module A; def a; end; end
module B; def b; end; end
class C; include A; end
module A; include B; end
class D; include A; end
C.new.b # undefined method error
D.new.b # nil
C.ancestors # [C, A, Object...]
D.ancestors # [D, A, B, Object...]
How to include module B inside of A, so that classes that already include module A will also get methods from module B?