Re: [BUG?] gitlink without .gitmodules no longer fails recursive clone

Jeff King [off-list ref] writes:

Certainly I think it _could_ be a valid state. But traditionally it
caused "clone --recursive" to barf. And from what Stefan and Brandon
have said, we are moving in the opposite direction entirely, with
.gitmodules becoming the source of truth.

I could see arguments for going in either direction (gitlinks versus
.gitmodules as source of truth for submodules). But it bothers me that
it's so easy to create a state that will behave in a confusing manner.
...
Allowing both is not in itself wrong.  But because we provide no
guidance for the expert route, it's easy to shoot yourself in the foot
and not even realize it. Which is why I suggested a warning and not
forbidding the operation. Or better still, an advise() block that tells
you how to recover (probably "git submodule add", though it might need
to learn to handle already-present gitlinks). And which can be disabled
if you really are an expert user.

Yeah, the current situation is bad in that having both .gitmodules
file and gitlinks in a tree allows for redundant pieces of
information to go out of sync and result in contradiction.  A gitlink
without an entry in the .gitmodules file is an obvious example.  An
entry in .gitmodules file whose path does not have a gitlink in the
tree would also be a broken case.  

While "git submodule" was the only/primary interface to the
submodule, it was rather easy to explain that ".gitmodules need to
be consistent with the index and the tree iff you do 'git submodule'
thing" (implying "if you only use gitlinks to bind two or more
projects locally without sharing with others, you do not need 'git
submodule' and you do not need .gitmodules"), but with the recent
push to add "--recurse-submodules" to everything, the extent of what
was historically "iff you do 'git submodule' thing" is getting
larger and it becomes more and more important to keep .gitmodules
consistent with gitlinks in the tree that house it.

I find it a bit sad, but I do not think of a better way X-<.