render fallback page regardless of trailingSlash - fixes #4340 (#4351)

Author: Rich-Harris

.changeset/few-carrots-sell.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+Populate fallback page when trailingSlash is "always"

packages/kit/src/runtime/server/index.js

@@ -18,7 +18,7 @@ export async function respond(request, options, state) {
 
 	const normalized = normalize_path(url.pathname, options.trailing_slash);
 
-	if (normalized !== url.pathname) {
+	if (normalized !== url.pathname && !state.prerender?.fallback) {
 		return new Response(undefined, {
 			status: 301,
 			headers: {

packages/kit/test/prerendering/options/svelte.config.js

@@ -4,7 +4,9 @@ import adapter from '../../../../adapter-static/index.js';
 /** @type {import('@sveltejs/kit').Config} */
 const config = {
 	kit: {
-		adapter: adapter(),
+		adapter: adapter({
+			fallback: '200.html'
+		}),
 
 		csp: {
 			directives: {

packages/kit/test/prerendering/options/test/test.js

@@ -31,4 +31,10 @@ test('does not copy `public` into `_app`', () => {
 	assert.ok(!fs.existsSync(`${build}/_app/robots.txt`));
 });
 
+// https://github.com/sveltejs/kit/issues/4340
+test('populates fallback 200.html file', () => {
+	const content = read('200.html');
+	assert.ok(content !== '');
+});
+
 test.run();