build_conditions

# File actionpack/lib/action_dispatch/routing/route_set.rb, line 475
      def build_conditions(current_conditions, path_values)
        conditions = current_conditions.dup

        # Rack-Mount requires that :request_method be a regular expression.
        # :request_method represents the HTTP verb that matches this route.
        #
        # Here we munge values before they get sent on to rack-mount.
        verbs = conditions[:request_method] || []
        unless verbs.empty?
          conditions[:request_method] = %[^#{verbs.join('|')}$]
        end

        conditions.keep_if do |k, _|
          k == :action || k == :controller || k == :required_defaults ||
            @request_class.public_method_defined?(k) || path_values.include?(k)
        end
      end