Support svelte.config.ts

.changeset/good-brooms-sing.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+Support `svelte.config.ts` as Typescript-based config file.

packages/kit/src/cli.js

@@ -54,7 +54,7 @@ prog
 			if (H) throw new Error('-H is no longer supported — use --https instead');
 
 			process.env.NODE_ENV = process.env.NODE_ENV || 'development';
-			const config = await load_config();
+			const config = await load_config({ mode: process.env.NODE_ENV });
 
 			const { dev } = await import('./core/dev/index.js');
 
@@ -89,7 +89,7 @@ prog
 	.action(async ({ verbose }) => {
 		try {
 			process.env.NODE_ENV = process.env.NODE_ENV || 'production';
-			const config = await load_config();
+			const config = await load_config({ mode: process.env.NODE_ENV });
 
 			const { build } = await import('./core/build/index.js');
 			const build_data = await build(config);
@@ -132,7 +132,7 @@ prog
 			await check_port(port);
 
 			process.env.NODE_ENV = process.env.NODE_ENV || 'production';
-			const config = await load_config();
+			const config = await load_config({ mode: process.env.NODE_ENV });
 
 			const { preview } = await import('./core/preview/index.js');
 

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

@@ -27,17 +27,33 @@ export function load_template(cwd, config) {
 	return fs.readFileSync(template, 'utf-8');
 }
 
-export async function load_config({ cwd = process.cwd() } = {}) {
+/**
+ * @param {{
+ *   cwd?: string;
+ *   mode?: string;
+ * }} opts
+ */
+export async function load_config({ cwd = process.cwd(), mode = 'development' } = {}) {
 	const config_file = path.join(cwd, 'svelte.config.js');
+	const ts_config_file = path.join(cwd, 'svelte.config.ts');
+	let config;
 
-	if (!fs.existsSync(config_file)) {
+	if (fs.existsSync(config_file)) {
+		config = await import(url.pathToFileURL(config_file).href);
+	} else if (fs.existsSync(ts_config_file)) {
+		const { loadConfigFromFile } = await import('vite');
+		const resolved_config = await loadConfigFromFile(
+			{ command: 'build', mode },
+			ts_config_file,
+			cwd
+		);
+		config = { default: resolved_config?.config };
+	} else {
 		throw new Error(
 			'You need to create a svelte.config.js file. See https://kit.svelte.dev/docs/configuration'
 		);
 	}
 
-	const config = await import(url.pathToFileURL(config_file).href);
-
 	const validated = validate_config(config.default);
 
 	validated.kit.files.assets = path.resolve(cwd, validated.kit.files.assets);