Merge pull request #33569 from eric-hemasystems/conditional-flash-helper

Conditionally use `helper_method` in Flash concern

actionpack/lib/action_controller/metal/flash.rb

@@ -33,10 +33,12 @@ module ActionController #:nodoc:
         types.each do |type|
           next if _flash_types.include?(type)
 
-          define_method(type) do
-            request.flash[type]
+          if respond_to? :helper_method
+            define_method(type) do
+              request.flash[type]
+            end
+            helper_method type
           end
-          helper_method type
 
           self._flash_types += [type]
         end

actionpack/test/controller/flash_test.rb

@@ -342,6 +342,14 @@ class FlashIntegrationTest < ActionDispatch::IntegrationTest
     end
   end
 
+  def test_flash_usable_in_metal_without_helper
+    assert_nothing_raised do
+      Class.new ActionController::Metal do
+        include ActionController::Flash
+      end
+    end
+  end
+
   private
 
     # Overwrite get to send SessionSecret in env hash