Avoid needless linebreaks on | in PEP-604 type annotations

[Zac-HD]

Describe the style change

Given the increasing popularity of Python 3.10 and PEP604 type annotations (arg: X | Y), it's unfortunate that Black is so eager to put linebreaks in the middle. This happens when it's not necessary to meet line-length limits; and also when splitting doesn't achieve line-length limits!

I propose that the | operator be treated as binding more tightly in type annotations, to make Python 3.10+ code more elegant.

Examples in the current Black style

def func(
    options: tuple[str]
    | None = (
        "one_option",
        "another_option",
    ),
    long_arg: str
    | None = (
        "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
    ),
    another_long_arg: str 
    | None = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",  # exceeds length limit!
):
    pass

Lines beginning | None = are all too common, and I'll admit that I don't like them at all. Instead, I think that we should keep annotations on a single line where possible (or parenthesized where not, instead of split out to a term per line).

Desired style

def func(
    options: tuple[str] | None = (
        "one_option",
        "another_option",
    ),
    long_arg: str | None = (
        "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
    ),
    # treat another_long_arg the same way as long_arg
):
    pass

Notably I think it's important to ship this before freezing the 2023 code style, preferably with enough time for a round of feedback from --preview users.

[ichard26]

Yup, see #2316.

[Zac-HD]

🤦‍♂️ should've searched for "PEP 604", right. Closing as duplicate.