[fix] allow any top-level keys in svelte config

.changeset/eight-keys-give.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+allow any top-level keys in svelte config

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

@@ -24,17 +24,19 @@ function validate(definition, option, keypath) {
 			);
 		}
 	}
-	for (const key in option) {
-		if (!(key in definition)) {
-			let message = `Unexpected option ${keypath}.${key}`;
-
-			if (keypath === 'config' && key in options.kit) {
-				message += ` (did you mean config.kit.${key}?)`;
-			} else if (keypath === 'config.kit' && key in options) {
-				message += ` (did you mean config.${key}?)`;
-			}
 
-			throw new Error(message);
+	// only validate nested key paths
+	if (keypath !== 'config') {
+		for (const key in option) {
+			if (!(key in definition)) {
+				let message = `Unexpected option ${keypath}.${key}`;
+
+				if (keypath === 'config.kit' && key in options) {
+					message += ` (did you mean config.${key}?)`;
+				}
+
+				throw new Error(message);
+			}
 		}
 	}
 

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

@@ -87,6 +87,15 @@ test('errors on invalid nested values', () => {
 	}, /^Unexpected option config\.kit\.files\.potato$/);
 });
 
+test('does not error on invalid top-level values', () => {
+	assert.not.throws(() => {
+		validate_config({
+			// @ts-expect-error
+			onwarn: () => {}
+		});
+	});
+});
+
 test('errors on extension without leading .', () => {
 	assert.throws(() => {
 		validate_config({