Re: [PATCH] submodule: use cheaper check for submodule pushes

[Junio C Hamano <gitster@pobox.com>]

Jonathan Nieder <jrnieder@gmail.com> writes:

>> In the function push_submodule[1] we use add_submodule_odb[2] to determine
>> if a submodule has been populated. However the function does not work with
>> the submodules objects that are added, instead a new child process is used
>> to perform the actual push in the submodule.
>>
>> Use is_submodule_populated[3] that is cheaper to guard from unpopulated
>> submodules.
>>
>> [1] 'push_submodule' was added in eb21c732d6 (push: teach
>>     --recurse-submodules the on-demand option, 2012-03-29)
>> [2] 'add_submodule_odb' was introduced in 752c0c2492 (Add the
>>     --submodule option to the diff option family, 2009-10-19)
>> [3] 'is_submodule_populated' was added in 5688c28d81 (submodules:
>>     add helper to determine if a submodule is populated, 2016-12-16)
>
> These footnotes don't answer the question that I really have: why did
> this use add_submodule_odb in the first place?
>
> E.g. did the ref iteration code require access to the object store
> previously and stop requiring it later?

Yes, the most important question is if it is safe to lose the access
to the object store of the submodule.  It is an endgame we should
aim for to get rid of add_submodule_odb(), but does the rest of this
codepath not require objects in the submodule at all or do we still
need to change something to make it so?