opearting_system.rb

Gem.pre_install do |gem_installer|
  unless gem_installer.spec.extensions.empty?
    require 'rubygems/defaults/which'

    unless Which::Gcc.exe
      raise Gem::InstallError,
        "#{gem_installer.spec.name} requires installed build tools to build native extension." +
	"Please update your path to include them or download DevKit from " +
	"http://github.com/downloads/oneclick/rubyinstaller/DevKit-4.5.0-20100819-1536-sfx.exe " +
	"and follow the instructions http://wiki.github.com/oneclick/rubyinstaller/development-kit"
    end
  end
end

pathname.rb

class Pathname

  def to_s
    @path.tr('/','\\').sub(/^(.):/){|s| s.upcase }
  end
  alias to_windows to_s
  
  def to_ruby
    @path.tr('\\','/').sub(/^(.):/){|s| s.upcase }
  end

  def to_bash
    @path.tr('\\','/').sub(/^(.):/){|s| "/#{s[0,1].downcase}"}
  end
  
  def ruby
    Pathname(self.to_ruby)
  end
  
  def windows
    Pathname(self.to_s)
  end
  
  def ==(other)
    return false unless Pathname === other
    self_ = self.dup.to_ruby.downcase
    other = other.dup.to_ruby.downcase
    self_ == other
  end
  
end

search_path.rb

class SearchPath

  include Enumerable

	def initialize(path)
	  @path = path.to_s.split(';').reject{|i| i.empty? }
	end

	def remove(old_path)
    old = Pathname(old_path).expand_path
    @path = @path.reject{|dir| Pathname(dir) == old }
    @path = @path.uniq
		self
	end

	def replace(old_path, new_path)
    old_path = Pathname(old_path)
    new_path = Pathname(new_path)
		@path.map!{|dir|
			if Pathname(dir) == old_path
 				new_path.to_windows.to_s
			else
 				dir 
			end
		}
    @path = @path.uniq.compact
		self
	end
  
  def each
    @path.each{|path| yield path }
  end

	def add(new_path)
    new_path = Pathname(new_path)
    @path.unshift new_path.to_windows.to_s
    self
	end

  def push(new_path)
    new_path = Pathname(new_path)
    @path.push new_path.to_windows.to_s
    self
  end

	def replace_or_add(old_path, new_path)
    if old_path.nil?
      add(new_path)
      return self
    end
    old_path = Pathname(old_path)
    new_path = Pathname(new_path)
	  return self if old_path == new_path
		old_search_path = @path.dup
		replace(old_path, new_path)
		add(new_path) if @path == old_search_path
		self
	end

	def join
		@path.join(';')
	end
	alias :to_s :join

  def to_bash
    @path.map{|i| Pathname.new(i).to_bash }.join(':')
  end

  def regex(string)
    Regexp.new(Regexp.escape(string.to_s), true)
  end
end

which.rb

require 'pathname'
require 'rubygems/defaults/pathname'
require 'rubygems/defaults/search_path'

module Which

  class Base

    class << self
      def find(search_path=ENV['PATH'])
        path = SearchPath.new(search_path)
        path = path.find{|dir| exist?(dir)}
        Pathname(path) rescue nil
      end
      
      def find_all(search_path=ENV['PATH'])
        path = SearchPath.new(search_path)
        path = path.find_all{|dir| exist?(dir)}
        path.map{|i| Pathname(i) }
      end
      
      def exist?(path)
        !!exe(path)
      end
      
      def exe(path=find)
        glob(path).first
      end
      alias :bat :exe
      
      def glob(path)
        return [] if path.nil?
        glob = "#{Pathname.new(path).to_ruby}/{#{executables.join(',')}}"
        Pathname.glob(glob)
      end
    end
  end

  class Gcc < Base
    def self.executables
      ['gcc.bat', 'gcc.exe']
    end
  end

end