include as many static assets as possible in exclude list (#8422)

* include as many static assets as possible in exclude list - closes #7640

* temporarily add trailing slash

* Revert "temporarily add trailing slash"

This reverts commit f3ff35f.

* add a warning

* fix typo

* fix string

* Update .changeset/giant-penguins-act.md

Co-authored-by: Ben McCann <322311+benmccann@users.noreply.github.com>

* fix

Co-authored-by: Simon H <5968653+dummdidumm@users.noreply.github.com>
Co-authored-by: Ben McCann <322311+benmccann@users.noreply.github.com>

.changeset/giant-penguins-act.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/adapter-cloudflare': minor
+---
+
+feat: include as many static assets as possible in exclude list

packages/adapter-cloudflare/index.js

@@ -34,7 +34,7 @@ export default function () {
 
 			writeFileSync(
 				`${dest}/_routes.json`,
-				JSON.stringify(get_routes_json(builder.config.kit.appDir, written_files))
+				JSON.stringify(get_routes_json(builder, written_files))
 			);
 
 			writeFileSync(`${dest}/_headers`, generate_headers(builder.config.kit.appDir));
@@ -62,29 +62,50 @@ export default function () {
 }
 
 /**
- * @param {string} app_dir
+ * @param {import('@sveltejs/kit').Builder} builder
  * @param {string[]} assets
  * @returns {import('.').RoutesJSONSpec}
  */
-function get_routes_json(app_dir, assets) {
+function get_routes_json(builder, assets) {
+	/**
+	 * The list of routes that will _not_ invoke functions (which cost money).
+	 * This is done on a best-effort basis, as there is a limit of 100 rules
+	 */
+	const exclude = [
+		`/${builder.config.kit.appDir}/*`,
+		...assets.filter((file) => !file.startsWith(`${builder.config.kit.appDir}/`))
+	];
+
+	const MAX_EXCLUSIONS = 99; // 100 minus existing `include` rules
+	let excess;
+
+	if (exclude.length > MAX_EXCLUSIONS) {
+		excess = 'static assets';
+
+		if (builder.prerendered.paths.length > 0) {
+			excess += ' or prerendered routes';
+		}
+	} else if (exclude.length + builder.prerendered.paths.length > MAX_EXCLUSIONS) {
+		excess = 'prerendered routes';
+	}
+
+	for (const path of builder.prerendered.paths) {
+		if (!builder.prerendered.redirects.has(path)) {
+			exclude.push(path);
+		}
+	}
+
+	if (excess) {
+		const message = `Static file count exceeds _routes.json limits (see https://developers.cloudflare.com/pages/platform/functions/routing/#limits). Accessing some ${excess} will cause function invocations.`;
+		builder.log.warn(message);
+		exclude.length = 99;
+	}
+
 	return {
 		version: 1,
 		description: 'Generated by @sveltejs/adapter-cloudflare',
 		include: ['/*'],
-		exclude: [
-			`/${app_dir}/immutable/*`,
-			...assets
-				// We're being conservative by not excluding all assets in
-				// /static just yet. If there are any upstream auth rules to
-				// protect certain things (e.g. a PDF that requires auth),
-				// then we wouldn't want to prevent those requests from going
-				// to the user functions worker.
-				// We do want to show an example of a _routes.json that
-				// excludes more than just /_app/immutable/*, and favicons
-				// are a reasonable choice
-				.filter((file) => file.startsWith('favicon'))
-				.map((file) => `/${file}`)
-		]
+		exclude
 	};
 }