find_template_extension_from_handler

# File actionpack/lib/action_view/template_finder.rb, line 146
    def find_template_extension_from_handler(template_path, template_format = @template.template_format)
      formatted_template_path = "#{template_path}.#{template_format}"

      view_paths.each do |path|
        if (extensions = @@file_extension_cache[path][formatted_template_path]).any?
          return "#{template_format}.#{extensions.first}"
        elsif (extensions = @@file_extension_cache[path][template_path]).any?
          return extensions.first.to_s
        end
      end
      nil
    end