Fix relative-time RangeError in headless browsers

Add 'en' fallback for navigator.language which can be undefined in
headless browsers (e.g. Playwright Firefox), causing RangeError in
Intl.DateTimeFormat. Add e2e test and shared assertNoJsError helper.

Co-Authored-By: Claude (Opus 4.6) <[email protected]>

Author: silverwind

tests/e2e/relative-time.test.ts

@@ -0,0 +1,17 @@
+import {test, expect} from '@playwright/test';
+import {apiCreateUser, apiDeleteUser, apiCreateRepo, apiUserHeaders, assertNoJsError} from './utils.ts';
+
+test('relative-time renders without errors', async ({page, request}) => {
+  const name = `rt-${Date.now()}-${Math.random().toString(36).slice(2, 6)}`;
+  await apiCreateUser(request, name);
+  await apiCreateRepo(request, {name, headers: apiUserHeaders(name)});
+
+  // Explore page shows repos with relative-time elements, no login needed
+  await page.goto('/explore/repos');
+  const relativeTime = page.locator('relative-time').first();
+  await expect(relativeTime).toHaveAttribute('data-tooltip-content', /.+/);
+  await expect(relativeTime).toContainText(/now|ago|minute|hour|day/);
+  await assertNoJsError(page);
+
+  await apiDeleteUser(request, name);
+});

tests/e2e/utils.ts

@@ -104,6 +104,10 @@ export async function login(page: Page, username = env.GITEA_TEST_E2E_USER, pass
   await expect(page.getByRole('link', {name: 'Sign In'})).toBeHidden();
 }
 
+export async function assertNoJsError(page: Page) {
+  await expect(page.locator('.js-global-error')).toHaveCount(0);
+}
+
 export async function logout(page: Page) {
   await page.context().clearCookies(); // workaround issues related to fomantic dropdown
   await page.goto('/');

web_src/js/webcomponents/relative-time.ts

@@ -259,12 +259,12 @@ class RelativeTime extends HTMLElement {
 
   get #lang(): string {
     const lang = this.closest('[lang]')?.getAttribute('lang');
-    if (!lang) return navigator.language;
-    try {
-      return new Intl.Locale(lang).toString();
-    } catch {
-      return navigator.language;
+    if (lang) {
+      try {
+        return new Intl.Locale(lang).toString();
+      } catch { /* invalid locale, fall through */ }
     }
+    return navigator.language ?? 'en';
   }
 
   get second(): 'numeric' | '2-digit' | undefined {