Re: [PATCH] unpack-trees.c: assume submodules are clean during check-out

[Eran Tromer <git2eran@tromer.org>]

On 2007-08-05 10:46, Sven Verdoolaege wrote:
>> $ git checkout experimental-death-ray
>> $ git submodules update
>> (return a week later, woozy from the vacation.)
>> $ git checkout master
> 
> Here, it'll warn that your submodule isn't up-to-date.
> 
>> (hack hack hack)
>> $ git commit -a -m "fixed typos"
> 
> And if you run "git status" first, it'll tell you that the submodule
> (still) isn't up-to-date.
> 
>> $ git push
>> (Oops. You've just accidentally committed the wrong submodule heads.)
> 
> You always have to be careful when doing "git commit -a".

Exactly. You now have to be very careful, whereas previously
$ git checkout master && vi foo && git commit -a -m "fixed typos"
was perfectly safe.

Worse yet, it could also be a script making similar assumptions. For
example, consider the tree filter in git-filter-branch. It used to be
fine, but will now corrupt the rewritten trees when submodules are
involved. Here's the relevant code from git-filter-branch.sh:

-----------------------------------------------------------------
while read commit parents; do
...
		git read-tree -i -m $commit
...
		git checkout-index -f -u -a ||
			die "Could not checkout the index"
...
		eval "$filter_tree" < /dev/null ||
			die "tree filter failed: $filter_tree"

		git diff-index -r $commit | cut -f 2- | tr '\n' '\0' | \
			xargs -0 git update-index --add --replace --remove
...
	sh -c "$filter_commit" "git commit-tree" \
		$(git write-tree) $parentstr < ../message > ../map/$commit
done <../revs
-----------------------------------------------------------------


>> Another approach is for pull, checkout etc. to automatically update the
>> submodule' head ref, but no more.
> 
> Then everything, including "git submodule update", would assume
> that the submodule is up-to-date.

With that approach, "git submodule update" would fetch the submodule's
head commit (which could be missing), and then check it against the
submodule's index (and maybe its work tree).

  Eran