gem

# File railties/lib/rails/engine/configuration.rb, line 70
      def gem(name, options = {})
        super name, options[:version] || ">= 0"
        require options[:lib] || name
      rescue Gem::LoadError
        msg = "config.gem is deprecated, and you tried to activate the '#{name}' gem (#{options.inspect}) using it.\n"

        if File.exist?("#{Rails.root}/Gemfile")
          msg << "Please add '#{name}' to your Gemfile."
        else
          msg << "Please update your application to use bundler."
        end
        ActiveSupport::Deprecation.warn(msg, caller)
        exit
      end