[Freeciv-Dev] Re: (PR#2464) patch: restrict techs by nation

["Gregory Berkolaiko via RT" <rt@xxxxxxxxxxxxxx>]

Sorry if I gatecrush the discussion without really understandiing who 
proposes what, but I thought that it'd be simpler to have, instead of 
nation_req, a root_req.

This root_req would be the tech (like Fire of Morgoth) which sits in the 
origin of one of the separate trees.  Knowledge of this root_tech would be 
required not only for the research but also for the transfer by theft or 
gift or conquest.  Effectively Per's function is_tech_available (which I 
would rename into is_tech_accessible) will check not for the name or ID of 
the player, but whether player has the root_req of this tech.

Then, for example, Uruk-Hai tech would have
req1 = Genetical Engineering
req2 = Stem Cells
root_req = Fire of Morgoth

The advantage is that if you want to add another nation which has access 
to a tech tree, you don't have to add the nation name to each tech.  Just 
give the nation Fire of Morgoth, that's all.

Obviously the root tech has to have itself as a root_req, so it is not 
transferable in the first place.  So Fire of Morgoth will be
req1 = Fire of Morgoth  /* Non-researchable */
req2 = 
root_req = Fire of Morgoth  /* Non-transferable */

G.