fix: differentiate between 404 and 500 when rendering an error page

.changeset/hip-tips-drum.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: correctly return 404 when navigating to a missing page and the root layout fetches a prerendered endpoint

packages/kit/src/runtime/server/page/respond_with_error.js

@@ -28,6 +28,11 @@ export async function respond_with_error({
 	error,
 	resolve_opts
 }) {
+	// reroute to the fallback page to prevent an infinite chain of requests.
+	if (event.request.headers.get('x-sveltekit-error')) {
+		return static_error_page(options, status, /** @type {Error} */ (error).message);
+	}
+
 	/** @type {import('./types').Fetched[]} */
 	const fetched = [];
 

packages/kit/src/runtime/server/respond.js

@@ -457,6 +457,14 @@ export async function respond(request, options, manifest, state) {
 				return response;
 			}
 
+			if (state.error && event.isSubRequest) {
+				return await fetch(request, {
+					headers: {
+						'x-sveltekit-error': 'true'
+					}
+				});
+			}
+
 			if (state.error) {
 				return text('Internal Server Error', {
 					status: 500

packages/kit/test/apps/basics/src/app.d.ts

@@ -5,6 +5,7 @@ declare global {
 			name?: string;
 			key: string;
 			params: Record<string, string>;
+			url?: URL;
 		}
 
 		interface Platform {}

packages/kit/test/apps/basics/src/hooks.server.js

@@ -128,6 +128,12 @@ export const handle = sequence(
 			throw redirect(303, '/actions/enhance');
 		}
 
+		return resolve(event);
+	},
+	async ({ event, resolve }) => {
+		if (['/non-existent-route', '/non-existent-route-loop'].includes(event.url.pathname)) {
+			event.locals.url = new URL(event.request.url);
+		}
 		return resolve(event);
 	}
 );

packages/kit/test/apps/basics/src/routes/+layout.server.js

@@ -12,7 +12,15 @@ if (JSON.parse(env.SOME_JSON).answer !== 42) {
 }
 
 /** @type {import('./$types').LayoutServerLoad} */
-export async function load({ cookies }) {
+export async function load({ cookies, locals, fetch }) {
+	if (locals.url?.pathname === '/non-existent-route') {
+		await fetch('/prerendering/prerendered-endpoint/api').then((r) => r.json());
+	}
+
+	if (locals.url?.pathname === '/non-existent-route-loop') {
+		await fetch('/non-existent-route-loop');
+	}
+
 	const should_fail = cookies.get('fail-type');
 	if (should_fail) {
 		cookies.delete('fail-type', { path: '/' });

packages/kit/test/apps/basics/test/test.js

@@ -515,6 +515,16 @@ test.describe('Load', () => {
 
 		expect(await page.textContent('p')).toBe('error: false');
 	});
+
+	test('404 and root layout load fetch to prerendered endpoint works', async ({ page }) => {
+		await page.goto('/non-existent-route');
+
+		expect(await page.textContent('h1')).toBe('404');
+
+		await page.goto('/non-existent-route-loop');
+
+		expect(await page.textContent('h1')).toBe('404');
+	});
 });
 
 test.describe('Nested layouts', () => {