[Freeciv-Dev] Re: (PR#6337) Hash registration

["Jason Short" <jdorje@xxxxxxxxxxxxxxxxxxxxx>]

Cameron Morland wrote:
> Hi,
> 
> I don't know what to do in this circumstance. In sanitycheck.c:279 we
> want to assert(!is_ground_unit(find_unit_by_id(punit->transported_by))),
> but find_unit_by_id returns NULL in my particular case, indicating that
> the unit is not "registered". I don't get this hash stuff; what should
> we do if the unit is not registered?
> 
> Unfortunately I seem unable to cause this particular crash to occur
> again, but if someone could answer, I'll know next time.

find_unit_by_id returns NULL because the id is invalid.  This is/was 
because the transported_by field wasn't getting updated at some point, 
and then the original transporter was destroyed.  This should be fixed 
now since transported_by is updated in server_remove_unit().

If transported_by was a pointer, then we'd be left with an invalid 
pointer and get a harder-to-track bug.  With the hash lookup returning 
NULL it's easier to catch the bug.  Of course there are disadvantages of 
using the ID as well...

jason