Add newline after module docstrings (`module_docstring_newlines`)

[DanielNoord]

"""Test docstring"""
a = 1

On the playground this does not currently get a newline added with the format option turned on.

Recently a PR of mine got merged to black to include a newline after the module docstring:
psf/black#3932
Most credits should go to others though for that PR as I mostly copied and rebased code.

It's still in the preview style but got generally favourable responses when initially proposed a couple of year ago. Since nobody has really objected to it during its previous iterations I expect it to be part of the default style some day.

Would ruff be open to to include this change to ruff format as well?

EDIT: Oh, and congrats on the 0.1.0 release 🎉

[charliermarsh]

Cool, so this is part of Black's preview style? If so, we'll likely add it under our own --preview flag soon.

(And thank you!)

[charliermarsh]

@konstin - Perhaps another good / easy one for preview.

[DanielNoord]

@charliermarsh Sorry should have been clearer. This is currently only available on black main as preview. (I run from master locally). You can see in the linked PR that it actually already applies to blacks own codebase. There hasn't been a release yet, I can ask them when they plan on doing so but I don't want to bother the maintainers too much.

[konstin]

I added a test case in #8044, it's not trivial to fix though

[MichaReiser]

I added a test case in #8044, it's not trivial to fix though

We could try to format it as part of the module if the first statement in the suite is a doc comment without any leading comments? Not sure how to handle trailing suppression comments though.