Accessibility issue in "Forms → Autocomplete" (missing roles)

[roelvangils]

Describe the bug

The dropdown looks and behaves like a list box (visually) but some roles are missing. In accordance with WCAG 2.1, this does not satisfy 1.3.1 Info and Relationships. In its current implementation, the list box is not usable by users of AT.

Note: this issue is blocking.

How to fix

Apply at least these attributes:

• List items need role="option"
• Turn the <ul> into a listbox with role="listbox"

Additional information

• See ARIA: listbox role - Accessibility | MDN for more information.
• Listbox Example with Grouped Options | WAI-ARIA Authoring Practices 1.2