code: func (tx *Tx) Rollback() error {
  	_assert(!tx.managed, "managed tx rollback not allowed")
  	if tx.db == nil {
  		return ErrTxClosed
  	}
  	tx.rollback()
  	return nil
  }
docs: // Rollback closes the transaction and ignores all previous updates. Read-only
  // transactions must be rolled back and not committed.