Comment 6 for bug 1722376

A barbarian weaving mill is useless when the map does not provide seafaring, because cloth is only used for building barbarian ships.

So the conclusion is:

if tribe = barbarian AND NOT 'able to build a port' then
   'do not build weaving mill'

But reading the config file(s) is maybe the better solution:

if needs_seafaring = true
  forbid this building

Are there more of such restrictions?