feat: provide PageProps, LayoutProps types (#13308)

Closes #12726

---------

Co-authored-by: Tee Ming <chewteeming01@gmail.com>

.changeset/ten-onions-talk.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': minor
+---
+
+feat: provide `PageProps` and `LayoutProps` types

documentation/docs/20-core-concepts/10-routing.md

@@ -42,7 +42,7 @@ Pages can receive data from `load` functions via the `data` prop.
 ```svelte
 <!--- file: src/routes/blog/[slug]/+page.svelte --->
 <script>
-	/** @type {{ data: import('./$types').PageData }} */
+	/** @type {import('./$types').PageProps} */
 	let { data } = $props();
 </script>
 
@@ -51,7 +51,9 @@ Pages can receive data from `load` functions via the `data` prop.
 ```
 
 > [!LEGACY]
-> In Svelte 4, you'd use `export let data` instead
+> `PageProps` was added in 2.16.0. In earlier versions, you had to type the `data` property manually with `PageData` instead, see [$types](#\$types).
+>
+> In Svelte 4, you'd use `export let data` instead.
 
 > [!NOTE] SvelteKit uses `<a>` elements to navigate between routes, rather than a framework-specific `<Link>` component.
 
@@ -212,7 +214,7 @@ We can create a layout that only applies to pages below `/settings` (while inher
 ```svelte
 <!--- file: src/routes/settings/+layout.svelte --->
 <script>
-	/** @type {{ data: import('./$types').LayoutData, children: import('svelte').Snippet }} */
+	/** @type {import('./$types').LayoutProps} */
 	let { data, children } = $props();
 </script>
 
@@ -227,6 +229,9 @@ We can create a layout that only applies to pages below `/settings` (while inher
 {@render children()}
 ```
 
+> [!LEGACY]
+> `LayoutProps` was added in 2.16.0. In earlier versions, you had to [type the properties manually instead](#\$types).
+
 You can see how `data` is populated by looking at the `+layout.js` example in the next section just below.
 
 By default, each layout inherits the layout above it. Sometimes that isn't what you want - in this case, [advanced layouts](advanced-routing#Advanced-layouts) can help you.
@@ -255,7 +260,7 @@ Data returned from a layout's `load` function is also available to all its child
 ```svelte
 <!--- file: src/routes/settings/profile/+page.svelte --->
 <script>
-	/** @type {{ data: import('./$types').PageData }} */
+	/** @type {import('./$types').PageProps} */
 	let { data } = $props();
 
 	console.log(data.sections); // [{ slug: 'profile', title: 'Profile' }, ...]
@@ -388,16 +393,33 @@ export async function fallback({ request }) {
 
 Throughout the examples above, we've been importing types from a `$types.d.ts` file. This is a file SvelteKit creates for you in a hidden directory if you're using TypeScript (or JavaScript with JSDoc type annotations) to give you type safety when working with your root files.
 
-For example, annotating `let { data } = $props()` with `PageData` (or `LayoutData`, for a `+layout.svelte` file) tells TypeScript that the type of `data` is whatever was returned from `load`:
+For example, annotating `let { data } = $props()` with `PageProps` (or `LayoutProps`, for a `+layout.svelte` file) tells TypeScript that the type of `data` is whatever was returned from `load`:
 
 ```svelte
 <!--- file: src/routes/blog/[slug]/+page.svelte --->
 <script>
-	/** @type {{ data: import('./$types').PageData }} */
+	/** @type {import('./$types').PageProps} */
 	let { data } = $props();
 </script>
 ```
 
+> [!NOTE]
+> The `PageProps` and `LayoutProps` types, added in 2.16.0, are a shortcut for typing the `data` prop as `PageData` or `LayoutData`, as well as other props, such as `form` for pages, or `children` for layouts. In earlier versions, you had to type these properties manually. For example, for a page:
+>
+> ```js
+> /// file: +page.svelte
+> /** @type {{ data: import('./$types').PageData, form: import('./$types').ActionData }} */
+> let { data, form } = $props();
+> ```
+>
+> Or, for a layout:
+>
+> ```js
+> /// file: +layout.svelte
+> /** @type {{ data: import('./$types').LayoutData, children: Snippet }} */
+> let { data, children } = $props();
+> ```
+
 In turn, annotating the `load` function with `PageLoad`, `PageServerLoad`, `LayoutLoad` or `LayoutServerLoad` (for `+page.js`, `+page.server.js`, `+layout.js` and `+layout.server.js` respectively) ensures that `params` and the return value are correctly typed.
 
 If you're using VS Code or any IDE that supports the language server protocol and TypeScript plugins then you can omit these types _entirely_! Svelte's IDE tooling will insert the correct types for you, so you'll get type checking without writing them yourself. It also works with our command line tool `svelte-check`.

documentation/docs/20-core-concepts/20-load.md

@@ -24,7 +24,7 @@ export function load({ params }) {
 ```svelte
 <!--- file: src/routes/blog/[slug]/+page.svelte --->
 <script>
-	/** @type {{ data: import('./$types').PageData }} */
+	/** @type {import('./$types').PageProps} */
 	let { data } = $props();
 </script>
 
@@ -33,7 +33,14 @@ export function load({ params }) {
 ```
 
 > [!LEGACY]
-> In Svelte 4, you'd use `export let data` instead
+> Before version 2.16.0, the props of a page and layout had to be typed individually:
+> ```js
+> /// file: +page.svelte
+> /** @type {{ data: import('./$types').PageData }} */
+> let { data } = $props();
+> ```
+>
+> In Svelte 4, you'd use `export let data` instead.
 
 Thanks to the generated `$types` module, we get full type safety.
 
@@ -88,7 +95,7 @@ export async function load() {
 ```svelte
 <!--- file: src/routes/blog/[slug]/+layout.svelte --->
 <script>
-	/** @type {{ data: import('./$types').LayoutData, children: Snippet }} */
+	/** @type {import('./$types').LayoutProps} */
 	let { data, children } = $props();
 </script>
 
@@ -111,14 +118,22 @@ export async function load() {
 </aside>
 ```
 
+> [!LEGACY]
+> `LayoutProps` was added in 2.16.0. In earlier versions, properties had to be typed individually:
+> ```js
+> /// file: +layout.svelte
+> /** @type {{ data: import('./$types').LayoutData, children: Snippet }} */
+> let { data, children } = $props();
+> ```
+
 Data returned from layout `load` functions is available to child `+layout.svelte` components and the `+page.svelte` component as well as the layout that it 'belongs' to.
 
 ```svelte
 /// file: src/routes/blog/[slug]/+page.svelte
 <script>
 	+++import { page } from '$app/state';+++
 
-	/** @type {{ data: import('./$types').PageData }} */
+	/** @type {import('./$types').PageProps} */
 	let { data } = $props();
 
 +++	// we can access `data.posts` because it's returned from
@@ -372,7 +387,7 @@ export async function load({ parent }) {
 ```svelte
 <!--- file: src/routes/abc/+page.svelte --->
 <script>
-	/** @type {{ data: import('./$types').PageData }} */
+	/** @type {import('./$types').PageProps} */
 	let { data } = $props();
 </script>
 
@@ -511,7 +526,7 @@ This is useful for creating skeleton loading states, for example:
 ```svelte
 <!--- file: src/routes/blog/[slug]/+page.svelte --->
 <script>
-	/** @type {{ data: import('./$types').PageData }} */
+	/** @type {import('./$types').PageProps} */
 	let { data } = $props();
 </script>
 
@@ -652,7 +667,7 @@ export async function load({ fetch, depends }) {
 <script>
 	import { invalidate, invalidateAll } from '$app/navigation';
 
-	/** @type {{ data: import('./$types').PageData }} */
+	/** @type {import('./$types').PageProps} */
 	let { data } = $props();
 
 	function rerunLoadFunction() {

documentation/docs/20-core-concepts/30-form-actions.md

@@ -140,7 +140,7 @@ export const actions = {
 ```svelte
 <!--- file: src/routes/login/+page.svelte --->
 <script>
-	/** @type {{ data: import('./$types').PageData, form: import('./$types').ActionData }} */
+	/** @type {import('./$types').PageProps} */
 	let { data, form } = $props();
 </script>
 
@@ -152,7 +152,14 @@ export const actions = {
 ```
 
 > [!LEGACY]
-> In Svelte 4, you'd use `export let data` and `export let form` instead to declare properties
+> `PageProps` was added in 2.16.0. In earlier versions, you had to type the `data` and `form` properties individually:
+> ```js
+> /// file: +page.svelte
+> /** @type {{ data: import('./$types').PageData, form: import('./$types').ActionData }} */
+> let { data, form } = $props();
+> ```
+>
+> In Svelte 4, you'd use `export let data` and `export let form` instead to declare properties.
 
 ### Validation errors
 
@@ -339,7 +346,7 @@ The easiest way to progressively enhance a form is to add the `use:enhance` acti
 <script>
 	+++import { enhance } from '$app/forms';+++
 
-	/** @type {{ form: import('./$types').ActionData }} */
+	/** @type {import('./$types').PageProps} */
 	let { form } = $props();
 </script>
 
@@ -390,7 +397,7 @@ If you return a callback, you may need to reproduce part of the default `use:enh
 <script>
 	import { enhance, +++applyAction+++ } from '$app/forms';
 
-	/** @type {{ form: import('./$types').ActionData }} */
+	/** @type {import('./$types').PageProps} */
 	let { form } = $props();
 </script>
 
@@ -427,7 +434,7 @@ We can also implement progressive enhancement ourselves, without `use:enhance`,
 	import { invalidateAll, goto } from '$app/navigation';
 	import { applyAction, deserialize } from '$app/forms';
 
-	/** @type {{ form: import('./$types').ActionData }} */
+	/** @type {import('./$types').PageProps} */
 	let { form } = $props();
 
 	/** @param {SubmitEvent & { currentTarget: EventTarget & HTMLFormElement}} event */

documentation/docs/20-core-concepts/50-state-management.md

@@ -89,7 +89,7 @@ You might wonder how we're able to use `page.data` and other [app state]($app-st
 <script>
 	import { setContext } from 'svelte';
 
-	/** @type {{ data: import('./$types').LayoutData }} */
+	/** @type {import('./$types').LayoutProps} */
 	let { data } = $props();
 
 	// Pass a function referencing our state
@@ -126,7 +126,7 @@ When you navigate around your application, SvelteKit reuses existing layout and
 ```svelte
 <!--- file: src/routes/blog/[slug]/+page.svelte --->
 <script>
-	/** @type {{ data: import('./$types').PageData }} */
+	/** @type {import('./$types').PageProps} */
 	let { data } = $props();
 
 	// THIS CODE IS BUGGY!
@@ -149,7 +149,7 @@ Instead, we need to make the value [_reactive_](/tutorial/svelte/state):
 ```svelte
 /// file: src/routes/blog/[slug]/+page.svelte
 <script>
-	/** @type {{ data: import('./$types').PageData }} */
+	/** @type {import('./$types').PageProps} */
 	let { data } = $props();
 
 +++	let wordCount = $derived(data.content.split(' ').length);

documentation/docs/25-build-and-deploy/90-adapter-vercel.md

@@ -162,7 +162,7 @@ export function load() {
 ```svelte
 <!--- file: +layout.svelte --->
 <script>
-	/** @type {{ data: import('./$types').LayoutServerData }} */
+	/** @type {import('./$types').LayoutProps} */
 	let { data } = $props();
 </script>
 

documentation/docs/98-reference/54-types.md

@@ -84,6 +84,37 @@ export async function load({ params, fetch }) {
 }
 ```
 
+The return types of the load functions are then available through the `$types` module as `PageData` and `LayoutData` respectively, while the union of the return values of all `Actions` is available as `ActionData`. Starting with version 2.16.0, two additional helper types are provided. `PageProps` defines `data: PageData`, as well as `form: ActionData`, when there are actions defined. `LayoutProps` defines `data: LayoutData`, as well as `children: Snippet`:
+
+```svelte
+<!--- file: src/routes/+page.svelte --->
+<script>
+	/** @type {import('./$types').PageProps} */
+	let { data, form } = $props();
+</script>
+```
+
+> [!LEGACY]
+> Before 2.16.0:
+> ```svelte
+> <!--- file: src/routes/+page.svelte --->
+> <script>
+> 	/** @type {{ data: import('./$types').PageData, form: import('./$types').ActionData }} */
+> 	let { data, form } = $props();
+> </script>
+> ```
+>
+> Using Svelte 4:
+> ```svelte
+> <!--- file: src/routes/+page.svelte --->
+> <script>
+>   /** @type {import('./$types').PageData} */
+>   export let data;
+>   /** @type {import('./$types').ActionData} */
+>   export let form;
+> </script>
+> ```
+
 > [!NOTE] For this to work, your own `tsconfig.json` or `jsconfig.json` should extend from the generated `.svelte-kit/tsconfig.json` (where `.svelte-kit` is your [`outDir`](configuration#outDir)):
 >
 > `{ "extends": "./.svelte-kit/tsconfig.json" }`

packages/kit/src/core/sync/write_types/index.js

@@ -270,6 +270,12 @@ function update_types(config, routes, route, to_delete = new Set()) {
 				'export type Actions<OutputData extends Record<string, any> | void = Record<string, any> | void> = Kit.Actions<RouteParams, OutputData, RouteId>'
 			);
 		}
+
+		if (route.leaf.server) {
+			exports.push('export type PageProps = { data: PageData; form: ActionData }');
+		} else {
+			exports.push('export type PageProps = { data: PageData }');
+		}
 	}
 
 	if (route.layout) {
@@ -333,6 +339,10 @@ function update_types(config, routes, route, to_delete = new Set()) {
 
 		if (proxies.server?.modified) to_delete.delete(proxies.server.file_name);
 		if (proxies.universal?.modified) to_delete.delete(proxies.universal.file_name);
+
+		exports.push(
+			'export type LayoutProps = { data: LayoutData; children: import("svelte").Snippet }'
+		);
 	}
 
 	if (route.endpoint) {