Black doesn't delete trailing commas in dictionary when shrinking to one line

[rmorshea]

Version: 19.10b

Given the following code:

[
    {
        "items": {
            "properties": {"type": {"const": "array"}},
            "required": ["type"],
        },
    }
]

Is shrunk to:

[{"items": {"properties": {"type": {"const": "array"}}, "required": ["type"],},}]

Which leaves a trailing commas in place that, according to flake8 (E231), ought to be removed.

[dandavison]

I think this is a dup of #1288

Worse yet, in those cases it leaves trailing commas behind when a collection ends up compressed into one line.

[whatisaphone]

Prettier has a nice rule:

• multiline sequences always have trailing commas
• single-line sequences never have trailing commas

Easy, simple, consistent. I hope black considers adopting this.

In the meantime, you can "fix" this by downgrading:

pip install black==19.3b0

[rmorshea]

Interesting. What feature-add introduced this bug?

[JelleZijlstra]

Yes, this is basically #1288. The behavior is an unfortunate consequence of #826.