fix: skip static optimisation for stateless deriveds after await (#17389)

Author: Rich-Harris

.changeset/deep-pears-juggle.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: skip static optimisation for stateless deriveds after `await`

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

@@ -336,7 +336,9 @@ export function RegularElement(node, context) {
 		trimmed.every(
 			(node) =>
 				node.type === 'Text' ||
-				(!node.metadata.expression.has_state && !node.metadata.expression.has_await)
+				(!node.metadata.expression.has_state &&
+					!node.metadata.expression.has_await &&
+					!node.metadata.expression.has_blockers())
 		) &&
 		trimmed.some((node) => node.type === 'ExpressionTag');
 

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

@@ -134,7 +134,7 @@ export function build_template_chunk(
 
 			const evaluated = state.scope.evaluate(value);
 
-			has_await ||= node.metadata.expression.has_await;
+			has_await ||= node.metadata.expression.has_await || node.metadata.expression.has_blockers();
 			has_state ||= has_await || (node.metadata.expression.has_state && !evaluated.is_known);
 
 			if (values.length === 1) {

packages/svelte/tests/runtime-runes/samples/async-static-derived-after-await/_config.js

@@ -0,0 +1,9 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		await tick();
+		assert.htmlEqual(target.innerHTML, `<p>hello</p>`);
+	}
+});

packages/svelte/tests/runtime-runes/samples/async-static-derived-after-await/main.svelte

@@ -0,0 +1,6 @@
+<script>
+	await 0;
+	let message = $derived('hello');
+</script>
+
+<p>{message}</p>