Message List: Fix flick when opening chat on message (#6715)

src/components/middle/MessageList.tsx

@@ -13,7 +13,7 @@ import {
   MESSAGE_LIST_SLICE,
   SERVICE_NOTIFICATIONS_USER_ID,
 } from '../../config';
-import { forceMeasure, requestForcedReflow, requestMeasure, requestMutation } from '../../lib/fasterdom/fasterdom';
+import { forceMeasure, requestMeasure, requestMutation } from '../../lib/fasterdom/fasterdom';
 import {
   getIsSavedDialog,
   getMessageHtmlId,
@@ -66,6 +66,7 @@ import { debounce, onTickEnd } from '../../util/schedulers';
 import getOffsetToContainer from '../../util/visibility/getOffsetToContainer';
 import { REM } from '../common/helpers/mediaDimensions';
 import { groupMessages } from './helpers/groupMessages';
+import { requestMessageListReflow } from './helpers/messageListReflow';
 import { preventMessageInputBlur } from './helpers/preventMessageInputBlur';
 
 import useInterval from '../../hooks/schedulers/useInterval';
@@ -677,7 +678,7 @@ const MessageList = ({
       }, MESSAGE_ANIMATION_DURATION);
     }
 
-    requestForcedReflow(() => {
+    requestMessageListReflow(() => {
       const { scrollTop, scrollHeight, offsetHeight } = container;
       const scrollOffset = scrollOffsetRef.current;
 

src/components/middle/helpers/messageListReflow.ts

@@ -0,0 +1,24 @@
+import { requestForcedReflow } from '../../../lib/fasterdom/fasterdom';
+
+type ReflowCallback = () => (NoneToVoidFunction | void);
+
+let afterReflowCallbacks: ReflowCallback[] = [];
+
+// For children effects that need to run after the message list reflow
+export function requestAfterMessageListReflow(cb: ReflowCallback) {
+  afterReflowCallbacks.push(cb);
+}
+
+export function requestMessageListReflow(cb: ReflowCallback) {
+  requestForcedReflow(() => {
+    const mutationFn = cb();
+
+    const callbacks = afterReflowCallbacks;
+    afterReflowCallbacks = [];
+    for (const afterCb of callbacks) {
+      requestForcedReflow(afterCb);
+    }
+
+    return mutationFn;
+  });
+}

src/components/middle/message/hooks/useFocusMessageListElement.ts

@@ -1,5 +1,5 @@
 import type { ElementRef } from '../../../../lib/teact/teact';
-import { useLayoutEffect } from '../../../../lib/teact/teact';
+import { useLayoutEffect, useRef } from '../../../../lib/teact/teact';
 import { addExtraClass } from '../../../../lib/teact/teact-dom';
 
 import type { FocusDirection, ScrollTargetPosition } from '../../../../types';
@@ -10,6 +10,7 @@ import {
 } from '../../../../lib/fasterdom/fasterdom';
 import animateScroll from '../../../../util/animateScroll';
 import { REM } from '../../../common/helpers/mediaDimensions';
+import { requestAfterMessageListReflow } from '../../helpers/messageListReflow';
 
 // This is used when the viewport was replaced.
 const BOTTOM_FOCUS_OFFSET = 500;
@@ -36,7 +37,12 @@ export default function useFocusMessageListElement({
   isQuote?: boolean;
   scrollTargetPosition?: ScrollTargetPosition;
 }) {
+  const isRelocatedRef = useRef(!isJustAdded);
+
   useLayoutEffect(() => {
+    const isRelocated = isRelocatedRef.current;
+    isRelocatedRef.current = false;
+
     if (isFocused && elementRef.current) {
       const messagesContainer = elementRef.current.closest<HTMLDivElement>('.MessageList');
       if (!messagesContainer) return;
@@ -72,9 +78,14 @@ export default function useFocusMessageListElement({
         return result;
       };
 
-      requestMeasure(() => {
-        requestMutation(exec()!);
-      });
+      if (isRelocated) {
+        // We need this to override scroll setting from Message List layout effect
+        requestAfterMessageListReflow(exec);
+      } else {
+        requestMeasure(() => {
+          requestMutation(exec()!);
+        });
+      }
     }
   }, [
     elementRef, isFocused, focusDirection, noFocusHighlight, isResizingContainer, isQuote, scrollTargetPosition,