Scroll: Fix scroll to unread divider (#5388)

src/components/middle/MessageList.tsx

@@ -56,6 +56,7 @@ import { orderBy } from '../../util/iteratees';
 import { isLocalMessageId } from '../../util/keys/messageKey';
 import resetScroll from '../../util/resetScroll';
 import { debounce, onTickEnd } from '../../util/schedulers';
+import { getOffsetToContainer } from '../../util/scroll';
 import { groupMessages } from './helpers/groupMessages';
 import { preventMessageInputBlur } from './helpers/preventMessageInputBlur';
 
@@ -585,7 +586,7 @@ const MessageList: FC<OwnProps & StateProps> = ({
         newScrollTop = scrollTop + (newAnchorTop - (anchorTopRef.current || 0));
       } else if (unreadDivider) {
         newScrollTop = Math.min(
-          unreadDivider.offsetTop - UNREAD_DIVIDER_TOP,
+          getOffsetToContainer(unreadDivider, container).top - UNREAD_DIVIDER_TOP,
           scrollHeight - scrollOffset,
         );
       } else {

src/util/animateScroll.ts

@@ -13,6 +13,7 @@ import {
 import { requestMeasure, requestMutation } from '../lib/fasterdom/fasterdom';
 import { selectCanAnimateInterface } from '../global/selectors';
 import { animateSingle, cancelSingleAnimation } from './animation';
+import { getOffsetToContainer } from './scroll';
 import { IS_ANDROID } from './windowEnvironment';
 
 export type AnimateScrollArgs = {
@@ -55,22 +56,6 @@ export function restartCurrentScrollAnimation() {
   });
 }
 
-function getOffsetToContainer(element: HTMLElement, container: HTMLElement) {
-  let offsetTop = 0;
-  let offsetLeft = 0;
-
-  let current: HTMLElement | null = element;
-
-  while (current && current !== container && !current.contains(container)) {
-    offsetTop += current.offsetTop;
-    offsetLeft += current.offsetLeft;
-
-    current = current.offsetParent as HTMLElement;
-  }
-
-  return { top: offsetTop, left: offsetLeft };
-}
-
 function createMutateFunction(args: AnimateScrollArgs) {
   const {
     container,

src/util/scroll.ts

@@ -0,0 +1,15 @@
+export function getOffsetToContainer(element: HTMLElement, container: HTMLElement) {
+  let offsetTop = 0;
+  let offsetLeft = 0;
+
+  let current: HTMLElement | null = element;
+
+  while (current && current !== container && !current.contains(container)) {
+    offsetTop += current.offsetTop;
+    offsetLeft += current.offsetLeft;
+
+    current = current.offsetParent as HTMLElement;
+  }
+
+  return { top: offsetTop, left: offsetLeft };
+}