Clear notifications when we can infer read status from receipts (#3139)

src/client.ts

@@ -1307,6 +1307,8 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
             this.on(ClientEvent.Sync, this.startCallEventHandler);
         }
 
+        this.on(ClientEvent.Sync, this.fixupRoomNotifications);
+
         this.timelineSupport = Boolean(opts.timelineSupport);
 
         this.cryptoStore = opts.cryptoStore;
@@ -6817,6 +6819,31 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
         }
     };
 
+    /**
+     * Once the client has been initialised, we want to clear notifications we
+     * know for a fact should be here.
+     * This issue should also be addressed on synapse's side and is tracked as part
+     * of https://github.com/matrix-org/synapse/issues/14837
+     *
+     * We consider a room or a thread as fully read if the current user has sent
+     * the last event in the live timeline of that context and if the read receipt
+     * we have on record matches.
+     */
+    private fixupRoomNotifications = (): void => {
+        if (this.isInitialSyncComplete()) {
+            const unreadRooms = (this.getRooms() ?? []).filter((room) => {
+                return room.getUnreadNotificationCount(NotificationCountType.Total) > 0;
+            });
+
+            for (const room of unreadRooms) {
+                const currentUserId = this.getSafeUserId();
+                room.fixupNotifications(currentUserId);
+            }
+
+            this.off(ClientEvent.Sync, this.fixupRoomNotifications);
+        }
+    };
+
     /**
      * @returns Promise which resolves: ITurnServerResponse object
      * @returns Rejects: with an error response.