Wrapping lines of a function signature that uses the new python 3.12 generic type parameter syntax

[Questionsdenombres]

Context:

• When a function has many parameters, it's more readable when on multiple lines, enforcing black to wrap lines adding a comma after the last parameter.
• See https://black.readthedocs.io/en/stable/the_black_code_style/current_style.html#how-black-wraps-lines

def func(a: int, b: int) -> int:
    return a + b 

def func(
    a: int,
    b: int,
) -> int:
    return a + b

python 3.12 new feature:

• https://docs.python.org/3/whatsnew/3.12.html#summary-release-highlights
• A generic function can now have type parameters used by the static type checker.
• See PEP 695, type parameter syntax and the type statement
• See https://peps.python.org/pep-0695/#summary-examples

def func[T](a: T, b: T) -> T:
    return a

Example in the current Black style:
Enforcing black to wrap lines gives the ugly:

def func[
    T
](a: T, b: T,) -> T:
    return a

Desired style:

def func[T](
    a: T,
    b: T,
) -> T:
    return a + b

Additional context
python==3.12
black==23.11.0
Windows==11
VScode==1.84.2
VScode extension! Black Formatter==v2023.6.0

Credits:
Thank you for your great tool.
Patrick, Paris, France.

[JelleZijlstra]

Yes, we should change this. PR welcome!

[JackismyShephard]

What is the ETA on this?

[hauntsaninja]

Are you interested in making a PR?

[JackismyShephard]

Well, sadly I don't quite have the time for that right now.

[AndreaCensi]

@JackismyShephard if you need to undo what black did, try ruff: it will do exactly what you want

[FlorinAsavoaie]

FYI: An attempt to fix this is found in #4272 but doesn't seem trivial.

[Feuermurmel]

I just converted a large-ish code-base to the new syntax and found an even more egregious example. 😅 I thought that this example could maybe serve as an additional test case where the return type is also wrapped:

def something_something_function[
    T: Model
](param: list[int], other_param: type[T], *, some_other_param: bool = True) -> QuerySet[
    T
]:
    pass

(playground)

Where I would prefer this instead. :)

def something_something_function[T: Model](
    param: list[int], other_param: type[T], *, some_other_param: bool = True
) -> QuerySet[T]:
	pass

[Pedro-Muller29]

Context

I am currently working on a PR for this, and I am facing some doubts on what should be the valid syntax on some trailing comma cases:

def trailing_comma1[T=int,](a: str):
    pass

def trailing_comma2[T=int](a: str,):
    pass

Current Behaviour

Right now the expected output in the type_param_defaults.py test case gives:

def trailing_comma1[
    T = int,
](a: str):
    pass


def trailing_comma2[
    T = int
](a: str,):
    pass

My Assessment

I believe the following adjustments should be made to align with valid and consistent formatting:

1. trailing_comma1 should keep the same output.
2. trailing_comma2 output should change to:

def trailing_comma2[T = int](
    a: str,
):
    pass

Am I correct in my assessment?

[hauntsaninja]

Yes, that sounds right (assuming default settings, not --skip-magic-trailing-comma)