fix: allow await in svelte boundary without pending (#16857)

Fix: #16856

Author: yuki0418

.changeset/poor-flies-serve.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: allow await in svelte:boundary without pending

packages/svelte/src/compiler/phases/3-transform/server/visitors/SvelteBoundary.js

@@ -2,7 +2,13 @@
 /** @import { AST } from '#compiler' */
 /** @import { ComponentContext } from '../types' */
 import * as b from '#compiler/builders';
-import { block_close, block_open, block_open_else, build_attribute_value } from './shared/utils.js';
+import {
+	block_close,
+	block_open,
+	block_open_else,
+	build_attribute_value,
+	create_async_block
+} from './shared/utils.js';
 
 /**
  * @param {AST.SvelteBoundary} node
@@ -37,6 +43,9 @@ export function SvelteBoundary(node, context) {
 		context.state.template.push(block_open_else, pending, block_close);
 	} else {
 		const block = /** @type {BlockStatement} */ (context.visit(node.fragment));
-		context.state.template.push(block_open, block, block_close);
+		const statement = node.fragment.metadata.has_await
+			? create_async_block(b.block([block]))
+			: block;
+		context.state.template.push(block_open, statement, block_close);
 	}
 }

packages/svelte/tests/server-side-rendering/samples/async-svelte-boundary/_expected.html

@@ -0,0 +1 @@
+<div>this should work</div>

packages/svelte/tests/server-side-rendering/samples/async-svelte-boundary/main.svelte

@@ -0,0 +1,4 @@
+<svelte:boundary>
+    {@const x = await 'this should work'}
+    <div>{x}</div>
+</svelte:boundary>