initial types testing

packages/kit/package.json

@@ -64,8 +64,9 @@
 		"format": "npm run check-format -- --write",
 		"check-format": "prettier --check . --config ../../.prettierrc --ignore-path .gitignore",
 		"prepublishOnly": "npm run build",
-		"test": "npm run test:unit && npm run test:packaging && npm run test:prerendering && npm run test:integration",
+		"test": "npm run test:unit && npm run test:typings && npm run test:packaging && npm run test:prerendering && npm run test:integration",
 		"test:unit": "uvu src \"(spec\\.js|test[\\\\/]index\\.js)\" -i packaging",
+		"test:typings": "tsc --project test/typings",
 		"test:prerendering": "pnpm test:prerendering:basics && pnpm test:prerendering:options",
 		"test:prerendering:basics": "cd test/prerendering/basics && pnpm test",
 		"test:prerendering:options": "cd test/prerendering/options && pnpm test",

packages/kit/test/typings/endpoint.test.ts

@@ -0,0 +1,128 @@
+import { RequestHandler } from '@sveltejs/kit';
+
+const valid_body = {
+	str: 'string',
+	num: 12345,
+	bool: true,
+	null: null,
+	custom: {
+		toJSON: () => 'custom toJSON function'
+	},
+	list: ['string', 12345, false, null],
+	nested: {
+		another: 'string',
+		big_num: 98765,
+		binary: false,
+		nullish: null,
+		custom: {
+			toJSON: () => 'hi mom'
+		},
+		list: [],
+		deeply: {
+			nested: {}
+		}
+	}
+};
+
+// valid - basic case of returning an object
+export const base_case: RequestHandler = () => {
+	return {
+		body: valid_body
+	};
+};
+
+// valid - raw Response instance should be allowed
+export const response_instance: RequestHandler = () => {
+	return new Response();
+};
+
+// valid - body instance of Uint8Array should be allowed
+export const uint8array_body: RequestHandler = () => {
+	return {
+		body: new Uint8Array()
+	};
+};
+
+// valid - body instance of ReadableStream should be allowed
+export const readable_stream_body: RequestHandler = () => {
+	return {
+		body: new ReadableStream()
+	};
+};
+
+// valid - body instance of stream.Readable should be allowed
+export const stream_readable_body: RequestHandler = async () => {
+	const { Readable } = await import('stream');
+	return {
+		body: new Readable()
+	};
+};
+
+// valid - different header pairs should be allowed
+export const differential_headers_assignment: RequestHandler = () => {
+	if (Math.random() < 0.5) {
+		return { headers: { foo: 'bar' } };
+	} else {
+		return { headers: { baz: 'foo' } };
+	}
+};
+
+// TODO https://github.com/sveltejs/kit/issues/1997
+// interface ExamplePost {
+// 	title: string;
+// 	description: string;
+// 	published_date?: string;
+// 	author_name?: string;
+// 	author_link?: string;
+// }
+// // valid - should not be any different
+// export const generic_case: RequestHandler<Record<string, string>, ExamplePost> = () => {
+// 	return {
+// 		body: {} as ExamplePost
+// 	};
+// };
+
+// --- invalid cases ---
+
+// @ts-expect-error - should not have undefined (should it not?)
+export const error_no_undefined: RequestHandler = () => {
+	return {
+		body: { no: Math.random() < 0.5 ? undefined : 'something' }
+	};
+};
+
+// @ts-expect-error - body must be JSON serializable
+export const error_body_must_be_serializable: RequestHandler = () => {
+	return {
+		body: () => {}
+	};
+};
+
+// @ts-expect-error - body typed array must only be Uint8Array
+export const error_other_typed_array_instances: RequestHandler = () => {
+	return {
+		body: new Uint16Array()
+	};
+};
+
+// @ts-expect-error - instances cannot be nested
+export const error_nested_instances: RequestHandler = () => {
+	return {
+		body: { typed: new Uint8Array() }
+	};
+};
+
+// @ts-expect-error - fallthrough must be isolated
+export const error_fallthrough_not_isolated: RequestHandler = () => {
+	return {
+		body: {},
+		fallthrough: true
+	};
+};
+
+// @ts-expect-error - fallthrough must be of value `true`
+export const error_fallthrough_not_true: RequestHandler = () => {
+	return {
+		fallthrough: null
+	};
+};

packages/kit/test/typings/tsconfig.json

@@ -0,0 +1,7 @@
+{
+	"extends": "../../tsconfig.json",
+	"compilerOptions": {
+		"noEmit": true
+	},
+	"include": ["**/*.test.ts"]
+}