fix(ui-a11y-utils): fix focus region missing mouse down target

[czeslaaw]

We noticed a weird issue where sometimes a Modal got closed unexpectedly when we clicked on any Button.

Minimal code to reproduce:

import { Button } from '@instructure/ui-buttons';
import { Modal } from '@instructure/ui-modal';
import { SimpleSelect } from '@instructure/ui-simple-select';
import React from 'react';

export const App: React.FC = () => {
	const [modalOpen, setModalOpen] = React.useState(false);

	return (
		<>
			<Button onClick={() => setModalOpen(true)}>Open modal</Button>
			<Modal open={modalOpen} onDismiss={() => setModalOpen(false)} label="Modal">
				<div style={{ display: 'flex', gap: '20px' }}>
					<SimpleSelect renderLabel="Use only keyboard to open this select">
						<SimpleSelect.Option id="foo" value="foo">
							Foo
						</SimpleSelect.Option>
						<SimpleSelect.Option id="bar" value="bar">
							Bar
						</SimpleSelect.Option>
						<SimpleSelect.Option id="baz" value="baz">
							Baz
						</SimpleSelect.Option>
					</SimpleSelect>
					<Button>Click by mouse when select is open</Button>
				</div>
			</Modal>
		</>
	);
};

Steps to reproduce

• Open modal
• Open select dropdown using only keyboard, do not interact with anything else
• Click on button inside modal while select is still open
• Modal is closed when it shouldn't be

Root cause

Between a mousedown and click event we change the active FocusRegion from select dropdown to modal. The mousedown event is captured in FocusRegion belonging to select and click is captured in FocusRegion belonging to modal. That means in modal FocusRegion captureDocumentMousedown is never fired and _contextContainsTarget defaults to false. This triggers a dismiss event even though we clicked on a button within FocusRegion.

[balzss]

hi @czeslaaw, thanks for the report and PR! I'll check out your example for the bug and also look into your solution. This part of the code had caused many headaches previously and we had quite a few fixes that introduced regressions with other issues so I want to be very thorough with it.