Black 23.1 no longer respects trailing magic comma for single length list

[gaborbernat]

from typing import Literal

A = Literal[
    "DEFAULT",
]

❯ black magic.py --check
would reformat magic.py

Oh no! 💥 💔 💥
1 file would be reformatted.

It turns it into:

from typing import Literal

A = Literal["DEFAULT",]

I personally would prefer to respect trailing magic commas here, but at the very least remove the trailing comma if is going to be inlined into a single line.

[ichard26]

This is as intended. See https://ichard26.github.io/blog/2022/12/black-23.1a1/#ignore-magic-trailing-comma-for-single-element-subscripts and #2918.

This probably isn't documented in the style documentation though. Definitely important to fix that.

[felix-hilden]

Definite +1 to removing the trailing comma on a single line though 😄

[JelleZijlstra]

Definite +1 to removing the trailing comma on a single line though 😄

That would be an AST-unsafe change. It happens to be safe for types, but it isn't safe in general.

In [30]: print(ast.dump(ast.parse("a[1]"), indent=2))
Module(
  body=[
    Expr(
      value=Subscript(
        value=Name(id='a', ctx=Load()),
        slice=Constant(value=1),
        ctx=Load()))],
  type_ignores=[])

In [31]: print(ast.dump(ast.parse("a[1,]"), indent=2))
Module(
  body=[
    Expr(
      value=Subscript(
        value=Name(id='a', ctx=Load()),
        slice=Tuple(
          elts=[
            Constant(value=1)],
          ctx=Load()),
        ctx=Load()))],
  type_ignores=[])

[felix-hilden]

Oh true 👍

[hauntsaninja]

The only alternative I see here is something like A = Literal[("DEFAULT",)] ... thoughts? Otherwise, we should just close this issue, because Black shouldn't modify AST.

[hauntsaninja]

Closing as per my comment above (since no one seems to have loved the parenthesised tuple suggestion)