sveltejs · Rich-Harris · Mar 14, 2022 · Mar 12, 2022 · Mar 12, 2022 · Mar 12, 2022
diff --git a/.changeset/calm-ravens-tell.md b/.changeset/calm-ravens-tell.md
@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+[breaking] allow `InputProps` and `OutputProps` to be typed separately in generated `Load`
diff --git a/.changeset/little-toys-camp.md b/.changeset/little-toys-camp.md
@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+allow `Output` to be typed in generated `RequestHandler`
diff --git a/documentation/docs/14-types.md b/documentation/docs/14-types.md
@@ -35,10 +35,10 @@ export type RequestHandler<Body = any> = GenericRequestHandler<
 	Body
 >;
 
-export type Load<Props = Record<string, any>> = GenericLoad<
-	{ foo: string; bar: string; baz: string },
-	Props
->;
+export type Load<
+	InputProps extends Record<string, any> = Record<string, any>,
+	OutputProps extends Record<string, any> = InputProps
+> = GenericLoad<{ foo: string; bar: string; baz: string }, InputProps, OutputProps>
 ```
 
 These files can be imported into your endpoints and pages as siblings, thanks to the [`rootDirs`](https://www.typescriptlang.org/tsconfig#rootDirs) option in your TypeScript configuration:

diff --git a/packages/kit/src/core/sync/write_types.js b/packages/kit/src/core/sync/write_types.js
@@ -1,5 +1,21 @@
 import { write_if_changed } from './utils.js';
 
+/** @param {string} imports */
+const header = (imports) => `
+// this file is auto-generated
+import type { ${imports} } from '@sveltejs/kit';`;
+
+/** @param {string} arg */
+const endpoint = (arg) => `
+export type RequestHandler<Output extends ResponseBody = ResponseBody> = GenericRequestHandler<${arg}, Output>;`;
+
+/** @param {string} arg */
+const page = (arg) => `
+export type Load<
+	InputProps extends Record<string, any> = Record<string, any>,
+	OutputProps extends Record<string, any> = InputProps
+> = GenericLoad<${arg}, InputProps, OutputProps>;`;
+
 /**
  * @param {import('types').ValidatedConfig} config
  * @param {import('types').ManifestData} manifest_data
@@ -53,24 +69,24 @@ export function write_types(config, manifest_data) {
 		const arg =
 			params.length > 0 ? `{ ${params.map((param) => `${param}: string`).join('; ')} }` : '{}';
 
-		const imports = [
-			type !== 'page' && 'RequestHandler as GenericRequestHandler',
-			type !== 'endpoint' && 'Load as GenericLoad'
-		]
-			.filter(Boolean)
-			.join(', ');
-
-		const file = `${config.kit.outDir}/types/${key || 'index'}.d.ts`;
-		const content = [
-			'// this file is auto-generated',
-			`import type { ${imports} } from '@sveltejs/kit';`,
-			type !== 'page' && `export type RequestHandler = GenericRequestHandler<${arg}>;`,
-			type !== 'endpoint' &&
-				`export type Load<Props = Record<string, any>> = GenericLoad<${arg}, Props>;`
-		]
-			.filter(Boolean)
-			.join('\n');
-
-		write_if_changed(file, content);
+		const imports = [];
+		const content = [];
+
+		if (type !== 'page') {
+			imports.push('RequestHandler as GenericRequestHandler, ResponseBody');
+			content.push(endpoint(arg));
+		}
+
+		if (type !== 'endpoint') {
+			imports.push('Load as GenericLoad');
+			content.push(page(arg));
+		}
+
+		content.unshift(header(imports.join(', ')));
+
+		write_if_changed(
+			`${config.kit.outDir}/types/${key || 'index'}.d.ts`,
+			content.join('\n').trim()
+		);
 	});
 }
diff --git a/packages/kit/types/index.d.ts b/packages/kit/types/index.d.ts
@@ -6,11 +6,11 @@ import './ambient';
 import { CompileOptions } from 'svelte/types/compiler/interfaces';
 import {
 	AdapterEntry,
-	Body,
 	CspDirectives,
 	Either,
 	ErrorLoadInput,
 	Fallthrough,
+	JSONValue,
 	LoadInput,
 	LoadOutput,
 	Logger,
@@ -158,7 +158,10 @@ export interface Config {
 	preprocess?: any;
 }
 
-export interface ErrorLoad<Params = Record<string, string>, Props = Record<string, any>> {
+export interface ErrorLoad<
+	Params extends Record<string, string> = Record<string, string>,
+	Props extends Record<string, any> = Record<string, any>
+> {
 	(input: ErrorLoadInput<Params>): MaybePromise<LoadOutput<Props>>;
 }
 
@@ -218,11 +221,14 @@ export interface Page<Params extends Record<string, string> = Record<string, str
  * Note that you can use [generated types](/docs/types#generated-types)
  * instead of manually specifying the `Params` generic argument.
  */
-export interface RequestHandler<Params = Record<string, string>, Output extends Body = Body> {
+export interface RequestHandler<
+	Params extends Record<string, string> = Record<string, string>,
+	Output extends ResponseBody = ResponseBody
+> {
 	(event: RequestEvent<Params>): RequestHandlerOutput<Output>;
 }
 
-export type RequestHandlerOutput<Output extends Body = Body> = MaybePromise<
+export type RequestHandlerOutput<Output extends ResponseBody = ResponseBody> = MaybePromise<
 	Either<
 		{
 			status?: number;
@@ -233,6 +239,8 @@ export type RequestHandlerOutput<Output extends Body = Body> = MaybePromise<
 	>
 >;
 
+export type ResponseBody = JSONValue | Uint8Array | ReadableStream | import('stream').Readable;
+
 export class Server {
 	constructor(manifest: SSRManifest);
 	respond(request: Request, options: RequestOptions): Promise<Response>;

diff --git a/packages/kit/types/private.d.ts b/packages/kit/types/private.d.ts
@@ -28,8 +28,6 @@ export interface AdapterEntry {
 	}) => void;
 }
 
-export type Body = JSONValue | Uint8Array | ReadableStream | import('stream').Readable;
-
 // Based on https://github.com/josh-hemphill/csp-typed-directives/blob/latest/src/csp.types.ts
 //
 // MIT License
@@ -140,7 +138,8 @@ export interface CspDirectives {
 
 export type Either<T, U> = Only<T, U> | Only<U, T>;
 
-export interface ErrorLoadInput<Params = Record<string, string>> extends LoadInput<Params> {
+export interface ErrorLoadInput<Params extends Record<string, string> = Record<string, string>>
+	extends LoadInput<Params> {
 	status?: number;
 	error?: Error;
 }
@@ -165,7 +164,10 @@ export type JSONValue =
 	| JSONValue[]
 	| JSONObject;
 
-export interface LoadInput<Params = Record<string, string>, Props = Record<string, any>> {
+export interface LoadInput<
+	Params extends Record<string, string> = Record<string, string>,
+	Props extends Record<string, any> = Record<string, any>
+> {
 	url: URL;
 	params: Params;
 	props: Props;
@@ -174,7 +176,7 @@ export interface LoadInput<Params = Record<string, string>, Props = Record<strin
 	stuff: Partial<App.Stuff>;
 }
 
-export interface LoadOutput<Props = Record<string, any>> {
+export interface LoadOutput<Props extends Record<string, any> = Record<string, any>> {
 	status?: number;
 	error?: string | Error;
 	redirect?: string;
@@ -233,7 +235,7 @@ export interface PrerenderErrorHandler {
 
 export type PrerenderOnErrorValue = 'fail' | 'continue' | PrerenderErrorHandler;
 
-export interface RequestEvent<Params = Record<string, string>> {
+export interface RequestEvent<Params extends Record<string, string> = Record<string, string>> {
 	clientAddress: string;
 	locals: App.Locals;
 	params: Params;