Restore to: option with an implicit controller

The `:to` option for routes can once again be a String without a
controller if the controller is implicitly provided by a nesting
`controller` or `resources` call.

actionpack/CHANGELOG.md

@@ -1,3 +1,15 @@
+*   Fix a regression in 7.1.3 passing a `to:` option without a controller when the controller is already defined by a scope.
+
+    ```ruby
+    Rails.application.routes.draw do
+      controller :home do
+        get "recent", to: "recent_posts"
+      end
+    end
+    ```
+
+    *Étienne Barrié*
+
 *   Request Forgery takes relative paths into account.
 
     *Stefan Wienert*

actionpack/lib/action_dispatch/routing/mapper.rb

@@ -231,12 +231,17 @@ def normalize_options!(options, path_params, modyoule)
               if to.nil?
                 controller = default_controller
                 action = default_action
-              elsif to.is_a?(String) && to.include?("#")
-                to_endpoint = to.split("#").map!(&:-@)
-                controller  = to_endpoint[0]
-                action      = to_endpoint[1]
+              elsif to.is_a?(String)
+                if to.include?("#")
+                  to_endpoint = to.split("#").map!(&:-@)
+                  controller  = to_endpoint[0]
+                  action      = to_endpoint[1]
+                else
+                  controller = default_controller
+                  action = to
+                end
               else
-                raise ArgumentError, ":to must respond to `action` or `call`, or it must be a String that includes '#'"
+                raise ArgumentError, ":to must respond to `action` or `call`, or it must be a String that includes '#', or the controller should be implicit"
               end
 
               controller = add_controller_module(controller, modyoule)

actionpack/test/dispatch/routing_test.rb

@@ -4037,6 +4037,7 @@ def draw(&block)
     routes = ActionDispatch::Routing::RouteSet.new
     routes.draw(&block)
     @app = self.class.build_app routes
+    @routes = routes
   end
 
   def test_missing_controller
@@ -4054,7 +4055,16 @@ def test_missing_controller_with_to
         get "/foo/bar", to: "foo"
       end
     }
-    assert_match(/:to must respond to/, ex.message)
+    assert_match(/Missing :controller/, ex.message)
+  end
+
+  def test_implicit_controller_with_to
+    draw do
+      controller :foo do
+        get "/foo/bar", to: "bar"
+      end
+    end
+    assert_routing "/foo/bar", controller: "foo", action: "bar"
   end
 
   def test_to_is_a_symbol
@@ -4066,7 +4076,7 @@ def test_to_is_a_symbol
     assert_match(/:to must respond to/, ex.message)
   end
 
-  def test_missing_action_on_hash
+  def test_missing_action_with_to
     ex = assert_raises(ArgumentError) {
       draw do
         get "/foo/bar", to: "foo#"