# File lib/nanoc/cli/commands/compile.rb, line 95
      def generate_diff_for(rep, old_content, new_content)
        return if old_content == new_content

        @diff_threads << Thread.new do
          # Generate diff
          diff = diff_strings(old_content, new_content)
          diff.sub!(/^--- .*/,    '--- ' + rep.raw_path)
          diff.sub!(/^\+\+\+ .*/, '+++ ' + rep.raw_path)

          # Write diff
          @diff_lock.synchronize do
            File.open('output.diff', 'a') { |io| io.write(diff) }
          end
        end
      end