select adapter immediately on startup (#4299)

* select adapter immediately on startup

* simplify

* changesets

* lint

Author: Rich-Harris

.changeset/cool-crabs-listen.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+Allow adapter.adapt to be synchronous

.changeset/tasty-squids-share.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/adapter-auto': patch
+---
+
+Select adapter immediately

packages/adapter-auto/index.js

@@ -1,40 +1,52 @@
 import { adapters } from './adapters.js';
 
-/** @type {import('.')} **/
-export default function () {
-	return {
-		name: '@sveltejs/adapter-auto',
+/** @type {import('./index')} */
+let fn;
+
+for (const candidate of adapters) {
+	if (candidate.test()) {
+		/** @type {{ default: () => import('@sveltejs/kit').Adapter }} */
+		let module;
 
-		async adapt(builder) {
-			for (const candidate of adapters) {
-				if (candidate.test()) {
-					builder.log.info(`Detected environment: ${candidate.name}. Using ${candidate.module}`);
-
-					let module;
-
-					try {
-						module = await import(candidate.module);
-					} catch (error) {
-						if (
-							error.code === 'ERR_MODULE_NOT_FOUND' &&
-							error.message.startsWith(`Cannot find package '${candidate.module}'`)
-						) {
-							throw new Error(
-								`It looks like ${candidate.module} is not installed. Please install it and try building your project again.`
-							);
-						}
-
-						throw error;
+		try {
+			module = await import(candidate.module);
+
+			fn = () => {
+				const adapter = module.default();
+				return {
+					...adapter,
+					adapt: (builder) => {
+						builder.log.info(`Detected environment: ${candidate.name}. Using ${candidate.module}`);
+						return adapter.adapt(builder);
 					}
+				};
+			};
 
-					const adapter = module.default();
-					return adapter.adapt(builder);
-				}
+			break;
+		} catch (error) {
+			if (
+				error.code === 'ERR_MODULE_NOT_FOUND' &&
+				error.message.startsWith(`Cannot find package '${candidate.module}'`)
+			) {
+				throw new Error(
+					`It looks like ${candidate.module} is not installed. Please install it and try building your project again.`
+				);
 			}
 
+			throw error;
+		}
+	}
+}
+
+if (!fn) {
+	fn = () => ({
+		name: '@sveltejs/adapter-auto',
+		adapt: (builder) => {
 			builder.log.warn(
 				'Could not detect a supported production environment. See https://kit.svelte.dev/docs/adapters to learn how to configure your app to run on the platform of your choosing'
 			);
 		}
-	};
+	});
 }
+
+export default fn;

packages/adapter-auto/tsconfig.json

@@ -4,6 +4,9 @@
 		"checkJs": true,
 		"noEmit": true,
 		"noImplicitAny": true,
+		"module": "esnext",
+		"target": "esnext",
+		"moduleResolution": "node",
 		"baseUrl": ".",
 		"paths": {
 			"@sveltejs/kit": ["../kit/types/index"]

packages/kit/types/index.d.ts

@@ -28,7 +28,7 @@ import { SSRNodeLoader, SSRRoute, ValidatedConfig } from './internal';
 
 export interface Adapter {
 	name: string;
-	adapt(builder: Builder): Promise<void>;
+	adapt(builder: Builder): MaybePromise<void>;
 }
 
 export interface Builder {