implicit-str-concat: allow wrapping implicitly concatenated strings in parenthesis.

[yilei]

Current problem

Internally, we have enabled the --check-str-concat-over-line-jumps option for implicit-str-concat. But we also allow wrapping implicitly concatenated strings in parenthesis. This is done by our internal patch to Pylint ~3 years ago.

Example code:

a = [
    "aa bb"
    "cc dd",
]

It raises implicit-str-concat on the "aa bb" line, that's good to catch bugs of missing commas.

But for long strings that must be put on multiple lines, currently you need to use explicit str concatenations:

a = [
    "aaaaaaaa aaaaaaaa "
    + "aaaaaaaa aaaaaaaa ",
]

We think it should also be fine to use implicit str concatenations BUT wrapped inside parenthesis:

a = [
    ("aaaaaaaa aaaaaaaa "
     "aaaaaaaa aaaaaaaa "),
]

Desired solution

Introduce an opt-in option allow-parenthesized-str-concat. When enabled, allow the use of parenthesis.

Additional context

WDYT? If you agree, I'll send out our patch.

[Pierre-Sassoulas]

I think we should be compatible with what black does when a line is too long. I'm on mobile so I can't check and be 100% sure of it but I think black use parenthesis and implicit string concatenation so the proposed approach would work.

[yilei]

Yes Black (in current's preview style) wraps long strings (used in sequences) in parens, see playground.

Longs strings in func calls are the same today, but we have received feedback that it causes destructive diffs. So I'm proposing to not wrap (but also not using explicit str concatenation). See #3640 and psf/black#2188 (comment). So if this goes in to Black, I also plan to send a PR to Pylint to add an option allowing implicit str concat in func calls.

[Pierre-Sassoulas]

Labeling this as Need PR because it's going to be easier to discuss the implication once a PR is tried and we can see the failing test cases.