just noting here, I poked at this some more to create the bug report upstream, and the behavior doeskind of make sense... it's just confusing
ruff --diff will exit 0 if there are no diffs (proposed changes) reported and exit 1 if there are. However, there are errors / findings that do not, or cannot, generate changes to files, but are still errors.

It may be worth addingruff --diff as part of the pipeline somewhere to display the changes (if we want) - however, using it the way we were originally probably doesn't make sense.

Thanks for looking into this, definitely is a weird result. Either way all I want is it to display where the error is located. The diff is a nice to have where it shows what to fix but I can also look up the rule for where it indicates an error exists.

Yeah, re-reading the docs for--diff and for--fix-only (which it notes is implied), it actually does make sense:

      --diff          Avoid writing any fixed files back; instead, output a diff for each changed          file to stdout. Implies `--fix-only`[...]      --fix-only          Apply fixes to resolve lint violations, but don't report on leftover          violations. Implies `--fix`. Use `--no-fix-only` to disable or `--unsafe-fixes`          to include unsafe fixes

I think in this case "report on" also implies the exit status as well, in other words, because--diff implies--fix-only, it is expected that it doesn't report non-fixable findingsand exits 0 for non-fixable findings. So the interaction of flags is a little unexpected.

I agree that things are fine as it is now. It would be nice to have a way to both report the fixable changes as a diff, and also check for findings, with a single command, but seems like not possible as-is. Short of some additional notes in the docs, or adding some additional flags, might be difficult to fix as well.