). In Ruff's case, it would fall back to the project.requires-python if the ruff.toml doesn't specify a target-version.

[MichaReiser]

This has just come up again and seems to -- understandably -- be very confusing to users. This, unfortunately will be a breaking change and implementing it under preview is difficult because it happens during configuration loading (we don't know yet if the user has preview enabled).

Either way, I think it would be good to have a fix ready for the next minor and, ideally, it would make the following two, but seperate, changes:

1. If we can't find any configuration but there's a pyproject.toml without a tool.ruff section, don't ignore it and instead use the requires-python from there
2. If we find a ruff.toml without a target-version fallback to the pyproject.toml's requires-python at the same level (if there's any).

@dylwil3 @ntBre is this something either of you could look into?