Junio C Hamano [off-list ref] writes:

* gc/recursive-fetch-with-unused-submodules (2022-02-10) 8 commits
 - submodule: fix bug and remove add_submodule_odb()
 - fetch: fetch unpopulated, changed submodules
 - submodule: extract get_fetch_task()
 - t5526: use grep to assert on fetches
 - t5526: introduce test helper to assert on fetches
 - submodule: make static functions read submodules from commits
 - submodule: store new submodule commits oid_array in a struct
 - submodule: inline submodule_commits() into caller

 When "git fetch --recurse-submodules" grabbed submodule commits
 that would be needed to recursively check out newly fetched commits
 in the superproject, it only paid attention to submodules that are
 in the current checkout of the superproject.  We now do so for all
 submodules that have been run "git submodule init" on.

 Will merge to 'next'?
 source: [ref]

I'm working on another version that should hopefully address some
reviewer feedback on v2. I'd prefer to hold off until that version is
reviewed :)