# File lib/rails-installer.rb, line 586
  def find_source_directory(gem_name, version=nil)
    if version == 'cwd'
      return Dir.pwd
    elsif version
      version_array = ["= #{version}"]
    else
      version_array = ["> 0.0.0"]
    end
    
    specs = Gem.source_index.find_name(gem_name,version_array)
    unless specs.to_a.size > 0
      raise InstallFailed, "Can't locate version #{version}!"
    end
    
    @install_version = specs.last.version
    message "Installing #{app_name} #{@install_version}"
    
    specs.last.full_gem_path
  end