Philippe Blain [off-list ref] writes:

I would maybe add more details here, something like the following 
(we can cite your previous attempt, because it was merged to 'master'):

The first attempt to fix this regression, in 1b7ac4e6d4
(submodules: fix of regression on fetching of non-init
subsub-repo, 2020-11-12), by simply reverting a62387b, resulted in
an infinite loop of submodule fetches in the simpler case of a
recursive fetch of a superproject with uninitialized submodules,
and so this commit was reverted in 7091499bc0 (Revert "submodules:
fix of regression on fetching of non-init subsub-repo",
2020-12-02).  To prevent future breakages, also add a regression
test for this scenario.

Forgot to mention in my other response, but I do find this a very
sensible addition.

Thanks.