feat: Validate locale returned from i18n/request.ts (#1695)

Author: amannn

packages/next-intl/src/routing/defineRouting.tsx

@@ -5,7 +5,6 @@ import type {
   Locales,
   Pathnames
 } from './types.js';
-import validateLocales from './validateLocales.js';
 
 export default function defineRouting<
   const AppLocales extends Locales,
@@ -20,8 +19,5 @@ export default function defineRouting<
     AppDomains
   >
 ) {
-  if (process.env.NODE_ENV !== 'production') {
-    validateLocales(config.locales);
-  }
   return config;
 }

packages/next-intl/src/routing/validateLocales.tsx

@@ -9,6 +9,7 @@ import {
 import {getRequestLocale} from './RequestLocale.js';
 import createRequestConfig from './createRequestConfig.js';
 import type {GetRequestConfigParams} from './getRequestConfig.js';
+import validateLocale from './validateLocale.js';
 
 // This is automatically inherited by `NextIntlClientProvider` if
 // the component is rendered from a Server Component
@@ -60,6 +61,9 @@ See also: https://next-intl.dev/docs/usage/configuration#i18n-request
       'No locale was returned from `getRequestConfig`.\n\nSee https://next-intl.dev/docs/usage/configuration#i18n-request'
     );
   }
+  if (process.env.NODE_ENV !== 'production') {
+    validateLocale(result.locale);
+  }
 
   return result;
 }

packages/next-intl/src/server/react-server/getConfig.tsx

@@ -1,5 +1,5 @@
 import {afterEach, beforeEach, describe, expect, it, vi} from 'vitest';
-import validateLocales from './validateLocales.js';
+import validateLocale from './validateLocale.js';
 
 describe('accepts valid formats', () => {
   let consoleErrorSpy: ReturnType<typeof vi.spyOn>;
@@ -34,7 +34,7 @@ describe('accepts valid formats', () => {
     // Somehow tolerated by Intl.Locale
     'english'
   ])('accepts: %s', (locale) => {
-    validateLocales([locale]);
+    validateLocale(locale);
     expect(consoleErrorSpy).not.toHaveBeenCalled();
   });
 });
@@ -65,7 +65,7 @@ describe('warns for invalid formats', () => {
     'en US',
     'en.US'
   ])('rejects: %s', (locale) => {
-    validateLocales([locale]);
+    validateLocale(locale);
     expect(consoleErrorSpy).toHaveBeenCalled();
   });
 });

packages/next-intl/src/routing/validateLocales.test.tsx packages/next-intl/src/server/react-server/validateLocale.test.tsx

@@ -0,0 +1,12 @@
+export default function validateLocale(locale: string) {
+  try {
+    const constructed = new Intl.Locale(locale);
+    if (!constructed.language) {
+      throw new Error('Language is required');
+    }
+  } catch {
+    console.error(
+      `An invalid locale was provided: "${locale}"\nPlease ensure you're using a valid Unicode locale identifier (e.g. "en-US").`
+    );
+  }
+}