Svelte 5: Can't set default snippet props

[Not-Jayden]

Describe the bug

A method that was working previously to ensure a snippet prop function will always be defined was by setting the snippet prop with a default snippet defined inside the current component.

i.e.

<script>
	let {children = fallback} = $props();
</script>

{#snippet fallback()}
	Fallback
{/snippet}

<button>
	{@render children()}
</button>

This seems to have stopped working though, potentially with the changes in #9759

Can still conditionally check the children prop is defined as a workaround for setting a fallback, but I do personally prefer being able to default it, given fallback and children should exist in the same scope anyway.

Reproduction

REPL

Logs

Error: `Cannot access 'fallback' before initialization`

System Info

Svelte REPL

Severity

annoyance

[dummdidumm]

Possible solution: unshift the snippet instead of pushing it to the init array, that way it comes first

[PP-Tom]

I would personally do:

<script>
	let { children } = $props();
</script>

<button>
	{#if children}
		{@render children()}
	{:else}
		Fallback
	{/if}
</button>

Would this not work for you?

[Not-Jayden]

I would personally do:

<script>
	let { children } = $props();
</script>

<button>
	{#if children}
		{@render children()}
	{:else}
		Fallback
	{/if}
</button>

Would this not work for you?

Works fine, I already mentioned that as an alternative in the description. Just reporting a regression of functionality that worked previously.