This is a sample Rails 4.2 application with an engine to show a bug with the config.relative_url_root option. The engine is mounted on the same path. Visit localhost:3000/relative after bundling the app and running ‘rails s` in the root directory. There are links to the main app and the engine in the simplified navigation.

The workaround for this problem is noted in config/application.rb. Namely, the following lines:

# In order to fix the problem, the following options must be set.
routes.default_url_options ||= {}
routes.default_url_options[:script_name]= ''