# File lib/bundler/source/rubygems.rb, line 120
      def cache(spec)
        cached_path = cached_gem(spec)
        raise GemNotFound, "Missing gem file '#{spec.full_name}.gem'." unless cached_path
        return if File.dirname(cached_path) == Bundler.app_cache.to_s
        Bundler.ui.info "  * #{File.basename(cached_path)}"
        FileUtils.cp(cached_path, Bundler.app_cache)
      end