[MM-64618] ResizeObserver callback fires after component unmount during channel switching (#32668)

webapp/channels/package.json

@@ -188,11 +188,11 @@
     "build": "cross-env NODE_ENV=production webpack",
     "run": "webpack --progress --watch",
     "dev-server": "webpack serve --mode development",
-    "test": "cross-env TZ=Etc/UTC jest",
+    "test": "cross-env TZ=Etc/UTC LC_ALL=en_US.UTF-8 LANG=en_US.UTF-8 jest",
-    "test:watch": "cross-env TZ=Etc/UTC jest --watch",
+    "test:watch": "cross-env TZ=Etc/UTC LC_ALL=en_US.UTF-8 LANG=en_US.UTF-8 jest --watch",
-    "test:updatesnapshot": "cross-env TZ=Etc/UTC jest --updateSnapshot",
+    "test:updatesnapshot": "cross-env TZ=Etc/UTC LC_ALL=en_US.UTF-8 LANG=en_US.UTF-8 jest --updateSnapshot",
-    "test:debug": "cross-env TZ=Etc/UTC jest --forceExit --detectOpenHandles --verbose",
+    "test:debug": "cross-env TZ=Etc/UTC LC_ALL=en_US.UTF-8 LANG=en_US.UTF-8 jest --forceExit --detectOpenHandles --verbose",
-    "test-ci": "cross-env TZ=Etc/UTC jest --ci --maxWorkers=100% --coverage",
+    "test-ci": "cross-env TZ=Etc/UTC LC_ALL=en_US.UTF-8 LANG=en_US.UTF-8 jest --ci --maxWorkers=100% --coverage",
     "clean": "rm -rf dist node_modules .eslintcache .stylelintcache tsconfig.tsbuildinfo",
     "stats": "cross-env NODE_ENV=production webpack --profile --json > webpack_stats.json",
     "mmjstool": "mmjstool",

webapp/channels/src/components/dynamic_virtualized_list/index.jsx

@@ -7,7 +7,7 @@
 import memoizeOne from 'memoize-one';
 import {createElement, PureComponent} from 'react';
 
-import ListItem from './item_row_shared';
+import ListItem from './list_item';
 
 const atBottomMargin = 10;
 

webapp/channels/src/components/dynamic_virtualized_list/list_item.test.tsx

@@ -0,0 +1,97 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+import {render, screen} from '@testing-library/react';
+import React from 'react';
+
+jest.mock('./list_item_size_observer', () => {
+    const mockObserve = jest.fn(() => jest.fn());
+    const mockUnobserve = jest.fn();
+
+    return {
+        ListItemSizeObserver: {
+            getInstance: jest.fn(() => ({
+                observe: mockObserve,
+                unobserve: mockUnobserve,
+            })),
+        },
+    };
+});
+
+jest.mock('lodash/debounce', () => {
+    return jest.fn((fn) => {
+        const debouncedFn = (...args: any[]) => fn(...args);
+        debouncedFn.cancel = jest.fn();
+        debouncedFn.flush = jest.fn();
+        return debouncedFn;
+    });
+});
+
+import ListItem from './list_item';
+
+describe('ListItem', () => {
+    const defaultProps = {
+        item: <div data-testid='test-item'>{'Test Item Content'}</div>,
+        itemId: 'test-item-1',
+        index: 0,
+        height: 100,
+        width: 300,
+        onHeightChange: jest.fn(),
+        onUnmount: jest.fn(),
+    };
+
+    beforeEach(() => {
+        jest.clearAllMocks();
+    });
+
+    test('renders the item content correctly', () => {
+        render(<ListItem {...defaultProps}/>);
+
+        expect(screen.getByTestId('test-item')).toBeInTheDocument();
+        expect(screen.getByText('Test Item Content')).toBeInTheDocument();
+    });
+
+    test('applies correct attributes to the wrapper div', () => {
+        render(<ListItem {...defaultProps}/>);
+
+        const wrapper = screen.getByRole('listitem');
+        expect(wrapper).toHaveClass('item_measurer');
+        expect(wrapper).toHaveAttribute('role', 'listitem');
+    });
+
+    test('calls onHeightChange on mount with initial height', () => {
+        const mockOnHeightChange = jest.fn();
+
+        Object.defineProperty(HTMLElement.prototype, 'offsetHeight', {
+            configurable: true,
+            value: 120,
+        });
+
+        render(
+            <ListItem
+                {...defaultProps}
+                onHeightChange={mockOnHeightChange}
+            />,
+        );
+
+        expect(mockOnHeightChange).toHaveBeenCalledWith('test-item-1', 120, false);
+    });
+
+    test('handles zero offsetHeight gracefully', () => {
+        const mockOnHeightChange = jest.fn();
+
+        Object.defineProperty(HTMLElement.prototype, 'offsetHeight', {
+            configurable: true,
+            value: 0,
+        });
+
+        render(
+            <ListItem
+                {...defaultProps}
+                onHeightChange={mockOnHeightChange}
+            />,
+        );
+
+        expect(mockOnHeightChange).toHaveBeenCalledWith('test-item-1', 0, false);
+    });
+});

webapp/channels/src/components/dynamic_virtualized_list/list_item.tsx

@@ -5,7 +5,7 @@ import debounce from 'lodash/debounce';
 import type {ReactNode} from 'react';
 import React, {memo, useEffect, useRef} from 'react';
 
-import {ListItemSizeObserver} from './item_row_size_observer';
+import {ListItemSizeObserver} from './list_item_size_observer';
 
 const RESIZE_DEBOUNCE_TIME = 200; // in ms
 
@@ -50,9 +50,15 @@ const ListItem = (props: Props) => {
     // This effects adds the observer which calls height change callback debounced
     useEffect(() => {
         const debouncedOnHeightChange = debounce((changedHeight: number) => {
+            // Check if component is still mounted as it may have been
+            // unmounted by the time the debounced function is called
+            if (!rowRef.current) {
+                return;
+            }
+
             // If width of container has changed then scroll bar position will be out of sync
             // so we need to force a scroll correction
-            const forceScrollCorrection = rowRef.current?.offsetWidth !== widthRef.current;
+            const forceScrollCorrection = rowRef.current.offsetWidth !== widthRef.current;
 
             heightRef.current = changedHeight;
 
@@ -76,11 +82,10 @@ const ListItem = (props: Props) => {
             cleanupSizeObserver = listItemSizeObserver.observe(props.itemId, rowRef.current, itemRowSizeObserverCallback);
         }
 
-        // We remove the observer here from a row
         return () => {
-            if (cleanupSizeObserver) {
+            // We remove the observer here from a row
-                cleanupSizeObserver();
+            cleanupSizeObserver?.();
-            }
+            debouncedOnHeightChange?.cancel();
             props.onUnmount(props.itemId, indexRef.current);
         };
     }, [props.itemId]);