mount

# File actionpack/lib/action_dispatch/routing/mapper.rb, line 612
        def mount(app, options = nil)
          if options
            path = options.delete(:at)
          elsif Hash === app
            options = app
            app, path = options.find { |k, _| k.respond_to?(:call) }
            options.delete(app) if app
          end

          raise ArgumentError, "A rack application must be specified" unless app.respond_to?(:call)
          raise ArgumentError, <<~MSG unless path
            Must be called with mount point

              mount SomeRackApp, at: "some_route"
              or
              mount(SomeRackApp => "some_route")
          MSG

          rails_app = rails_app? app
          options[:as] ||= app_name(app, rails_app)

          target_as       = name_for_action(options[:as], path)
          options[:via] ||= :all

          match(path, options.merge(to: app, anchor: false, format: false))

          define_generate_prefix(app, target_as) if rails_app
          self
        end