React warns about memory leak in Search/SelectControl component.

[tomalec]

Describe the bug
Context: I discovered this bug fixing #6061

When the Search component is disconnected/unmounted before options promise is resolved, React throws a warning:

    Warning: Can't perform a React state update on an unmounted component. This is a no-op, but it indicates a memory leak in your application. To fix, cancel all subscriptions and asynchronous tasks in the componentWillUnmount method.
        in SelectControl (created by WithFocusOutside(SelectControl))
        in div (created by WithFocusOutside(SelectControl))
        in WithFocusOutside(SelectControl) (created by WithInstanceId(WithFocusOutside(SelectControl)))
        in WithInstanceId(WithFocusOutside(SelectControl)) (created by WithSpokenMessages(WithInstanceId(WithFocusOutside(SelectControl))))
        in WithSpokenMessages(WithInstanceId(WithFocusOutside(SelectControl))) (created by Search)
        in div (created by Search)
        in Search

That issue probably didn't surface before because the Search component has a single test that creates an instance, and the suite was probably finished before the promise resolves. However, it gets clearly visible, when you add a little bit of delay in the second test:

it( 'returns an object with decoded text', async () => {
	await new Promise( ( resolve ) => setTimeout( resolve, 1000 ) );
	const decodedText = computeSuggestionMatch(

See this commit/branch: https://github.com/woocommerce/woocommerce-admin/compare/bug/6883-Search-mem-leak

To Reproduce
Steps to reproduce the behavior:

1. Stamp <Search type="products" />
2. Type something in it.
3. Remove the component before the options promise is resolved.

Alternatively:

1. Do the change suggested above / checkout branch

git checkout bug/6883-Search-mem-leak
npm run test -- packages/components/src/search/test/index.js

Expected behavior
No warning should be thrown, no memory leak should be indicated.

Screenshots

Desktop (please complete the following information):

• OS: Ubuntu 20.04.2 LTS
• Browser CLI

Smartphone (please complete the following information):
n/a

[joelclimbsthings]

Closing this in preparation for The Merge. Feel free to reopen afterwards in the core repo if it's still an issue.