fix: use render tag when generating a default fallback page (#12653)

fixes #12652

Adds a fallback component using the Svelte 5 render tag and uses that if it detects the app is using Svelte 5.

Author: eltigerchino

.changeset/pretty-planets-deliver.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: use `{@render ...}` tag when generating default fallback page for svelte 5 apps

packages/kit/.prettierignore

@@ -1,2 +1,3 @@
 test/build-errors/apps/syntax-error/src/routes/+page.svelte
 /types
+src/runtime/components/svelte-5/layout.svelte

packages/kit/src/core/sync/create_manifest_data/index.js

@@ -6,6 +6,7 @@ import { list_files, runtime_directory } from '../../utils.js';
 import { posixify, resolve_entry } from '../../../utils/filesystem.js';
 import { parse_route_id } from '../../../utils/routing.js';
 import { sort_routes } from './sort.js';
+import { isSvelte5Plus } from '../utils.js';
 
 /**
  * Generates the manifest data used for the client-side manifest and types generation.
@@ -18,7 +19,7 @@ import { sort_routes } from './sort.js';
  */
 export default function create_manifest_data({
 	config,
-	fallback = `${runtime_directory}/components`,
+	fallback = `${runtime_directory}/components/${isSvelte5Plus() ? 'svelte-5' : 'svelte-4'}`,
 	cwd = process.cwd()
 }) {
 	const assets = create_assets(config);

packages/kit/src/runtime/components/error.svelte renamed to packages/kit/src/runtime/components/svelte-4/error.svelte

@@ -0,0 +1,6 @@
+<script>
+	import { page } from '$app/stores';
+</script>
+
+<h1>{$page.status}</h1>
+<p>{$page.error?.message}</p>

packages/kit/src/runtime/components/layout.svelte renamed to packages/kit/src/runtime/components/svelte-4/layout.svelte

@@ -0,0 +1,5 @@
+<script>
+  let { children } = $props();
+</script>
+
+{@render children()}