CustomSelectControl: Button description doesn't update correctly when uncontrolled

[mirka]

When in uncontrolled mode, the trigger button of the CustomSelectControl doesn't get its ARIA description updated properly after a selection change.

Steps to reproduce

In the Storybook for CustomSelectControl, add a temporary story to test uncontrolled mode.

export const Uncontrolled = {
	args: {
		...Default.args,
	},
};

In DevTools, see the the accessibility panel for the main combobox button. The button description will not update after changing the selected options.

Proposed solution

In uncontrolled mode, the outer component (CustomSelectControl) doesn't get re-rendered on selection change, so the currentValue is not updated accordingly:

gutenberg/packages/components/src/custom-select-control/index.tsx

Line 208 in f430cd7

{ getDescribedBy( currentValue, describedBy ) }

We might want to subscribe to _CustomSelect store updates via onChange so this part can be re-rendered on store state changes.