walk/walk.go
func shouldCall(rel string, mode Mode, updateRels map[string]bool) bool {
	return mode != UpdateDirsMode || updateRels[rel]
}
func shouldCall(rel string, mode Mode, updateRels map[string]bool) bool {
	return mode != UpdateDirsMode || updateRels[rel]
}
// shouldCall returns true if Walk should call the callback in the
// directory rel.