Support MSC3946 in the RoomCreate tile

src/components/views/messages/RoomCreate.tsx

@@ -28,6 +28,7 @@ import EventTileBubble from "./EventTileBubble";
 import { ViewRoomPayload } from "../../../dispatcher/payloads/ViewRoomPayload";
 import RoomContext from "../../../contexts/RoomContext";
 import { useRoomState } from "../../../hooks/useRoomState";
+import SettingsStore from "../../../settings/SettingsStore";
 
 interface IProps {
     /** The m.room.create MatrixEvent that this tile represents */
@@ -40,14 +41,19 @@ interface IProps {
  * room.
  */
 export const RoomCreate: React.FC<IProps> = ({ mxEvent, timestamp }) => {
+    const msc3946ProcessDynamicPredecessor = SettingsStore.getValue("feature_dynamic_room_predecessors");
+
     // Note: we ask the room for its predecessor here, instead of directly using
     // the information inside mxEvent. This allows us the flexibility later to
     // use a different predecessor (e.g. through MSC3946) and still display it
     // in the timeline location of the create event.
     const roomContext = useContext(RoomContext);
     const predecessor = useRoomState(
         roomContext.room,
-        useCallback((state) => state.findPredecessor(), []),
+        useCallback(
+            (state) => state.findPredecessor(msc3946ProcessDynamicPredecessor),
+            [msc3946ProcessDynamicPredecessor],
+        ),
     );
 
     const onLinkClicked = useCallback(

test/components/views/messages/RoomCreate-test.tsx

@@ -52,10 +52,35 @@ describe("<RoomCreate />", () => {
         content: {},
         event_id: "$create",
     });
+    const predecessorEvent = new MatrixEvent({
+        type: EventType.RoomPredecessor,
+        state_key: "",
+        sender: userId,
+        room_id: roomId,
+        content: {
+            predecessor_room_id: "old_room_id_from_predecessor",
+        },
+        event_id: "$create",
+    });
+    const predecessorEventWithEventId = new MatrixEvent({
+        type: EventType.RoomPredecessor,
+        state_key: "",
+        sender: userId,
+        room_id: roomId,
+        content: {
+            predecessor_room_id: "old_room_id_from_predecessor",
+            last_known_event_id: "tombstone_event_id_from_predecessor",
+        },
+        event_id: "$create",
+    });
     stubClient();
     const client = mocked(MatrixClientPeg.get());
-    const room = new Room(roomId, client, userId);
-    upsertRoomStateEvents(room, [createEvent]);
+    const roomJustCreate = new Room(roomId, client, userId);
+    upsertRoomStateEvents(roomJustCreate, [createEvent]);
+    const roomCreateAndPredecessor = new Room(roomId, client, userId);
+    upsertRoomStateEvents(roomCreateAndPredecessor, [createEvent, predecessorEvent]);
+    const roomCreateAndPredecessorWithEventId = new Room(roomId, client, userId);
+    upsertRoomStateEvents(roomCreateAndPredecessorWithEventId, [createEvent, predecessorEventWithEventId]);
     const roomNoPredecessors = new Room(roomId, client, userId);
     upsertRoomStateEvents(roomNoPredecessors, [createEventWithoutPredecessor]);
 
@@ -81,12 +106,12 @@ describe("<RoomCreate />", () => {
     }
 
     it("Renders as expected", () => {
-        const roomCreate = renderRoomCreate(room);
+        const roomCreate = renderRoomCreate(roomJustCreate);
         expect(roomCreate.asFragment()).toMatchSnapshot();
     });
 
     it("Links to the old version of the room", () => {
-        renderRoomCreate(room);
+        renderRoomCreate(roomJustCreate);
         expect(screen.getByText("Click here to see older messages.")).toHaveAttribute(
             "href",
             "https://matrix.to/#/old_room_id/tombstone_event_id",
@@ -99,7 +124,7 @@ describe("<RoomCreate />", () => {
     });
 
     it("Opens the old room on click", async () => {
-        renderRoomCreate(room);
+        renderRoomCreate(roomJustCreate);
         const link = screen.getByText("Click here to see older messages.");
 
         await act(() => userEvent.click(link));
@@ -115,4 +140,48 @@ describe("<RoomCreate />", () => {
             }),
         );
     });
+
+    it("Ignores m.predecessor if labs flag is off", () => {
+        renderRoomCreate(roomCreateAndPredecessor);
+        expect(screen.getByText("Click here to see older messages.")).toHaveAttribute(
+            "href",
+            "https://matrix.to/#/old_room_id/tombstone_event_id",
+        );
+    });
+
+    describe("When feature_dynamic_room_predecessors = true", () => {
+        beforeEach(() => {
+            jest.spyOn(SettingsStore, "getValue").mockImplementation(
+                (settingName) => settingName === "feature_dynamic_room_predecessors",
+            );
+        });
+
+        afterEach(() => {
+            jest.spyOn(SettingsStore, "getValue").mockReset();
+        });
+
+        it("Uses the create event if there is no m.predecessor", () => {
+            renderRoomCreate(roomJustCreate);
+            expect(screen.getByText("Click here to see older messages.")).toHaveAttribute(
+                "href",
+                "https://matrix.to/#/old_room_id/tombstone_event_id",
+            );
+        });
+
+        it("Uses m.predecessor when it's there", () => {
+            renderRoomCreate(roomCreateAndPredecessor);
+            expect(screen.getByText("Click here to see older messages.")).toHaveAttribute(
+                "href",
+                "https://matrix.to/#/old_room_id_from_predecessor",
+            );
+        });
+
+        it("Links to the event in the room if event ID is provided", () => {
+            renderRoomCreate(roomCreateAndPredecessorWithEventId);
+            expect(screen.getByText("Click here to see older messages.")).toHaveAttribute(
+                "href",
+                "https://matrix.to/#/old_room_id_from_predecessor/tombstone_event_id_from_predecessor",
+            );
+        });
+    });
 });