name_for_action

# File actionpack/lib/action_dispatch/routing/mapper.rb, line 1748
          def name_for_action(as, action) #:nodoc:
            prefix = prefix_name_for_action(as, action)
            name_prefix = @scope[:as]

            if parent_resource
              return nil unless as || action

              collection_name = parent_resource.collection_name
              member_name = parent_resource.member_name
            end

            name = @scope.action_name(name_prefix, prefix, collection_name, member_name)

            if candidate = name.compact.join("_").presence
              # If a name was not explicitly given, we check if it is valid
              # and return nil in case it isn't. Otherwise, we pass the invalid name
              # forward so the underlying router engine treats it and raises an exception.
              if as.nil?
                candidate unless candidate !~ /\A[_a-z]/ || @set.named_routes.key?(candidate)
              else
                candidate
              end
            end
          end