[Freeciv-Dev] (PR#4260) Re: (PR#4332) get_defender bug

["Gregory Berkolaiko" <Gregory.Berkolaiko@xxxxxxxxxxxx>]

I just hit another occurence of this bug.  As a reminder the anatomy of 
the bug is as follows:

A transport of player A carries a unit of player B and player C considers 
attacking them.  If C-allied-A, then the transport is ignored by 
get_defender and it looks as if land unit of B is in the sea on it's own.

I advocated a change to get_defender, since the above situation is not 
wrong (or wrong outside jurisdiction of get_defender function).

Why it could be wrong?  The only case when the above bug surfaces is when 
there is a LLH triangle: A-allied-C, A-allied-B (so that the transport can 
carry the unit) and B-war-C.  LLH triangle has been recently outlawed by 
Per, but not quite: B-war-C apperently includes the situation when 
B-no_contact-C.  Which is not impossible.

Here are my recommendations:

1. DS_NO_CONTACT should be considered as neutral, because you cannot 
attack a no-contact player.  As your unit approaches their unit, you 
establish contact and the state changes to DS_NEUTRAL (function 
make_contact), so the attack is impossible.

2. get_defender should return a defender irrespectfully of alliances (what 
if AI wants to consider feasibility of attack on it's now-ally?).  
Corresponding changes should be made to handle_unit_move_request, to 
prevent actual attack against allies.

Please comment,
G.