fix: allow await expressions inside `{#await ...}` argument

.changeset/long-roses-train.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: allow await expressions inside `{#await ...}` argument

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

@@ -1,7 +1,7 @@
 /** @import { BlockStatement, Pattern, Statement } from 'estree' */
 /** @import { AST } from '#compiler' */
 /** @import { ComponentClientTransformState, ComponentContext } from '../types' */
-import { extract_identifiers } from '../../../../utils/ast.js';
+import { extract_identifiers, is_expression_async } from '../../../../utils/ast.js';
 import * as b from '#compiler/builders';
 import { create_derived } from '../utils.js';
 import { get_value } from './shared/declarations.js';
@@ -15,7 +15,11 @@ export function AwaitBlock(node, context) {
 	context.state.template.push_comment();
 
 	// Visit {#await <expression>} first to ensure that scopes are in the correct order
-	const expression = b.thunk(build_expression(context, node.expression, node.metadata.expression));
+	const unthunked = build_expression(context, node.expression, node.metadata.expression);
+	const expression = b.thunk(
+		unthunked,
+		context.state.options.experimental.async && is_expression_async(unthunked)
+	);
 
 	let then_block;
 	let catch_block;