feat: configure edge function at route level

.changeset/modern-scissors-shout.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/adapter-netlify': minor
+---
+
+feat: configure edge function at route level

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

@@ -48,7 +48,22 @@ New projects will use the current Node LTS version by default. However, if you'r
 
 ## Netlify Edge Functions
 
-SvelteKit supports [Netlify Edge Functions](https://docs.netlify.com/netlify-labs/experimental-features/edge-functions/). 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.
+SvelteKit supports [Netlify Edge Functions](https://docs.netlify.com/netlify-labs/experimental-features/edge-functions/). To control how your routes are deployed to Netlify as functions, you can export const config inside +server.js, +page(.server).js and +layout(.server).js files.
+
+For example you could deploy some parts of your app as Edge Functions...
+
+```js
+// @errors: 2307
+/// file: about/+page.js
+/** @type {import('@sveltejs/adapter-netlify').Config} */
+export const config = {
+	runtime: 'edge'
+};
+```
+
+...and others as Serverless Functions (note that by specifying config inside a layout, it applies to all child pages).
+
+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 for all pages. If set to `false` (the default), the site will deploy to Node-based Netlify Functions.
 
 ```js
 // @errors: 2307

packages/adapter-netlify/index.d.ts

@@ -2,3 +2,11 @@ import { Adapter } from '@sveltejs/kit';
 import './ambient.js';
 
 export default function plugin(opts?: { split?: boolean; edge?: boolean }): Adapter;
+
+export interface Config {
+	/**
+	 * Whether to use [Edge Functions](https://docs.netlify.com/edge-functions/overview/) (`'edge'`)
+	 * @default undefined
+	 */
+	runtime?: 'edge';
+}

packages/adapter-netlify/index.js

@@ -90,10 +90,29 @@ export default function ({ split = false, edge = edge_set_in_env_var } = {}) {
 				if (split) {
 					throw new Error('Cannot use `split: true` alongside `edge: true`');
 				}
+			}
+
+			/** @type {{ edge: import('@sveltejs/kit').RouteDefinition<import('./index.js').Config>[], lambda: import('@sveltejs/kit').RouteDefinition<import('./index.js').Config>[] }} */
+			const mutated_routes = { edge: [], lambda: [] };
+			for (let i = 0; i < builder.routes.length; i++) {
+				/** @type {import('@sveltejs/kit').RouteDefinition<import('./index.js').Config>} */
+				const route = builder.routes[i];
+
+				if (route.config?.runtime === 'edge') {
+					mutated_routes.edge.push(route);
+				} else {
+					mutated_routes.lambda.push(route);
+				}
+			}
 
+			if (mutated_routes.edge.length) {
+				builder.routes = mutated_routes.edge;
 				await generate_edge_functions({ builder });
-			} else {
-				generate_lambda_functions({ builder, split, publish });
+			}
+
+			if (mutated_routes.lambda.length) {
+				builder.routes = mutated_routes.lambda;
+				generate_lambda_functions({ builder, publish, split });
 			}
 		},
 
@@ -204,7 +223,10 @@ function generate_lambda_functions({ builder, publish, split }) {
 	builder.copy(`${files}/esm`, '.netlify', { replace });
 
 	// Configuring the function to use ESM as the output format.
-	const fn_config = JSON.stringify({ config: { nodeModuleFormat: 'esm' }, version: 1 });
+	const fn_config = JSON.stringify({
+		config: { nodeModuleFormat: 'esm' },
+		version: 1
+	});
 
 	builder.log.minor('Generating serverless functions...');