def warn(filename, line, column_or_message, message = nil)
      return if !@@allow_double_warnings && @seen.add?([filename, line]).nil?
      if message
        column = column_or_message
      else
        message = column_or_message
      end

      location = "line #{line}"
      location << ", column #{column}" if column
      location << " of #{filename}" if filename

      Sass::Util.sass_warn("DEPRECATION WARNING on #{location}:\n#{message}")
    end
def warn(filename, line, column_or_message, message = nil)
      return if !@@allow_double_warnings && @seen.add?([filename, line]).nil?
      if message
        column = column_or_message
      else
        message = column_or_message
      end

      location = "line #{line}"
      location << ", column #{column}" if column
      location << " of #{filename}" if filename

      Sass::Util.sass_warn("DEPRECATION WARNING on #{location}:\n#{message}")
    end
Prints `message` as a deprecation warning associated with `filename`,
 `line`, and optionally `column`.

 This ensures that only one message will be printed for each line of a
 given file.

 @overload warn(filename, line, message)
   @param filename [String, nil]
   @param line [Number]
   @param message [String]
 @overload warn(filename, line, column, message)
   @param filename [String, nil]
   @param line [Number]
   @param column [Number]
   @param message [String]