Update adapter-vercel to use new build output API

.changeset/giant-ants-hang.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/adapter-vercel': patch
+---
+
+Support build output API, with edge functions and code-splitting

.changeset/smooth-dodos-clap.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+builder.createEntries returns a promise that awaits complete() callbacks

packages/adapter-vercel/README.md

@@ -6,6 +6,8 @@ If you're using [adapter-auto](../adapter-auto), you don't need to install this
 
 ## Usage
 
+> The `edge` and `split` options depend on the Vercel Build Output API which is currently in beta. For now, you must opt in by visiting `https://vercel.com/svelte/[YOUR_PROJECT]/settings/environment-variables` and adding `ENABLE_VC_BUILD` with the value `1`.
+
 Add `"@sveltejs/adapter-vercel": "next"` to the `devDependencies` in your `package.json` and run `npm install`.
 
 Then in your `svelte.config.js`:
@@ -15,18 +17,25 @@ import vercel from '@sveltejs/adapter-vercel';
 
 export default {
 	kit: {
-		...
-		adapter: vercel(options)
+		// default options are shown
+		adapter: vercel({
+			// if true, will deploy the app using edge functions
+			// (https://vercel.com/docs/concepts/functions/edge-functions)
+			// rather than serverless functions
+			edge: false,
+
+			// an array of dependencies that esbuild should treat
+			// as external when bundling functions
+			external: [],
+
+			// if true, will split your app into multiple functions
+			// instead of creating a single one for the entire app
+			split: false
+		})
 	}
 };
 ```
 
-## Options
-
-You can pass an `options` argument, if necessary, with the following:
-
-- `external` — an array of dependencies that [esbuild](https://esbuild.github.io/api/#external) should treat as external
-
 ## Changelog
 
 [The Changelog for this package is available on GitHub](https://github.com/sveltejs/kit/blob/master/packages/adapter-vercel/CHANGELOG.md).

packages/adapter-vercel/files/edge.js

@@ -0,0 +1,15 @@
+import { Server } from 'SERVER';
+import { manifest } from 'MANIFEST';
+
+const server = new Server(manifest);
+
+/**
+ * @param {Request} request
+ */
+export default (request) => {
+	return server.respond(request, {
+		getClientAddress() {
+			return request.headers.get('x-forwarded-for');
+		}
+	});
+};

packages/adapter-vercel/files/entry.js → packages/adapter-vercel/files/serverless.js

@@ -1,8 +1,10 @@
-import './shims';
+import { installFetch } from '@sveltejs/kit/install-fetch';
 import { getRequest, setResponse } from '@sveltejs/kit/node';
 import { Server } from 'SERVER';
 import { manifest } from 'MANIFEST';
 
+installFetch();
+
 const server = new Server(manifest);
 
 /**

packages/adapter-vercel/index.d.ts

@@ -1,7 +1,9 @@
 import { Adapter } from '@sveltejs/kit';
 
 type Options = {
+	edge?: boolean;
 	external?: string[];
+	split?: boolean;
 };
 
 declare function plugin(options?: Options): Adapter;