name_for_action

# File actionpack/lib/action_dispatch/routing/mapper.rb, line 1603
          def name_for_action(as, action) #:nodoc:
            prefix = prefix_name_for_action(as, action)
            prefix = Mapper.normalize_name(prefix) if prefix
            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 = case @scope[:scope_level]
            when :nested
              [name_prefix, prefix]
            when :collection
              [prefix, name_prefix, collection_name]
            when :new
              [prefix, :new, name_prefix, member_name]
            when :member
              [prefix, shallow_scoping? ? @scope[:shallow_prefix] : name_prefix, member_name]
            when :root
              [name_prefix, collection_name, prefix]
            else
              [name_prefix, member_name, prefix]
            end

            if candidate = name.select(&:present?).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 @set.routes.find { |r| r.name == candidate } || candidate !~ /\A[_a-z]/
              else
                candidate
              end
            end
          end