Ensure root routes inside optional scopes works as expected.

actionpack/lib/action_dispatch/routing/mapper.rb

@@ -157,10 +157,11 @@ def default_controller
       end
 
       # Invokes Rack::Mount::Utils.normalize path and ensure that
-      # (:locale) becomes (/:locale) instead of /(:locale).
+      # (:locale) becomes (/:locale) instead of /(:locale). Except
+      # for root cases, where the latter is the correct one.
       def self.normalize_path(path)
         path = Rack::Mount::Utils.normalize_path(path)
-        path.sub!(%r{/\(+/?:}, '(/:')
+        path.sub!(%r{/(\(+)/?:}, '\1/:') unless path =~ %r{^/\(+:.*\)$}
         path
       end
 

actionpack/test/dispatch/routing_test.rb

@@ -141,19 +141,18 @@ def self.matches?(request)
         resources :rooms
       end
 
-      scope '(:locale)', :locale => /en|pl/ do
-        resources :descriptions
-      end
+      match '/info' => 'projects#info', :as => 'info'
 
       namespace :admin do
-        scope '(/:locale)', :locale => /en|pl/ do
+        scope '(:locale)', :locale => /en|pl/ do
           resources :descriptions
         end
       end
 
-      match '/info' => 'projects#info', :as => 'info'
-
-      root :to => 'projects#index'
+      scope '(:locale)', :locale => /en|pl/ do
+        resources :descriptions
+        root :to => 'projects#index'
+      end
     end
   end
 
@@ -660,6 +659,14 @@ def test_normalize_namespaced_matches
     end
   end
 
+  def test_optional_scoped_root
+    with_test_routes do
+      assert_equal '/en', root_path("en")
+      get '/en'
+      assert_equal 'projects#index', @response.body
+    end
+  end
+
   def test_optional_scoped_path
     with_test_routes do
       assert_equal '/en/descriptions', descriptions_path("en")