Make permalinks to the same event work more than once (#34483)

Co-authored-by: Michael Telatynski <7t3chguy@gmail.com>

apps/web/src/components/structures/TimelinePanel.tsx

@@ -341,8 +341,12 @@ class TimelinePanel extends React.Component<IProps, IState> {
 
         const differentEventId = prevProps.eventId != this.props.eventId;
         const differentHighlightedEventId = prevProps.highlightedEventId != this.props.highlightedEventId;
-        const differentAvoidJump = prevProps.eventScrollIntoView && !this.props.eventScrollIntoView;
+        // Both directions matter. The flag is cleared once a jump has landed, so clicking the same
-        if (differentEventId || differentHighlightedEventId || differentAvoidJump) {
+        // permalink again flips it back to true and has to jump afresh. An unset prop means true,
+        // matching the default in loadTimeline.
+        const differentScrollIntoView =
+            (prevProps.eventScrollIntoView ?? true) !== (this.props.eventScrollIntoView ?? true);
+        if (differentEventId || differentHighlightedEventId || differentScrollIntoView) {
             logger.log(
                 `TimelinePanel switching to eventId ${this.props.eventId} (was ${prevProps.eventId}), ` +
                     `scrollIntoView: ${this.props.eventScrollIntoView} (was ${prevProps.eventScrollIntoView})`,

apps/web/test/unit-tests/components/structures/TimelinePanel-test.tsx

@@ -439,6 +439,32 @@ describe("TimelinePanel", () => {
         expect(props.onEventScrolledIntoView).toHaveBeenCalledWith(events[1].getId());
     });
 
+    it("should scroll the event into view again when the same event is re-requested", () => {
+        const client = MatrixClientPeg.safeGet();
+        const room = mkRoom(client, "roomId");
+        const events = mockEvents(room);
+
+        const props = {
+            ...getProps(room, events),
+            eventId: events[1].getId(),
+            eventScrollIntoView: true,
+            onEventScrolledIntoView: jest.fn(),
+        };
+
+        const { rerender } = render(<TimelinePanel {...props} />);
+        expect(props.onEventScrolledIntoView).toHaveBeenCalledTimes(1);
+
+        // RoomView clears the flag once the jump has landed, so the event stays put on re-render.
+        props.eventScrollIntoView = false;
+        rerender(<TimelinePanel {...props} />);
+        expect(props.onEventScrolledIntoView).toHaveBeenCalledTimes(1);
+
+        // Clicking the same permalink a second time asks for the very same event again.
+        props.eventScrollIntoView = true;
+        rerender(<TimelinePanel {...props} />);
+        expect(props.onEventScrolledIntoView).toHaveBeenCalledTimes(2);
+    });
+
     it("paginates", async () => {
         const [client, room, events] = setupTestData();
         const eventsPage1 = events.slice(0, 1);