Re: Migrating svn to git with heavy use of externals

["Avery Pennarun" <apenwarr@gmail.com>]

On Tue, Apr 8, 2008 at 4:49 PM, D. Stuart Freeman
<stuart.freeman@et.gatech.edu> wrote:
>  It's possible to have svn:externals point at a specific revision, but
>  that's not the point.

Right, I forgot that they added that.

>  cd ../access
>  git checkout -b 2-5-x sakai_2-5-x  # sakai_2-5-x is an svn import
>  cd ../sakai
>  git checkout -b 2-5-x sakai_2-5-x
>  git submodule add -b 2-5-x ../access access
>
>  Which gives me an error about access already existing.

You should only ever need to add a given submodule once.  As far as I
can tell, this is a bit of confusion in the way git-submodule works,
but I don't have any suggestions for what to do about it yet so I
don't complain :)

The way to understand git-submodule's operation is in terms of what it
actually does.  Roughly speaking, git-submodule-add puts things into
.gitmodules and .git/config; git-submodule-init copies that stuff from
.gitmodules to .git/config (so if you're the guy who did the add, you
can skip this step).  Then git-commit actually checks the submodule
reference into the parent tree, and someone who pulls your parent tree
needs to run git-submodule-update in order to actually retrieve the
new submodule pointer.

In other words, git-submodule is very powerful, but also very
complicated, and at least one of the things I said up above is
probably wrong :)  By comparison, svn:externals is at least easy to
understand.

Anyway, in this case, what you need to know is that .git/config
already contains your submodule information.  Sadly, .gitmodules is
probably sitting somewhere on your original branch, so it probably
doesn't exist.  You could remove the entry from .git/config by hand
and use git-submodule-add again (thus putting it in both places), or
copy the .gitmodules file from the original branch, or git-cherry-pick
the commit where you added it.

You should *also* cd into the access subdir and checkout the right
revision there; at that time, the next commit to the sakai repository
will make sure the submodule reference is to the right place.

Phew, I hope that made things more clear instead of less clear. :)

Have fun,

Avery