Set historyVisibility for backfilled events over federation (#2656)

This should hopefully deflake Backfill works correctly with history visibility set to joined as we were using the default shared visibility, even if the events are set to joined (or something else)

syncapi/routing/messages.go

@@ -350,8 +350,10 @@ func (r *messagesReq) retrieveEvents() (
 	startTime := time.Now()
 	filteredEvents, err := internal.ApplyHistoryVisibilityFilter(r.ctx, r.db, r.rsAPI, events, nil, r.device.UserID, "messages")
 	logrus.WithFields(logrus.Fields{
-		"duration": time.Since(startTime),
-		"room_id":  r.roomID,
+		"duration":      time.Since(startTime),
+		"room_id":       r.roomID,
+		"events_before": len(events),
+		"events_after":  len(filteredEvents),
 	}).Debug("applied history visibility (messages)")
 	return gomatrixserverlib.HeaderedToClientEvents(filteredEvents, gomatrixserverlib.FormatAll), start, end, err
 }
@@ -513,6 +515,9 @@ func (r *messagesReq) backfill(roomID string, backwardsExtremities map[string][]
 
 	// Store the events in the database, while marking them as unfit to show
 	// up in responses to sync requests.
+	if res.HistoryVisibility == "" {
+		res.HistoryVisibility = gomatrixserverlib.HistoryVisibilityShared
+	}
 	for i := range res.Events {
 		_, err = r.db.WriteEvent(
 			context.Background(),
@@ -521,7 +526,7 @@ func (r *messagesReq) backfill(roomID string, backwardsExtremities map[string][]
 			[]string{},
 			[]string{},
 			nil, true,
-			gomatrixserverlib.HistoryVisibilityShared,
+			res.HistoryVisibility,
 		)
 		if err != nil {
 			return nil, err
@@ -534,6 +539,9 @@ func (r *messagesReq) backfill(roomID string, backwardsExtremities map[string][]
 		// last `limit` events
 		events = events[len(events)-limit:]
 	}
+	for _, ev := range events {
+		ev.Visibility = res.HistoryVisibility
+	}
 
 	return events, nil
 }