fix

Author: Rich-Harris

packages/svelte/src/compiler/phases/3-transform/client/visitors/RegularElement.js

@@ -309,7 +309,7 @@ export function RegularElement(node, context) {
 					attribute.value,
 					context,
 					(value, metadata) =>
-						metadata.has_call
+						metadata.has_call || metadata.has_await
 							? get_expression_id(
 									metadata.has_await ? context.state.async_expressions : context.state.expressions,
 									value

packages/svelte/src/internal/client/reactivity/deriveds.js

@@ -119,7 +119,7 @@ export function async_derived(fn, location) {
 
 	render_effect(() => {
 		if (DEV) from_async_derived = active_effect;
-		promise = fn();
+		promise = Promise.resolve(fn());
 		if (DEV) from_async_derived = null;
 
 		var restore = capture();

packages/svelte/tests/runtime-runes/samples/async-attribute-without-state/_config.js

@@ -0,0 +1,18 @@
+import { flushSync, tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `
+		<p>pending</p>
+	`,
+
+	async test({ assert, target }) {
+		await Promise.resolve();
+		await Promise.resolve();
+		await Promise.resolve();
+		await Promise.resolve();
+		flushSync();
+
+		assert.htmlEqual(target.innerHTML, '<p data-foo="bar">hello</p>');
+	}
+});

packages/svelte/tests/runtime-runes/samples/async-attribute-without-state/main.svelte

@@ -0,0 +1,7 @@
+<svelte:boundary>
+	<p data-foo={await 'bar'}>hello</p>
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>