gem_backtracer.rb

class GemBacktracer

  class << self
    def cleanup(backtrace)
      backtrace.collect do |line|
        path = gem_path_for(line)
        if path.nil?
          line
        else
          "(#{bundle_paths[path]}):#{Pathname(line).relative_path_from(Pathname(path)).to_s}"
        end
      end
    end

    private
    
      def bundle_paths
        @bundle_paths ||= { Rails.root.to_s => Rails.application.class.name }.tap do |result|
          all_specs = Bundler.load.specs.to_hash
          all_specs.each_pair do |name, specs|
            specs.each do |spec|
              result[spec.full_gem_path] = spec.full_name
            end
          end
        end
      end

      def gem_path_for(line)
        bundle_paths.keys.find do |path|
          line.start_with?(path)
        end
      end
  end
end