[selectlist] Add showPicker() method to <selectlist>

[lukewarlow]

All input elements with some concept of a picker have a showPicker function that opens that UI. Adding this to <select> was marked as future work in whatwg/html#7319. However, a subsequent request for this behaviour was raised in whatwg/html#7957.

It would seem like a relatively simple addition to <selectlist> and I imagine there's more use cases for it like the above issue.

It's worth noting that while showPicker() doesn't exist for <select>s it does work for inputs with a datalist attached (inside of Chrome other browser may vary).

[josepharhar]

I am tentatively supportive. I was just writing some reftests and I had to do interesting things to get the listbox open, and I was disappointed to find that something like this didn't already exist

[mfreed7]

Adding Agenda+ per the request at today's OpenUI meeting.

I'm supportive of adding showPicker() to HTMLSelectListElement.

[css-meeting-bot]

The Open UI Community Group just discussed [selectlist] Add `showPicker()` method to `<selectlist>` , and agreed to the following:

• RESOLVED: Add showPicker to selectlist matching existing input conventions, other methods can be added across the board in future if need be.

The full IRC log of that discussion

<hdv> Luke_W_: I noticed WHATWG added showPicker to input elemenets and it was deferred to the future for being added to select
<hdv> Luke_W_: so I could see it would make sense for it to be added to selectlist too
<masonf> +1
<una> q+
<gregwhitworth> ack una
<hdv> una: sounds good to me… is there a toggle method also? or just show?
<hdv> masonf: open question we haven't talked about, I think, for selectlist. We do have it for popover
<hdv> una: it looks like from the issue that there is future work for closePicker
<masonf> q?
<gregwhitworth> q+
<hdv> Luke_W_: sounds like worth adding as well
<masonf> q+
<gregwhitworth> ack masonf
<hdv> masonf: I remember the convo, but not sure if there was a reason it wasn't added to select before?
<hdv> Luke_W_: there didn't seem to be solid reason for adding… 
<hdv> s/adding/not adding
<hdv> gregwhitworth: feels like we should do it in totality
<hdv> gregwhitworth: would like to see the marriage between popover and this idea for selectlist to work out, like similar states and stuff
<gregwhitworth> we're on google meet as jitsi is down
<hdv> masonf: showPicker was added relatively recently… a complaint about it was that not all browsers had pickers for all the elements, like some browsers didn't have a picker for datepicker
<gregwhitworth> link is in discord telecon channel
<jarhar> q+
<hdv> masonf: so being able to find out if a picker was shown was regarded as something the platform probably shouldn't be revealing
<gregwhitworth> ack gregwhitworth
<gregwhitworth> ack jarhar
<hdv> masonf: though that conversation probably doesn't apply to select or selectlist as they always have pickers by definition
<hdv> jarhar: seems like we want to have showPicker, togglePicker and closePicker
<masonf> q?
<masonf> q+
<hdv> jarhar: I think we should certainly add showPicker and possibly closePicker as well.
<gregwhitworth> ack masonf
<brecht_dr> +1
<hdv> jarhar: and follow conventions
<hdv> masonf: +1 to what you just said… selectlist should follow convention of all the other things that support showPicker
<una> +1 to masonf
<Luke_W_> proposed resolution: Add showPicker to selectlist matching existing input conventions, other methods can be added across the board in future if need be.
<masonf> +1
<Luke_W_> RESOLVED: Add showPicker to selectlist matching existing input conventions, other methods can be added across the board in future if need be.
<hdv> +1