fix(i18n): manual routing with rewrite (#12718)

.changeset/fuzzy-windows-cover.md

@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fixes an issue where Astro couldn't correctly handle i18n fallback when using the i18n middleware

packages/astro/src/i18n/index.ts

@@ -298,9 +298,14 @@ export function redirectToDefaultLocale({
 }
 
 // NOTE: public function exported to the users via `astro:i18n` module
-export function notFound({ base, locales }: MiddlewarePayload) {
+export function notFound({ base, locales, fallback }: MiddlewarePayload) {
 	return function (context: APIContext, response?: Response): Response | undefined {
-		if (response?.headers.get(REROUTE_DIRECTIVE_HEADER) === 'no') return response;
+		if (
+			response?.headers.get(REROUTE_DIRECTIVE_HEADER) === 'no' &&
+			typeof fallback === 'undefined'
+		) {
+			return response;
+		}
 
 		const url = context.url;
 		// We return a 404 if:

packages/astro/src/i18n/middleware.ts

@@ -83,7 +83,6 @@ export function createI18nMiddleware(
 		}
 
 		const { currentLocale } = context;
-
 		switch (i18n.strategy) {
 			// NOTE: theoretically, we should never hit this code path
 			case 'manual': {

packages/astro/src/virtual-modules/i18n.ts

@@ -378,10 +378,10 @@ if (i18n?.routing === 'manual') {
 		fallbackType = toFallbackType(customOptions);
 		const manifest: SSRManifest['i18n'] = {
 			...i18n,
-			fallback: undefined,
 			strategy,
 			domainLookupTable: {},
 			fallbackType,
+			fallback: i18n.fallback,
 		};
 		return I18nInternals.createMiddleware(manifest, base, trailingSlash, format);
 	};

packages/astro/test/fixtures/i18n-routing-manual-with-default-middleware/astro.config.mjs

@@ -9,6 +9,9 @@ export default defineConfig({
 				codes: ["es", "es-ar"]
 			}
 		],
-		routing: "manual"
+		routing: "manual",
+		fallback: {
+			it: 'en'
+		}
 	}
 })

packages/astro/test/fixtures/i18n-routing-manual-with-default-middleware/src/middleware.js

@@ -18,5 +18,6 @@ export const onRequest = sequence(
 	customLogic,
 	middleware({
 		prefixDefaultLocale: true,
+		fallbackType: "rewrite"
 	})
 );

packages/astro/test/i18n-routing-manual-with-default-middleware.test.js

@@ -117,4 +117,13 @@ describe('SSR manual routing', () => {
 		const $ = cheerio.load(html);
 		assert.equal($('p').text(), '/en/blog/title/');
 	});
+
+	it('should use the fallback', async () => {
+		let request = new Request('http://example.com/it/start');
+		let response = await app.render(request);
+		assert.equal(response.status, 200);
+		const html = await response.text();
+		const $ = cheerio.load(html);
+		assert.equal($('p').text(), '/en/blog/title/');
+	});
 });