fix: Always include root layout/error nodes in manifest (#13522)

Fixes #13518.

This optimization doesn't work when an app (or a specific bundle, such as the ones generated for edge functions or when split: true in Vercel) has all prerendered routes. Given that the optimization probably isn't actually saving us much, it's probably not worth it to try to find some convoluted workaround.


---------

Co-authored-by: Simon H <[email protected]>

Author: elliott-with-the-longest-name-on-github

.changeset/long-hounds-listen.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: Include root layout and error nodes even when apps have only prerendered pages

package.json

@@ -38,7 +38,8 @@
 	"pnpm": {
 		"onlyBuiltDependencies": [
 			"svelte-preprocess",
-			"workerd"
+			"workerd",
+			"esbuild"
 		]
 	}
-}
+}

packages/kit/src/core/generate_manifest/index.js

@@ -27,12 +27,10 @@ export function generate_manifest({ build_data, prerendered, relative_path, rout
 	const reindexed = new Map();
 	/**
 	 * All nodes actually used in the routes definition (prerendered routes are omitted).
-	 * If `routes` is empty, it means that this manifest is only used for server-side resolution
-	 * and the root layout/error is therefore not needed.
-	 * Else, root layout/error is always included as they are needed for 404 and root errors.
+	 * Root layout/error is always included as they are needed for 404 and root errors.
 	 * @type {Set<any>}
 	 */
-	const used_nodes = new Set(routes.length > 0 ? [0, 1] : []);
+	const used_nodes = new Set([0, 1]);
 
 	const server_assets = find_server_assets(build_data, routes);
 

packages/kit/test/apps/prerendered-app-error-pages/.gitignore

@@ -0,0 +1,3 @@
+/test/errors.json
+!/.env
+/src/routes/routing/symlink-from

packages/kit/test/apps/prerendered-app-error-pages/README.md

@@ -0,0 +1 @@
+Please do not edit this app unless you're absolutely sure it's not going to affect the tests.

packages/kit/test/apps/prerendered-app-error-pages/jsconfig.json

@@ -0,0 +1,19 @@
+{
+	"extends": "./.svelte-kit/tsconfig.json",
+	"compilerOptions": {
+		"allowJs": true,
+		"checkJs": true,
+		"esModuleInterop": true,
+		"forceConsistentCasingInFileNames": true,
+		"resolveJsonModule": true,
+		"skipLibCheck": true,
+		"sourceMap": true,
+		"strict": true,
+		"moduleResolution": "bundler"
+	}
+	// Path aliases are handled by https://svelte.dev/docs/kit/configuration#alias
+	// except $lib which is handled by https://svelte.dev/docs/kit/configuration#files
+	//
+	// If you want to overwrite includes/excludes, make sure to copy over the relevant includes/excludes
+	// from the referenced tsconfig.json - TypeScript does not merge them in
+}

packages/kit/test/apps/prerendered-app-error-pages/package.json

@@ -0,0 +1,26 @@
+{
+	"name": "test-prerendered-app-error-pages",
+	"private": true,
+	"version": "0.0.1",
+	"type": "module",
+	"scripts": {
+		"dev": "vite dev",
+		"build": "vite build",
+		"preview": "vite preview",
+		"prepare": "svelte-kit sync || echo ''",
+		"check": "svelte-kit sync && svelte-check --tsconfig ./jsconfig.json",
+		"check:watch": "svelte-kit sync && svelte-check --tsconfig ./jsconfig.json --watch",
+		"test": "pnpm test:dev && pnpm test:build",
+		"test:dev": "cross-env DEV=true playwright test",
+		"test:build": "playwright test"
+	},
+	"devDependencies": {
+		"@sveltejs/kit": "workspace:^",
+		"@sveltejs/vite-plugin-svelte": "^5.0.1",
+		"cross-env": "^7.0.3",
+		"svelte": "^5.2.9",
+		"svelte-check": "^4.1.1",
+		"typescript": "^5.5.4",
+		"vite": "^6.0.11"
+	}
+}

packages/kit/test/apps/prerendered-app-error-pages/playwright.config.js

@@ -0,0 +1 @@
+export { config as default } from '../../utils.js';

packages/kit/test/apps/prerendered-app-error-pages/src/app.d.ts

@@ -0,0 +1,13 @@
+// See https://svelte.dev/docs/kit/types#app.d.ts
+// for information about these interfaces
+declare global {
+	namespace App {
+		// interface Error {}
+		// interface Locals {}
+		// interface PageData {}
+		// interface PageState {}
+		// interface Platform {}
+	}
+}
+
+export {};

packages/kit/test/apps/prerendered-app-error-pages/src/app.html

@@ -0,0 +1,12 @@
+<!doctype html>
+<html lang="en">
+	<head>
+		<meta charset="utf-8" />
+		<link rel="icon" href="%sveltekit.assets%/favicon.png" />
+		<meta name="viewport" content="width=device-width, initial-scale=1" />
+		%sveltekit.head%
+	</head>
+	<body data-sveltekit-preload-data="hover">
+		<div style="display: contents">%sveltekit.body%</div>
+	</body>
+</html>

packages/kit/test/apps/prerendered-app-error-pages/src/routes/+error.svelte

@@ -0,0 +1 @@
+<p>This is your custom error page.</p>

packages/kit/test/apps/prerendered-app-error-pages/src/routes/+layout.ts

@@ -0,0 +1 @@
+export const prerender = true;

packages/kit/test/apps/prerendered-app-error-pages/src/routes/+page.svelte

@@ -0,0 +1,4 @@
+<p>
+	This app exists to assert that an app with only prerendered routes successfully renders custom
+	error pages.
+</p>

packages/kit/test/apps/prerendered-app-error-pages/static/favicon.png

@@ -0,0 +1,6 @@
+/** @type {import('@sveltejs/kit').Config} */
+const config = {
+	kit: {}
+};
+
+export default config;

packages/kit/test/apps/prerendered-app-error-pages/svelte.config.js

@@ -0,0 +1,9 @@
+import { expect } from '@playwright/test';
+import { test } from '../../../utils.js';
+
+test.describe.configure({ mode: 'parallel' });
+
+test('renders error page on nonexistent route', async ({ page }) => {
+	await page.goto('/nonexistent', { wait_for_started: false });
+	expect(await page.textContent('p')).toBe('This is your custom error page.');
+});

packages/kit/test/apps/prerendered-app-error-pages/test/test.js

@@ -0,0 +1,12 @@
+import { sveltekit } from '@sveltejs/kit/vite';
+import path from 'node:path';
+import { defineConfig } from 'vite';
+
+export default defineConfig({
+	plugins: [sveltekit()],
+	server: {
+		fs: {
+			allow: [path.resolve('../../../src')]
+		}
+	}
+});