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.