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Brent Westbrook f3714fd3c1
Fix leading comment formatting for lambdas with multiple parameters (#21879) 
## Summary

This is a follow-up to #21868. As soon as I started merging #21868 into
#21385, I realized that I had missed a test case with `**kwargs` after
the `*args` parameter. Such a case is supposed to be formatted on one
line like:

```py
# input
(
    lambda
    # comment
    *x,
    **y: x
)

# output
(
    lambda
    # comment
    *x, **y: x
)
```

which you can still see on the
[playground](https://play.ruff.rs/bd88d339-1358-40d2-819f-865bfcb23aef?secondary=Format),
but on `main` after #21868, this was formatted as:

```py
(
    lambda
    # comment
    *x,
    **y: x
)
```

because the leading comment on the first parameter caused the whole
group around the parameters to break.

Instead of making these comments leading comments on the first
parameter, this PR makes them leading comments on the parameters list as
a whole.

## Test Plan

New tests, and I will also try merging this into #21385 _before_ opening
it for review this time.

<hr>

(labeling `internal` since #21868 should not be released before some
kind of fix)
 		2025-12-09 18:15:12 -05:00
..
resources/test/fixtures Fix leading comment formatting for lambdas with multiple parameters (#21879) 2025-12-09 18:15:12 -05:00
src Fix leading comment formatting for lambdas with multiple parameters (#21879) 2025-12-09 18:15:12 -05:00
tests Fix leading comment formatting for lambdas with multiple parameters (#21879) 2025-12-09 18:15:12 -05:00
CONTRIBUTING.md Use `npm ci --ignore-scripts` everywhere (#21742) 2025-12-01 17:13:52 -05:00
Cargo.toml [`ruff`] Update schemars to v1 (#20942) 2025-10-20 08:59:52 +02:00
README.md Add f-string formatting to the docs (#15367) 2025-01-09 10:20:06 +01:00
generate.py Implement template strings (#17851) 2025-05-30 15:00:56 -05:00
orphan_rules_in_the_formatter.svg Generate FormatRule definitions (#4724) 2023-06-01 08:38:53 +02:00

README.md

Ruff Formatter

The Ruff formatter is an extremely fast Python code formatter that ships as part of the ruff CLI.

Goals

The formatter is designed to be a drop-in replacement for Black, but with an excessive focus on performance and direct integration with Ruff.

Specifically, the formatter is intended to emit near-identical output when run over Black-formatted code. When run over extensive Black-formatted projects like Django and Zulip, > 99.9% of lines are formatted identically. When migrating an existing project from Black to Ruff, you should expect to see a few differences on the margins, but the vast majority of your code should be unchanged.

If you identify deviations in your project, spot-check them against the intentional deviations enumerated below, as well as the unintentional deviations filed in the issue tracker. If you've identified a new deviation, please file an issue.

When run over non-Black-formatted code, the formatter makes some different decisions than Black, and so more deviations should be expected, especially around the treatment of end-of-line comments. For details, see Style Guide.

Getting started

Head to The Ruff Formatter for usage instructions and a comparison to Black.