Allow via_servers property in findPredecessor (update to MSC3946)

spec/unit/room.spec.ts

@@ -3343,11 +3343,16 @@ describe("Room", function () {
             newRoomId: string,
             predecessorRoomId: string,
             tombstoneEventId: string | null = null,
+            viaServers: string[] = [],
         ): MatrixEvent {
             const content =
                 tombstoneEventId === null
-                    ? { predecessor_room_id: predecessorRoomId }
-                    : { predecessor_room_id: predecessorRoomId, last_known_event_id: tombstoneEventId };
+                    ? { predecessor_room_id: predecessorRoomId, via_servers: viaServers }
+                    : {
+                          predecessor_room_id: predecessorRoomId,
+                          last_known_event_id: tombstoneEventId,
+                          via_servers: viaServers,
+                      };
 
             return new MatrixEvent({
                 content,
@@ -3387,19 +3392,21 @@ describe("Room", function () {
             expect(room.findPredecessor(useMsc3946)).toEqual({
                 roomId: "otherreplacedroomid",
                 eventId: undefined, // m.predecessor did not include an event_id
+                viaServers: [],
             });
         });
 
         it("uses the m.predecessor event ID if provided", () => {
             const room = new Room("roomid", client!, "@u:example.com");
             room.addLiveEvents([
                 roomCreateEvent("roomid", "replacedroomid"),
-                predecessorEvent("roomid", "otherreplacedroomid", "lstevtid"),
+                predecessorEvent("roomid", "otherreplacedroomid", "lstevtid", ["one.example.com", "two.example.com"]),
             ]);
             const useMsc3946 = true;
             expect(room.findPredecessor(useMsc3946)).toEqual({
                 roomId: "otherreplacedroomid",
                 eventId: "lstevtid",
+                viaServers: ["one.example.com", "two.example.com"],
             });
         });
 

src/models/room-state.ts

@@ -972,13 +972,21 @@ export class RoomState extends TypedEventEmitter<EmittedEvents, EventHandlerMap>
      * @param msc3946ProcessDynamicPredecessor - if true, look for an
      * m.room.predecessor state event and use it if found (MSC3946).
      * @returns null if this room has no predecessor. Otherwise, returns
-     * the roomId and last eventId of the predecessor room.
+     * the roomId, last eventId and viaServers of the predecessor room.
+     *
      * If msc3946ProcessDynamicPredecessor is true, use m.predecessor events
      * as well as m.room.create events to find predecessors.
+     *
      * Note: if an m.predecessor event is used, eventId may be undefined
      * since last_known_event_id is optional.
+     *
+     * Note: viaServers may be undefined, and will definitely be undefined if
+     * this predecessor comes from a RoomCreate event (rather than a
+     * RoomPredecessor, which has the optional via_servers property).
      */
-    public findPredecessor(msc3946ProcessDynamicPredecessor = false): { roomId: string; eventId?: string } | null {
+    public findPredecessor(
+        msc3946ProcessDynamicPredecessor = false,
+    ): { roomId: string; eventId?: string; viaServers?: string[] } | null {
         // Note: the tests for this function are against Room.findPredecessor,
         // which just calls through to here.
 
@@ -988,14 +996,19 @@ export class RoomState extends TypedEventEmitter<EmittedEvents, EventHandlerMap>
                 const content = predecessorEvent.getContent<{
                     predecessor_room_id: string;
                     last_known_event_id?: string;
+                    via_servers?: string[];
                 }>();
                 const roomId = content.predecessor_room_id;
                 let eventId = content.last_known_event_id;
                 if (typeof eventId !== "string") {
                     eventId = undefined;
                 }
+                let viaServers = content.via_servers;
+                if (!Array.isArray(viaServers)) {
+                    viaServers = undefined;
+                }
                 if (typeof roomId === "string") {
-                    return { roomId, eventId };
+                    return { roomId, eventId, viaServers };
                 }
             }
         }

src/models/room.ts

@@ -3057,13 +3057,21 @@ 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 null if this room has no predecessor. Otherwise, returns
-     * the roomId and last eventId of the predecessor room.
+     * the roomId, last eventId and viaServers of the predecessor room.
+     *
      * If msc3946ProcessDynamicPredecessor is true, use m.predecessor events
      * as well as m.room.create events to find predecessors.
+     *
      * Note: if an m.predecessor event is used, eventId may be undefined
      * since last_known_event_id is optional.
+     *
+     * Note: viaServers may be undefined, and will definitely be undefined if
+     * this predecessor comes from a RoomCreate event (rather than a
+     * RoomPredecessor, which has the optional via_servers property).
      */
-    public findPredecessor(msc3946ProcessDynamicPredecessor = false): { roomId: string; eventId?: string } | null {
+    public findPredecessor(
+        msc3946ProcessDynamicPredecessor = false,
+    ): { roomId: string; eventId?: string; viaServers?: string[] } | null {
         const currentState = this.getLiveTimeline().getState(EventTimeline.FORWARDS);
         if (!currentState) {
             return null;