Subject: Re: [PATCH 07/16] git-read-tree: take --submodules option

From: Martin Waitz <[email-masked]>
Date: Mon, 21 May 2007 23:11:34 +0200

hoi :)

On Mon, May 21, 2007 at 06:59:38PM +0200, Jan Hudec wrote:
> Here is one possible idea:
> 
> We could store the GIT_DIR of submodule within the GIT_DIR of the
> superproject instead of the submodule directory itself. So instead of:
>  /
>  /.git
>  /subdir
>  /subdir/.git
> 
> There would be:
>  /
>  /.git
>  /subdir
>  /.git/submodules/submodule-name.git
> 
> This would require changes to the logic how git finds GIT_DIR (which would be
> really deep change), but it would provide place to store the submodule data
> while the submodule is not being checked out. 

I agree that we need something like that.

We don't have to move the entire subproject.git into the superproject,
but we need to have all _referenced_ objects in the .git dir of the
superproject.

There are several possibilities to do so:

 * move the entire .git dir
 * move .git/objects
 * explicitly copy all referenced objects

I have some experimental code to configure a per-subproject directory
in the superproject/.git as alternate object store for the submodule
to make the last two solutions possible.  Perhaps I should dig it out again
and adapt it to current git.

If there is a 1:1 relationship between subproject and object store then
even efficient fsck and repack/prune are possible for the submodule without
loosing objects.
But such a 1:1 relationship is bad when you move subprojects to another
location (or include the same subproject several times in different
locations of the tree).
Perhaps the user should be able to choose which one he wants.

> > Not at all.  There is no reason to believe that the case that
> > superproject and subproject come from related URLs is more
> > common.  One of the reasons to do a separated project
> 
> I definitely don't think it's more common. But it's the harder case and it
> might happen. Generally it will happen if some people work on both the
> superproject and the subproject. Of course the argument is that than it
> should not be separate projects, but maybe the teams just partly overlap.

I think it will be _very_ common to store super and subprojects in
related locations.  First to be independent from third-party servers
while working on the superproject.
Second (and I think more important) because many times there will
be superproject related adaptations in the subproject.  Yes they
are independent, and exactly for that reason the subproject upstream
maintainers may not take every change which is needed to satisfy the
superproject.  We _now_ see that in all Linux distributions already.
So when you use superprojects to integrate several independent projects,
then the superproject maintainer/administrator should really keep a
clone of all subprojects handy on his site.

-- 
Martin Waitz