Show an error tile when the predecessor room is not found

src/components/views/messages/RoomPredecessorTile.tsx

@@ -88,7 +88,21 @@ export const RoomPredecessorTile: React.FC<IProps> = ({ mxEvent, timestamp }) =>
     const prevRoom = MatrixClientPeg.get().getRoom(predecessor.roomId);
     if (!prevRoom) {
         logger.warn(`Failed to find predecessor room with id ${predecessor.roomId}`);
-        return <></>;
+        return (
+            <EventTileBubble
+                className="mx_CreateEvent"
+                title={_t("This room is a continuation of another conversation.")}
+                timestamp={timestamp}
+            >
+                <div className="mx_EventTile_body">
+                    <span className="mx_EventTile_tileError">
+                        {_t("Can't find the old version of this room (room id: %(roomId)s).", {
+                            roomId: predecessor.roomId,
+                        })}
+                    </span>
+                </div>
+            </EventTileBubble>
+        );
     }
     const permalinkCreator = new RoomPermalinkCreator(prevRoom, predecessor.roomId);
     permalinkCreator.load();

src/i18n/strings/en_EN.json

@@ -2464,8 +2464,9 @@
     "%(senderDisplayName)s changed the avatar for %(roomName)s": "%(senderDisplayName)s changed the avatar for %(roomName)s",
     "%(senderDisplayName)s removed the room avatar.": "%(senderDisplayName)s removed the room avatar.",
     "%(senderDisplayName)s changed the room avatar to <img/>": "%(senderDisplayName)s changed the room avatar to <img/>",
-    "Click here to see older messages.": "Click here to see older messages.",
     "This room is a continuation of another conversation.": "This room is a continuation of another conversation.",
+    "Can't find the old version of this room (room id: %(roomId)s).": "Can't find the old version of this room (room id: %(roomId)s).",
+    "Click here to see older messages.": "Click here to see older messages.",
     "Add an Integration": "Add an Integration",
     "You are about to be taken to a third-party site so you can authenticate your account for use with %(integrationsUrl)s. Do you wish to continue?": "You are about to be taken to a third-party site so you can authenticate your account for use with %(integrationsUrl)s. Do you wish to continue?",
     "Edited at %(date)s": "Edited at %(date)s",

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

@@ -26,7 +26,7 @@ import { RoomPredecessorTile } from "../../../../src/components/views/messages/R
 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 { filterConsole, getRoomContext } from "../../../test-utils";
 import { MatrixClientPeg } from "../../../../src/MatrixClientPeg";
 
 jest.mock("../../../../src/dispatcher/dispatcher");
@@ -118,9 +118,14 @@ describe("<RoomPredecessorTile />", () => {
         );
     });
 
-    it("Shows an empty div if there is no predecessor", () => {
-        renderTile(roomNoPredecessors);
-        expect(screen.queryByText("Click here to see older messages.", { exact: false })).toBeNull();
+    describe("(filtering warnings about no predecessor)", () => {
+        filterConsole("RoomPredecessorTile unexpectedly used in a room with no predecessor.");
+
+        it("Shows an empty div if there is no predecessor", () => {
+            filterConsole;
+            renderTile(roomNoPredecessors);
+            expect(screen.queryByText("Click here to see older messages.", { exact: false })).toBeNull();
+        });
     });
 
     it("Opens the old room on click", async () => {
@@ -149,6 +154,19 @@ describe("<RoomPredecessorTile />", () => {
         );
     });
 
+    describe("If the predecessor room is not found", () => {
+        filterConsole("Failed to find predecessor room with id old_room_id");
+
+        beforeEach(() => {
+            mocked(MatrixClientPeg.get().getRoom).mockReturnValue(null);
+        });
+
+        it("Shows an error", () => {
+            renderTile(roomCreateAndPredecessor);
+            expect(screen.getByText("Can't find the old version of this room", { exact: false })).toBeInTheDocument();
+        });
+    });
+
     describe("When feature_dynamic_room_predecessors = true", () => {
         beforeEach(() => {
             jest.spyOn(SettingsStore, "getValue").mockImplementation(