fix: change enhance function return type to void | Promise<void>

Closes #15700

Author: Stadly

.changeset/gold-carrots-guess.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+Change enhance function return type to void | Promise<void>.

packages/kit/src/exports/public.d.ts

@@ -2095,7 +2095,7 @@ export type RemoteForm<Input extends RemoteFormInput | void, Output> = {
 			submit: () => Promise<boolean> & {
 				updates: (...updates: RemoteQueryUpdate[]) => Promise<boolean>;
 			};
-		}) => void
+		}) => void | Promise<void>
 	): {
 		method: 'POST';
 		action: string;

packages/kit/test/apps/async/src/routes/remote/form/for-duplicate/+page.svelte

@@ -6,6 +6,10 @@
 <p id="count">{count.current}</p>
 
 <!-- this looks weird but forces the spread into being reactive -->
-<form {...increment.for((count.current || 1) && 'a').enhance(async ({ submit }) => await submit())}>
+<form
+	{...increment.for((count.current || 1) && 'a').enhance(async ({ submit }) => {
+		await submit();
+	})}
+>
 	<button type="submit" id="submit">Submit</button>
 </form>

packages/kit/types/index.d.ts

@@ -2069,7 +2069,7 @@ declare module '@sveltejs/kit' {
 				submit: () => Promise<boolean> & {
 					updates: (...updates: RemoteQueryUpdate[]) => Promise<boolean>;
 				};
-			}) => void
+			}) => void | Promise<void>
 		): {
 			method: 'POST';
 			action: string;