Format function and class definitions into a single line if its body is an ellipsis

[tjkuson]

Summary

Formats

class A:
    ...

to

class A: ...

Closes #5822.

Test Plan

cargo test

[github-actions]

PR Check Results

Benchmark

Linux

group                                      main                                   pr
-----                                      ----                                   --
formatter/large/dataset.py                 1.00      3.3±0.02ms    12.2 MB/sec    1.00      3.3±0.03ms    12.3 MB/sec
formatter/numpy/ctypeslib.py               1.00    671.3±7.06µs    24.8 MB/sec    1.00    674.7±6.34µs    24.7 MB/sec
formatter/numpy/globals.py                 1.00     69.1±0.39µs    42.7 MB/sec    1.00     69.3±0.43µs    42.6 MB/sec
formatter/pydantic/types.py                1.00  1310.0±13.27µs    19.5 MB/sec    1.01  1324.9±14.02µs    19.2 MB/sec
linter/all-rules/large/dataset.py          1.00     11.1±0.04ms     3.7 MB/sec    1.00     11.1±0.04ms     3.7 MB/sec
linter/all-rules/numpy/ctypeslib.py        1.01      3.0±0.01ms     5.5 MB/sec    1.00      3.0±0.03ms     5.5 MB/sec
linter/all-rules/numpy/globals.py          1.03    337.1±1.20µs     8.8 MB/sec    1.00    326.5±1.11µs     9.0 MB/sec
linter/all-rules/pydantic/types.py         1.00      5.8±0.02ms     4.4 MB/sec    1.00      5.8±0.02ms     4.4 MB/sec
linter/default-rules/large/dataset.py      1.02      5.8±0.02ms     7.0 MB/sec    1.00      5.7±0.02ms     7.1 MB/sec
linter/default-rules/numpy/ctypeslib.py    1.01   1208.3±5.44µs    13.8 MB/sec    1.00   1194.0±8.99µs    13.9 MB/sec
linter/default-rules/numpy/globals.py      1.00    124.7±0.44µs    23.7 MB/sec    1.01    125.4±5.41µs    23.5 MB/sec
linter/default-rules/pydantic/types.py     1.01      2.6±0.01ms     9.9 MB/sec    1.00      2.5±0.01ms    10.1 MB/sec

Windows

group                                      main                                    pr
-----                                      ----                                    --
formatter/large/dataset.py                 1.02      4.6±0.28ms     8.8 MB/sec     1.00      4.5±0.20ms     9.0 MB/sec
formatter/numpy/ctypeslib.py               1.02   964.0±67.52µs    17.3 MB/sec     1.00   947.7±44.68µs    17.6 MB/sec
formatter/numpy/globals.py                 1.04     99.4±6.72µs    29.7 MB/sec     1.00     95.5±4.08µs    30.9 MB/sec
formatter/pydantic/types.py                1.01  1937.5±114.58µs    13.2 MB/sec    1.00  1917.2±156.22µs    13.3 MB/sec
linter/all-rules/large/dataset.py          1.00     16.5±0.49ms     2.5 MB/sec     1.01     16.6±0.45ms     2.5 MB/sec
linter/all-rules/numpy/ctypeslib.py        1.00      4.5±0.20ms     3.7 MB/sec     1.00      4.5±0.18ms     3.7 MB/sec
linter/all-rules/numpy/globals.py          1.02   569.9±39.92µs     5.2 MB/sec     1.00   560.9±37.18µs     5.3 MB/sec
linter/all-rules/pydantic/types.py         1.02      8.6±0.33ms     3.0 MB/sec     1.00      8.5±0.34ms     3.0 MB/sec
linter/default-rules/large/dataset.py      1.00      9.0±0.30ms     4.5 MB/sec     1.02      9.2±0.36ms     4.4 MB/sec
linter/default-rules/numpy/ctypeslib.py    1.00  1912.2±80.18µs     8.7 MB/sec     1.08      2.1±0.13ms     8.1 MB/sec
linter/default-rules/numpy/globals.py      1.01   228.3±14.48µs    12.9 MB/sec     1.00   225.5±12.04µs    13.1 MB/sec
linter/default-rules/pydantic/types.py     1.00      4.1±0.15ms     6.3 MB/sec     1.01      4.1±0.17ms     6.2 MB/sec

[MichaReiser]

This starts to looking good. I left a few comments that hopefully help to solve the TODOs. We have to use the new clause_body everywhere where we do block_indent(&body.format()) today (all compound statements). But we can do this once the class and function formatting is stable.

[MichaReiser]

Wow, nice work. This shoots our typeshed compatibility up by more than 20%

project	similarity index before	after
cpython	0.75473	0.75473
django	0.99805	0.99805
transformers	0.99620	0.99620
twine	0.99876	0.99876
typeshed	0.74292	0.99953
warehouse	0.99601	0.99601
zulip	0.99727	0.99727

[tjkuson]

I'm trying to work out why it formats

class EllipsisWithLeadingComment:
	# leading
	... 

to

class EllipsisWithLeadingComment: # leading
...

Once that's sorted, it should be possible to do the same for every other clause body...

[MichaReiser]

I'm trying to work out why it formats

class EllipsisWithLeadingComment:
	# leading
	... 

to

class EllipsisWithLeadingComment: # leading
...

Once that's sorted, it should be possible to do the same for every other clause body...

Sounds good. Let me know if you want any help.

[tjkuson]

The logic for match statements seems different to other compound statements

let mut last_case = first;

for case in cases_iter {
    write!(
        f,
        [block_indent(&format_args!(
            leading_alternate_branch_comments(
                comments.leading(case),
                last_case.body.last(),
            ),
            case.format()
        ))]
    )?;
    last_case = case;
}

I'm not quite sure how this would with clause_body.

[MichaReiser]

Nice, this change is so cool. Thanks for working on it.

Do we need to change the try formatting as well?

The logic for match statements seems different to other compound statements

I understand this isn't needed on the match level (that renders the cases), only on the case level. You can find its implementation here

ruff/crates/ruff_python_formatter/src/other/match_case.rs

Lines 27 to 63 in 0cea497

	write!(
	f,
	[
	clause_header(
	ClauseHeader::MatchCase(item),
	dangling_item_comments,
	&format_with(|f| {
	write!(f, [text("case"), space()])?;
	let leading_pattern_comments = comments.leading(pattern);
	if !leading_pattern_comments.is_empty() {
	parenthesized(
	"(",
	&format_args![
	leading_comments(leading_pattern_comments),
	pattern.format()
	],
	")",
	)
	.fmt(f)?;
	} else if is_match_case_pattern_parenthesized(item, pattern, f.context())? {
	parenthesized("(", &pattern.format(), ")").fmt(f)?;
	} else {
	pattern.format().fmt(f)?;
	}
	if let Some(guard) = guard {
	write!(f, [space(), text("if"), space(), guard.format()])?;
	}
	Ok(())
	}),
	),
	block_indent(&body.format())
	]
	)
	}

[MichaReiser]

I think the last thing now is to add the handling to the try statement

ruff/crates/ruff_python_formatter/src/statement/stmt_try.rs

Lines 136 to 143 in 0cea497

	write!(
	f,
	[
	clause_header(header, trailing_case_comments, &text(kind.keyword()))
	.with_leading_comments(leading_case_comments, previous_node),
	block_indent(&body.format())
	]
	)?;