$$slots is always empty in custom element

[half2me]

When I enable the customElement: true option to create a web component, $$slots always returns {} instead of the slots being used.

Example:

<svelte:options tag="my-wc"/>

<script>
$: console.log($$slots);
</script>

<slot name="foo"></slot>

<my-wc>
  <span slot="foo">Foobar</span>
</my-wc>

Svelte v3.29.4 using Rollup

Severity
Mostly annoying, I can work around it.

[Conduitry]

This should be fixed now in 3.29.5..