This is an interesting proposal.

Could you explain a bit of the backstory about why you are checking to see if Tx has been committed or rolled back?

I actually can't remember much anymore because it was for some contract work I did for a random client many months ago.

I vaguely remember it was a package with a function to be used by a third party user. The third party user provides a *Tx object to the function.

The adjustment to be made is:

func (tx *Tx) IsDone() bool {
   tx.closemu.RLock()
   defer tx.closemu.RUnlock()
   return tx.isDone()
}

That is certainly a fine implementation, but without a concrete use case the proposal won't go anywhere.

My usecase is a unified cleanup function. Something like

defer func() {
    e := recover()
    if e != nil {
        log.Errorln("panic happened: ", e)
    }
    if !tx.IsDone() {
        tx.Rollback()
    }
}()