Rule PYI019 should not flag metaclass methods

[Geo5]

Description

This code which includes a metaclass and passes mypy without errors:

from typing import TypeVar

F = TypeVar("F")


class FooMeta(type):
    def bar(cls: F) -> F:
        return cls

is fixed to:

ruff check --isolated --select PYI --preview --fix --diff

--- test.py
+++ test.py
@@ -1,8 +1,9 @@
 from typing import TypeVar
+from typing_extensions import Self
 
 F = TypeVar("F")
 
 
 class FooMeta(type):
-    def bar(cls: F) -> F:
+    def bar(cls) -> Self:
         return cls

Would fix 1 error.

Which mypy does not like:

$ mypy --strict test.py 
test.py:8: error: Self type cannot be used in a metaclass  [misc]
Found 1 error in 1 file (checked 1 source file)

---

$ python --version
Python 3.11.10
$ ruff --version
ruff 0.9.6
$ mypy --version
mypy 1.15.0 (compiled: yes)

[Geo5]

See also #8353 for a similar case where the relevant PEP is linked: https://peps.python.org/pep-0673/#valid-locations-for-self
Seems like the fix is indeed incorrect and the mypy docs example seems to be incorrect aswell

[ntBre]

Thanks for the report and the for the additional links! I agree that it looks like a bug in ruff based on the PEP.

[Geo5]

(I also created an issue for the mypy documentation linked above python/mypy#18668)

[AlexWaygood]

Yup, this is a bug here -- thanks for the report @Geo5! For some reason we check whether the class is a metaclass for PYI034 before issuing a diagnostic:

ruff/crates/ruff_linter/src/rules/flake8_pyi/rules/non_self_return_type.rs

Lines 133 to 136 in f8093b6

	// PEP 673 forbids the use of `typing(_extensions).Self` in metaclasses.
	if analyze::class::is_metaclass(class_def, semantic).is_yes() {
	return;
	}

but not for PYI019.

Should be easy to fix!

[vladNed]

is this issue still unassigned ? I would like to give it a go

[AlexWaygood]

@vladNed go for it!