Fix .html.astro file routing in dev (#5346)

* Fix .html.astro file routing in dev

* Fix error

* Add comment

6 files changed, 63 insertions, 9 deletions

diff --git a/.changeset/chatty-kiwis-fail.md b/.changeset/chatty-kiwis-fail.md
new file mode 100644
index 000000000..823cbbc31
--- /dev/null
+++ b/.changeset/chatty-kiwis-fail.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fix .html.astro file routing in dev
diff --git a/packages/astro/src/vite-plugin-astro-server/request.ts b/packages/astro/src/vite-plugin-astro-server/request.ts
index 29431a929..29964f031 100644
--- a/packages/astro/src/vite-plugin-astro-server/request.ts
+++ b/packages/astro/src/vite-plugin-astro-server/request.ts
@@ -23,10 +23,7 @@ export async function handleRequest(
 	const { config } = settings;
 	const origin = `${moduleLoader.isHttps() ? 'https' : 'http'}://${req.headers.host}`;
 	const buildingToSSR = config.output === 'server';
-	// Ignore `.html` extensions and `index.html` in request URLS to ensure that
-	// routing behavior matches production builds. This supports both file and directory
-	// build formats, and is necessary based on how the manifest tracks build targets.
-	const url = new URL(origin + req.url?.replace(/(index)?\.html$/, ''));
+	const url = new URL(origin + req.url);
 	const pathname = decodeURI(url.pathname);
 
 	// Add config.base back to url before passing it to SSR
@@ -60,8 +57,18 @@ export async function handleRequest(
 		pathname,
 		async run() {
 			const matchedRoute = await matchRoute(pathname, env, manifest);
-
-			return await handleRoute(matchedRoute, url, pathname, body, origin, env, manifest, req, res);
+			const resolvedPathname = matchedRoute?.resolvedPathname ?? pathname;
+			return await handleRoute(
+				matchedRoute,
+				url,
+				resolvedPathname,
+				body,
+				origin,
+				env,
+				manifest,
+				req,
+				res
+			);
 		},
 		onError(_err) {
 			const err = createSafeError(_err);
diff --git a/packages/astro/src/vite-plugin-astro-server/route.ts b/packages/astro/src/vite-plugin-astro-server/route.ts
index aab47ecc7..9cd4ab239 100644
--- a/packages/astro/src/vite-plugin-astro-server/route.ts
+++ b/packages/astro/src/vite-plugin-astro-server/route.ts
@@ -1,7 +1,7 @@
 import type http from 'http';
 import mime from 'mime';
-import type { AstroSettings, ManifestData } from '../@types/astro';
-import { DevelopmentEnvironment, SSROptions } from '../core/render/dev/index';
+import type { AstroSettings, ComponentInstance, ManifestData, RouteData } from '../@types/astro';
+import { ComponentPreload, DevelopmentEnvironment, SSROptions } from '../core/render/dev/index';
 
 import { attachToResponse } from '../core/cookies/index.js';
 import { call as callEndpoint } from '../core/endpoint/dev/index.js';
@@ -23,6 +23,14 @@ type AsyncReturnType<T extends (...args: any) => Promise<any>> = T extends (
 	? R
 	: any;
 
+interface MatchedRoute {
+	route: RouteData;
+	filePath: URL;
+	resolvedPathname: string;
+	preloadedComponent: ComponentPreload;
+	mod: ComponentInstance;
+}
+
 function getCustom404Route({ config }: AstroSettings, manifest: ManifestData) {
 	// For Windows compat, use relative page paths to match the 404 route
 	const relPages = resolvePages(config).href.replace(config.root.href, '');
@@ -34,7 +42,7 @@ export async function matchRoute(
 	pathname: string,
 	env: DevelopmentEnvironment,
 	manifest: ManifestData
-) {
+): Promise<MatchedRoute | undefined> {
 	const { logging, settings, routeCache } = env;
 	const matches = matchAllRoutes(pathname, manifest);
 
@@ -57,12 +65,21 @@ export async function matchRoute(
 			return {
 				route: maybeRoute,
 				filePath,
+				resolvedPathname: pathname,
 				preloadedComponent,
 				mod,
 			};
 		}
 	}
 
+	// Try without `.html` extensions or `index.html` in request URLs to mimic
+	// routing behavior in production builds. This supports both file and directory
+	// build formats, and is necessary based on how the manifest tracks build targets.
+	const altPathname = pathname.replace(/(index)?\.html$/, '');
+	if (altPathname !== pathname) {
+		return await matchRoute(altPathname, env, manifest);
+	}
+
 	if (matches.length) {
 		const possibleRoutes = matches.flatMap((route) => route.component);
 
@@ -86,6 +103,7 @@ export async function matchRoute(
 		return {
 			route: custom404,
 			filePath,
+			resolvedPathname: pathname,
 			preloadedComponent,
 			mod,
 		};
diff --git a/packages/astro/test/dev-routing.test.js b/packages/astro/test/dev-routing.test.js
index 7188e1ff0..5b46cf249 100644
--- a/packages/astro/test/dev-routing.test.js
+++ b/packages/astro/test/dev-routing.test.js
@@ -322,5 +322,17 @@ describe('Development Routing', () => {
 			const response = await fixture.fetch('/1');
 			expect(response.status).to.equal(200);
 		});
+
+		it('200 when loading /html-ext/1', async () => {
+			const response = await fixture.fetch('/html-ext/1');
+			expect(response.status).to.equal(200);
+			expect(await response.text()).includes('none: 1')
+		});
+
+		it('200 when loading /html-ext/1.html', async () => {
+			const response = await fixture.fetch('/html-ext/1.html');
+			expect(response.status).to.equal(200);
+			expect(await response.text()).includes('html: 1')
+		});
 	});
 });
diff --git a/packages/astro/test/fixtures/without-site-config/src/pages/html-ext/[slug].astro b/packages/astro/test/fixtures/without-site-config/src/pages/html-ext/[slug].astro
new file mode 100644
index 000000000..599fd0f26
--- /dev/null
+++ b/packages/astro/test/fixtures/without-site-config/src/pages/html-ext/[slug].astro
@@ -0,0 +1,6 @@
+---
+export function getStaticPaths() {
+  return [{ params: { slug: '1' } }];
+}
+---
+<h1>none: {Astro.params.slug}</h1>
diff --git a/packages/astro/test/fixtures/without-site-config/src/pages/html-ext/[slug].html.astro b/packages/astro/test/fixtures/without-site-config/src/pages/html-ext/[slug].html.astro
new file mode 100644
index 000000000..79ab2d434
--- /dev/null
+++ b/packages/astro/test/fixtures/without-site-config/src/pages/html-ext/[slug].html.astro
@@ -0,0 +1,6 @@
+---
+export function getStaticPaths() {
+  return [{ params: { slug: '1' } }];
+}
+---
+<h1>html: {Astro.params.slug}</h1>