func checkPrefix(prefix string) error {
	if strings.HasPrefix(prefix, "/") || build.IsLocalImport(prefix) {
		return fmt.Errorf("invalid prefix: %q", prefix)
	}
	return nil
}
func checkPrefix(prefix string) error {
	if strings.HasPrefix(prefix, "/") || build.IsLocalImport(prefix) {
		return fmt.Errorf("invalid prefix: %q", prefix)
	}
	return nil
}
// checkPrefix checks that a string may be used as a prefix. We forbid local
// (relative) imports and those beginning with "/". We allow the empty string,
// but generated rules must not have an empty importpath.