Black no longer removes the trailing comma from function arguments

[alexwlchan]

If a function has a trailing comma in the argument list, black does not remove it.

Start from:

def one(
    a,
):
    pass

def two(
    a,
    b,
):
    pass

Run black over that file, and you get:

def one(a,):
    pass


def two(
    a, b,
):
    pass

I would expect something more like:

def one(a):
    pass


def two(a, b):
    pass

Environment:

• Version: I can reproduce this in release and master builds; 19.10b0 and 19.10b1.dev16+g1ab87a3
• OS and Python version: macOS, Python 3.7.5

Does this bug also happen on master? Yes.

Additional context

Possibly related issues:

• Trailing comma for function with one arg #880 Trailing comma for function with one arg, which is where I took the minimal example from. Unlike that issue, this seems to affect functions with more than one argument.
• Black 19.10b0 no longer fixes short argument lists to a single line #1136 tracks the bug where it's not collapsing the argument list of two(a, b) into a single line.

I had a look for duplicates in the trailing-comma label, couldn't find any.

[duichwer]

I think, what is even worse that black also adds a trailing comma to my parameter list.

[zsol]

This is the same as #1202.