Fix member events breaking on timeline reset, 2

Re-use the same RoomState from the old live timeline so we re-use
all the same member objects etc, so all the listeners stay attached

src/client.js

@@ -2089,7 +2089,7 @@ MatrixClient.prototype.resetNotifTimelineSet = function() {
     // know about /notifications, so we have no choice but to start paginating
     // from the current point in time.  This may well overlap with historical
     // notifs which are then inserted into the timeline by /sync responses.
-    this._notifTimelineSet.resetLiveTimeline('end', true);
+    this._notifTimelineSet.resetLiveTimeline('end', null);
 
     // we could try to paginate a single event at this point in order to get
     // a more valid pagination token, but it just ends up with an out of order

src/models/event-timeline-set.js

@@ -149,13 +149,14 @@ EventTimelineSet.prototype.replaceEventId = function(oldEventId, newEventId) {
  * <p>This is used when /sync returns a 'limited' timeline.
  *
  * @param {string=} backPaginationToken   token for back-paginating the new timeline
- * @param {?bool} flush  Whether to flush the non-live timelines too.
+ * @param {string=} forwardPaginationToken token for forward-paginating the old live timeline,
+ * if absent or null, all timelines are reset.
  *
  * @fires module:client~MatrixClient#event:"Room.timelineReset"
  */
-EventTimelineSet.prototype.resetLiveTimeline = function(backPaginationToken, flush) {
+EventTimelineSet.prototype.resetLiveTimeline = function(backPaginationToken, forwardPaginationToken) {
     // if timeline support is disabled, forget about the old timelines
-    const resetAllTimelines = !this._timelineSupport || flush;
+    const resetAllTimelines = !this._timelineSupport || !forwardPaginationToken;
 
     let newTimeline;
     if (resetAllTimelines) {
@@ -166,7 +167,18 @@ EventTimelineSet.prototype.resetLiveTimeline = function(backPaginationToken, flu
         newTimeline = this.addTimeline();
     }
 
-    // initialise the state in the new timeline from our last known state
+    // move the state objects over from the old live timeline, then we'll
+    // keep using the same RoomMember objects for the 'live' set of members
+    newTimeline._startState = this._liveTimeline._startState;
+    newTimeline._endState = this._liveTimeline._endState;
+
+    if (!resetAllTimelines) {
+        // Now regenerate the state for the previously-live timeline, because
+        // we just stole it and put it on the new live timeline
+        // (If we're resetting all timelines, don't bother because the old live
+        // timeline is about to be thrown away anyway.
+        this._liveTimeline._startState = new RoomState(this._roomId);
+        this._liveTimeline._endState = new RoomState(this._roomId);
         const evMap = this._liveTimeline.getState(EventTimeline.FORWARDS).events;
         const events = [];
         for (const evtype in evMap) {
@@ -180,7 +192,10 @@ EventTimelineSet.prototype.resetLiveTimeline = function(backPaginationToken, flu
                 events.push(evMap[evtype][stateKey]);
             }
         }
-    newTimeline.initialiseState(events);
+        this._liveTimeline.initialiseState(events);
+
+        this._liveTimeline.setPaginationToken(forwardPaginationToken, EventTimeline.FORWARDS);
+    }
 
     // make sure we set the pagination token before firing timelineReset,
     // otherwise clients which start back-paginating will fail, and then get

src/models/room.js

@@ -205,12 +205,12 @@ Room.prototype.getLiveTimeline = function() {
  * <p>This is used when /sync returns a 'limited' timeline.
  *
  * @param {string=} backPaginationToken   token for back-paginating the new timeline
- * @param {boolean=} flush True to remove all events in all timelines. If false, only
+ * @param {string=} forwardPaginationToken token for forward-paginating the old live timeline,
- * the live timeline is reset.
+ * if absent or null, all timelines are reset.
  */
-Room.prototype.resetLiveTimeline = function(backPaginationToken, flush) {
+Room.prototype.resetLiveTimeline = function(backPaginationToken, forwardPaginationToken) {
     for (let i = 0; i < this._timelineSets.length; i++) {
-        this._timelineSets[i].resetLiveTimeline(backPaginationToken, flush);
+        this._timelineSets[i].resetLiveTimeline(backPaginationToken, forwardPaginationToken);
     }
 
     this._fixUpLegacyTimelineFields();

src/sync.js

@@ -884,14 +884,10 @@ SyncApi.prototype._processSyncResponse = function(syncToken, data) {
             }
 
             if (limited) {
-                // save the old 'next_batch' token as the
-                // forward-pagination token for the previously-active
-                // timeline.
-                room.currentState.paginationToken = syncToken;
                 self._deregisterStateListeners(room);
                 room.resetLiveTimeline(
                     joinObj.timeline.prev_batch,
-                    self.opts.canResetEntireTimeline(room.roomId),
+                    self.opts.canResetEntireTimeline(room.roomId) ? null : syncToken,
                 );
 
                 // We have to assume any gap in any timeline is