From efe28db631bd07240dea53280d8c8f2ecc20684a Mon Sep 17 00:00:00 2001
From: Till <2353100+S7evinK@users.noreply.github.com>
Date: Fri, 4 Nov 2022 15:39:09 +0100
Subject: [PATCH] Update `latestPosition` when getting reversed room delta
 (#2860)

Regression test added in
https://github.com/matrix-org/complement/pull/551
Should fix https://github.com/matrix-org/dendrite/issues/2514?
---
 syncapi/streams/stream_pdu.go | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/syncapi/streams/stream_pdu.go b/syncapi/streams/stream_pdu.go
index b21be6c5e..65ca8e2a3 100644
--- a/syncapi/streams/stream_pdu.go
+++ b/syncapi/streams/stream_pdu.go
@@ -264,6 +264,9 @@ func (p *PDUStreamProvider) addRoomDeltaToResponse(
 	// Work out what the highest stream position is for all of the events in this
 	// room that were returned.
 	latestPosition := r.To
+	if r.Backwards {
+		latestPosition = r.From
+	}
 	updateLatestPosition := func(mostRecentEventID string) {
 		var pos types.StreamPosition
 		if _, pos, err = snapshot.PositionInTopology(ctx, mostRecentEventID); err == nil {