Intricacies of submodules [was: Migrating svn to git with heavy use of externals]

[Roman Shaposhnik <rvs@sun.com>]

On Wed, 2008-04-09 at 02:34 -0400, Avery Pennarun wrote:
> On Wed, Apr 9, 2008 at 12:39 AM, Roman Shaposhnik <rvs@sun.com> wrote:
> > > In my own use case, I think having all the objects from the
> > > supermodule *and* submodules all be in the same repo is what I want.
> > > This kind of obviates the need for .gitmodules entirely, if
> > > git-checkout and friends will do the right thing.  I think I'll submit
> > > some patches eventually once I have this figured out properly.
> >
> >  Hm. But what about those who might want to pull from you? .git/config
> >  doesn't propagate, which means that they'll be kind of stuck, don't
> >  you think?
> 
> Not exactly.  The idea is that if the supermodule and submodules are
> all lumped into a single repo (and your refs are set up correctly),
> then cloning the supermodule will also clone all the submodules.  

Interesting! How do you make it happen? Do you use git hooks or
something? On my end, I can't really reproduce that behavior of clone
but I would very much like to:
  $ alias mkrepo="git init; touch file; git add file; git commit -mInit"
  $ mkdir super ; cd super
  $ mkrepo
  $ mkdir submodule ; cd submodule
  $ mkrepo
  $ cd ..
  $ git submodule add submodule
  Adding existing repo at 'submodule' to the index
  $ git commit -mSubmodule
  Created commit 5921c87: Submodule
     2 files changed, 4 insertions(+), 0 deletions(-) 
     create mode 100644 .gitmodules
     create mode 160000 submodule

Now, when I clone super I don't actually have submodule cloned:
   $ git clone super super-clone
   $ cd  super-clone
   $ git submodule status
   -7482d0433ed681aa243629f13cd97ca5be242393 submodule

In fact, it seems that I can't even do "submodule update", which
seems like a bug to me, by the way:
    $ git submodule init  
    Submodule 'submodule' (submodule) registered for path 'submodule'

    $ git submodule update
    Initialized empty Git repository in /tmp/TEST/super-clone/submodule/.git/
    fatal: no matching remote head
    fetch-pack from 'submodule' failed.
    Clone of 'submodule' into submodule path 'submodule' failed

Any ideas on what's going on here? Or what am I doing wrong?

> So everyone will have all the necessary refs anyway; as long as
> git-checkout checks them out, .gitmodules shouldn't have to exist at
> all, becaues there's nothing "special" for git-submodule to do.

I would very much like to have that, yes. Please do provide additional
details on how's your setup is different from mine.

Thanks,
Roman.