[bug][docs]: `<rh-alert>` DSD & Hydration + hasSlotted

[zeroedin]

There is an issue when <rh-alert> and most likely any element that relies on SlotController and the hasSlotted method to tell if the component if something has been slotted and then DSD'ing that element.

IIRC The server doesn't have the ability to understand if something has been slotted or not and will have to be hydrated up to that point (Maybe CLS here). However upon load on the client this hydration also doesn't seem to happening correctly currently.

We can recreate this here (although demo is currently broken in other ways too) https://ux.redhat.com/elements/alert/demo/

• First note the lack of 16px spacer between the body text and the footer action buttons.
• Then remove the buttons from the html by editing the <rh-alert> in inspector in Chrome:
• Delete slotted buttons (Copy the HTML first):
• Save element by clicking outside of the edit textarea, the element should update with no slotted buttons
• Edit the component again and paste the copied HTML for the buttons back in and save
• You should see the 16px spacer now and the shadowroot footer class="hasActions"

[bennypowers]

Lit SSR cannot read children. Dsd templates have to be able to stream. In eleventy we don't have that limitation, but nonetheless LitLabs ssr can't do it atm. We could investigate alternatives like https://indieweb.social/@deebloo/113113826701184888

The best we can do with the current crop of tools is set props, either as attributes, or in the node process as properties on the litelememt objects, but AFAIK eleventy-plugin-lit doesn't support that.

A has-slotted="a,b,c" attribute on the host is something we could investigate building into slotcontroller.

[bennypowers]

https://github.com/patternfly/patternfly-elements/pull/2845