fix: correctly check index file exists when resolving an entry (#13354)

fixes #13350

#13188 caused a regression where index.js and index.ts files would not be resolved as entries because of the additional isFile() check that was added to prioritise matching files over folders.

.changeset/cyan-dancers-tap.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: correctly resolve index file entrypoints such as `src/service-worker/index.js`

packages/kit/src/utils/filesystem.js

@@ -169,11 +169,12 @@ export function from_fs(str) {
 export function resolve_entry(entry) {
 	if (fs.existsSync(entry)) {
 		const stats = fs.statSync(entry);
-		const index = path.join(entry, 'index');
-
 		if (stats.isFile()) {
 			return entry;
-		} else if (fs.existsSync(index)) {
+		}
+
+		const index = path.join(entry, 'index');
+		if (fs.existsSync(index + '.js') || fs.existsSync(index + '.ts')) {
 			return resolve_entry(index);
 		}
 	}

packages/kit/src/utils/filesystem.spec.js

@@ -100,27 +100,35 @@ test('replaces strings', () => {
 	);
 });
 
-test('ignores hooks.server folder when resolving hooks', () => {
-	write(join('hooks.server', 'index.js'), '');
+test('resolves index files', () => {
+	write(join('service-worker', 'index.js'), '');
 
-	expect(resolve_entry(source_dir + '/hooks')).null;
+	expect(resolve_entry(source_dir + '/service-worker')).toBe(
+		join(source_dir, 'service-worker', 'index.js')
+	);
+});
+
+test('resolves entries that have an extension', () => {
+	write('hooks.js', '');
+
+	expect(resolve_entry(join(source_dir, 'hooks.js'))).toBe(join(source_dir, 'hooks.js'));
 });
 
-test('ignores hooks folder that has no index file when resolving hooks', () => {
+test('resolves universal hooks file when hooks folder exists', () => {
 	write(join('hooks', 'not-index.js'), '');
 	write('hooks.js', '');
 
 	expect(resolve_entry(source_dir + '/hooks')).toBe(join(source_dir, 'hooks.js'));
 });
 
-test('ignores hooks folder when resolving universal hooks', () => {
-	write(join('hooks', 'hooks.server.js'), '');
+test('ignores hooks.server folder when resolving universal hooks file', () => {
+	write(join('hooks.server', 'index.js'), '');
 
 	expect(resolve_entry(source_dir + '/hooks')).null;
 });
 
-test('resolves entries that have an extension', () => {
-	write('hooks.js', '');
+test('ignores hooks folder when resolving universal hooks file', () => {
+	write(join('hooks', 'hooks.server.js'), '');
 
-	expect(resolve_entry(join(source_dir, 'hooks.js'))).toBe(join(source_dir, 'hooks.js'));
+	expect(resolve_entry(source_dir + '/hooks')).null;
 });