[flake8-bugbear] Implement return-in-generator (B901)

[tobb10001]

Summary

This PR implements the rule B901, which is part of the opinionated rules of flake8-bugbear.

This rule seems to be desired in ruff as per #3758 and #2954 (comment).

Test Plan

As this PR was made closely following the CONTRIBUTING.md, it tests using the snapshot approach, that is described there.

Sources

The implementation is inspired by the original implementation in the flake8-bugbear repository. The error message and test file where also copied from there.

The documentation I came up with on my own and needs improvement. Maybe the example given in #2954 (comment) could be used, but maybe they are too complex, I'm not sure.

Open Questions

• Documentation. (See above.)

• Can I access the parent in a visitor?

  The original implementation references the yield statement's parent to check if it is an expression statement. I didn't find a way to do this in ruff and used the is_expresssion_statement field on the visitor instead. What are your thoughts on this? Is it possible and / or desired to access the parent node here?

• Is Option::is_some(...) -> ...unwrap() the right thing to do?

  Referring to this piece of code. From my understanding, the .unwrap() is safe, because it is checked that return_ is not None. However, I feel like I missed a more elegant solution that does both in one.

Other

I don't know a lot about this rule, I just implemented it because I found it in a good first issue Good for newcomers .

I'm new to Rust, so any constructive critisism is appreciated.

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

ℹ️ ecosystem check detected linter changes. (+2 -0 violations, +0 -0 fixes in 2 projects; 48 projects unchanged)

apache/airflow (+1 -0 violations, +0 -0 fixes)

ruff check --no-cache --exit-zero --ignore RUF9 --output-format concise --preview --select ALL

+ tests/models/test_taskinstance.py:2421:17: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior

reflex-dev/reflex (+1 -0 violations, +0 -0 fixes)

ruff check --no-cache --exit-zero --ignore RUF9 --output-format concise --preview

+ integration/test_server_side_event.py:24:13: B901 Using `yield` and `return {value}` in a generator function can lead to confusing behavior

Changes by rule (1 rules affected)

code	total	+ violation	- violation	+ fix	- fix
B901	2	2	0	0	0

[charliermarsh]

I think I would do this by checking Stmt::Expr here, and then just introspecting the value directly to see if the value is Expr::Yield.

[tobb10001]

Good idea, I updated the implementation to this.

[charliermarsh]

Thanks! Two small comments based on your questions.

[charliermarsh]

Thanks!