Re: is it kosher for pre-commit to change what's staged?

Joey Hess [off-list ref] writes:

I've noticed that if I make a pre-commit hook change the files that are
staged, those changes are not reflected in the commit message. For
example, if a pre-commit hook git add's somefile, the commit message
won't reflect that. I guess prepare-commit-msg is being run before
pre-commit for some reason?

My intention was that Documentation/githooks.txt would document things
that are allowed (e.g. "applypatch-msg" explicitly says "The hook is
allowed to edit the message"), and anything that is not specifically
allowed is not.

"Is it kosher" is a difficult question to answer, as something may not be
allowed but there may not be an enforcement mechanism to deny it, iow, it
may happen to work by accident.

In general, pre-anything is about checking and denying and is supposed to
be free of side effects.