feat(VirtualSelectList): add virtualized list for Select/Menu dropdowns

Add VirtualSelectList, a virtualized replacement for PatternFly's
SelectList that renders only visible items in a scrollable dropdown.
This enables Select menus with thousands of options without DOM
performance degradation.

Motivation: In OpenShift Console (openshift/console#16252), the Search
page Resources dropdown has 1000+ items. Even after algorithmic
optimizations, PatternFly's Select refCallback forced reflow on 100+
DOM nodes takes ~566ms. VirtualSelectList reduces INP from 270ms
("needs improvement") to 107ms ("good") by rendering only ~10-20
visible items.

Changes:
- VirtualGrid: add innerScrollContainerClassName prop so non-table
  consumers can override the hardcoded pf-v6-c-table__tbody class
- VirtualSelectList: new component wrapping VirtualGrid for menu/list
  semantics (ul[role=listbox]), with keyboard navigation and a11y
- Documentation: basic, typeahead, and multi-select examples
- Tests: 14 unit tests covering rendering, ARIA, keyboard nav

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: stefanonardo

packages/module/patternfly-docs/content/examples/VirtualSelectList.md

@@ -0,0 +1,40 @@
+---
+id: Virtual select list
+section: extensions
+source: react
+sourceLink: https://github.com/patternfly/react-virtualized-extension
+propComponents: ['VirtualSelectList']
+---
+
+Note: React Virtualized Extension lives in its own package at [`@patternfly/react-virtualized-extension`](https://www.npmjs.com/package/@patternfly/react-virtualized-extension)!
+
+import { VirtualSelectList } from '@patternfly/react-virtualized-extension';
+import { Select, SelectOption, MenuToggle, TextInputGroup, TextInputGroupMain, TextInputGroupUtilities, Button, Badge } from '@patternfly/react-core';
+import TimesIcon from '@patternfly/react-icons/dist/esm/icons/times-icon';
+import { useState, useMemo, useRef } from 'react';
+
+## About
+
+VirtualSelectList is a virtualized replacement for PatternFly's SelectList component. It renders only the visible items in a scrollable dropdown, enabling Select menus with thousands of options without DOM performance degradation.
+
+Use VirtualSelectList as a drop-in replacement for `<SelectList>` inside a composable `<Select>`. The `itemRenderer` callback receives positioning styles that must be applied to each rendered `<SelectOption>`.
+
+## Examples
+
+### Basic
+
+```js file="./VirtualSelectListBasic.tsx"
+
+```
+
+### Typeahead with filtering
+
+```js file="./VirtualSelectListTypeahead.tsx"
+
+```
+
+### Multi-select
+
+```js file="./VirtualSelectListMulti.tsx"
+
+```

packages/module/patternfly-docs/content/examples/VirtualSelectListBasic.tsx

@@ -0,0 +1,52 @@
+import { useState, FunctionComponent } from 'react';
+import { Select, SelectOption, MenuToggle, MenuToggleElement } from '@patternfly/react-core';
+import { VirtualSelectList } from '@patternfly/react-virtualized-extension';
+
+export const VirtualSelectListBasicExample: FunctionComponent = () => {
+  const [isOpen, setIsOpen] = useState(false);
+  const [selected, setSelected] = useState<string>();
+
+  const items: string[] = [];
+  for (let i = 0; i < 10000; i++) {
+    items.push(`Option ${i}`);
+  }
+
+  const onSelect = (_event: React.MouseEvent<Element, MouseEvent> | undefined, value: string | number | undefined) => {
+    setSelected(value as string);
+    setIsOpen(false);
+  };
+
+  const toggle = (toggleRef: React.Ref<MenuToggleElement>) => (
+    <MenuToggle
+      ref={toggleRef}
+      onClick={() => setIsOpen((prev) => !prev)}
+      isExpanded={isOpen}
+      style={{ width: '200px' } as React.CSSProperties}
+    >
+      {selected || 'Select an option'}
+    </MenuToggle>
+  );
+
+  return (
+    <Select
+      isOpen={isOpen}
+      selected={selected}
+      onSelect={onSelect}
+      onOpenChange={setIsOpen}
+      toggle={toggle}
+      isScrollable
+    >
+      <VirtualSelectList
+        rowCount={items.length}
+        rowHeight={36}
+        maxHeight={300}
+        aria-label="Basic virtualized select"
+        rowRenderer={({ index, style, key }) => (
+          <SelectOption key={key} style={style} value={items[index]} isSelected={selected === items[index]}>
+            {items[index]}
+          </SelectOption>
+        )}
+      />
+    </Select>
+  );
+};

packages/module/patternfly-docs/content/examples/VirtualSelectListMulti.tsx

@@ -0,0 +1,76 @@
+import { useState, FunctionComponent } from 'react';
+import {
+  Select,
+  SelectOption,
+  MenuToggle,
+  MenuToggleElement,
+  Badge
+} from '@patternfly/react-core';
+import { VirtualSelectList } from '@patternfly/react-virtualized-extension';
+
+export const VirtualSelectListMultiExample: FunctionComponent = () => {
+  const [isOpen, setIsOpen] = useState(false);
+  const [selectedItems, setSelectedItems] = useState<string[]>([]);
+
+  const items: string[] = [];
+  for (let i = 0; i < 1000; i++) {
+    items.push(`Option ${i}`);
+  }
+
+  const onSelect = (_event: React.MouseEvent<Element, MouseEvent> | undefined, value: string | number | undefined) => {
+    const val = value as string;
+    setSelectedItems((prev) =>
+      prev.includes(val) ? prev.filter((item) => item !== val) : [...prev, val]
+    );
+  };
+
+  const toggle = (toggleRef: React.Ref<MenuToggleElement>) => (
+    <MenuToggle
+      ref={toggleRef}
+      onClick={() => setIsOpen((prev) => !prev)}
+      isExpanded={isOpen}
+      style={{ width: '300px' } as React.CSSProperties}
+    >
+      {selectedItems.length > 0 ? (
+        <>
+          {selectedItems.length} selected
+          <Badge isRead className="pf-v6-u-ml-sm">
+            {selectedItems.length}
+          </Badge>
+        </>
+      ) : (
+        'Select options'
+      )}
+    </MenuToggle>
+  );
+
+  return (
+    <Select
+      isOpen={isOpen}
+      selected={selectedItems}
+      onSelect={onSelect}
+      onOpenChange={setIsOpen}
+      toggle={toggle}
+      isScrollable
+    >
+      <VirtualSelectList
+        rowCount={items.length}
+        rowHeight={36}
+        maxHeight={300}
+        isAriaMultiselectable
+        aria-label="Multi-select virtualized list"
+        rowRenderer={({ index, style, key }) => (
+          <SelectOption
+            key={key}
+            style={style}
+            value={items[index]}
+            hasCheckbox
+            isSelected={selectedItems.includes(items[index])}
+          >
+            {items[index]}
+          </SelectOption>
+        )}
+      />
+    </Select>
+  );
+};

packages/module/patternfly-docs/content/examples/VirtualSelectListTypeahead.tsx

@@ -0,0 +1,114 @@
+import { useState, useMemo, useRef, FunctionComponent } from 'react';
+import {
+  Select,
+  SelectOption,
+  MenuToggle,
+  MenuToggleElement,
+  TextInputGroup,
+  TextInputGroupMain,
+  TextInputGroupUtilities,
+  Button
+} from '@patternfly/react-core';
+import TimesIcon from '@patternfly/react-icons/dist/esm/icons/times-icon';
+import { VirtualSelectList, VirtualSelectListRef } from '@patternfly/react-virtualized-extension';
+
+const allItems: string[] = [];
+for (let i = 0; i < 10000; i++) {
+  allItems.push(`Option ${i}`);
+}
+
+export const VirtualSelectListTypeaheadExample: FunctionComponent = () => {
+  const [isOpen, setIsOpen] = useState(false);
+  const [selected, setSelected] = useState<string>();
+  const [filterValue, setFilterValue] = useState('');
+  const listRef = useRef<VirtualSelectListRef>(null);
+
+  const filteredItems = useMemo(
+    () =>
+      filterValue
+        ? allItems.filter((item) => item.toLowerCase().includes(filterValue.toLowerCase()))
+        : allItems,
+    [filterValue]
+  );
+
+  const onSelect = (_event: React.MouseEvent<Element, MouseEvent> | undefined, value: string | number | undefined) => {
+    setSelected(value as string);
+    setFilterValue('');
+    setIsOpen(false);
+  };
+
+  const onInputChange = (_event: React.FormEvent<HTMLInputElement>, value: string) => {
+    setFilterValue(value);
+    if (!isOpen) {
+      setIsOpen(true);
+    }
+  };
+
+  const toggle = (toggleRef: React.Ref<MenuToggleElement>) => (
+    <MenuToggle
+      ref={toggleRef}
+      variant="typeahead"
+      onClick={() => setIsOpen((prev) => !prev)}
+      isExpanded={isOpen}
+      isFullWidth
+    >
+      <TextInputGroup isPlain>
+        <TextInputGroupMain
+          value={filterValue || selected || ''}
+          onClick={() => setIsOpen(true)}
+          onChange={onInputChange}
+          autoComplete="off"
+          placeholder="Search from 10,000 options..."
+        />
+        {(filterValue || selected) && (
+          <TextInputGroupUtilities>
+            <Button
+              variant="plain"
+              onClick={() => {
+                setSelected(undefined);
+                setFilterValue('');
+              }}
+              aria-label="Clear input"
+            >
+              <TimesIcon />
+            </Button>
+          </TextInputGroupUtilities>
+        )}
+      </TextInputGroup>
+    </MenuToggle>
+  );
+
+  return (
+    <Select
+      isOpen={isOpen}
+      selected={selected}
+      onSelect={onSelect}
+      onOpenChange={(open) => {
+        setIsOpen(open);
+        if (!open) {
+          setFilterValue('');
+        }
+      }}
+      toggle={toggle}
+      isScrollable
+    >
+      <VirtualSelectList
+        ref={listRef}
+        rowCount={filteredItems.length}
+        rowHeight={36}
+        maxHeight={300}
+        aria-label="Typeahead virtualized select"
+        noRowsRenderer={() => (
+          <li className="pf-v6-c-menu__list-item pf-m-disabled" role="option" aria-disabled="true">
+            No results found for &quot;{filterValue}&quot;
+          </li>
+        )}
+        rowRenderer={({ index, style, key }) => (
+          <SelectOption key={key} style={style} value={filteredItems[index]} isSelected={selected === filteredItems[index]}>
+            {filteredItems[index]}
+          </SelectOption>
+        )}
+      />
+    </Select>
+  );
+};

packages/module/src/components/Virtualized/VirtualGrid.ts

@@ -239,6 +239,11 @@ export interface VirtualGridProps {
 
   /** Inner Scroll Container element to render */
   innerScrollContainerComponent?: string | ComponentType<any>;
+
+  /** Optional custom CSS class name for the inner scroll container.
+   *  Defaults to 'pf-v6-c-table__tbody' for backward compatibility with table-based usage.
+   */
+  innerScrollContainerClassName?: string;
 }
 
 interface InstanceProps {
@@ -920,7 +925,8 @@ export class VirtualGrid extends Component<VirtualGridProps, VirtualGridState> {
       tabIndex,
       width,
       scrollContainerComponent,
-      innerScrollContainerComponent
+      innerScrollContainerComponent,
+      innerScrollContainerClassName
     } = this.props;
     const { instanceProps, needToResetStyleCache } = this.state;
 
@@ -1008,7 +1014,7 @@ export class VirtualGrid extends Component<VirtualGridProps, VirtualGridState> {
     let innerScrollContainer = null;
     if (childrenToDisplay.length > 0) {
       const innerScrollContainerProps = {
-        className: 'ReactVirtualized__VirtualGrid__innerScrollContainer pf-v6-c-table__tbody',
+        className: css('ReactVirtualized__VirtualGrid__innerScrollContainer', innerScrollContainerClassName ?? 'pf-v6-c-table__tbody'),
         key: 'ReactVirtualized__VirtualGrid__innerScrollContainer',
         role: containerRole,
         style: {