Declare support for Python 3.10

[hugovk]

Description

Python 3.10 final is already tested, just needs the Trove classifier.

Checklist - did you ...

• Add a CHANGELOG entry if necessary?
• [n/a] Add / update tests if necessary?
• [n/a] Add new / update outdated documentation?

Is a changelog entry needed?

---

By the way, Black was first released in March 2018 and took the forward-thinking view to only support Python 3.6, which was the newest release, and therefore Black hasn't needed to drop any EOL versions yet.

Python 3.6 is EOL on 2021-12-23; will Black be dropping 3.6 before the (potentially stable) 2022 Q1 release?

[cooperlees]

Do we wish to do this before we support all the syntax?

[hugovk]

Good point, probably not!

[Zac-HD]

We already declare Python 3.9 support without formatting all such syntax (e.g. parenthesised context managers), so I'd support adding this classifier - black does run on 3.10 after all!

[cooperlees]

But it crashes if you have the new syntax elements. We don’t crash on context managers. Or has that been fixed? If so, sure. Let’s add away.

[hugovk]

$ cat 1.py
def http_error(status):
    match status:
        case 400:
            return "Bad request"
        case 404:
            return "Not found"
        case 418:
            return "I'm a teapot"
        case _:
            return "Something's wrong with the internet"
$ black 1.py
error: cannot format 1.py: Cannot parse: 2:10:     match status:
Oh no! 💥 💔 💥
1 file failed to reformat.

[Zac-HD]

No, we do crash on context managers: see #1948, #2318 and

$ cat 2.py
from contextlib import nullcontext
with (
    nullcontext() as a,
    nullcontext() as b,
):
    pass

$ python3.9 2.py
$ black 2.py
error: cannot format 2.py: Cannot parse: 4:18:     nullcontext() as a,
Oh no! 💥 💔 💥
1 file failed to reformat.

[JelleZijlstra]

But parenthesized CMs are an undocumented feature in 3.9, not a flagship new feature like pattern matching in 3.10.

[Zac-HD]

PEP-614 "relaxed grammar restrictions on decorators" is documented in the what's new page, and also crashes.

[cooperlees]

Python 3.6 is EOL on 2021-12-23; will Black be dropping 3.6 before the (potentially stable) 2022 Q1 release?

I vote yes. I'm pretty sure we're all in favor to drop Python support when cpython EOL's the version. I think that's mentioned in the stable doc/policy, if not, we should add it.

[hugovk]

3.6 (or supporting upstream CPython generally) isn't mentioned in the stability policy:

https://black.readthedocs.io/en/latest/the_black_code_style/index.html#stability-policy

But the stability policy PR (#2529) added this to the Python 2 FAQ:

In terms of running Black though, Python 3.6 or newer is required.

https://black.readthedocs.io/en/latest/faq.html#does-black-support-python-2

[kukushking]

Hi folks, not quite sure this is the right place but shouldn't 3.10 be added to supported target versions as part of this PR, too?

[Jackenmen]

Classifier just means that Black can run on Python 3.10, not that it can parse Python 3.10 code (which it currently can't when it comes to new syntax like match statement and parenthesized with) which is what would constitute to adding 3.10 target version.

[kukushking]

Yep, I understand - just have no idea how are you handling 3.10 story so thought I'd mention it here in case you missed it.

[kukushking]

Just found a PR that has that covered. Thanks guys 🙌

[JelleZijlstra]

Let's add this to the changelog

[hugovk]

Let's add this to the changelog

Added!