On Thu, Feb 23, 2017 at 3:47 PM, Brandon Williams [off-list ref] wrote:

There are two motivations for decoupling a submodule's existence from the url
that is stored in .git/config.

1. Worktrees can't really be used with submodules since the existence is
   checked based on the shared .git/config.  This means that two different
   worktress have to have the same initialized submodules.  By decoupling a
   submodule's existence from the url, two different work trees can be
   configured to have different submodules checked out.

cc Duy for this one:

Well once we have the per-worktree configuration, e.g. [1] we can *technically*
have different submodules in different worktrees by saying

  workingtree0: submodule.<name>.url = git://example.org/real-submodule
  workingtree1: submodule.<name>.url = bogus
  workingtree2: submodule.<name>.url = more bogus

and once we used the URL in the first workingtree all urls are
degraded to a boolean flag,
so the different (possible bogus) content does not do harm, only user-confusion,
because the model of the URL being the flag indicating existence doesn't quite
fit multiple working trees.

[1] https://public-inbox.org/git/20170110112524.12870-3-pclouds@gmail.com/

2. Easily configure gorups of submodules that a user is interested in.  In a
   repository with hundreds of submodules it would be difficult to easily tell git
   which modules to worry about without having to individually init all of
   them.  Instead, a pathspec can be used to more easily select or deselect
   groups of submodules.

This patch series works to do this decoupling and instead allows a user to
configure submodule.active with a pathspec to use to check if a submodule is
initialized.

Thanks for stating both intentions!
Stefan