Slot fallback content shown when rehydrating

[dxlbnl]

The example shows the bug: https://v3.svelte.technology/repl?version=3.0.0-beta.22&example=slot-fallbacks

edit:
So the issue is icw rehydration, where textcontent nodes in a slot are rendered before the content supplied through slot

I'm not sure how to reproduce this in a REPL env.

[athif23]

I think it's because you have two <Box> there.

<Box>
	<h2>Hello!</h2>
	<p>This is a box. It can contain anything.</p>
</Box>

<Box/> <--- This is a second Box without content in it, so it should show the fallback, right?

[dxlbnl]

Yes, you're right, I found that out when trying to find where the "bug" was introduced.
The issue is with sapper, rehydration, and textContent nodes.
So the SSR'ed content is good, but when rehydrating it also renders the fallback content.

[btakita]

I was able to reproduce the issue at https://github.com/btakita/svelte-slot-default-issue

It's an issue when there is a Text DOM node around or within the slot during rehydration. No Text DOM node, no problem.

See #2394