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

From: Joey Hess <[email-masked]>
Date: Wed, 10 Nov 2010 16:45:42 -0400

Jonathan Nieder wrote:
> In this case, isn't it only a half accident?  For example, I think
> v1.5.4-rc0~78^2~12 (builtin-commit: fix partial-commit support,
> 2007-11-18) taught git to support this a little better.

Partial commits modified by pre-commit still don't work entirely right IME.
After the commit, the index is such that git wants to revert any changes
added to the commit by the pre-commit hook.

> That said, I would be interested to hear the use case, since modifying
> staged content on the fly for a commit sounds a little crazy. :)

Well, with git-annex (which I should probably properly announce here
sometime), large files are not committed to git, but instead a symlink
pointing at the content is committed. That symlink can temporarily be
replaced with a copy of the file when the user wants to modify it, and
if the user then commits, it's nice if it can move away the large file's
content, and arrange for the commit to contain an updated symlink pointing
at the new content.

That said, since git commit stages the whole large file into the index,
which is the kind of expensive operation git-annex exists to avoid,
it's still not very practical to intercept the commit like that. What
I ideally need is a hook that is run before git commit stages anything.

BTW, githooks says pre-commit is "invoked before obtaining the proposed
commit log message", which is a bit confusing. I actually see
prepare-commit-msg and commit-msg both called after pre-commit.

-- 
see shy jo