Fix docs (#15781)

extracted from sveltejs/svelte.dev#1959

---------

Co-authored-by: Tee Ming <[email protected]>

Author: Rich-Harris

documentation/docs/20-core-concepts/60-remote-functions.md

@@ -562,7 +562,14 @@ In addition to declarative schema validation, you can programmatically mark fiel
 - It accepts multiple arguments that can be strings (for issues relating to the form as a whole — these will only show up in `fields.allIssues()`) or standard-schema-compliant issues (for those relating to a specific field). Use the `issue` parameter for type-safe creation of such issues:
 
 ```js
+// @errors: 18046
 /// file: src/routes/shop/data.remote.js
+// @filename: ambient.d.ts
+declare module '$lib/server/database' {
+	export function buy(qty: number): Promise<void>
+}
+// @filename: index.js
+// ---cut---
 import * as v from 'valibot';
 import { invalid } from '@sveltejs/kit';
 import { form } from '$app/server';
@@ -1227,7 +1234,7 @@ As long as _you're_ not passing invalid data to your remote functions, there are
 In the second case, we don't want to give the attacker any help, so SvelteKit will generate a generic [400 Bad Request](https://http.dog/400) response. You can control the message by implementing the [`handleValidationError`](hooks#Server-hooks-handleValidationError) server hook, which, like [`handleError`](hooks#Shared-hooks-handleError), must return an [`App.Error`](errors#Type-safety) (which defaults to `{ message: string }`):
 
 ```js
-/// file: src/hooks.server.ts
+/// file: src/hooks.server.js
 /** @type {import('@sveltejs/kit').HandleValidationError} */
 export function handleValidationError({ event, issues }) {
 	return {
@@ -1253,14 +1260,26 @@ export const getStuff = query('unchecked', async ({ id }: { id: string }) => {
 Inside `query`, `form` and `command` you can use [`getRequestEvent`]($app-server#getRequestEvent) to get the current [`RequestEvent`](@sveltejs-kit#RequestEvent) object. This makes it easy to build abstractions for interacting with cookies, for example:
 
 ```ts
-/// file: user.remote.ts
+/// file: user.remote.js
+// @filename: ambient.d.ts
+interface User {
+	name: string;
+	avatar: string;
+}
+
+declare module '$lib/server/database' {
+	export function findUser(sessionId: string | undefined): Promise<User | null>;
+}
+
+// @filename: index.js
+// ---cut---
 import { getRequestEvent, query } from '$app/server';
 import { findUser } from '$lib/server/database';
 
 export const getProfile = query(async () => {
 	const user = await getUser();
 
-	return {
+	return user && {
 		name: user.name,
 		avatar: user.avatar
 	};

documentation/docs/25-build-and-deploy/50-adapter-static.md

@@ -11,6 +11,7 @@ This will prerender your entire site as a collection of static files. If you'd l
 Install with `npm i -D @sveltejs/adapter-static`, then add the adapter to your `svelte.config.js`:
 
 ```js
+// @errors: 2307
 /// file: svelte.config.js
 import adapter from '@sveltejs/adapter-static';
 
@@ -55,6 +56,7 @@ Some platforms have zero-config support (more to come in future):
 On these platforms, you should omit the adapter options so that `adapter-static` can provide the optimal configuration:
 
 ```js
+// @errors: 2307
 /// file: svelte.config.js
 import adapter from '@sveltejs/adapter-static';
 
@@ -80,7 +82,7 @@ The directory to write static assets (the contents of `static`, plus client-side
 
 ### fallback
 
-To create a [single page app (SPA)](single-page-apps) you must specify the name of the fallback page to be generated by SvelteKit, which is used as the entry point for URLs that have not been prerendered. This is commonly `200.html`, but can vary depending on your deployment platform. You should avoid `index.html` where possible to avoid conflicting with a prerendered homepage. 
+To create a [single page app (SPA)](single-page-apps) you must specify the name of the fallback page to be generated by SvelteKit, which is used as the entry point for URLs that have not been prerendered. This is commonly `200.html`, but can vary depending on your deployment platform. You should avoid `index.html` where possible to avoid conflicting with a prerendered homepage.
 
 > [!NOTE] This option has large negative performance and SEO impacts. It is only recommended in certain circumstances such as wrapping the site in a mobile app. See the [single page apps](single-page-apps) documentation for more details and alternatives.
 
@@ -101,7 +103,7 @@ You'll also want to generate a fallback `404.html` page to replace the default 4
 A config for GitHub Pages might look like the following:
 
 ```js
-// @errors: 2322
+// @errors: 2307 2322
 /// file: svelte.config.js
 import adapter from '@sveltejs/adapter-static';
 

documentation/docs/25-build-and-deploy/55-single-page-apps.md

@@ -19,6 +19,7 @@ export const ssr = false;
 If you don't have any server-side logic (i.e. `+page.server.js`, `+layout.server.js` or `+server.js` files) you can use [`adapter-static`](adapter-static) to create your SPA. Install `adapter-static` with `npm i -D @sveltejs/adapter-static` and add it to your `svelte.config.js` with the `fallback` option:
 
 ```js
+// @errors: 2307
 /// file: svelte.config.js
 import adapter from '@sveltejs/adapter-static';
 

documentation/docs/25-build-and-deploy/60-adapter-cloudflare.md

@@ -17,6 +17,7 @@ This adapter will be installed by default when you use [`adapter-auto`](adapter-
 Install with `npm i -D @sveltejs/adapter-cloudflare`, then add the adapter to your `svelte.config.js`:
 
 ```js
+// @errors: 2307
 /// file: svelte.config.js
 import adapter from '@sveltejs/adapter-cloudflare';
 

documentation/docs/25-build-and-deploy/80-adapter-netlify.md

@@ -11,6 +11,7 @@ This adapter will be installed by default when you use [`adapter-auto`](adapter-
 Install with `npm i -D @sveltejs/adapter-netlify`, then add the adapter to your `svelte.config.js`:
 
 ```js
+// @errors: 2307
 /// file: svelte.config.js
 import adapter from '@sveltejs/adapter-netlify';
 
@@ -53,6 +54,7 @@ New projects will use the current Node LTS version by default. However, if you'r
 SvelteKit supports [Netlify Edge Functions](https://docs.netlify.com/build/edge-functions/overview/). If you pass the option `edge: true` to the `adapter` function, server-side rendering will happen in a Deno-based edge function that's deployed close to the site visitor. If set to `false` (the default), the site will deploy to Node-based Netlify Functions.
 
 ```js
+// @errors: 2307
 /// file: svelte.config.js
 import adapter from '@sveltejs/adapter-netlify';
 

documentation/docs/30-advanced/68-observability.md

@@ -74,6 +74,7 @@ To view your first trace, you'll need to set up a local collector. We'll use [Ja
 - Create `src/instrumentation.server.js` with the following:
 
 ```js
+// @errors: 2307
 /// file: src/instrumentation.server.js
 import { NodeSDK } from '@opentelemetry/sdk-node';
 import { getNodeAutoInstrumentations } from '@opentelemetry/auto-instrumentations-node';
@@ -97,4 +98,4 @@ Now, server-side requests will begin generating traces, which you can view in Ja
 
 ## `@opentelemetry/api`
 
-SvelteKit uses `@opentelemetry/api` to generate its spans. This is declared as an optional peer dependency so that users not needing traces see no impact on install size or runtime performance. In most cases, if you're configuring your application to collect SvelteKit's spans, you'll end up installing a library like `@opentelemetry/sdk-node` or `@vercel/otel`, which in turn depend on `@opentelemetry/api`, which will satisfy SvelteKit's dependency as well. If you see an error from SvelteKit telling you it can't find `@opentelemetry/api`, it may just be because you haven't set up your trace collection yet. If you _have_ done that and are still seeing the error, you can install `@opentelemetry/api` yourself. 
+SvelteKit uses `@opentelemetry/api` to generate its spans. This is declared as an optional peer dependency so that users not needing traces see no impact on install size or runtime performance. In most cases, if you're configuring your application to collect SvelteKit's spans, you'll end up installing a library like `@opentelemetry/sdk-node` or `@vercel/otel`, which in turn depend on `@opentelemetry/api`, which will satisfy SvelteKit's dependency as well. If you see an error from SvelteKit telling you it can't find `@opentelemetry/api`, it may just be because you haven't set up your trace collection yet. If you _have_ done that and are still seeing the error, you can install `@opentelemetry/api` yourself.

documentation/docs/40-best-practices/10-accessibility.md

@@ -65,12 +65,13 @@ If your content is available in multiple languages, you should set the `lang` at
 
 ```js
 /// file: src/hooks.server.js
-/**
- * @param {import('@sveltejs/kit').RequestEvent} event
- */
-function get_lang(event) {
+// @filename: utils.ts
+export function get_lang(event: import('@sveltejs/kit').RequestEvent) {
 	return 'en';
 }
+
+// @filename: hooks.server.js
+import { get_lang } from './utils';
 // ---cut---
 /** @type {import('@sveltejs/kit').Handle} */
 export function handle({ event, resolve }) {