Treat form feed as valid whitespace before a line continuation

[soundsonacid]

Fixes #19175

[ntBre]

Thanks for working on this! Could you add a regression test based on the example in the issue?

I'm slightly concerned that is_whitespace is too permissive, but I'm also not quite sure why it was only limited to spaces and tabs before.

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

[soundsonacid]

Thanks for working on this! Could you add a regression test based on the example in the issue?

I'm slightly concerned that is_whitespace is too permissive, but I'm also not quite sure why it was only limited to spaces and tabs before.

No problem! I had a similar thought about the is_whitespace check, but I couldn't find (with admittedly not a ton of time searching) a comprehensive list of all valid whitespace Python characters. If you have one handy, I'm happy to make the change to that -- in the meantime I'll keep looking for one myself.

[dscorbett]

Section 2.1.9 “Whitespace between tokens” says:

Except at the beginning of a logical line or in string literals, the whitespace characters space, tab and formfeed can be used interchangeably to separate tokens. Whitespace is needed between two tokens only if their concatenation could otherwise be interpreted as a different token (e.g., ab is one token, but a b is two tokens).

Those are the only three characters Python treats as white space within a line.

[ntBre]

Thanks, this looks great!

And thanks @dscorbett for the report and for the whitespace reference.

I just had a couple of very small suggestions, but this is good to go otherwise.

[MichaReiser]

We could use

ruff/crates/ruff_python_trivia/src/whitespace.rs

Lines 40 to 46 in 9f3a38d

	pub const fn is_python_whitespace(c: char) -> bool {
	matches!(
	c,
	// Space, tab, or form-feed
	' ' | '\t' | '\x0C'
	)
	}

[soundsonacid]

thanks for lmk about this, updated to use this fn

[ntBre]

Thanks!

[ntBre]

Looks like we need to update the snapshot for the new comment

[soundsonacid]

Weird, i ran cargo insta review and it said no changes, also ran cargo test on my local and it was fine

Happy to do whatever it takes here just let me know what to do, not super familiar with how the tests work yet

[MichaReiser]

Can you verify that you have no uncommited changes (git status, git diff)

[ntBre]

I checked out the branch locally and see the same test failures, so it might be something with git as Micha said.

I can push a commit if you'd like but wanted to give you the solo credit for the PR if possible :)

[soundsonacid]

yep, nothing unstaged, no diffs, no snapshots to review