Thank you for this feature request, @jonahgoldsaito. I'm actually working on adding CancellationToken parameters to some methods in the Firestore Unity SDK right now; however, methods like SetAsync() are not in scope. The reason is that these operations do not natively support cancellation and so providing a CancellationToken argument incorrectly suggests that these operations could be cancelled when in reality it would provide no such benefit.

The 4 methods that are planned to gain a CancellationToken parameter include:

1. FirebaseFirestore.RunTransactionAsync()
2. FirebaseFirestore.ListenForSnapshotsInSync()
3. DocumentReference.Listen()
4. Query.Listen()

As for the "dangling" CancellationTokenSource in the Firestore quickstart app

If we ever change the implementation of Firestore to natively support the concept of "cancellation" then we will revisit adding CancellationToken parameters to methods like SetAsync(). I'm going to leave this ticket opened for now but we may close it in the future if we decide that we will never add CancellationToken parameters to methods like SetAsync().

Note to Googlers: This feature is being tracked in b/159752361.

Thanks @dconeybe so much for clearing all that up.

If I were to do a RunTransactionAsync() that contained a single SetAsync() and utilized the fancy new CancellationToken you're adding, would that cancel the SetAsync? Or would it actually do the Set, but then revert it? Or neither?

In that case it would actually do the "set", but only because transactions do not influence calls to DocumentReference.SetAsync(). In fact, if you're calling SetAsync() inside a transaction that's probably a bug.

In a transaction, instead of calling doc.SetAsync(...) you call Transaction.Set(doc, ...), which is synchronous and simply adds an action to the set of actions that will be performed atomically later when the transaction is committed. When it comes time to commit, if the provided CancellationToken's IsCancellationRequested property equals true then the commit will never be attempted and the transaction will be aborted; however, if the IsCancellationRequested property equaled false and the commit request was sent then the cancellation request will have no effect and the commit operation will run to completion.

https://firebase.google.com/docs/reference/unity/class/firebase/firestore/transaction

Again, thank you for taking the time! You rock 🤘