[Infinite loop] Conflict between F401 and PLC0414; redundant alias is removed, redundant alias is added as re-export

[GideonBear]

Ref #14283

pyproject.toml:

[tool.ruff]
lint.select = [ "F401", "PLC0414" ]
lint.preview = true

package/__init__.py:

from package.module import function

package/module.py:

def function(): ...

Run this command: ruff check --unsafe-fixes --fix
Result:

$ ruff check --unsafe-fixes --fix

error: Failed to converge after 100 iterations.

This indicates a bug in Ruff. If you could open an issue at:

    https://github.com/astral-sh/ruff/issues/new?title=%5BInfinite%20loop%5D

...quoting the contents of `package/__init__.py`, the rule codes F401, along with the `pyproject.toml` settings and executed command, we'd be very appreciative!

package/__init__.py:1:28: F401 `package.module.function` imported but unused; consider removing, adding to `__all__`, or using a redundant alias
  |
1 | from package.module import function
  |                            ^^^^^^^^ F401
  |
  = help: Use an explicit re-export: `function as function`

Found 101 errors (100 fixed, 1 remaining).
[*] 1 fixable with the --fix option.

[ntBre]

Thanks for the report and the great example! I can reproduce this.

I'm not sure about the best way to fix this, but one option could be some kind of special handling for __init__.py files in PLC0414. I know we have that for F401. We should probably just avoid offering a fix that would conflict with F401 in __init__.py files.

[GideonBear]

I'm not sure about the best way to fix this, but one option could be some kind of special handling for __init__.py files in PLC0414. I know we have that for F401. We should probably just avoid offering a fix that would conflict with F401 in __init__.py files.

Is it also acceptable to just disable PLC0414 in __init__.py files entirely? Seeing as there's an exception for F401 already, I don't think it makes sense to warn for redundant aliases there.

[GideonBear]

Or is PLC0414 just in general incompatible with the idea of using redundant aliases?

[ntBre]

Oh you're right, we probably shouldn't offer a diagnostic at all in __init__.py, not just avoid a fix.

And yeah, I think PLC0414 is a pretty straightforward rule currently, it forbids any redundant alias even if removing it would change the program's behavior. That's why the fix is unsafe:

This fix is marked as always unsafe because the user may be intentionally re-exporting the import. While statements like import numpy as numpy appear redundant, they can have semantic meaning in certain contexts.

[GideonBear]

I'm working on this

[injust]

Related: #6294

[Avasam]

I've been ignoring this rule in __init__.py: #6294 (comment)

[GideonBear]

If I'm not mistaken, that means that #18400 closes #6294