check_diagram

# File lib/rdoc/options.rb, line 600
  def check_diagram
    return if RUBY_PLATFORM =~ /mswin|cygwin|mingw|bccwin/

    ok = false
    ver = nil

    IO.popen "dot -V 2>&1" do |io|
      ver = io.read
      if ver =~ /dot.+version(?:\s+gviz)?\s+(\d+)\.(\d+)/ then
        ok = ($1.to_i > 1) || ($1.to_i == 1 && $2.to_i >= 8)
      end
    end

    unless ok then
      if ver =~ /^dot.+version/ then
        $stderr.puts "Warning: You may need dot V1.8.6 or later to use\n",
          "the --diagram option correctly. You have:\n\n   ",
          ver,
          "\nDiagrams might have strange background colors.\n\n"
      else
        $stderr.puts "You need the 'dot' program to produce diagrams.",
          "(see http://www.research.att.com/sw/tools/graphviz/)\n\n"
        exit
      end
    end
  end