gems_completion.rb

#!/usr/bin/env ruby

require "rubygems"
require "rubygems/command_manager"

cm = Gem::CommandManager.instance
commands = cm.instance_variable_get(:@commands).keys.map { |c| cm[c.to_s] }
commands.sort_by{ |c| c.command }.each do |command|
  options = command.instance_variable_get(:@option_groups)

  args = options[:options].map do |opts|
    flags, other = opts.first.partition { |x| x =~ /^-/ }
    long, short = flags.partition { |x| x =~ /^--/ }.map { |x| x.first }
    description = other.select { |x| String === x }.join(' ')

    long = case long
           when / /
             long.split(' ').first
           when /\[.*\]/
             long.gsub(/[\[\]]/, '')
           else
             long
           end
    
    if long and short
      %Q<    "(#{short} #{long})"{#{short},#{long}}"[#{description}]" \\>
    elsif long
      %Q<    "*#{long}[#{description}]" \\>
    else
      %Q<    "*#{short}[#{description}]" \\>
    end
  end.sort.join("\n")


  puts "_gem_#{command.command}() {"
  puts "  _arguments \\"

  case command.usage
  when /FILE/
    puts "    *:file:_files -f \\"
  when /GEMNAME/    	
    puts '    ":gemname:__all_gems" \\'
  end
  
  puts args unless args.empty?
  puts "    $gem_general_flags && ret=0"
  puts "}"
  puts
end