breaking: generate plaintext 404.html for Cloudflare Pages, instead of SPA-style fallback

.changeset/gold-rocks-compare.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/adapter-cloudflare': major
+---
+
+breaking: generate plaintext 404.html instead of SPA-style fallback page

packages/adapter-cloudflare/index.d.ts

@@ -4,6 +4,18 @@ import './ambient.js';
 export default function plugin(options?: AdapterOptions): Adapter;
 
 export interface AdapterOptions {
+	/**
+	 * Whether to render a plaintext 404.html page, or a rendered SPA fallback page. This page will
+	 * only be served when a request that matches an entry in `routes.exclude` fails to match an asset.
+	 *
+	 * Most of the time `plaintext` is sufficient, but if you are using `routes.exclude` to manually
+	 * exclude a set of prerendered pages without exceeding the 100 route limit, you may wish to
+	 * use `spa` instead to avoid showing an unstyled 404 page to users.
+	 *
+	 * @default 'plaintext'
+	 */
+	fallback?: 'plaintext' | 'spa';
+
 	/**
 	 * Customize the automatically-generated `_routes.json` file
 	 * https://developers.cloudflare.com/pages/platform/functions/routing/#create-a-_routesjson-file

packages/adapter-cloudflare/index.js

@@ -14,10 +14,17 @@ export default function (options = {}) {
 
 			builder.rimraf(dest);
 			builder.rimraf(tmp);
+
+			builder.mkdirp(dest);
 			builder.mkdirp(tmp);
 
-			// generate 404.html first which can then be overridden by prerendering, if the user defined such a page
-			await builder.generateFallback(path.join(dest, '404.html'));
+			// generate plaintext 404.html first which can then be overridden by prerendering, if the user defined such a page
+			const fallback = path.join(dest, '404.html');
+			if (options.fallback === 'spa') {
+				await builder.generateFallback(fallback);
+			} else {
+				writeFileSync(fallback, 'Not Found');
+			}
 
 			const dest_dir = `${dest}${builder.config.kit.paths.base}`;
 			const written_files = builder.writeClient(dest_dir);