# File lib/rubygems.rb, line 836
  def self.required_location(gemname, libfile, *requirements)
    requirements = Gem::Requirement.default if requirements.empty?

    matches = Gem.source_index.find_name gemname, requirements

    return nil if matches.empty?

    spec = matches.last
    spec.require_paths.each do |path|
      result = File.join spec.full_gem_path, path, libfile
      return result if File.exist? result
    end

    nil
  end