Add --check CLI option similar to Black for CI usage

[skilkis]

@nschloe thanks for the awesome package, I'm enjoying using it so far! A feature request would be to have a --check option similar to the black code formatter that results in a non-zero exit code if betterbib were to make any changes. This would primarily be useful to use in CI services to check if the .bib file is up-to-date and has the right formatting.

[nschloe]

I don't think it'd be useful for betterbib or betterbib-sync, but it could perhaps added to betterbib-format.

[skilkis]

@nschloe the main use-case I have in mind would be to reject a PR if a bibliography file wasn't run through betterbib before a commit. What do you think?

[nschloe]

What do you think?

For sync it's not such a good idea because the online sources change once in a while which would suddenly break your tests.

[skilkis]

It's not a bug it's a feature 😂 Let's see if anyone else has a use for this feature request, otherwise I can implement the desired functionality with a diff as well. Thanks for the quick replies @nschloe

[JensHeinrich]

Dirty hack for you @skilkis :
Use the pre-commit hook and pack it into your ci.
If betterbib formatchanges anything, the hook fails

[skilkis]

@JensHeinrich that's a great suggestion! pre-commit would work well for this 🎉