From 9b48130f4f04da2fdaaf9b7de7dbe05763a61965 Mon Sep 17 00:00:00 2001
From: Travis Ralston <travpc@gmail.com>
Date: Wed, 8 Jul 2020 11:48:34 -0600
Subject: [PATCH] Protect rooms from getting lost due to complex transitions

Fixes https://github.com/vector-im/riot-web/issues/14378

Rooms transitioning between multiple states are often at risk of going missing due to the sticky room handling. We now protect that transition by bluntly ensuring the room can't go missing, and by always ensuring we have an updated reference to the room.
---
 src/stores/room-list/algorithms/Algorithm.ts | 33 +++++++++++++++-----
 1 file changed, 25 insertions(+), 8 deletions(-)

diff --git a/src/stores/room-list/algorithms/Algorithm.ts b/src/stores/room-list/algorithms/Algorithm.ts
index 8c7bbc8615..eee8e60b86 100644
--- a/src/stores/room-list/algorithms/Algorithm.ts
+++ b/src/stores/room-list/algorithms/Algorithm.ts
@@ -655,18 +655,35 @@ export class Algorithm extends EventEmitter {
                 cause = RoomUpdateCause.PossibleTagChange;
             }
 
-            // If we have tags for a room and don't have the room referenced, the room reference
-            // probably changed. We need to swap out the problematic reference.
-            if (hasTags && !this.rooms.includes(room) && !isSticky) {
-                console.warn(`${room.roomId} is missing from room array but is known - trying to find duplicate`);
+            // Check to see if the room is known first
+            let knownRoomRef = this.rooms.includes(room);
+            if (hasTags && !knownRoomRef) {
+                console.warn(`${room.roomId} might be a reference change - attempting to update reference`);
                 this.rooms = this.rooms.map(r => r.roomId === room.roomId ? room : r);
-
-                // Sanity check
-                if (!this.rooms.includes(room)) {
-                    throw new Error(`Failed to replace ${room.roomId} with an updated reference`);
+                knownRoomRef = this.rooms.includes(room);
+                if (!knownRoomRef) {
+                    console.warn(`${room.roomId} is still not referenced. It may be sticky.`);
                 }
             }
 
+            if (hasTags && isForLastSticky && !knownRoomRef) {
+                // we have a fairly good chance at losing a room right now. Under some circumstances,
+                // we can end up with a room which transitions references and tag changes, then gets
+                // lost when the sticky room changes. To counter this, we try and add the room to the
+                // list manually as the condition below to update the reference will fail.
+                //
+                // Other conditions *should* result in the room being sorted into the right place.
+                console.warn(`${room.roomId} was about to be lost - inserting at end of room list`);
+                this.rooms.push(room);
+                knownRoomRef = true;
+            }
+
+            // If we have tags for a room and don't have the room referenced, something went horribly
+            // wrong - the reference should have been updated above.
+            if (hasTags && !knownRoomRef && !isSticky) {
+                throw new Error(`${room.roomId} is missing from room array but is known - trying to find duplicate`);
+            }
+
             // Like above, update the reference to the sticky room if we need to
             if (hasTags && isSticky) {
                 // Go directly in and set the sticky room's new reference, being careful not