add_line_numbers

# File lib/rdoc/generators/html_generator.rb, line 1095
    def add_line_numbers(src)
      if src =~ /\A.*, line (\d+)/
        first = $1.to_i - 1
        last  = first + src.count("\n")
        size = last.to_s.length
        real_fmt = "%#{size}d: "
        fmt = " " * (size+2)
        src.gsub!(/^/) do
          res = sprintf(fmt, first) 
          first += 1
          fmt = real_fmt
          res
        end
      end
    end