fix: ensure generated tsconfig paths start with ./ if aliasing to ./svelte-kit (#12220)

Author: eltigerchino

.changeset/wicked-kangaroos-swim.md

@@ -0,0 +1,5 @@
+---
+"@sveltejs/kit": patch
+---
+
+fix: correctly handle aliases to files in the `.svelte-kit` directory

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

@@ -192,7 +192,13 @@ const value_regex = /^(.*?)((\/\*)|(\.\w+))?$/;
  */
 function get_tsconfig_paths(config) {
 	/** @param {string} file */
-	const config_relative = (file) => posixify(path.relative(config.outDir, file));
+	const config_relative = (file) => {
+		let relative_path = path.relative(config.outDir, file);
+		if (!relative_path.startsWith('..')) {
+			relative_path = './' + relative_path;
+		}
+		return posixify(relative_path);
+	};
 
 	const alias = { ...config.alias };
 	if (fs.existsSync(project_relative(config.files.lib))) {

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

@@ -9,7 +9,8 @@ test('Creates tsconfig path aliases from kit.alias', () => {
 				simpleKey: 'simple/value',
 				key: 'value',
 				'key/*': 'some/other/value/*',
-				keyToFile: 'path/to/file.ts'
+				keyToFile: 'path/to/file.ts',
+				$routes: '.svelte-kit/types/src/routes'
 			}
 		}
 	});
@@ -23,7 +24,9 @@ test('Creates tsconfig path aliases from kit.alias', () => {
 		'simpleKey/*': ['../simple/value/*'],
 		key: ['../value'],
 		'key/*': ['../some/other/value/*'],
-		keyToFile: ['../path/to/file.ts']
+		keyToFile: ['../path/to/file.ts'],
+		$routes: ['./types/src/routes'],
+		'$routes/*': ['./types/src/routes/*']
 	});
 });