fix(timeline): Keep extremities a local event did not reference

changelog.d/+local-event-extremities.bugfix.md

@@ -0,0 +1 @@
+Fixed local events dropping forward extremities they did not reference. Contributed by @eleboucher.

src/service/rooms/timeline/build.rs

@@ -8,7 +8,7 @@ use conduwuit_core::{
 };
 use futures::{FutureExt, StreamExt};
 use ruma::{
-	OwnedEventId, OwnedServerName, RoomId, UserId,
+	EventId, OwnedEventId, OwnedServerName, RoomId, UserId,
 	events::{
 		TimelineEventType,
 		room::{
@@ -112,14 +112,27 @@ impl super::Service {
 		let statehashid = self.services.state.append_to_state(&pdu, &room_id).await?;
 		trace!("State hash ID for {room_id}: {statehashid:?}");
 
+		// prev_events is capped at the room version's limit, so this PDU does not
+		// necessarily reference every extremity. Any it did not reference is still a
+		// head of the DAG and has to be kept.
+		let prev_events: HashSet<&EventId> = pdu.prev_events().collect();
+		let unreferenced: Vec<OwnedEventId> = self
+			.services
+			.state
+			.get_forward_extremities(&room_id)
+			.ready_filter(|extremity| !prev_events.contains(&**extremity))
+			.collect()
+			.await;
+
 		trace!("Generating raw ID for PDU {}", pdu.event_id());
 		let pdu_id = self
 			.append_pdu(
 				&pdu,
 				pdu_json,
-				// Since this PDU references all pdu_leaves we can update the leaves
-				// of the room
-				once(pdu.event_id()),
+				unreferenced
+					.iter()
+					.map(AsRef::as_ref)
+					.chain(once(pdu.event_id())),
 				state_lock,
 				&room_id,
 			)