On 03/13, Stefan Beller wrote:

+ cc Jens, FYI.

Once upon a time I brought up different addressing/activating mechanism for
submodules and I remember Jens having some uneasy thoughts about
that back in the day. This series addresses the user confusion and documentation
better than what I had back then.

On Mon, Mar 13, 2017 at 2:43 PM, Brandon Williams [off-list ref] wrote:

quoted

Currently the submodule.<name>.url config option is used to determine
if a given submodule exists and is interesting to the user.  This
however doesn't work very well because the URL is a config option for
the scope of a repository, whereas the existence of a submodule is an
option scoped to the working tree.

In a future with worktree support for submodules, there will be multiple
working trees, each of which may only need a subset of the submodules
checked out.  The URL (which is where the submodule repository can be
obtained) should not differ between different working trees.

It may also be convenient for users to more easily specify groups of
submodules they are interested in as apposed to running "git submodule
init <path>" on each submodule they want checked out in their working
tree.

To this end two config options are introduced, submodule.active and
submodule.<name>.active.  The submodule.active config holds a pathspec
that specifies which submodules should exist in the working tree.  The
submodule.<name>.active config is a boolean flag used to indicate if
that particular submodule should exist in the working tree.

Given these multiple ways to check for a submodule's existence the more
fine-grained submodule.<name>.active option has the highest order of
precedence followed by the pathspec check against submodule.active. To
ensure backwards compatibility, if neither of these options are set git
falls back to checking the submodule.<name>.url option to determine a
submodule's existence.

quoted

+submodule.<name>.active::
+       Boolean value indicating if the submodule is of interest to git
+       commands.  This config option takes precedence over the
+       submodule.active config option.

... which itself takes precedence over the (deprecated) .URL
We conveniently do not talk about the URL here anymore.
But! We need to change submodule.<name>.URL now?

yeah this patch introduces a change to the documentation for URL to
indicate the change.

-- 
Brandon Williams