1 files changed, 12 insertions, 0 deletions
diff --git a/actionpack/lib/action_dispatch/journey/route.rb b/actionpack/lib/action_dispatch/journey/route.rb
index 50e1853094..c8eb0f6f2d 100644
--- a/actionpack/lib/action_dispatch/journey/route.rb
+++ b/actionpack/lib/action_dispatch/journey/route.rb
@@ -16,6 +16,14 @@ module ActionDispatch
         @app         = app
         @path        = path
 
+        # Unwrap any constraints so we can see what's inside for route generation.
+        # This allows the formatter to skip over any mounted applications or redirects
+        # that shouldn't be matched when using a url_for without a route name.
+        while app.is_a?(Routing::Mapper::Constraints) do
+          app = app.app
+        end
+        @dispatcher  = app.is_a?(Routing::RouteSet::Dispatcher)
+
         @constraints = constraints
         @defaults    = defaults
         @required_defaults = nil
@@ -93,6 +101,10 @@ module ActionDispatch
         end
       end
 
+      def dispatcher?
+        @dispatcher
+      end
+
       def matches?(request)
         constraints.all? do |method, value|
           next true unless request.respond_to?(method)