Using ruff check diff suppresses errors

[aminalaee]

Hey, thanks for the great work.
I don't know if this is a bug or maybe unclear flag, but doing ruff check --diff . does not fail:

try:
    pass
except:
    pass

But running ruff check . shows proper errors:

E722 Do not use bare `except`

Is this expected? I didn't expect --diff to have this side-effect, maybe the help is not clear?

[JonathanPlasse]

If the help of the CLI you can find

--diff Avoid writing any fixed files back; instead, output a diff for each changed file to stdout

--diff is to be used in conjunction with --fix.
Without --fix, it will always return nothing with exit code 0.

[aminalaee]

Thanks for the clarification, that makes more sense now.
Maybe it might be a good idea to force this combination since without one it's not really doing much.

[dhruvmanila]

I think updating the --help text to include this would help. Better option would be to exit with an appropriate message stating the usage of the flag (--diff is to be used in conjunction with --fix flag).

[aminalaee]

I just opened this so the maintainers can decide if it needs any action.
Thanks for the info.

[charliermarsh]

@dhruvmanila - Agreed, would be nice if we could exit with a meaningful error there.

[odie5533]

Is there an option to output both diffs it could make as well as errors that don't have fixes? It would be useful for me to output all errors + all fixes and return code 1 if there are any.

[zanieb]

Hey @odie5533 that should become the default ruff check behavior after #7352 — it's on our roadmap!