trace_line_numbers (LineCache)

    # File lib/linecache.rb, line 273
      def trace_line_numbers(filename, reload_on_change=false)
        fullname = cache(filename, reload_on_change)
        return nil unless fullname
        e = @@file_cache[filename]
        unless e.line_numbers
          e.line_numbers =
            TraceLineNumbers.lnums_for_str_array(e.lines)
          e.line_numbers = false unless e.line_numbers
        end
        e.line_numbers
      end