Option for auto-commiting hook-made changes

[ArturGajowy]

The docs say:
The hook must exit nonzero on failure or modify files in the working directory (since 0.6.3).

That is also the observed behavior. In case of a formatter hook though, that means most commits need to be attempted twice: once to re-format them, twice to commit them successfully.

For a sufficiently mature formatter tool, it should be OK to just set sth like auto_commit_changes: true in its hook config. This issue is about adding such an option to pre-commit. WDYT?

[asottile]

pre-commit will never ever ever modify the staging area, that's not a safe operation and one of the worst anti-features of related tools

See also #879 #806 #999 #747 (please search the issue tracker next time!)

[ArturGajowy]

Thanks, I found your remark in one of those issues helpful: I can always make my hook do run_formatter && git add -u.

(I did search the tracker)