code: public String convertError(String filename, int line,
                               int column, String message)
    {
      String srcFilename = null;
      int destLine = 0;
      int srcLine = 0;
      
      for (int i = 0; i < _lines.size(); i++) {
        Line map = _lines.get(i);
  
        if (filename != null && ! filename.endsWith(_dstFilename)) {
        }
        else if (map._dstLine <= line && line <= map.getLastDestinationLine()) {
          srcFilename = map._srcFilename;
          srcLine = map.getSourceLine(line);
        }
      }
  
      if (srcFilename != null)
        return srcFilename + ":" + srcLine + ": " + message;
      else
        return filename + ":" + line + ": " + message;
    }
docs: Converts an error in the generated file to a CompileError based on
  the source.