ComboboxControl improve loading/fetching state.

[adamsilverstein]

Is your feature request related to a problem? Please describe.
The ComboboxControl could be improved by adding a loading/fetching state that indicates the results are being fetched.

In #25442 we enhanced the ComboboxControl component to enable new use cases, including the Post Author selector in #23237 and the Page Parent selector in #25267.

The current experience would be improved with the addition of a loading indicator.

Describe the solution you'd like
When using the ComboboxControl and searching a large number of items, it would be helpful to show some sort of loading or progress indicator such as a spinner.

Two initial ideas that could use some design feedback:

• A spinner showing that results are being fetched. Where does this go, in the right/far end of the field
• Keep the results open during search (greyed out?) - if feels jarring to have the results close and open for each new search. Possibly combine with loading state idea, eg. pulsating boxes during load that fill in with results.

Also, from an accessibility perspective - should anything get announced for "searching"?

Screencast of current behavior in the author select field:

https://share.getcloudapp.com/mXu6E9oz

[paaljoachim]

Hey Adam.

I see the PR has been merged. Which I believe this issue can be closed.

Btw
There has been some reports of people not understanding the new "drop down" as it does not contain the drop down arrows etc. I heard about it earlier today. Issue #27513

[adamsilverstein]

Hey @paaljoachim - thanks for the reminder on this issue.

I see the PR has been merged. Which I believe this issue can be closed.

This is still relevant - it is a follow up to #25267 to add a loading indicator during searches - maybe a spinner for example - the users know something is happening as they type.

There has been some reports of people not understanding the new "drop down" as it does not contain the drop down arrows etc. I heard about it earlier today.

I can see how it could be confusing. For many sites, when there are a small number of users, switching back to the standard HTML select element will help, see #26077.