From e53c26f934b7d14fcd660e9ea9904d075a35e3bb Mon Sep 17 00:00:00 2001
From: Matt Van Horn <455140+mvanhorn@users.noreply.github.com>
Date: Sun, 26 Apr 2026 03:33:51 -0700
Subject: [PATCH] fix(timeline): suppress dividers when the underlying event
 renders null
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Closes #701

The hook hands the renderer a `willRenderDayDivider` / `willRenderNewDivider`
flag attached to the FIRST event of a new day (or the readUptoEventId
boundary). The render layer in RoomTimeline always emitted those dividers
even when `useTimelineEventRenderer` returned `null` for the event itself
— for example when `hideMembershipEvents` / `hideNickAvatarEvents` /
`hideMemberInReadOnly` filtered the underlying event out at render time.

Result: announcement channels and similar rooms whose only events on a
given day are hidden (joins/leaves/profile changes) showed a bare day
divider with no message under it. Same orphan pattern produced the
"dates showing without content" complaint in #701.

Fix: gate the dividers JSX on `renderedEvent !== null`. When the event
renders null, the dividers are skipped too. When at least one event of
a day passes the renderer, the divider is attached to it the same way
as before.

Edge case: a day where the first hook-eligible event is rendered as null
but a later event renders correctly will lose the day divider entirely.
That is strictly better than an orphan divider in the symptom case the
issue reports, and the proper fix (propagate the divider forward in
useProcessedTimeline based on render prediction) is a larger refactor
that can land separately.
---
 src/app/features/room/RoomTimeline.tsx | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/app/features/room/RoomTimeline.tsx b/src/app/features/room/RoomTimeline.tsx
index 8bc5d770c..e1d7fb504 100644
--- a/src/app/features/room/RoomTimeline.tsx
+++ b/src/app/features/room/RoomTimeline.tsx
@@ -921,7 +921,13 @@ export function RoomTimeline({
               eventData.collapsed
             );
 
-            const dividers = (
+            // Suppress dividers when the underlying event will not render.
+            // Otherwise rooms whose only events on a given day are hidden
+            // (e.g. announcement channels full of profile changes / joins)
+            // show a bare day divider with no message under it (#701).
+            const showDividers = renderedEvent !== null;
+
+            const dividers = showDividers ? (
               <>
                 {eventData.willRenderDayDivider && (
                   <MessageBase space={messageSpacing}>
@@ -942,7 +948,7 @@ export function RoomTimeline({
                   </MessageBase>
                 )}
               </>
-            );
+            ) : null;
 
             if (index === 0) {
               return (