From 0e103a3cd1c43d871ef3b1e338c911549dc11942 Mon Sep 17 00:00:00 2001
From: Michael Weimann <michaelw@matrix.org>
Date: Tue, 16 May 2023 13:08:32 +0200
Subject: [PATCH] Let TimelinePanel not send a receipt if there is no event

---
 src/components/structures/TimelinePanel.tsx       |  6 ++++--
 test/components/structures/TimelinePanel-test.tsx | 12 ++++++++++++
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/src/components/structures/TimelinePanel.tsx b/src/components/structures/TimelinePanel.tsx
index c921b2e3330..b00b6ed132a 100644
--- a/src/components/structures/TimelinePanel.tsx
+++ b/src/components/structures/TimelinePanel.tsx
@@ -1082,7 +1082,9 @@ class TimelinePanel extends React.Component<IProps, IState> {
         currentReadReceiptEventIndex: number | null,
         lastReadEvent: MatrixEvent | null,
         lastReadEventIndex: number | null,
-    ): boolean {
+    ): lastReadEvent is MatrixEvent {
+        if (!lastReadEvent) return false;
+
         // We want to avoid sending out read receipts when we are looking at
         // events in the past which are before the latest RR.
         //
@@ -1133,7 +1135,7 @@ class TimelinePanel extends React.Component<IProps, IState> {
         const lastReadEventIndex = this.getLastDisplayedEventIndex({
             ignoreOwn: true,
         });
-        const lastReadEvent: MatrixEvent | null = this.state.events[lastReadEventIndex ?? 0];
+        const lastReadEvent: MatrixEvent | null = this.state.events[lastReadEventIndex ?? 0] ?? null;
 
         const shouldSendReadReceipt = this.shouldSendReadReceipt(
             currentReadReceiptEventId,
diff --git a/test/components/structures/TimelinePanel-test.tsx b/test/components/structures/TimelinePanel-test.tsx
index 101ae9b716e..a77e30b313b 100644
--- a/test/components/structures/TimelinePanel-test.tsx
+++ b/test/components/structures/TimelinePanel-test.tsx
@@ -242,6 +242,18 @@ describe("TimelinePanel", () => {
             TimelinePanel.roomReadMarkerTsMap = {};
         });
 
+        it("when there is no event, it should not send any receipt", async () => {
+            setUpTimelineSet();
+            await renderTimelinePanel();
+            await flushPromises();
+
+            // @ts-ignore
+            await timelinePanel.sendReadReceipts();
+
+            expect(client.setRoomReadMarkers).not.toHaveBeenCalled();
+            expect(client.sendReadReceipt).not.toHaveBeenCalled();
+        });
+
         describe("when there is a non-threaded timeline", () => {
             beforeEach(() => {
                 setUpTimelineSet();