fix: generate a never Path type when there are no routes

.changeset/empty-path-never.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: generate a `never` `Path` type when there are no routes

packages/kit/src/core/sync/sync.spec.js

@@ -7,6 +7,7 @@ import { load_explicit_env } from '../env.js';
 import { relative_path } from '../../utils/filesystem.js';
 import { posixify } from '../../utils/os.js';
 import { create, update } from './sync.js';
+import { write_app_types } from './write_app_types.js';
 import create_manifest_data from './create_manifest_data/index.js';
 
 test('generates client manifest imports relative to the project root', () => {
@@ -38,6 +39,23 @@ test('generates client manifest imports relative to the project root', () => {
 	}
 });
 
+test('generates a `never` Path type when there are no routes', () => {
+	const root = fs.mkdtempSync(path.join(os.tmpdir(), 'svelte-kit-sync-'));
+
+	try {
+		const config = process_config(validate_config({}), root);
+		write_app_types(config, create_manifest_data(config, root), root);
+		const generated = fs.readFileSync(
+			path.join(root, 'node_modules/$app/types/index.d.ts'),
+			'utf8'
+		);
+
+		expect(generated).toContain('\t\tPath(): never;');
+	} finally {
+		fs.rmSync(root, { recursive: true, force: true });
+	}
+});
+
 test('explains circular imports through $app/env/private', async () => {
 	const root = path.resolve(import.meta.dirname, '../../../test/apps/basics');
 	const dir = fs.mkdtempSync(path.join(root, 'node_modules/.svelte-kit-env-'));

packages/kit/src/core/sync/write_app_types.js

@@ -285,7 +285,7 @@ function generate_app_types(manifest_data, config, dir) {
 		`\t\tRouteId(): ${app_route_ids.join(' | ') || 'never'};`,
 		`\t\tRouteParams(): {\n\t\t\t${dynamic_routes.join(';\n\t\t\t')}\n\t\t};`,
 		`\t\tLayoutParams(): {\n\t\t\t${layouts.join(';\n\t\t\t')}\n\t\t};`,
-		`\t\tPath(): ${Array.from(pathnames).join(' | ')};`,
+		`\t\tPath(): ${Array.from(pathnames).join(' | ') || 'never'};`,
 		'\t\tResolvedPathname(): `${"/" | `/${string}/`}${ReturnType<AppTypes[\'Path\']>}`;',
 		`\t\tAssetPath(): ${assets.join(' | ') || 'never'};`,
 		'\t}',