Calling `showPopover` during popover show causes infinite recursion

[jakearchibald]

What is the issue with the HTML Standard?

https://random-stuff.jakearchibald.com/bug-repros/nested-showpopover/

If showPopover called on popoverA during the beforetoggle of popoverA, you get recursion until max-stack-size.

It seems like one of the following should happen:

• It should throw (without recursion)
• It should show the popover without firing beforetoggle, and the outer showPopover call should early-return since the popover is now shown (which might just happen due to "check popover validity".

Thoughts @mfreed7 @keithamus @lukewarlow @bramus? (the popover posse)

[lukewarlow]

Yeah we should avoid infinite loops, the same issue is guarded against for requestClose on dialogs.

We could have a flag on the popover to say it's showing and then early return if that's already set. And vice versa if there's a hidePopover equivalent.

[keithamus]

In terms of implementation - one thing to watch out for is that removing the popover attribute would clear the popoverdata slot. So we should add a test for .addEventListener('beforetoggle', e => e.target.showPopover()) but also .addEventListener('beforetoggle', e => { e.target.removeAttribute('popover'); e.target.setAttribute('popover', ''); e.showPopover() }).