From 48f2fa22c0c941ac6e550151212845adc628b3de Mon Sep 17 00:00:00 2001
From: ComputerGuy <63362464+Ocean-OS@users.noreply.github.com>
Date: Mon, 28 Jul 2025 12:04:06 -0700
Subject: [PATCH] fix: allow await expressions inside `{#await ...}` argument
 (#16514)

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

* add test

* apply suggestion from review

---------

Co-authored-by: 7nik <kifiranet@gmail.com>
---
 .changeset/long-roses-train.md                |  5 +++
 .../3-transform/client/visitors/AwaitBlock.js |  7 ++-
 .../samples/async-await/_config.js            | 43 +++++++++++++++++++
 .../samples/async-await/main.svelte           | 22 ++++++++++
 4 files changed, 75 insertions(+), 2 deletions(-)
 create mode 100644 .changeset/long-roses-train.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-await/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-await/main.svelte

diff --git a/.changeset/long-roses-train.md b/.changeset/long-roses-train.md
new file mode 100644
index 0000000000..10920ac5c4
--- /dev/null
+++ b/.changeset/long-roses-train.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: allow await expressions inside `{#await ...}` argument
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/AwaitBlock.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/AwaitBlock.js
index c550c8e17b..4246091bcf 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/AwaitBlock.js
+++ b/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 +15,10 @@ 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 expression = b.thunk(
+		build_expression(context, node.expression, node.metadata.expression),
+		node.metadata.expression.has_await
+	);
 
 	let then_block;
 	let catch_block;
diff --git a/packages/svelte/tests/runtime-runes/samples/async-await/_config.js b/packages/svelte/tests/runtime-runes/samples/async-await/_config.js
new file mode 100644
index 0000000000..dda6a7a895
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-await/_config.js
@@ -0,0 +1,43 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		const [reset, one, two, reject] = target.querySelectorAll('button');
+
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			'<button>reset</button><button>one</button><button>two</button><button>reject</button> waiting'
+		);
+
+		one.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			'<button>reset</button><button>one</button><button>two</button><button>reject</button> one_res'
+		);
+
+		reset.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			'<button>reset</button><button>one</button><button>two</button><button>reject</button> waiting'
+		);
+
+		two.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			'<button>reset</button><button>one</button><button>two</button><button>reject</button> two_res'
+		);
+
+		reset.click();
+		reject.click();
+		await tick();
+		assert.htmlEqual(
+			target.innerHTML,
+			'<button>reset</button><button>one</button><button>two</button><button>reject</button> reject_catch'
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-await/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-await/main.svelte
new file mode 100644
index 0000000000..8673e45414
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-await/main.svelte
@@ -0,0 +1,22 @@
+<script>
+	let deferred = $state(Promise.withResolvers());
+</script>
+
+<button onclick={() => deferred = Promise.withResolvers()}>reset</button>
+<button onclick={() => deferred.resolve("one")}>one</button>
+<button onclick={() => deferred.resolve("two")}>two</button>
+<button onclick={() => deferred.reject("reject")}>reject</button>
+
+<svelte:boundary>
+	{#await await deferred.promise + "_res"}
+		waiting
+	{:then res}
+		{res}
+	{:catch err}
+		{err}_catch
+	{/await}
+
+	{#snippet pending()}
+		<p>pending</p>
+	{/snippet}
+</svelte:boundary>