If !args->oids then we say "we want to request object-info to learn
size and type for the following objects: oh, there are no objects we
are interested in".  I wonder if an early return

        if (!args->oids)
                return;

at the beginning of the function that turns it into a benign no-op,
may make more sense?  Calling "send_X()" helper and seeing nothing
come out on the wire might make it look awkward, though.

If I add this change, then I should also add a check to ensure
args->object_info_options is also not empty. The question I think we
should answer is whether checking for oids and options should
happen inside this function or not. I'm leaning towards outside
the function for the reason you stated above about nothing
coming out of the wire being awkward.

quoted

+     struct ref *object_info_refs = xcalloc(1, sizeof (struct ref));

Style: no SP between "sizeof" and "(".

ack