Add coroutines Flow extension functions for Firestore

[martinbonnin]

What feature would you like to see?

Firestore has DocumentReference.addSnapshotListener and Query.addSnapshotListener.

Both of these are callback based and it would be nice to have coroutines equivalents. Something like:

fun DocumentReference.toFlow(): Flow<DocumentSnapShot> { 
      TODO()
}

fun Query.toFlow(): Flow<QuerySnapShot> { 
      TODO()
}

How would you use it?

This would be useful to leverage coroutines to make the code look nicer. Also it can be used together with coroutines scopes to bind Firestore queries to the Android lifecycle.

[google-oss-bot]

I couldn't figure out how to label this issue, so I've labeled it for a human to triage. Hang tight.

[aguatno]

Thank you for sending this feature request. We will keep this FR open and update it as we prioritize new features. Thank you.

[svenjacobs]

Also looking forward to this! I'm using my own implementations of toFlow() for DocumentReference and Query but would really like to use some official solution :)

[vkryachko]

This was added in firebase-firestore-ktx version 24.3.0