cache

# File lib/bundler/source/rubygems.rb, line 192
      def cache(spec, custom_path = nil)
        if builtin_gem?(spec)
          cached_path = cached_built_in_gem(spec)
        else
          cached_path = cached_gem(spec)
        end
        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(custom_path))
      rescue Errno::EACCES => e
        Bundler.ui.debug(e)
        raise InstallError, e.message
      end