Composite: make items tabbable if active element gets removed

packages/components/CHANGELOG.md

@@ -9,6 +9,7 @@
 -   `ToggleGroupControl`: Fix arrow key navigation in RTL ([#65735](https://github.com/WordPress/gutenberg/pull/65735)).
 -   `ToggleGroupControl`: indicator doesn't jump around when the layout around it changes ([#65175](https://github.com/WordPress/gutenberg/pull/65175)).
 -   `Composite`: fix legacy support for the store prop ([#65821](https://github.com/WordPress/gutenberg/pull/65821)).
+-   `Composite`: make items tabbable if active element gets removed ([#65720](https://github.com/WordPress/gutenberg/pull/65720)).
 
 ### Deprecations
 

packages/components/src/composite/item.tsx

@@ -26,5 +26,23 @@ export const CompositeItem = forwardRef<
 	// obfuscated to discourage its use outside of the component's internals.
 	const store = ( props.store ?? context.store ) as Ariakit.CompositeStore;
 
-	return <Ariakit.CompositeItem store={ store } { ...props } ref={ ref } />;
+	// If the active item is not connected, Composite may end up in a state
+	// where none of the items are tabbable. In this case, we force all items to
+	// be tabbable, so that as soon as an item received focus, it becomes active
+	// and Composite goes back to working as expected.
+	const tabbable = Ariakit.useStoreState( store, ( state ) => {
+		return (
+			state?.activeId !== null &&
+			! store?.item( state?.activeId )?.element?.isConnected
+		);
+	} );
+
+	return (
+		<Ariakit.CompositeItem
+			store={ store }
+			tabbable={ tabbable }
+			{ ...props }
+			ref={ ref }
+		/>
+	);
 } );

packages/components/src/composite/test/index.tsx

@@ -0,0 +1,123 @@
+/**
+ * External dependencies
+ */
+import { queryByAttribute, render, screen } from '@testing-library/react';
+import { click, press, waitFor } from '@ariakit/test';
+import type { ComponentProps } from 'react';
+
+/**
+ * WordPress dependencies
+ */
+import { useState } from '@wordpress/element';
+
+/**
+ * Internal dependencies
+ */
+import { Composite } from '..';
+
+// This is necessary because of how Ariakit calculates page up and
+// page down. Without this, nothing has a height, and so paging up
+// and down doesn't behave as expected in tests.
+
+let clientHeightSpy: jest.SpiedGetter<
+	typeof HTMLElement.prototype.clientHeight
+>;
+
+beforeAll( () => {
+	clientHeightSpy = jest
+		.spyOn( HTMLElement.prototype, 'clientHeight', 'get' )
+		.mockImplementation( function getClientHeight( this: HTMLElement ) {
+			if ( this.tagName === 'BODY' ) {
+				return window.outerHeight;
+			}
+			return 50;
+		} );
+} );
+
+afterAll( () => {
+	clientHeightSpy?.mockRestore();
+} );
+
+async function renderAndValidate( ...args: Parameters< typeof render > ) {
+	const view = render( ...args );
+	await waitFor( () => {
+		const activeButton = queryByAttribute(
+			'data-active-item',
+			view.baseElement,
+			'true'
+		);
+		expect( activeButton ).not.toBeNull();
+	} );
+	return view;
+}
+
+function RemoveItemTest( props: ComponentProps< typeof Composite > ) {
+	const [ showThirdItem, setShowThirdItem ] = useState( true );
+	return (
+		<>
+			<button>Focus trap before composite</button>
+			<Composite { ...props }>
+				<Composite.Item>Item 1</Composite.Item>
+				<Composite.Item>Item 2</Composite.Item>
+				{ showThirdItem && <Composite.Item>Item 3</Composite.Item> }
+			</Composite>
+			<button onClick={ () => setShowThirdItem( ( value ) => ! value ) }>
+				Toggle third item
+			</button>
+		</>
+	);
+}
+
+describe( 'Composite', () => {
+	it( 'should remain focusable even when there are no elements in the DOM associated with the currently active ID', async () => {
+		await renderAndValidate( <RemoveItemTest /> );
+
+		const toggleButton = screen.getByRole( 'button', {
+			name: 'Toggle third item',
+		} );
+
+		await press.Tab();
+		await press.Tab();
+
+		expect(
+			screen.getByRole( 'button', { name: 'Item 1' } )
+		).toHaveFocus();
+
+		await press.ArrowRight();
+		await press.ArrowRight();
+
+		expect(
+			screen.getByRole( 'button', { name: 'Item 3' } )
+		).toHaveFocus();
+
+		await click( toggleButton );
+
+		expect(
+			screen.queryByRole( 'button', { name: 'Item 3' } )
+		).not.toBeInTheDocument();
+
+		await press.ShiftTab();
+
+		expect(
+			screen.getByRole( 'button', { name: 'Item 2' } )
+		).toHaveFocus();
+
+		await click( toggleButton );
+
+		expect(
+			screen.getByRole( 'button', { name: 'Item 3' } )
+		).toBeVisible();
+
+		await press.ShiftTab();
+
+		expect(
+			screen.getByRole( 'button', { name: 'Item 2' } )
+		).toHaveFocus();
+
+		await press.ArrowRight();
+
+		expect(
+			screen.getByRole( 'button', { name: 'Item 3' } )
+		).toHaveFocus();
+	} );
+} );