List gems which use a C extension

list_ext.rb

#!/usr/bin/env ruby

# list all gems in your Gemfile which have a C extension

require 'bundler'

gemfile = []
File.new("Gemfile").readlines.each do |line|
  next if line =~ /^\s*#/
  if line =~ /gem\s+['"](.*?)['"]/ then
    gemfile << $1
  end
end

b = Bundler.setup(:default)
gems = b.requested_specs.to_a


direct = []
indirect = []
gems.each do |g|
  if File.directory? File.join(g.full_gem_path, "ext") then
    if gemfile.include?(g.name) then
      next if g.name == "facter" # doesn't actually use an ext
      direct << g.name
    else
      indirect << g.name
    end
  end
end

puts "gems requiring an ext:"
puts "----------------------"
direct.each{ |g| puts g }

puts
puts "gems requiring an ext (not in gemfile):"
puts "---------------------------------------"
indirect.each{ |g| puts g }