fix: allow optional types for remote query/command/prerender functions

.changeset/violet-things-wear.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: allow optional types for remote query/command/prerender functions

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

@@ -2110,7 +2110,7 @@ export type RemoteForm<Input extends RemoteFormInput | void, Output> = {
  * The return value of a remote `command` function. See [Remote functions](https://svelte.dev/docs/kit/remote-functions#command) for full documentation.
  */
 export type RemoteCommand<Input, Output> = {
-	(arg: Input): Promise<Awaited<Output>> & {
+	(arg: undefined extends Input ? Input | void : Input): Promise<Awaited<Output>> & {
 		updates(...queries: Array<RemoteQuery<any> | RemoteQueryOverride>): Promise<Awaited<Output>>;
 	};
 	/** The number of pending command executions */
@@ -2180,11 +2180,15 @@ export interface RemoteQueryOverride {
 /**
  * The return value of a remote `prerender` function. See [Remote functions](https://svelte.dev/docs/kit/remote-functions#prerender) for full documentation.
  */
-export type RemotePrerenderFunction<Input, Output> = (arg: Input) => RemoteResource<Output>;
+export type RemotePrerenderFunction<Input, Output> = (
+	arg: undefined extends Input ? Input | void : Input
+) => RemoteResource<Output>;
 
 /**
  * The return value of a remote `query` function. See [Remote functions](https://svelte.dev/docs/kit/remote-functions#query) for full documentation.
  */
-export type RemoteQueryFunction<Input, Output> = (arg: Input) => RemoteQuery<Output>;
+export type RemoteQueryFunction<Input, Output> = (
+	arg: undefined extends Input ? Input | void : Input
+) => RemoteQuery<Output>;
 
 export * from './index.js';

packages/kit/test/types/remote.test.ts

@@ -10,6 +10,7 @@ import {
 
 const schema: StandardSchemaV1<string> = null as any;
 const schema2: StandardSchemaV1<string, number> = null as any;
+const schema3: StandardSchemaV1<string | undefined, number> = null as any;
 
 function query_tests() {
 	const no_args: RemoteQueryFunction<void, string> = query(() => 'Hello world');
@@ -40,6 +41,21 @@ function query_tests() {
 	}
 	void query_without_args();
 
+	async function query_with_optional_arg() {
+		const q = query(schema3, () => 'Hello world');
+		void q();
+		void q('hi');
+		// @ts-expect-error
+		void q(1);
+
+		const q2 = query('unchecked', (a?: string) => a);
+		void q2();
+		void q2('hi');
+		// @ts-expect-error
+		void q2(1);
+	}
+	void query_with_optional_arg();
+
 	async function query_unsafe() {
 		const q = query('unchecked', (a: number) => a);
 		const result: number = await q(1);
@@ -106,6 +122,21 @@ function prerender_tests() {
 	}
 	void prerender_unsafe();
 
+	async function prerender_with_optional_arg() {
+		const q = prerender(schema3, () => 'Hello world');
+		void q();
+		void q('hi');
+		// @ts-expect-error
+		void q(1);
+
+		const q2 = prerender('unchecked', (a?: string) => a);
+		void q2();
+		void q2('hi');
+		// @ts-expect-error
+		void q2(1);
+	}
+	void prerender_with_optional_arg();
+
 	async function prerender_schema() {
 		const q = prerender(schema, (a) => a);
 		const result: string = await q('1');
@@ -141,6 +172,21 @@ function command_tests() {
 	}
 	void command_without_args();
 
+	async function command_with_optional_arg() {
+		const q = command(schema3, () => 'Hello world');
+		void q();
+		void q('hi');
+		// @ts-expect-error
+		void q(1);
+
+		const q2 = command('unchecked', (a?: string) => a);
+		void q2();
+		void q2('hi');
+		// @ts-expect-error
+		void q2(1);
+	}
+	void command_with_optional_arg();
+
 	async function command_unsafe() {
 		const cmd = command('unchecked', (a: string) => a);
 		const result: string = await cmd('test');

packages/kit/types/index.d.ts

@@ -2085,7 +2085,7 @@ declare module '@sveltejs/kit' {
 	 * The return value of a remote `command` function. See [Remote functions](https://svelte.dev/docs/kit/remote-functions#command) for full documentation.
 	 */
 	export type RemoteCommand<Input, Output> = {
-		(arg: Input): Promise<Awaited<Output>> & {
+		(arg: undefined extends Input ? Input | void : Input): Promise<Awaited<Output>> & {
 			updates(...queries: Array<RemoteQuery<any> | RemoteQueryOverride>): Promise<Awaited<Output>>;
 		};
 		/** The number of pending command executions */
@@ -2155,12 +2155,16 @@ declare module '@sveltejs/kit' {
 	/**
 	 * The return value of a remote `prerender` function. See [Remote functions](https://svelte.dev/docs/kit/remote-functions#prerender) for full documentation.
 	 */
-	export type RemotePrerenderFunction<Input, Output> = (arg: Input) => RemoteResource<Output>;
+	export type RemotePrerenderFunction<Input, Output> = (
+		arg: undefined extends Input ? Input | void : Input
+	) => RemoteResource<Output>;
 
 	/**
 	 * The return value of a remote `query` function. See [Remote functions](https://svelte.dev/docs/kit/remote-functions#query) for full documentation.
 	 */
-	export type RemoteQueryFunction<Input, Output> = (arg: Input) => RemoteQuery<Output>;
+	export type RemoteQueryFunction<Input, Output> = (
+		arg: undefined extends Input ? Input | void : Input
+	) => RemoteQuery<Output>;
 	interface AdapterEntry {
 		/**
 		 * A string that uniquely identifies an HTTP service (e.g. serverless function) and is used for deduplication.