# File lib/rubygems.rb, line 528
  def self.required_location(gemname, libfile, *version_constraints)
    version_constraints = Gem::Requirement.default if version_constraints.empty?
    matches = Gem.source_index.find_name(gemname, version_constraints)
    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