$derived(await ...) is a symbol

[dylan1951]

Describe the bug

Since 5.43.0, sometimes the value of a $derived(await ...) is unexpectedly a symbol which can cause errors.

Reproduction

REPL

<script>
    let foo = $state(null);

    $effect(() => {
        foo = 69;
    });

    let bar = $derived(await 1);

    let baz = $derived(foo ? foo * bar : null);

    const qux = "qux";
</script>

<p>baz: {baz}</p>

<svelte:boundary>
    {#snippet pending()}
        <p>Loading...</p>
    {/snippet}

    {#if qux}
        <p></p>
    {/if}
</svelte:boundary>

Logs

Unhandled Promise Rejection: TypeError: Cannot convert a symbol to a number

	in <unknown>
	in __wrapper.svelte



TypeError
@
update_reaction@
execute_derived@
update_derived@
is_dirty@
flush_queued_effects@
process@
flush_effects@
flush@
revive@
decrement@
@
@[native code]

System Info

Svelte playground

Severity

blocking an upgrade