Fix rooms with no messages appearing at the top of the room list (#31798)

* Extract and move timestamp function

* Use new function in BaseRecencySorter

* Remove deprecated method usage

* Add jsdoc

* Avoid unnecessary exports

* Fix tests

src/stores/room-list-v3/skip-list/sorters/BaseRecencySorter.ts

@@ -7,7 +7,7 @@ Please see LICENSE files in the repository root for full details.
 
 import type { Room } from "matrix-js-sdk/src/matrix";
 import type { Sorter, SortingAlgorithm } from ".";
-import { getLastTs } from "../../../room-list/algorithms/tag-sorting/RecentAlgorithm";
+import { getLastTimestamp } from "./utils/getLastTimestamp";
 
 export abstract class BaseRecencySorter implements Sorter {
     public constructor(protected myUserId: string) {}
@@ -29,7 +29,7 @@ export abstract class BaseRecencySorter implements Sorter {
     }
 
     private getTs(room: Room, cache?: { [roomId: string]: number }): number {
-        const ts = cache?.[room.roomId] ?? getLastTs(room, this.myUserId);
+        const ts = cache?.[room.roomId] ?? getLastTimestamp(room, this.myUserId);
         if (cache) {
             cache[room.roomId] = ts;
         }

src/stores/room-list-v3/skip-list/sorters/utils/getLastTimestamp.ts

@@ -0,0 +1,84 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE files in the repository root for full details.
+*/
+
+import { EventTimeline, EventType, type MatrixEvent, type Room } from "matrix-js-sdk/src/matrix";
+
+import { EffectiveMembership, getEffectiveMembership } from "../../../../../utils/membership";
+import * as Unread from "../../../../../Unread";
+
+function shouldCauseReorder(event: MatrixEvent): boolean {
+    const type = event.getType();
+    const content = event.getContent();
+    const prevContent = event.getPrevContent();
+
+    // Never ignore membership changes
+    if (type === EventType.RoomMember && prevContent.membership !== content.membership) return true;
+
+    // Ignore display name changes
+    if (type === EventType.RoomMember && prevContent.displayname !== content.displayname) return false;
+    // Ignore avatar changes
+    if (type === EventType.RoomMember && prevContent.avatar_url !== content.avatar_url) return false;
+
+    return true;
+}
+
+/**
+ * For a given room, this function returns a timestamp that can be used for recency sorting.
+ * @param r room for which the timestamp is calculated
+ * @param userId mxId of the current user
+ * @returns timestamp
+ */
+export const getLastTimestamp = (r: Room, userId: string): number => {
+    const mainTimelineLastTs = ((): number => {
+        const timeline = r.getLiveTimeline().getEvents();
+
+        // MSC4186: Simplified Sliding Sync sets this.
+        // If it's present, sort by it.
+        const bumpStamp = r.getBumpStamp();
+        if (bumpStamp) {
+            return bumpStamp;
+        }
+
+        // If the room hasn't been joined yet, it probably won't have a timeline to
+        // parse. We'll still fall back to the timeline if this fails, but chances
+        // are we'll at least have our own membership event to go off of.
+        const effectiveMembership = getEffectiveMembership(r.getMyMembership());
+        if (effectiveMembership !== EffectiveMembership.Join) {
+            const membershipEvent = r
+                .getLiveTimeline()
+                .getState(EventTimeline.FORWARDS)
+                ?.getStateEvents(EventType.RoomMember, userId);
+            if (membershipEvent && !Array.isArray(membershipEvent)) {
+                return membershipEvent.getTs();
+            }
+        }
+
+        for (let i = timeline.length - 1; i >= 0; --i) {
+            const ev = timeline[i];
+            if (!ev.getTs()) continue; // skip events that don't have timestamps (tests only?)
+
+            if (
+                (ev.getSender() === userId && shouldCauseReorder(ev)) ||
+                Unread.eventTriggersUnreadCount(r.client, ev)
+            ) {
+                return ev.getTs();
+            }
+        }
+
+        // we might only have events that don't trigger the unread indicator,
+        // in which case use the oldest event even if normally it wouldn't count.
+        // This is better than just assuming the last event was forever ago.
+        return timeline[0]?.getTs() ?? 0;
+    })();
+
+    const threadLastEventTimestamps = r.getThreads().map((thread) => {
+        const event = thread.replyToEvent ?? thread.rootEvent;
+        return event?.getTs() ?? 0;
+    });
+
+    return Math.max(mainTimelineLastTs, ...threadLastEventTimestamps);
+};

test/unit-tests/stores/room-list-v3/RoomListStoreV3-test.ts

@@ -106,7 +106,7 @@ describe("RoomListStoreV3", () => {
             // Let's pretend like a new timeline event came on the room in 37th index.
             const room = rooms[37];
             const event = mkMessage({ room: room.roomId, user: `@foo${3}:matrix.org`, ts: 1000, event: true });
-            room.timeline.push(event);
+            jest.spyOn(room.getLiveTimeline(), "getEvents").mockReturnValue([event]);
 
             const payload = {
                 action: "MatrixActions.Room.timeline",
@@ -827,7 +827,7 @@ describe("RoomListStoreV3", () => {
             let ts = 1000;
             for (const room of [rooms[14], rooms[34]]) {
                 const event = mkMessage({ room: room.roomId, user: `@foo${3}:matrix.org`, ts: 1000, event: true });
-                room.timeline.push(event);
+                jest.spyOn(room.getLiveTimeline(), "getEvents").mockReturnValue([event]);
 
                 const payload = {
                     action: "MatrixActions.Room.timeline",

test/unit-tests/stores/room-list-v3/skip-list/RoomSkipList-test.ts

@@ -83,7 +83,7 @@ describe("RoomSkipList", () => {
                 ts: totalRooms - i,
                 event: true,
             });
-            room.timeline.push(event);
+            jest.spyOn(room.getLiveTimeline(), "getEvents").mockReturnValue([event]);
             skipList.reInsertRoom(room);
             expect(skipList.size).toEqual(rooms.length);
         }

test/unit-tests/stores/room-list-v3/skip-list/getMockedRooms.ts

@@ -14,7 +14,7 @@ export function getMockedRooms(client: MatrixClient, roomCount: number = 100): R
         const roomId = `!foo${i}:matrix.org`;
         const room = mkStubRoom(roomId, `Foo Room ${i}`, client);
         const event = mkMessage({ room: roomId, user: `@foo${i}:matrix.org`, ts: i + 1, event: true });
-        room.timeline.push(event);
+        jest.spyOn(room.getLiveTimeline(), "getEvents").mockReturnValue([event]);
         rooms.push(room);
     }
     return rooms;

test/unit-tests/stores/room-list-v3/sorters/utils/getLastTimestamp-test.ts

@@ -0,0 +1,185 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE files in the repository root for full details.
+*/
+
+import { Room, type RoomState } from "matrix-js-sdk/src/matrix";
+import { KnownMembership } from "matrix-js-sdk/src/types";
+
+import { mkEvent, mkMessage, mkRoom, stubClient } from "../../../../../test-utils";
+import { getLastTimestamp } from "../../../../../../src/stores/room-list-v3/skip-list/sorters/utils/getLastTimestamp";
+
+describe("getLastTimestamp", () => {
+    it("should return last timestamp", () => {
+        const cli = stubClient();
+        const room = new Room("room123", cli, "@john:matrix.org");
+
+        const event1 = mkMessage({
+            room: room.roomId,
+            msg: "Hello world!",
+            user: "@alice:matrix.org",
+            ts: 5,
+            event: true,
+        });
+        const event2 = mkMessage({
+            room: room.roomId,
+            msg: "Howdy!",
+            user: "@bob:matrix.org",
+            ts: 10,
+            event: true,
+        });
+
+        room.getMyMembership = () => KnownMembership.Join;
+
+        room.addLiveEvents([event1], { addToState: true });
+        expect(getLastTimestamp(room, "@jane:matrix.org")).toBe(5);
+        expect(getLastTimestamp(room, "@john:matrix.org")).toBe(5);
+
+        room.addLiveEvents([event2], { addToState: true });
+
+        expect(getLastTimestamp(room, "@jane:matrix.org")).toBe(10);
+        expect(getLastTimestamp(room, "@john:matrix.org")).toBe(10);
+    });
+
+    it("should return timestamp of membership event if user not joined to room", () => {
+        const cli = stubClient();
+        const room = mkRoom(cli, "!new:example.org");
+        // Mock a membership event
+        jest.spyOn(room.getLiveTimeline(), "getState").mockImplementation((_) => {
+            return {
+                getStateEvents: () =>
+                    mkEvent({
+                        type: "m.room.member",
+                        user: "@john:matrix.org",
+                        content: {},
+                        ts: 500,
+                        event: true,
+                    }),
+            } as unknown as RoomState;
+        });
+        jest.spyOn(room, "getMyMembership").mockReturnValue(KnownMembership.Invite);
+        expect(getLastTimestamp(room, "@john:matrix.org")).toBe(500);
+    });
+
+    it("should return bump stamp when using sliding sync", () => {
+        const cli = stubClient();
+        const room = new Room("room123", cli, "@john:matrix.org");
+
+        const event1 = mkMessage({
+            room: room.roomId,
+            msg: "Hello world!",
+            user: "@alice:matrix.org",
+            ts: 5,
+            event: true,
+        });
+        const event2 = mkMessage({
+            room: room.roomId,
+            msg: "Howdy!",
+            user: "@bob:matrix.org",
+            ts: 10,
+            event: true,
+        });
+
+        jest.spyOn(room, "getMyMembership").mockReturnValue(KnownMembership.Join);
+        jest.spyOn(room, "getBumpStamp").mockReturnValue(314);
+        room.addLiveEvents([event1, event2], { addToState: true });
+        expect(getLastTimestamp(room, "@john:matrix.org")).toBe(314);
+    });
+
+    describe("membership event special cases", () => {
+        it("should consider event if membership has changed", () => {
+            const cli = stubClient();
+            const room = new Room("room123", cli, "@john:matrix.org");
+
+            const event1 = mkMessage({
+                room: room.roomId,
+                msg: "Hello world!",
+                user: "@alice:matrix.org",
+                ts: 5,
+                event: true,
+            });
+            // Display name change that should be ignored during timestamp calculation
+            const event2 = mkEvent({
+                type: "m.room.member",
+                user: "@john:matrix.org",
+                content: {
+                    membership: "leave",
+                },
+                prev_content: {
+                    membership: "join",
+                },
+                ts: 400,
+                event: true,
+            });
+
+            jest.spyOn(room, "getMyMembership").mockReturnValue(KnownMembership.Join);
+            room.addLiveEvents([event1, event2], { addToState: true });
+
+            expect(getLastTimestamp(room, "@john:matrix.org")).toBe(400);
+        });
+
+        it("should skip display name changes", () => {
+            const cli = stubClient();
+            const room = new Room("room123", cli, "@john:matrix.org");
+
+            const event1 = mkMessage({
+                room: room.roomId,
+                msg: "Hello world!",
+                user: "@alice:matrix.org",
+                ts: 5,
+                event: true,
+            });
+            // Display name change that should be ignored during timestamp calculation
+            const event2 = mkEvent({
+                type: "m.room.member",
+                user: "@john:matrix.org",
+                content: {
+                    displayname: "bar",
+                },
+                prev_content: {
+                    displayname: "foo",
+                },
+                ts: 500,
+                event: true,
+            });
+
+            jest.spyOn(room, "getMyMembership").mockReturnValue(KnownMembership.Join);
+            room.addLiveEvents([event1, event2], { addToState: true });
+
+            expect(getLastTimestamp(room, "@john:matrix.org")).toBe(5);
+        });
+
+        it("should skip avatar changes", () => {
+            const cli = stubClient();
+            const room = new Room("room123", cli, "@john:matrix.org");
+
+            const event1 = mkMessage({
+                room: room.roomId,
+                msg: "Hello world!",
+                user: "@alice:matrix.org",
+                ts: 5,
+                event: true,
+            });
+            // Avatar url change that should be ignored during timestamp calculation
+            const event2 = mkEvent({
+                type: "m.room.member",
+                user: "@john:matrix.org",
+                content: {
+                    avatar_url: "bar",
+                },
+                prev_content: {
+                    avatar_url: "foo",
+                },
+                ts: 500,
+                event: true,
+            });
+
+            jest.spyOn(room, "getMyMembership").mockReturnValue(KnownMembership.Join);
+            room.addLiveEvents([event1, event2], { addToState: true });
+
+            expect(getLastTimestamp(room, "@john:matrix.org")).toBe(5);
+        });
+    });
+});