Skip locale-prefix check in finalizeI18n for integration-injected routes

.changeset/injected-routes-i18n-prefix.md

@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fixes a bug where page routes added with `injectRoute()` returned a 404 when `i18n.routing.prefixDefaultLocale` was `true` and the route path had no locale prefix

packages/astro/src/core/i18n/handler.ts

@@ -102,14 +102,21 @@ export async function finalizeI18n(
 	// raw request URL again, so locale checks use the same path as routing.
 	const url = state.url;
 	const currentLocale = state.computeCurrentLocale();
-	const isPrerendered = state.routeData!.prerender;
+	const routeData = state.routeData!;
+	const isPrerendered = routeData.prerender;
 
 	// Build context for router (responseRouteType is guaranteed to be 'page' | 'fallback' here)
 	const routerContext: I18nRouterContext = {
 		currentLocale,
 		currentDomain: url.hostname,
 		routeType: state.responseRouteType,
 		isReroute: false,
+		// Routes injected by integrations live in a URL space the site author
+		// can't move under a locale prefix (#18223). Injected routes whose first
+		// segment is dynamic (e.g. `/[locale]/...`) are treated as locale-aware
+		// and still have their locale validated.
+		allowUnprefixedPath:
+			routeData.origin === 'external' && !routeData.segments?.[0]?.some((part) => part.dynamic),
 	};
 
 	// Step 1: Apply routing strategy

packages/astro/src/i18n/router.ts

@@ -43,6 +43,11 @@ export interface I18nRouterContext {
 	routeType?: 'page' | 'fallback';
 	/** Whether this is a reroute from response headers */
 	isReroute: boolean;
+	/**
+	 * Whether a non-root path without a locale segment is served instead of
+	 * returning 404 under the `prefix-always` strategies.
+	 */
+	allowUnprefixedPath?: boolean;
 }
 
 /**
@@ -146,7 +151,7 @@ export class I18nRouter {
 	 * Strategy: pathname-prefix-always
 	 * All locales must have a prefix, including the default locale.
 	 */
-	private matchPrefixAlways(pathname: string, _context: I18nRouterContext): I18nRouterMatch {
+	private matchPrefixAlways(pathname: string, context: I18nRouterContext): I18nRouterMatch {
 		const isRoot = pathname === this.#base + '/' || pathname === this.#base;
 
 		if (isRoot) {
@@ -160,7 +165,7 @@ export class I18nRouter {
 		}
 
 		// Check if pathname has a locale
-		if (!pathHasLocale(pathname, this.#locales)) {
+		if (!context.allowUnprefixedPath && !pathHasLocale(pathname, this.#locales)) {
 			return { type: 'notFound' };
 		}
 
@@ -199,7 +204,7 @@ export class I18nRouter {
 	 */
 	private matchPrefixAlwaysNoRedirect(
 		pathname: string,
-		_context: I18nRouterContext,
+		context: I18nRouterContext,
 	): I18nRouterMatch {
 		const isRoot = pathname === this.#base + '/' || pathname === this.#base;
 
@@ -209,7 +214,7 @@ export class I18nRouter {
 		}
 
 		// Non-root paths must have a locale
-		if (!pathHasLocale(pathname, this.#locales)) {
+		if (!context.allowUnprefixedPath && !pathHasLocale(pathname, this.#locales)) {
 			return { type: 'notFound' };
 		}
 

packages/astro/test/units/i18n/i18n-middleware.test.ts

@@ -111,6 +111,57 @@ describe('createI18nMiddleware', () => {
 			assert.equal(await result.text(), 'en page');
 		});
 
+		it('passes through a non-locale-prefixed path for a route injected by an integration', async () => {
+			const ctx = createMockAPIContext({ url: 'http://localhost/_admin/settings' });
+			getFetchStateFromAPIContext(ctx).routeData!.origin = 'external';
+			const next = async () => makePageResponse('admin page');
+
+			const result = await callHandler(handler, ctx, next);
+
+			assert.equal(result.status, 200);
+			assert.equal(await result.text(), 'admin page');
+		});
+
+		it('returns null-body 404 for an invalid locale on an injected [locale] route', async () => {
+			const ctx = createMockAPIContext({ url: 'http://localhost/xx/page' });
+			const state = getFetchStateFromAPIContext(ctx);
+			state.routeData!.origin = 'external';
+			state.routeData!.segments = [
+				[{ content: 'locale', dynamic: true, spread: false }],
+				[{ content: 'page', dynamic: false, spread: false }],
+			];
+			const next = async () => makePageResponse('should not render');
+
+			const result = await callHandler(handler, ctx, next);
+
+			assert.equal(result.status, 404);
+			assert.equal(result.body, null);
+		});
+
+		it('redirects root / to /{defaultLocale}/ for an injected route', async () => {
+			const ctx = createMockAPIContext({ url: 'http://localhost/' });
+			const state = getFetchStateFromAPIContext(ctx);
+			state.routeData!.origin = 'external';
+			state.routeData!.segments = [];
+			const next = async () => makePageResponse('root');
+
+			const result = await callHandler(handler, ctx, next);
+
+			assert.equal(result.status, 302);
+			assert.ok(result.headers.get('Location')?.includes('/en'));
+		});
+
+		it('returns null-body 404 for a non-locale-prefixed path of a project route', async () => {
+			const ctx = createMockAPIContext({ url: 'http://localhost/_admin/settings' });
+			getFetchStateFromAPIContext(ctx).routeData!.origin = 'project';
+			const next = async () => makePageResponse('should not render');
+
+			const result = await callHandler(handler, ctx, next);
+
+			assert.equal(result.status, 404);
+			assert.equal(result.body, null);
+		});
+
 		it('redirects root / to /{defaultLocale}/', async () => {
 			const ctx = createMockAPIContext({ url: 'http://localhost/' });
 			const next = async () => makePageResponse('root');