feat!: trailing slash never for endpoints with file extension

.changeset/giant-areas-press.md

@@ -0,0 +1,18 @@
+---
+'astro': major
+---
+
+Updates trailing slash behavior of endpoint URLs.
+
+In Astro v5.0, custom endpoints whose URL ended in a file extension (e.g. `/src/pages/sitemap.xml.ts` ) could be accessed with a trailing slash (`/sitemap.xml/`) or without (`/sitemap.xml`), regardless of the value configured for `build.trailingSlash`.
+
+In Astro v6.0, these endpoints can only be accessed without a trailing slash. This is true regardless of your `build.trailingSlash` configuration.
+
+#### What should I do?
+
+Review your links to your custom endpoints that include a file extension in the URL and remove any trailing slashes:
+
+```diff
+-<a href="/sitemap.xml/">Sitemap</a>
++<a href="/sitemap.xml">Sitemap</a>
+```

packages/astro/src/core/routing/manifest/create.ts

@@ -255,12 +255,11 @@ function createFileBasedRoutes(
 }
 
 // Get trailing slash rule for a path, based on the config and whether the path has an extension.
-// TODO: in Astro 6, change endpoints with extentions to use 'never'
 const trailingSlashForPath = (
 	pathname: string | null,
 	config: AstroConfig,
 ): AstroConfig['trailingSlash'] =>
-	pathname && hasFileExtension(pathname) ? 'ignore' : config.trailingSlash;
+	pathname && hasFileExtension(pathname) ? 'never' : config.trailingSlash;
 
 function createInjectedRoutes({ settings, cwd }: CreateRouteManifestParams): RouteData[] {
 	const { config } = settings;

packages/astro/test/units/routing/trailing-slash.test.js

@@ -171,14 +171,15 @@ describe('trailingSlash', () => {
 		assert.equal(json, '{"success":true}');
 	});
 
-	it('should match the API route when request has a trailing slash, with a file extension', async () => {
+	it('should NOT match the API route when request has a trailing slash, with a file extension', async () => {
 		const { req, res, text } = createRequestAndResponse({
 			method: 'GET',
 			url: '/dot.json/',
 		});
 		container.handle(req, res);
-		const json = await text();
-		assert.equal(json, '{"success":true}');
+		const html = await text();
+		assert.equal(html.includes(`<span class="statusMessage">Not found</span>`), true);
+		assert.equal(res.statusCode, 404);
 	});
 
 	it('should also match the API route when request lacks a trailing slash, with a file extension', async () => {