MSC3946 Dynamic predecessors for getVisibleRooms

Author: andybalaam

spec/unit/matrix-client.spec.ts

@@ -2234,6 +2234,20 @@ describe("MatrixClient", function () {
             });
         }
 
+        function predecessorEvent(newRoomId: string, predecessorRoomId: string): MatrixEvent {
+            return new MatrixEvent({
+                content: {
+                    predecessor_room_id: predecessorRoomId,
+                },
+                event_id: `predecessor_event_id_pred_${predecessorRoomId}`,
+                origin_server_ts: 1432735824653,
+                room_id: newRoomId,
+                sender: "@daryl:alexandria.example.com",
+                state_key: "",
+                type: "org.matrix.msc3946.room_predecessor",
+            });
+        }
+
         it("Returns an empty list if there are no rooms", () => {
             client.store = new StubStore();
             client.store.getRooms = () => [];
@@ -2274,5 +2288,114 @@ describe("MatrixClient", function () {
             expect(rooms).toContain(room1);
             expect(rooms).toContain(room2);
         });
+
+        function setUpReplacedRooms(): {
+            room1: Room;
+            room2: Room;
+            replacedByCreate1: Room;
+            replacedByCreate2: Room;
+            replacedByDynamicPredecessor1: Room;
+            replacedByDynamicPredecessor2: Room;
+        } {
+            const room1 = new Room("room1", client, "@carol:alexandria.example.com");
+            const replacedByCreate1 = new Room("replacedByCreate1", client, "@carol:alexandria.example.com");
+            const replacedByCreate2 = new Room("replacedByCreate2", client, "@carol:alexandria.example.com");
+            const replacedByDynamicPredecessor1 = new Room("dyn1", client, "@carol:alexandria.example.com");
+            const replacedByDynamicPredecessor2 = new Room("dyn2", client, "@carol:alexandria.example.com");
+            const room2 = new Room("room2", client, "@daryl:alexandria.example.com");
+            client.store = new StubStore();
+            client.store.getRooms = () => [
+                room1,
+                replacedByCreate1,
+                replacedByCreate2,
+                replacedByDynamicPredecessor1,
+                replacedByDynamicPredecessor2,
+                room2,
+            ];
+            room1.addLiveEvents(
+                [
+                    roomCreateEvent(room1.roomId, replacedByCreate1.roomId),
+                    predecessorEvent(room1.roomId, replacedByDynamicPredecessor1.roomId),
+                ],
+                {},
+            );
+            room2.addLiveEvents(
+                [
+                    roomCreateEvent(room2.roomId, replacedByCreate2.roomId),
+                    predecessorEvent(room2.roomId, replacedByDynamicPredecessor2.roomId),
+                ],
+                {},
+            );
+            replacedByCreate1.addLiveEvents([tombstoneEvent(room1.roomId, replacedByCreate1.roomId)], {});
+            replacedByCreate2.addLiveEvents([tombstoneEvent(room2.roomId, replacedByCreate2.roomId)], {});
+            replacedByDynamicPredecessor1.addLiveEvents(
+                [tombstoneEvent(room1.roomId, replacedByDynamicPredecessor1.roomId)],
+                {},
+            );
+            replacedByDynamicPredecessor2.addLiveEvents(
+                [tombstoneEvent(room2.roomId, replacedByDynamicPredecessor2.roomId)],
+                {},
+            );
+
+            return {
+                room1,
+                room2,
+                replacedByCreate1,
+                replacedByCreate2,
+                replacedByDynamicPredecessor1,
+                replacedByDynamicPredecessor2,
+            };
+        }
+
+        it("Considers rooms replaced with m.predecessor events to be replaced", () => {
+            // Given 6 rooms, 2 of which have been replaced, and 2 of which WERE
+            // replaced by create events, but are now NOT replaced, because an
+            // m.predecessor event has changed the room's predecessor.
+            const {
+                room1,
+                room2,
+                replacedByCreate1,
+                replacedByCreate2,
+                replacedByDynamicPredecessor1,
+                replacedByDynamicPredecessor2,
+            } = setUpReplacedRooms();
+
+            // When we ask for the visible rooms
+            const useMsc3946 = true;
+            const rooms = client.getVisibleRooms(useMsc3946);
+
+            // Then we only get the ones that have not been replaced
+            expect(rooms).not.toContain(replacedByDynamicPredecessor1);
+            expect(rooms).not.toContain(replacedByDynamicPredecessor2);
+            expect(rooms).toContain(replacedByCreate1);
+            expect(rooms).toContain(replacedByCreate2);
+            expect(rooms).toContain(room1);
+            expect(rooms).toContain(room2);
+        });
+
+        it("Ignores m.predecessor if we don't ask to use it", () => {
+            // Given 6 rooms, 2 of which have been replaced, and 2 of which WERE
+            // replaced by create events, but are now NOT replaced, because an
+            // m.predecessor event has changed the room's predecessor.
+            const {
+                room1,
+                room2,
+                replacedByCreate1,
+                replacedByCreate2,
+                replacedByDynamicPredecessor1,
+                replacedByDynamicPredecessor2,
+            } = setUpReplacedRooms();
+
+            // When we ask for the visible rooms
+            const rooms = client.getVisibleRooms(); // Don't supply msc3946ProcessDynamicPredecessor
+
+            // Then we only get the ones that have not been replaced
+            expect(rooms).not.toContain(replacedByCreate1);
+            expect(rooms).not.toContain(replacedByCreate2);
+            expect(rooms).toContain(replacedByDynamicPredecessor1);
+            expect(rooms).toContain(replacedByDynamicPredecessor2);
+            expect(rooms).toContain(room1);
+            expect(rooms).toContain(room2);
+        });
     });
 });

spec/unit/room.spec.ts

@@ -3257,6 +3257,20 @@ describe("Room", function () {
             });
         }
 
+        function predecessorEvent(newRoomId: string, predecessorRoomId: string): MatrixEvent {
+            return new MatrixEvent({
+                content: {
+                    predecessor_room_id: predecessorRoomId,
+                },
+                event_id: `predecessor_event_id_pred_${predecessorRoomId}`,
+                origin_server_ts: 1432735824653,
+                room_id: newRoomId,
+                sender: "@daryl:alexandria.example.com",
+                state_key: "",
+                type: "org.matrix.msc3946.room_predecessor",
+            });
+        }
+
         it("Returns null if there is no create event", () => {
             const room = new Room("roomid", null as unknown as MatrixClient, "@u:example.com");
             expect(room.findPredecessorRoomId()).toBeNull();
@@ -3273,5 +3287,37 @@ describe("Room", function () {
             room.addLiveEvents([roomCreateEvent("roomid", "replacedroomid")]);
             expect(room.findPredecessorRoomId()).toBe("replacedroomid");
         });
+
+        it("Prefers the m.predecessor event if one exists", () => {
+            const room = new Room("roomid", null as unknown as MatrixClient, "@u:example.com");
+            room.addLiveEvents([
+                roomCreateEvent("roomid", "replacedroomid"),
+                predecessorEvent("roomid", "otherreplacedroomid"),
+            ]);
+            const useMsc3946 = true;
+            expect(room.findPredecessorRoomId(useMsc3946)).toBe("otherreplacedroomid");
+        });
+
+        it("Ignores the m.predecessor event if we don't ask to use it", () => {
+            const room = new Room("roomid", null as unknown as MatrixClient, "@u:example.com");
+            room.addLiveEvents([
+                roomCreateEvent("roomid", "replacedroomid"),
+                predecessorEvent("roomid", "otherreplacedroomid"),
+            ]);
+            // Don't provide an argument for msc3946ProcessDynamicPredecessor -
+            // we should ignore the predecessor event.
+            expect(room.findPredecessorRoomId()).toBe("replacedroomid");
+        });
+
+        it("Ignores the m.predecessor event and returns null if we don't ask to use it", () => {
+            const room = new Room("roomid", null as unknown as MatrixClient, "@u:example.com");
+            room.addLiveEvents([
+                roomCreateEvent("roomid", null), // Create event has no predecessor
+                predecessorEvent("roomid", "otherreplacedroomid"),
+            ]);
+            // Don't provide an argument for msc3946ProcessDynamicPredecessor -
+            // we should ignore the predecessor event.
+            expect(room.findPredecessorRoomId()).toBeNull();
+        });
     });
 });

src/@types/event.ts

@@ -33,6 +33,7 @@ export enum EventType {
     RoomGuestAccess = "m.room.guest_access",
     RoomServerAcl = "m.room.server_acl",
     RoomTombstone = "m.room.tombstone",
+    RoomPredecessor = "org.matrix.msc3946.room_predecessor",
 
     SpaceChild = "m.space.child",
     SpaceParent = "m.space.parent",

src/client.ts

@@ -3763,14 +3763,18 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      * This is essentially getRooms() with some rooms filtered out, eg. old versions
      * of rooms that have been replaced or (in future) other rooms that have been
      * marked at the protocol level as not to be displayed to the user.
+     *
+     * @param msc3946ProcessDynamicPredecessor - if true, look for an
+     *                                           m.room.predecessor state event and
+     *                                           use it if found (MSC3946).
      * @returns A list of rooms, or an empty list if there is no data store.
      */
-    public getVisibleRooms(): Room[] {
+    public getVisibleRooms(msc3946ProcessDynamicPredecessor = false): Room[] {
         const allRooms = this.store.getRooms();
 
         const replacedRooms = new Set();
         for (const r of allRooms) {
-            const predecessor = r.findPredecessorRoomId();
+            const predecessor = r.findPredecessorRoomId(msc3946ProcessDynamicPredecessor);
             if (predecessor) {
                 replacedRooms.add(predecessor);
             }

src/models/room.ts

@@ -2970,14 +2970,26 @@ export class Room extends ReadReceipt<RoomEmittedEvents, RoomEventHandlerMap> {
     }
 
     /**
+     * @param msc3946ProcessDynamicPredecessor - if true, look for an
+     *                                           m.room.predecessor state event and
+     *                                           use it if found (MSC3946).
      * @returns the ID of the room that was this room's predecessor, or null if
      *          this room has no predecessor.
      */
-    public findPredecessorRoomId(): string | null {
+    public findPredecessorRoomId(msc3946ProcessDynamicPredecessor = false): string | null {
         const currentState = this.getLiveTimeline().getState(EventTimeline.FORWARDS);
         if (!currentState) {
             return null;
         }
+        if (msc3946ProcessDynamicPredecessor) {
+            const predecessorEvent = currentState.getStateEvents(EventType.RoomPredecessor, "");
+            if (predecessorEvent) {
+                const roomId = predecessorEvent.getContent()["predecessor_room_id"];
+                if (roomId) {
+                    return roomId;
+                }
+            }
+        }
 
         const createEvent = currentState.getStateEvents(EventType.RoomCreate, "");
         if (createEvent) {