Support esm config files (#936)

.changeset/violet-spies-play.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+Add esm config support

packages/kit/package.json

@@ -35,7 +35,7 @@
 		"vite": "^2.2.3"
 	},
 	"peerDependencies": {
-		"svelte": "^3.32.1",
+		"svelte": "^3.34.0",
 		"vite": "^2.2.3"
 	},
 	"bin": {

packages/kit/src/cli.js

@@ -26,16 +26,11 @@ async function get_config() {
 
 		if (
 			error.code === 'MODULE_NOT_FOUND' &&
-			/Cannot find module svelte\.config\.cjs/.test(error.message)
+			/Cannot find module svelte\.config\./.test(error.message)
 		) {
-			if (existsSync('svelte.config.js')) {
-				// TODO this is temporary, for the benefit of early adopters
-				message = 'You must rename svelte.config.js to svelte.config.cjs';
-			} else {
-				message = 'Missing svelte.config.cjs';
-			}
+			message = 'Missing svelte.config.js';
 		} else if (error.name === 'SyntaxError') {
-			message = 'Malformed svelte.config.cjs';
+			message = 'Malformed svelte.config.js';
 		}
 
 		console.error(colors.bold().red(message));

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

@@ -1,6 +1,7 @@
 import options from './options.js';
 import * as url from 'url';
 import path from 'path';
+import fs from 'fs';
 import { resolve_entry } from '../utils.js';
 
 /** @typedef {import('./types').ConfigDefinition} ConfigDefinition */
@@ -81,7 +82,10 @@ function remove_trailing_slash(str) {
 }
 
 export async function load_config({ cwd = process.cwd() } = {}) {
-	const config_file = path.join(cwd, 'svelte.config.cjs');
+	const config_file_esm = path.join(cwd, 'svelte.config.js');
+	const config_file = fs.existsSync(config_file_esm)
+		? config_file_esm
+		: path.join(cwd, 'svelte.config.cjs');
 	const config = await import(url.pathToFileURL(config_file).href);
 	const validated = validate_config(config.default);
 

packages/kit/src/core/load_config/test/fixtures/default-esm/svelte.config.js

@@ -0,0 +1 @@
+export default {};

packages/kit/src/core/load_config/test/index.js

@@ -7,8 +7,11 @@ import { load_config } from '../index.js';
 const __filename = fileURLToPath(import.meta.url);
 const __dirname = join(__filename, '..');
 
-test('load default config', async () => {
-	const cwd = join(__dirname, 'fixtures');
+/**
+ * @param {string} path
+ */
+async function testLoadDefaultConfig(path) {
+	const cwd = join(__dirname, 'fixtures', path);
 
 	const config = await load_config({ cwd });
 
@@ -42,6 +45,14 @@ test('load default config', async () => {
 		},
 		preprocess: null
 	});
+}
+
+test('load default config (cjs)', async () => {
+	await testLoadDefaultConfig('default-cjs');
+});
+
+test('load default config (esm)', async () => {
+	await testLoadDefaultConfig('default-esm');
 });
 
 test.run();