always dispatch to controllers the same way

controllers should always go through the `action` class method so that
their middleware is respected.

actionpack/lib/action_controller/metal.rb

@@ -247,6 +247,7 @@ def self.call(env)
       req = ActionDispatch::Request.new env
       action(req.path_parameters[:action]).call(env)
     end
+    class << self; deprecate :call; end
 
     # Returns a Rack endpoint for the given action name.
     def self.action(name)

actionpack/lib/action_dispatch/routing/mapper.rb

@@ -283,6 +283,9 @@ def normalize_defaults(options)
           end
 
           def app(blocks)
+            if to.is_a?(Class) && to < ActionController::Metal
+              Routing::RouteSet::StaticDispatcher.new to
+            else
               if to.respond_to?(:call)
                 Constraints.new(to, blocks, Constraints::CALL)
               elsif blocks.any?
@@ -291,6 +294,7 @@ def app(blocks)
                 dispatcher(defaults.key?(:controller))
               end
             end
+          end
 
           def check_controller_and_action(path_params, controller, action)
             hash = check_part(:controller, controller, path_params, {}) do |part|

actionpack/lib/action_dispatch/routing/route_set.rb

@@ -28,8 +28,7 @@ def dispatcher?; true; end
 
         def serve(req)
           params = req.path_parameters
-          controller = req.controller_class
-          dispatch(controller, params[:action], req)
+          dispatch(controller(req), params[:action], req)
         rescue NameError => e
           if @raise_on_name_error
             raise ActionController::RoutingError, e.message, e.backtrace
@@ -40,11 +39,26 @@ def serve(req)
 
       private
 
+        def controller(req)
+          req.controller_class
+        end
+
         def dispatch(controller, action, req)
           controller.action(action).call(req.env)
         end
       end
 
+      class StaticDispatcher < Dispatcher
+        def initialize(controller_class)
+          super(false)
+          @controller_class = controller_class
+        end
+
+        private
+
+        def controller(_); @controller_class; end
+      end
+
       # A NamedRouteCollection instance is a collection of named routes, and also
       # maintains an anonymous module that can be used to install helpers for the
       # named routes.