# File lib/nanoc/cli/commands/compile.rb, line 174
    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