sveltejs · Rich-Harris · Mar 2, 2022 · Feb 24, 2022 · Feb 24, 2022 · Feb 24, 2022
diff --git a/.changeset/honest-cows-notice.md b/.changeset/honest-cows-notice.md
@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+Generate types for each page/endpoint
diff --git a/documentation/docs/01-routing.md b/documentation/docs/01-routing.md
@@ -56,11 +56,15 @@ declare module '$lib/database' {
 	export const get: (id: string) => Promise<Item>;
 }
 
+// @filename: [id].d.ts
+import type { RequestHandler as GenericRequestHandler } from '@sveltejs/kit';
+export type RequestHandler<Body = any> = GenericRequestHandler<{ id: string }, Body>;
+
 // @filename: index.js
 // ---cut---
 import db from '$lib/database';
 
-/** @type {import('@sveltejs/kit').RequestHandler} */
+/** @type {import('./[id]').RequestHandler} */
 export async function get({ params }) {
 	// `params.id` comes from [id].js
 	const item = await db.get(params.id);
@@ -74,11 +78,13 @@ export async function get({ params }) {
 	return {
 		status: 404
 	};
-};
+}
 ```
 
 > All server-side code, including endpoints, has access to `fetch` in case you need to request data from external APIs. Don't worry about the `$lib` import, we'll get to that [later](/docs/modules#$lib).
 
+The type of the `get` function above comes from `./[id].d.ts`, which is a file generated by SvelteKit (in a hidden directory, using the [`rootDirs`](https://www.typescriptlang.org/tsconfig#rootDirs) option) that provides type safety when accessing `params`. See the section on [generated types](/docs/types#generated-types) for more detail.
+
 The job of a [request handler](/docs/types#sveltejs-kit-requesthandler) is to return a `{ status, headers, body }` object representing the response, where `status` is an [HTTP status code](https://httpstatusdogs.com):
 
 - `2xx` — successful response (default is `200`)
@@ -148,11 +154,15 @@ declare module '$lib/database' {
 	export const create: (request: Request) => Promise<[Record<string, ValidationError>, Item]>;
 }
 
+// @filename: items.d.ts
+import type { RequestHandler as GenericRequestHandler } from '@sveltejs/kit';
+export type RequestHandler<Body = any> = GenericRequestHandler<{}, Body>;
+
 // @filename: index.js
 // ---cut---
 import * as db from '$lib/database';
 
-/** @type {import('@sveltejs/kit').RequestHandler} */
+/** @type {import('./items').RequestHandler} */
 export async function get() {
 	const items = await db.list();
 
@@ -161,7 +171,7 @@ export async function get() {
 	};
 }
 
-/** @type {import('@sveltejs/kit').RequestHandler} */
+/** @type {import('./items').RequestHandler} */
 export async function post({ request }) {
 	const [errors, item] = await db.create(request);
 
@@ -358,9 +368,15 @@ Higher priority routes can _fall through_ to lower priority routes by returning
 
 ```js
 /// file: src/routes/[a].js
+
+// @filename: [a].d.ts
+import type { RequestHandler as GenericRequestHandler } from '@sveltejs/kit';
+export type RequestHandler<Body = any> = GenericRequestHandler<{ a: string }, Body>;
+
+// @filename: index.js
 // @errors: 2366
-/** @type {import('@sveltejs/kit').RequestHandler} */
 // ---cut---
+/** @type {import('./[a]').RequestHandler} */
 export function get({ params }) {
 	if (params.a === 'foo-def') {
 		return { fallthrough: true };

diff --git a/documentation/docs/03-loading.md b/documentation/docs/03-loading.md
@@ -9,7 +9,7 @@ If the data for a page comes from its endpoint, you may not need a `load` functi
 ```html
 /// file: src/routes/blog/[slug].svelte
 <script context="module">
-	/** @type {import('@sveltejs/kit').Load} */
+	/** @type {import('./[slug]').Load} */
 	export async function load({ params, fetch, session, stuff }) {
 		const url = `https://cms.example.com/article/${params.slug}.json`;
 		const response = await fetch(url);
@@ -26,6 +26,8 @@ If the data for a page comes from its endpoint, you may not need a `load` functi
 
 > Note the `<script context="module">` — this is necessary because `load` runs before the component is rendered. Code that is per-component instance should go into a second `<script>` tag.
 
+As with [endpoints](/docs/routing#endpoints), pages can import [generated types](/docs/types#generated) — the `./[slug]` in the example above — to ensure that `params` are correctly typed.
+
 `load` is similar to `getStaticProps` or `getServerSideProps` in Next.js, except that `load` runs on both the server and the client. In the example above, if a user clicks on a link to this page the data will be fetched from `cms.example.com` without going via our server.
 
 If `load` returns `{fallthrough: true}`, SvelteKit will [fall through](/docs/routing#advanced-routing-fallthrough-routes) to other routes until something responds, or will respond with a generic 404.

diff --git a/documentation/docs/14-types.md b/documentation/docs/14-types.md
@@ -3,3 +3,74 @@ title: Types
 ---
 
 **TYPES**
+
+### Generated types
+
+The [`RequestHandler`](#sveltejs-kit-requesthandler) and [`Load`](#sveltejs-kit-load) types both accept a `Params` argument allowing you to type the `params` object. For example this endpoint expects `foo`, `bar` and `baz` params:
+
+```js
+/// file: src/routes/[foo]/[bar]/[baz].js
+// @errors: 2355
+/** @type {import('@sveltejs/kit').RequestHandler<{
+ *   foo: string;
+ *   bar: string;
+ *   baz: string
+ * }>} */
+export async function get({ params }) {
+	// ...
+}
+```
+
+Needless to say, this is cumbersome to write out, and less portable (if you were to rename the `[foo]` directory to `[qux]`, the type would no longer reflect reality).
+
+To solve this problem, SvelteKit generates `.d.ts` files for each of your endpoints and pages:
+
+```ts
+/// file: .svelte-kit/types/src/routes/[foo]/[bar]/[baz].d.ts
+/// link: false
+import type { RequestHandler as GenericRequestHandler, Load as GenericLoad } from '@sveltejs/kit';
+
+export type RequestHandler<Body = any> = GenericRequestHandler<
+	{ foo: string; bar: string; baz: string },
+	Body
+>;
+
+export type Load<Props = Record<string, any>> = GenericLoad<
+	{ foo: string; bar: string; baz: string },
+	Props
+>;
+```
+
+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:
+
+```js
+/// file: src/routes/[foo]/[bar]/[baz].js
+// @filename: [baz].d.ts
+import type { RequestHandler as GenericRequestHandler, Load as GenericLoad } from '@sveltejs/kit';
+
+export type RequestHandler<Body = any> = GenericRequestHandler<
+	{ foo: string, bar: string, baz: string },
+	Body
+>;
+
+// @filename: index.js
+// @errors: 2355
+// ---cut---
+/** @type {import('./[baz]').RequestHandler} */
+export async function get({ params }) {
+	// ...
+}
+```
+
+```svelte
+<script context="module">
+	/** @type {import('./[baz]').Load} */
+	export async function load({ params, fetch, session, stuff }) {
+		// ...
+	}
+</script>
+```
+
+> For this to work, your own `tsconfig.json` or `jsconfig.json` should extend from the generated `.svelte-kit/tsconfig.json`:
+>
+>     { "extends": ".svelte-kit/tsconfig.json" }
diff --git a/packages/create-svelte/templates/default/tsconfig.json b/packages/create-svelte/templates/default/tsconfig.json
@@ -1,30 +1,3 @@
 {
-	"compilerOptions": {
-		"moduleResolution": "node",
-		"module": "es2020",
-		"lib": ["es2020"],
-		"target": "es2020",
-		/**
-			svelte-preprocess cannot figure out whether you have a value or a type, so tell TypeScript
-			to enforce using \`import type\` instead of \`import\` for Types.
-			*/
-		"importsNotUsedAsValues": "error",
-		"isolatedModules": true,
-		"resolveJsonModule": true,
-		/**
-			To have warnings/errors of the Svelte compiler at the correct position,
-			enable source maps by default.
-			*/
-		"sourceMap": true,
-		"esModuleInterop": true,
-		"skipLibCheck": true,
-		"forceConsistentCasingInFileNames": true,
-		"baseUrl": ".",
-		"allowJs": true,
-		"checkJs": true,
-		"paths": {
-			"$lib/*": ["src/lib/*"]
-		}
-	},
-	"include": ["src/**/*.d.ts", "src/**/*.js", "src/**/*.ts", "src/**/*.svelte"]
+	"extends": "./.svelte-kit/tsconfig.json"
 }
diff --git a/packages/kit/package.json b/packages/kit/package.json
@@ -60,7 +60,15 @@
 		"build": "rollup -c && node scripts/cp.js src/runtime/components assets/components && npm run types",
 		"dev": "rollup -cw",
 		"lint": "eslint --ignore-path .gitignore --ignore-pattern \"src/packaging/test/**\" \"{src,test}/**/*.{ts,mjs,js,svelte}\" && npm run check-format",
-		"check": "tsc && svelte-check --ignore test/prerendering,src/packaging/test",
+		"check": "tsc && npm run check:integration && npm run check:prerendering",
+		"check:integration": "npm run check:integration:amp && npm run check:integration:basics && npm run check:integration:options && npm run check:integration:options-2",
+		"check:integration:amp": "cd test/apps/amp && pnpm check",
+		"check:integration:basics": "cd test/apps/basics && pnpm check",
+		"check:integration:options": "cd test/apps/options && pnpm check",
+		"check:integration:options-2": "cd test/apps/options-2 && pnpm check",
+		"check:prerendering": "npm run check:prerendering:basics && npm run check:prerendering:options",
+		"check:prerendering:basics": "cd test/prerendering/basics && pnpm check",
+		"check:prerendering:options": "cd test/prerendering/options && pnpm check",
 		"format": "npm run check-format -- --write",
 		"check-format": "prettier --check . --config ../../.prettierrc --ignore-path .gitignore",
 		"prepublishOnly": "npm run build",

diff --git a/packages/kit/src/core/build/build_client.js b/packages/kit/src/core/build/build_client.js
@@ -34,8 +34,8 @@ export async function build_client({
 	process.env.VITE_SVELTEKIT_APP_VERSION_POLL_INTERVAL = `${config.kit.version.pollInterval}`;
 
 	create_app({
+		config,
 		manifest_data,
-		output: `${SVELTE_KIT}/generated`,
 		cwd
 	});
 

diff --git a/packages/kit/src/core/create_app/index.js b/packages/kit/src/core/create_app/index.js
@@ -2,6 +2,7 @@ import fs from 'fs';
 import path from 'path';
 import { s } from '../../utils/misc.js';
 import { mkdirp } from '../../utils/filesystem.js';
+import { SVELTE_KIT } from '../constants.js';
 
 /** @type {Map<string, string>} */
 const previous_contents = new Map();
@@ -22,16 +23,19 @@ export function write_if_changed(file, code) {
 
 /**
  * @param {{
+ *   config: import('types').ValidatedConfig;
  *   manifest_data: ManifestData;
- *   output: string;
  *   cwd: string;
  * }} options
  */
-export function create_app({ manifest_data, output, cwd = process.cwd() }) {
+export function create_app({ config, manifest_data, cwd = process.cwd() }) {
+	const output = `${SVELTE_KIT}/generated`;
 	const base = path.relative(cwd, output);
 
 	write_if_changed(`${output}/manifest.js`, generate_client_manifest(manifest_data, base));
 	write_if_changed(`${output}/root.svelte`, generate_app(manifest_data));
+
+	create_types(config, manifest_data);
 }
 
 /**
@@ -189,3 +193,72 @@ function generate_app(manifest_data) {
 		{/if}
 	`);
 }
+
+/**
+ * @param {import('types').ValidatedConfig} config
+ * @param {ManifestData} manifest_data
+ */
+function create_types(config, manifest_data) {
+	/** @type {Map<string, { params: string[], type: 'page' | 'endpoint' | 'both' }>} */
+	const shadow_types = new Map();
+
+	/** @param {string} key */
+	function extract_params(key) {
+		/** @type {string[]} */
+		const params = [];
+
+		const pattern = /\[([^\]]+)\]/g;
+		let match;
+
+		while ((match = pattern.exec(key))) {
+			params.push(match[1]);
+		}
+
+		return params;
+	}
+
+	manifest_data.routes.forEach((route) => {
+		if (route.type === 'endpoint') {
+			const key = route.file.slice(0, -path.extname(route.file).length);
+			shadow_types.set(key, { params: extract_params(key), type: 'endpoint' });
+		} else if (route.shadow) {
+			const key = route.shadow.slice(0, -path.extname(route.shadow).length);
+			shadow_types.set(key, { params: extract_params(key), type: 'both' });
+		}
+	});
+
+	manifest_data.components.forEach((component) => {
+		if (component.startsWith('.')) return; // exclude fallback components
+
+		const ext = /** @type {string} */ (config.extensions.find((ext) => component.endsWith(ext)));
+		const key = component.slice(0, -ext.length);
+
+		if (!shadow_types.has(key)) {
+			shadow_types.set(key, { params: extract_params(key), type: 'page' });
+		}
+	});
+
+	shadow_types.forEach(({ params, type }, key) => {
+		const arg = `{ ${params.map((param) => `${param}: string`).join('; ')} }`;
+
+		const imports = [
+			type !== 'page' && 'RequestHandler as GenericRequestHandler',
+			type !== 'endpoint' && 'Load as GenericLoad'
+		]
+			.filter(Boolean)
+			.join(', ');
+
+		const file = `${SVELTE_KIT}/types/${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);
+	});
+}
diff --git a/packages/kit/src/core/dev/plugin.js b/packages/kit/src/core/dev/plugin.js
@@ -44,7 +44,7 @@ export async function create_plugin(config, cwd) {
 			function update_manifest() {
 				const manifest_data = create_manifest_data({ config, cwd });
 
-				create_app({ manifest_data, output: `${SVELTE_KIT}/generated`, cwd });
+				create_app({ config, manifest_data, cwd });
 
 				manifest = {
 					appDir: config.kit.appDir,
@@ -200,7 +200,6 @@ export async function create_plugin(config, cwd) {
 
 						/** @type {import('types').Hooks} */
 						const hooks = {
-							// @ts-expect-error this picks up types that belong to the tests
 							getSession: user_hooks.getSession || (() => ({})),
 							handle: amp ? sequence(amp, handle) : handle,
 							handleError: