add_gem_filters

# File railties/lib/rails/backtrace_cleaner.rb, line 19
      def add_gem_filters
        return unless defined?(Gem)

        gems_paths = (Gem.path + [Gem.default_dir]).uniq.map!{ |p| Regexp.escape(p) }
        return if gems_paths.empty?

        gems_regexp = %{(#{gems_paths.join('|')})/gems/([^/]+)-([\w\.]+)/(.*)}
        add_filter { |line| line.sub(gems_regexp, '\2 (\3) \4') }
      end