On Sun, Nov 11, 2012 at 02:33:45AM -0800, Junio C Hamano wrote:
> The change seems to think "branch" is the _only_ thing the user
> might want to record per submodule upon "git submodule add".

I felt that earlier floating/tracking submodule patches were biting
off more than they could chew, so I was looking for a lightweight fix
to make the tracking workflow easier.  It seems like I ended up with
something that is too lightweight ;).

> On the other hand, if this were one small part of a series to define
> the "tip following mode" where (at least)
> 
>  (1) "git submodule update [$path]" makes sure that the checkout of
>      the submodule at $path matches the commit at the tip of the
>      branch named by submodule.$name.branch in .gitmodules of the
>      superproject, instead of the commit that is recorded in the
>      index of the superproject; and

As I mentioned earlier, I think

  $ git submodule update [$path]

should keep its current “checkout the already-registered SHA”
functionality, with

  $ git submodule update --pull [$path]

pulling the tracked branch.  I'll add a patch implementing this to v4.

In order to avoid losing (or creating) local-only submodule commits,
I'll probably bail (with an error) on non-fast-forward pulls.  Can
anyone else think of other safety concerns?

This means that I'll probably drop Phil's $submodule_* export in v4,
because the only explicit use we have for it is this branch tracking.
I still think it is a useful idea, but it may not be useful enough to
be worth the complexity.

>  (2) "git diff [$path]" and friends in the superproject compares the
>      HEAD of the checkout of the submodule at $path with the tip of
>      the branch named by submodule.$name.branch in .gitmodules of
>      the superproject, instead of the commit that is recorded in the
>      index of the superproject.
> 

Hmm.  “git diff” compares the working tree with the local HEAD (just a
SHA for submodules), so I don't think it should care about the status
of a remote branch.  This sounds like you want something like:

  $ git submodule foreach 'git diff origin/$submodule_branch'

Perhaps this is enough motivation for keeping $submodule_* exports?

> and the option were called something like "--follow-branch=$branch",
> …

I'll replace -r/--record with --follow-branch in v4.

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