black adds trailing comma despite using --target-version py35

[bjoernricks]

Hi,

black 19.3b0 adds trailing commas for function signatures containing * despite setting target version 3.5. This creates invalid code for python 3.5 which will raise a SyntaxError. Setting
target version to py34 or using the auto detection doesn't add a trailing comma in this case.

def foo_func(bar, *, lorem=None, ipsum=None, dolor=None, sit=None, amet=None, consectetur=None):
    print('lorem ipsum dolor sit amet')

running

> black --target-version py35 --line-length 80 foo.py

creates

def foo_func(
    bar,
    *,
    lorem=None,
    ipsum=None,
    dolor=None,
    sit=None,
    amet=None,
    consectetur=None,
):
    print("lorem ipsum dolor sit amet")

Operating system: Ubuntu 18.04
Python version: Python 3.5/3.6
Black version:

> black --version
black, version 19.3b0

Does also happen on master: yes

[JelleZijlstra]

Looks like we improperly merged two different syntax changes: f(**x,) (trailing comma in a call) first became legal in 3.5, but def f(**x,): pass (trailing comma in a definition) became legal only in 3.6. I'll try to disentangle the two in the code.

[bjoernricks]

Thanks a lot!

[mikenerone]

Seems like there's a regression -I'm seeing this behavior with 20.8b1. It could be something more specific: my affected function has a return type annotation.

[ichard26]

@mikenerone could you please post the bug-inducing code? Might be a case of #1356.

[mikenerone]

@mikenerone could you please post the bug-inducing code? Might be a case of #1356.

I believe you're right. My triggering sample below closely resembles a case shown there.

class LongishClassNameToHelpTriggerTheBug:
    ...


def only_seems_to_trigger_bug_if_definition_is_long_enough_to_require_wrapping(
    *some_args: LongishClassNameToHelpTriggerTheBug
) -> LongishClassNameToHelpTriggerTheBug:
    pass

black 20.8b1 adds a trailing comma on the *some_args line, and the bug does not manifest if I remove the * first.