Use Room.findPredecessor when rendering RoomCreate tiles

src/components/views/messages/RoomCreate.tsx

@@ -1,6 +1,6 @@
 /*
 Copyright 2018 New Vector Ltd
-Copyright 2019 The Matrix.org Foundation C.I.C.
+Copyright 2019, 2023 The Matrix.org Foundation C.I.C.
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -15,7 +15,8 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import React, { useCallback } from "react";
+import React, { useCallback, useContext } from "react";
+import { logger } from "matrix-js-sdk/src/logger";
 import { MatrixEvent } from "matrix-js-sdk/src/models/event";
 
 import dis from "../../../dispatcher/dispatcher";
@@ -25,6 +26,8 @@ import { _t } from "../../../languageHandler";
 import { MatrixClientPeg } from "../../../MatrixClientPeg";
 import EventTileBubble from "./EventTileBubble";
 import { ViewRoomPayload } from "../../../dispatcher/payloads/ViewRoomPayload";
+import RoomContext from "../../../contexts/RoomContext";
+import { useRoomState } from "../../../hooks/useRoomState";
 
 interface IProps {
     /** The m.room.create MatrixEvent that this tile represents */
@@ -37,31 +40,53 @@ interface IProps {
  * room.
  */
 export const RoomCreate: React.FC<IProps> = ({ mxEvent, timestamp }) => {
+    // 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(), []),
+    );
+
     const onLinkClicked = useCallback(
         (e: React.MouseEvent): void => {
             e.preventDefault();
 
-            const predecessor = mxEvent.getContent()["predecessor"];
-
             dis.dispatch<ViewRoomPayload>({
                 action: Action.ViewRoom,
-                event_id: predecessor["event_id"],
+                event_id: predecessor.eventId,
                 highlighted: true,
-                room_id: predecessor["room_id"],
+                room_id: predecessor.roomId,
                 metricsTrigger: "Predecessor",
                 metricsViaKeyboard: e.type !== "click",
             });
         },
-        [mxEvent],
+        [predecessor?.eventId, predecessor?.roomId],
     );
-    const predecessor = mxEvent.getContent()["predecessor"];
-    if (predecessor === undefined) {
-        return <div />; // We should never have been instantiated in this case
+
+    if (!roomContext.room || roomContext.room.roomId !== mxEvent.getRoomId()) {
+        logger.warn(
+            "RoomCreate unexpectedly used outside of the context of the room containing this m.room.create event.",
+        );
+        return <></>;
     }
-    const prevRoom = MatrixClientPeg.get().getRoom(predecessor["room_id"]);
-    const permalinkCreator = new RoomPermalinkCreator(prevRoom, predecessor["room_id"]);
+
+    if (!predecessor) {
+        logger.warn("RoomCreate unexpectedly used in a room with no predecessor.");
+        return <div />;
+    }
+
+    const prevRoom = MatrixClientPeg.get().getRoom(predecessor.roomId);
+    const permalinkCreator = new RoomPermalinkCreator(prevRoom, predecessor.roomId);
     permalinkCreator.load();
-    const predecessorPermalink = permalinkCreator.forEvent(predecessor["event_id"]);
+    let predecessorPermalink: string;
+    if (predecessor.eventId) {
+        predecessorPermalink = permalinkCreator.forEvent(predecessor.eventId);
+    } else {
+        predecessorPermalink = permalinkCreator.forRoom();
+    }
     const link = (
         <a href={predecessorPermalink} onClick={onLinkClicked}>
             {_t("Click here to see older messages.")}

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

@@ -18,13 +18,16 @@ import React from "react";
 import { act, render, screen, waitFor } from "@testing-library/react";
 import userEvent from "@testing-library/user-event";
 import { mocked } from "jest-mock";
-import { EventType, MatrixEvent } from "matrix-js-sdk/src/matrix";
+import { EventType, MatrixEvent, Room } from "matrix-js-sdk/src/matrix";
 
 import dis from "../../../../src/dispatcher/dispatcher";
 import SettingsStore from "../../../../src/settings/SettingsStore";
 import { RoomCreate } from "../../../../src/components/views/messages/RoomCreate";
-import { stubClient } from "../../../test-utils/test-utils";
+import { stubClient, upsertRoomStateEvents } from "../../../test-utils/test-utils";
 import { Action } from "../../../../src/dispatcher/actions";
+import RoomContext from "../../../../src/contexts/RoomContext";
+import { getRoomContext } from "../../../test-utils";
+import { MatrixClientPeg } from "../../../../src/MatrixClientPeg";
 
 jest.mock("../../../../src/dispatcher/dispatcher");
 
@@ -33,13 +36,28 @@ describe("<RoomCreate />", () => {
     const roomId = "!room:server.org";
     const createEvent = new MatrixEvent({
         type: EventType.RoomCreate,
+        state_key: "",
         sender: userId,
         room_id: roomId,
         content: {
             predecessor: { room_id: "old_room_id", event_id: "tombstone_event_id" },
         },
         event_id: "$create",
     });
+    const createEventWithoutPredecessor = new MatrixEvent({
+        type: EventType.RoomCreate,
+        state_key: "",
+        sender: userId,
+        room_id: roomId,
+        content: {},
+        event_id: "$create",
+    });
+    stubClient();
+    const client = mocked(MatrixClientPeg.get());
+    const room = new Room(roomId, client, userId);
+    upsertRoomStateEvents(room, [createEvent]);
+    const roomNoPredecessors = new Room(roomId, client, userId);
+    upsertRoomStateEvents(roomNoPredecessors, [createEventWithoutPredecessor]);
 
     beforeEach(() => {
         jest.clearAllMocks();
@@ -54,21 +72,34 @@ describe("<RoomCreate />", () => {
         jest.spyOn(SettingsStore, "setValue").mockRestore();
     });
 
+    function renderRoomCreate(room: Room) {
+        return render(
+            <RoomContext.Provider value={getRoomContext(room, {})}>
+                <RoomCreate mxEvent={createEvent} />
+            </RoomContext.Provider>,
+        );
+    }
+
     it("Renders as expected", () => {
-        const roomCreate = render(<RoomCreate mxEvent={createEvent} />);
+        const roomCreate = renderRoomCreate(room);
         expect(roomCreate.asFragment()).toMatchSnapshot();
     });
 
     it("Links to the old version of the room", () => {
-        render(<RoomCreate mxEvent={createEvent} />);
+        renderRoomCreate(room);
         expect(screen.getByText("Click here to see older messages.")).toHaveAttribute(
             "href",
             "https://matrix.to/#/old_room_id/tombstone_event_id",
         );
     });
 
+    it("Shows an empty div if there is no predecessor", () => {
+        renderRoomCreate(roomNoPredecessors);
+        expect(screen.queryByText("Click here to see older messages.", { exact: false })).toBeNull();
+    });
+
     it("Opens the old room on click", async () => {
-        render(<RoomCreate mxEvent={createEvent} />);
+        renderRoomCreate(room);
         const link = screen.getByText("Click here to see older messages.");
 
         await act(() => userEvent.click(link));