COM812 fails even with one line of code and it's autofix doesn't respect line-length

[koevgeny10]

The documentation has an example with a 2-line dictionary. But it fails even with one line of code.

Versions:

• Python: 3.13
• ruff: 0.9.7

pyproject.toml

[tool.ruff]
target-version = "py313"
line-length = 79
output-format = "concise"

[tool.ruff.lint]
select = ["COM812",  "E501"]

def a(
    b, cccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccccc
): pass

Ruff reports:

a.py:2:80: COM812 [*] Trailing comma missing
Found 1 error.
[*] 1 fixable with the `--fix` option.

I propose that COM812 doesn't fail in such cases.

And it's autofix doesn't respect line-length and adds comma at character 80. Then E501 fails.

[MichaReiser]

Thanks for opening this discussion.

You can use ruff format and disable COM812. The formatter does allow your example but it also breaks overlong-arguments automatically to stay within the desired line length.

We may decide to change COM812 in the future but it's not clear yet how because allowing your example would make the rule less useful to some users. You can read more in #9216