fix: prerender optional parameters as empty when entries contains '*'

.changeset/good-jars-relax.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: prerender optional parameters as empty when `entries` contains `'*'`

packages/kit/src/core/postbuild/prerender.js

@@ -426,8 +426,12 @@ async function prerender({ out, manifest_path, metadata, verbose, env }) {
 		if (entry === '*') {
 			for (const [id, prerender] of prerender_map) {
 				if (prerender) {
-					if (id.includes('[')) continue;
-					const path = `/${get_route_segments(id).join('/')}`;
+					// remove optional parameters from the route
+					const segments = get_route_segments(id).filter((segment) => !segment.startsWith('[['));
+					const processed_id = '/' + segments.join('/');
+
+					if (processed_id.includes('[')) continue;
+					const path = `/${get_route_segments(processed_id).join('/')}`;
 					enqueue(null, config.paths.base + path);
 				}
 			}

packages/kit/src/exports/public.d.ts

@@ -498,7 +498,7 @@ export interface KitConfig {
 		 */
 		crawl?: boolean;
 		/**
-		 * An array of pages to prerender, or start crawling from (if `crawl: true`). The `*` string includes all non-dynamic routes (i.e. pages with no `[parameters]`, because SvelteKit doesn't know what value the parameters should have).
+		 * An array of pages to prerender, or start crawling from (if `crawl: true`). The `*` string includes all routes containing no required `[parameters]`  with optional parameters included as being empty (since SvelteKit doesn't know what value any parameters should have).
 		 * @default ["*"]
 		 */
 		entries?: Array<'*' | `/${string}`>;

packages/kit/test/prerendering/basics/src/routes/optional-params/[[optional]]/+page.svelte

@@ -0,0 +1 @@
+<a href="/optional-params/with-value">Path with Value</a>

packages/kit/test/prerendering/basics/test/tests.spec.js

@@ -244,3 +244,8 @@ test('prerenders responses with immutable Headers', () => {
 	const content = read('immutable-headers');
 	expect(content).toMatch('foo');
 });
+
+test('prerenders paths with optional parameters with empty values', () => {
+	const content = read('optional-params.html');
+	expect(content).includes('Path with Value');
+});

packages/kit/types/index.d.ts

@@ -480,7 +480,7 @@ declare module '@sveltejs/kit' {
 			 */
 			crawl?: boolean;
 			/**
-			 * An array of pages to prerender, or start crawling from (if `crawl: true`). The `*` string includes all non-dynamic routes (i.e. pages with no `[parameters]`, because SvelteKit doesn't know what value the parameters should have).
+			 * An array of pages to prerender, or start crawling from (if `crawl: true`). The `*` string includes all routes containing no required `[parameters]`  with optional parameters included as being empty (since SvelteKit doesn't know what value any parameters should have).
 			 * @default ["*"]
 			 */
 			entries?: Array<'*' | `/${string}`>;