[fix] correctly pass Vite options in preview mode

.changeset/unlucky-vans-allow.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+[fix] correctly pass Vite options in preview mode

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

@@ -91,8 +91,8 @@ class Watcher extends EventEmitter {
 	async init_server() {
 		if (!this.manifest) throw new Error('Must call init() before init_server()');
 
-		/** @type {any} */
-		const user_config = (this.config.kit.vite && this.config.kit.vite()) || {};
+		/** @type {import('vite').UserConfig} */
+		const vite_config = (this.config.kit.vite && this.config.kit.vite()) || {};
 
 		const default_config = {
 			server: {
@@ -105,15 +105,15 @@ class Watcher extends EventEmitter {
 		/** @type {(req: import("http").IncomingMessage, res: import("http").ServerResponse) => void} */
 		let handler = (req, res) => {};
 
-		this.server = await get_server(this.https, user_config, (req, res) => handler(req, res));
+		this.server = await get_server(this.https, vite_config, (req, res) => handler(req, res));
 
-		const alias = user_config.resolve && user_config.resolve.alias;
+		const alias = vite_config.resolve && vite_config.resolve.alias;
 
 		// don't warn on overriding defaults
-		const [modified_user_config] = deep_merge(default_config, user_config);
+		const [modified_vite_config] = deep_merge(default_config, vite_config);
 
 		/** @type {[any, string[]]} */
-		const [merged_config, conflicts] = deep_merge(modified_user_config, {
+		const [merged_config, conflicts] = deep_merge(modified_vite_config, {
 			configFile: false,
 			root: this.cwd,
 			resolve: {
@@ -153,7 +153,8 @@ class Watcher extends EventEmitter {
 				entries: []
 			},
 			ssr: {
-				noExternal: get_no_external(this.cwd, user_config.ssr && user_config.ssr.noExternal)
+				// @ts-expect-error ssr is considered in beta, so not exposed by Vite
+				noExternal: get_no_external(this.cwd, vite_config.ssr && vite_config.ssr.noExternal)
 			}
 		});
 

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

@@ -59,7 +59,10 @@ export async function preview({
 		read: (file) => fs.readFileSync(join(config.kit.files.assets, file))
 	});
 
-	const server = await get_server(use_https, config.kit, (req, res) => {
+	/** @type {import('vite').UserConfig} */
+	const vite_config = (config.kit.vite && config.kit.vite()) || {};
+
+	const server = await get_server(use_https, vite_config, (req, res) => {
 		const parsed = parse(req.url || '');
 
 		assets_handler(req, res, () => {

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

@@ -1,9 +1,9 @@
 import http from 'http';
 import https from 'https';
+
 /**
- *
  * @param {boolean} use_https
- * @param {any} user_config
+ * @param {import('vite').UserConfig} user_config
  * @param {(req: http.IncomingMessage, res: http.ServerResponse) => void} handler
  * @returns {Promise<import('net').Server>}
  */
@@ -12,14 +12,13 @@ export async function get_server(use_https, user_config, handler) {
 	const https_options = {};
 
 	if (use_https) {
-		if (
-			user_config.server &&
-			user_config.server.https &&
-			user_config.server.https.key &&
-			user_config.server.https.cert
-		) {
-			https_options.key = user_config.server.https.key.toString();
-			https_options.cert = user_config.server.https.cert.toString();
+		const secure_opts = user_config.server
+			? /** @type {import('tls').SecureContextOptions} */ (user_config.server.https)
+			: {};
+
+		if (secure_opts.key && secure_opts.cert) {
+			https_options.key = secure_opts.key.toString();
+			https_options.cert = secure_opts.cert.toString();
 		} else {
 			https_options.key = https_options.cert = (await import('./cert')).createCertificate();
 		}