module T::Private::Methods

def self._hook_impl(target, singleton_class, source)

methods M on source, M is not defined on any of target's ancestors.
the module target is adding the methods from the module source to itself. we need to check that for all instance 
def self._hook_impl(target, singleton_class, source)
  # we do not need to call add_was_ever_final here, because we have already marked
  # any such methods when source was originally defined.
  if !@modules_with_final.include?(target)
    if !@modules_with_final.include?(source)
      return
    end
    note_module_deals_with_final(target)
    install_hooks(target)
    return
  end
  methods = source.instance_methods
  methods.select! do |method_name|
    @was_ever_final_names.include?(method_name)
  end
  if methods.empty?
    return
  end
  target_ancestors = singleton_class ? target.singleton_class.ancestors : target.ancestors
  _check_final_ancestors(target, target_ancestors, methods, source)
end