Fix scroll-to-status in threaded view being unreliable (#36927)

app/javascript/mastodon/features/status/components/detailed_status.tsx

@@ -4,7 +4,7 @@
                   @typescript-eslint/no-unsafe-assignment */
 
 import type { CSSProperties } from 'react';
-import { useState, useRef, useCallback } from 'react';
+import { useState, useRef, useCallback, useEffect } from 'react';
 
 import { FormattedMessage } from 'react-intl';
 
@@ -55,6 +55,8 @@ export const DetailedStatus: React.FC<{
   pictureInPicture: any;
   onToggleHidden?: (status: any) => void;
   onToggleMediaVisibility?: () => void;
+  ancestors?: number;
+  multiColumn?: boolean;
 }> = ({
   status,
   onOpenMedia,
@@ -69,6 +71,8 @@ export const DetailedStatus: React.FC<{
   pictureInPicture,
   onToggleMediaVisibility,
   onToggleHidden,
+  ancestors = 0,
+  multiColumn = false,
 }) => {
   const properStatus = status?.get('reblog') ?? status;
   const [height, setHeight] = useState(0);
@@ -123,6 +127,30 @@ export const DetailedStatus: React.FC<{
     if (onTranslate) onTranslate(status);
   }, [onTranslate, status]);
 
+  // The component is managed and will change if the status changes
+  // Ancestors can increase when loading a thread, in which case we want to scroll,
+  // or decrease if a post is deleted, in which case we don't want to mess with it
+  const previousAncestors = useRef(-1);
+  useEffect(() => {
+    if (nodeRef.current && previousAncestors.current < ancestors) {
+      nodeRef.current.scrollIntoView(true);
+
+      // In the single-column interface, `scrollIntoView` will put the post behind the header, so compensate for that.
+      if (!multiColumn) {
+        const offset = document
+          .querySelector('.column-header__wrapper')
+          ?.getBoundingClientRect().bottom;
+
+        if (offset) {
+          const scrollingElement = document.scrollingElement ?? document.body;
+          scrollingElement.scrollBy(0, -offset);
+        }
+      }
+    }
+
+    previousAncestors.current = ancestors;
+  }, [ancestors, multiColumn]);
+
   if (!properStatus) {
     return null;
   }

app/javascript/mastodon/features/status/index.jsx

@@ -164,8 +164,6 @@ class Status extends ImmutablePureComponent {
 
   componentDidMount () {
     attachFullscreenListener(this.onFullScreenChange);
-
-    this._scrollStatusIntoView();
   }
 
   UNSAFE_componentWillReceiveProps (nextProps) {
@@ -487,35 +485,11 @@ class Status extends ImmutablePureComponent {
     this.statusNode = c;
   };
 
-  _scrollStatusIntoView () {
-    const { status, multiColumn } = this.props;
-
-    if (status) {
-      requestIdleCallback(() => {
-        this.statusNode?.scrollIntoView(true);
-
-        // In the single-column interface, `scrollIntoView` will put the post behind the header,
-        // so compensate for that.
-        if (!multiColumn) {
-          const offset = document.querySelector('.column-header__wrapper')?.getBoundingClientRect()?.bottom;
-          if (offset) {
-            const scrollingElement = document.scrollingElement || document.body;
-            scrollingElement.scrollBy(0, -offset);
-          }
-        }
-      });
-    }
-  }
-
   componentDidUpdate (prevProps) {
-    const { status, ancestorsIds, descendantsIds } = this.props;
+    const { status, descendantsIds } = this.props;
 
     const isSameStatus = status && (prevProps.status?.get('id') === status.get('id'));
 
-    if (status && (ancestorsIds.length > prevProps.ancestorsIds.length || !isSameStatus)) {
-      this._scrollStatusIntoView();
-    }
-
     // Only highlight replies after the initial load
     if (prevProps.descendantsIds.length && isSameStatus) {
       const newRepliesIds = difference(descendantsIds, prevProps.descendantsIds);
@@ -619,6 +593,8 @@ class Status extends ImmutablePureComponent {
                   showMedia={this.state.showMedia}
                   onToggleMediaVisibility={this.handleToggleMediaVisibility}
                   pictureInPicture={pictureInPicture}
+                  ancestors={this.props.ancestorsIds.length}
+                  multiColumn={multiColumn}
                 />
 
                 <ActionBar