Make `ActionDispatch::Response#content_type` behavior configurable

I changed return value of `ActionDispatch::Response#content_type` in #36034.
But this change seems to an obstacle to upgrading. https://github.com/rails/rails/pull/36034#issuecomment-498795893

Therefore, I restored the behavior of `ActionDispatch::Response#content_type`
to 5.2 and deprecated old behavior. Also, made it possible to control the
behavior with the config.

1 files changed, 27 insertions, 0 deletions

diff --git a/railties/test/application/configuration_test.rb b/railties/test/application/configuration_test.rb
index 6f9711cb37..f6bec3242a 100644
--- a/railties/test/application/configuration_test.rb
+++ b/railties/test/application/configuration_test.rb
@@ -2436,6 +2436,33 @@ module ApplicationTests
       assert_nil ActiveStorage.queues[:purge]
     end
 
+    test "ActionDispatch::Response.return_only_media_type_on_content_type is false by default" do
+      app "development"
+
+      assert_equal false, ActionDispatch::Response.return_only_media_type_on_content_type
+    end
+
+    test "ActionDispatch::Response.return_only_media_type_on_content_type is true in the 5.x defaults" do
+      remove_from_config '.*config\.load_defaults.*\n'
+      add_to_config 'config.load_defaults "5.2"'
+
+      app "development"
+
+      assert_equal true, ActionDispatch::Response.return_only_media_type_on_content_type
+    end
+
+    test "ActionDispatch::Response.return_only_media_type_on_content_type can be configured in the new framework defaults" do
+      remove_from_config '.*config\.load_defaults.*\n'
+
+      app_file "config/initializers/new_framework_defaults_6_0.rb", <<-RUBY
+        Rails.application.config.action_dispatch.return_only_media_type_on_content_type = true
+      RUBY
+
+      app "development"
+
+      assert_equal true, ActionDispatch::Response.return_only_media_type_on_content_type
+    end
+
     test "ActionMailbox.logger is Rails.logger by default" do
       app "development"