[Webkit-unassigned] [Bug 209975] New: AX: combobox aria-activedescendant is not read in VoiceOver unless the listbox has `display: none` until input has focus

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=209975

            Bug ID: 209975
           Summary: AX: combobox aria-activedescendant is not read in
                    VoiceOver unless the listbox has `display: none` until
                    input has focus
           Product: WebKit
           Version: Safari 12
          Hardware: Macintosh
                OS: macOS 10.14
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Accessibility
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: account at cmurphy.me
                CC: webkit-bug-importer at group.apple.com

Created attachment 395394

  --> https://bugs.webkit.org/attachment.cgi?id=395394&action=review

Sample HTML to reproduce the issue

For a combobox that contains an input and owns a listbox (following this pattern: https://www.w3.org/TR/wai-aria-practices/examples/combobox/aria1.1pattern/listbox-combo.html):

If the listbox does not start out with `display: none` at the time the input receives focus, then VoiceOver does not announce the active option as the input's `aria-activedescendant` gets updated. However, if the listbox starts with `display: none` and dynamically changes to `display: block` some time after the input receives focus, VoiceOver will announce the active option correctly.

Steps to reproduce, using attached sample HTML:

1. Focus the input field
2. Press ArrowDown to set `aria-activedescendant` to the IDs of one of the options

EXPECTED: VoiceOver should announce the active options as user arrows through them
ACTUAL: VoiceOver does not announce anything


However, if the `display: none` property for the .hidden class is uncommented so that the listbox is initially `display: none`, the same steps listed above will cause VoiceOver to read the options while arrowing through.

Also tested Chrome (Version 80.0.3987.122) and Firefox (76.0a1), where VoiceOver does correctly announce the options even when the listbox never has `display: none`

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