fix(mobile): polyfill Intl.PluralRules on Hermes

apps/mobile/package.json

@@ -30,6 +30,7 @@
     "@formatjs/intl-listformat": "^8.3.13",
     "@formatjs/intl-locale": "^5.3.10",
     "@formatjs/intl-numberformat": "^9.4.0",
+    "@formatjs/intl-pluralrules": "^6.3.13",
     "@formatjs/intl-relativetimeformat": "^12.3.13",
     "@formatjs/intl-segmenter": "^12.2.13",
     "@kilocode/app-shared": "workspace:*",

apps/mobile/src/app/_layout.tsx

@@ -369,11 +369,13 @@ function RootLayoutNav() {
         router.replace('/(app)/(tabs)/(3_profile)/preferences');
       }
       try {
-        await i18n.changeLanguage(resolved);
+        // The plural-rules polyfill must be in place before the first render in the new language.
         prewarmIntl(resolved);
+        await i18n.changeLanguage(resolved);
       } catch {
-        await i18n.changeLanguage('en');
+        // The plural-rules polyfill must be in place before the first render in the new language.
         prewarmIntl('en');
+        await i18n.changeLanguage('en');
       }
       void renameAndroidNotificationChannels();
       if (!cancelled) {

apps/mobile/src/i18n/apply-language.ts

@@ -66,17 +66,19 @@ export async function applyLanguagePreference(
 
   const previousLanguage = i18n.language;
   try {
-    await i18n.changeLanguage(resolved);
+    // The plural-rules polyfill must be in place before the first render in the new language.
     prewarmIntl(resolved);
+    await i18n.changeLanguage(resolved);
   } catch {
     return { kind: 'catalog-failed' };
   }
 
   const persisted = await setLanguagePreferenceAsync(preference, previousLanguage);
   if (!persisted) {
     try {
-      await i18n.changeLanguage(previousLanguage);
+      // The plural-rules polyfill must be in place before the first render in the new language.
       prewarmIntl(previousLanguage);
+      await i18n.changeLanguage(previousLanguage);
     } catch {
       // Ignore: the rollback is best-effort; the persist failure already surfaced.
     }

apps/mobile/src/lib/formatjs-locale-data.ts

@@ -182,10 +182,104 @@ const LIST_FORMAT_LOCALE_LOADERS = {
   zu: () => void require('@formatjs/intl-listformat/locale-data/zu.js'),
 } satisfies Record<SupportedLanguage, () => void>;
 
+const PLURAL_RULES_LOCALE_LOADERS = {
+  af: () => void require('@formatjs/intl-pluralrules/locale-data/af.js'),
+  sq: () => void require('@formatjs/intl-pluralrules/locale-data/sq.js'),
+  am: () => void require('@formatjs/intl-pluralrules/locale-data/am.js'),
+  ar: () => void require('@formatjs/intl-pluralrules/locale-data/ar.js'),
+  hy: () => void require('@formatjs/intl-pluralrules/locale-data/hy.js'),
+  az: () => void require('@formatjs/intl-pluralrules/locale-data/az.js'),
+  eu: () => void require('@formatjs/intl-pluralrules/locale-data/eu.js'),
+  be: () => void require('@formatjs/intl-pluralrules/locale-data/be.js'),
+  bn: () => void require('@formatjs/intl-pluralrules/locale-data/bn.js'),
+  bs: () => void require('@formatjs/intl-pluralrules/locale-data/bs.js'),
+  bg: () => void require('@formatjs/intl-pluralrules/locale-data/bg.js'),
+  my: () => void require('@formatjs/intl-pluralrules/locale-data/my.js'),
+  ca: () => void require('@formatjs/intl-pluralrules/locale-data/ca.js'),
+  'zh-Hans': () => void require('@formatjs/intl-pluralrules/locale-data/zh.js'),
+  'zh-Hant': () => void require('@formatjs/intl-pluralrules/locale-data/zh.js'),
+  hr: () => void require('@formatjs/intl-pluralrules/locale-data/hr.js'),
+  cs: () => void require('@formatjs/intl-pluralrules/locale-data/cs.js'),
+  da: () => void require('@formatjs/intl-pluralrules/locale-data/da.js'),
+  nl: () => void require('@formatjs/intl-pluralrules/locale-data/nl.js'),
+  en: () => void require('@formatjs/intl-pluralrules/locale-data/en.js'),
+  et: () => void require('@formatjs/intl-pluralrules/locale-data/et.js'),
+  fil: () => void require('@formatjs/intl-pluralrules/locale-data/fil.js'),
+  fi: () => void require('@formatjs/intl-pluralrules/locale-data/fi.js'),
+  fr: () => void require('@formatjs/intl-pluralrules/locale-data/fr.js'),
+  gl: () => void require('@formatjs/intl-pluralrules/locale-data/gl.js'),
+  ka: () => void require('@formatjs/intl-pluralrules/locale-data/ka.js'),
+  de: () => void require('@formatjs/intl-pluralrules/locale-data/de.js'),
+  el: () => void require('@formatjs/intl-pluralrules/locale-data/el.js'),
+  gu: () => void require('@formatjs/intl-pluralrules/locale-data/gu.js'),
+  ht: () => void require('@formatjs/intl-pluralrules/locale-data/en.js'),
+  ha: () => void require('@formatjs/intl-pluralrules/locale-data/ha.js'),
+  he: () => void require('@formatjs/intl-pluralrules/locale-data/he.js'),
+  hi: () => void require('@formatjs/intl-pluralrules/locale-data/hi.js'),
+  hu: () => void require('@formatjs/intl-pluralrules/locale-data/hu.js'),
+  is: () => void require('@formatjs/intl-pluralrules/locale-data/is.js'),
+  ig: () => void require('@formatjs/intl-pluralrules/locale-data/ig.js'),
+  id: () => void require('@formatjs/intl-pluralrules/locale-data/id.js'),
+  ga: () => void require('@formatjs/intl-pluralrules/locale-data/ga.js'),
+  it: () => void require('@formatjs/intl-pluralrules/locale-data/it.js'),
+  ja: () => void require('@formatjs/intl-pluralrules/locale-data/ja.js'),
+  kn: () => void require('@formatjs/intl-pluralrules/locale-data/kn.js'),
+  kk: () => void require('@formatjs/intl-pluralrules/locale-data/kk.js'),
+  km: () => void require('@formatjs/intl-pluralrules/locale-data/km.js'),
+  ko: () => void require('@formatjs/intl-pluralrules/locale-data/ko.js'),
+  ckb: () => void require('@formatjs/intl-pluralrules/locale-data/ckb.js'),
+  lo: () => void require('@formatjs/intl-pluralrules/locale-data/lo.js'),
+  lv: () => void require('@formatjs/intl-pluralrules/locale-data/lv.js'),
+  lt: () => void require('@formatjs/intl-pluralrules/locale-data/lt.js'),
+  mk: () => void require('@formatjs/intl-pluralrules/locale-data/mk.js'),
+  mg: () => void require('@formatjs/intl-pluralrules/locale-data/mg.js'),
+  ms: () => void require('@formatjs/intl-pluralrules/locale-data/ms.js'),
+  ml: () => void require('@formatjs/intl-pluralrules/locale-data/ml.js'),
+  mt: () => void require('@formatjs/intl-pluralrules/locale-data/mt.js'),
+  mi: () => void require('@formatjs/intl-pluralrules/locale-data/en.js'),
+  mr: () => void require('@formatjs/intl-pluralrules/locale-data/mr.js'),
+  mn: () => void require('@formatjs/intl-pluralrules/locale-data/mn.js'),
+  ne: () => void require('@formatjs/intl-pluralrules/locale-data/ne.js'),
+  nb: () => void require('@formatjs/intl-pluralrules/locale-data/nb.js'),
+  or: () => void require('@formatjs/intl-pluralrules/locale-data/or.js'),
+  om: () => void require('@formatjs/intl-pluralrules/locale-data/om.js'),
+  ps: () => void require('@formatjs/intl-pluralrules/locale-data/ps.js'),
+  fa: () => void require('@formatjs/intl-pluralrules/locale-data/fa.js'),
+  pl: () => void require('@formatjs/intl-pluralrules/locale-data/pl.js'),
+  pt: () => void require('@formatjs/intl-pluralrules/locale-data/pt.js'),
+  'pt-BR': () => void require('@formatjs/intl-pluralrules/locale-data/pt.js'),
+  pa: () => void require('@formatjs/intl-pluralrules/locale-data/pa.js'),
+  ro: () => void require('@formatjs/intl-pluralrules/locale-data/ro.js'),
+  ru: () => void require('@formatjs/intl-pluralrules/locale-data/ru.js'),
+  sr: () => void require('@formatjs/intl-pluralrules/locale-data/sr.js'),
+  si: () => void require('@formatjs/intl-pluralrules/locale-data/si.js'),
+  sk: () => void require('@formatjs/intl-pluralrules/locale-data/sk.js'),
+  sl: () => void require('@formatjs/intl-pluralrules/locale-data/sl.js'),
+  so: () => void require('@formatjs/intl-pluralrules/locale-data/so.js'),
+  es: () => void require('@formatjs/intl-pluralrules/locale-data/es.js'),
+  sw: () => void require('@formatjs/intl-pluralrules/locale-data/sw.js'),
+  sv: () => void require('@formatjs/intl-pluralrules/locale-data/sv.js'),
+  ta: () => void require('@formatjs/intl-pluralrules/locale-data/ta.js'),
+  te: () => void require('@formatjs/intl-pluralrules/locale-data/te.js'),
+  th: () => void require('@formatjs/intl-pluralrules/locale-data/th.js'),
+  tr: () => void require('@formatjs/intl-pluralrules/locale-data/tr.js'),
+  uk: () => void require('@formatjs/intl-pluralrules/locale-data/uk.js'),
+  ur: () => void require('@formatjs/intl-pluralrules/locale-data/ur.js'),
+  uz: () => void require('@formatjs/intl-pluralrules/locale-data/uz.js'),
+  vi: () => void require('@formatjs/intl-pluralrules/locale-data/vi.js'),
+  cy: () => void require('@formatjs/intl-pluralrules/locale-data/cy.js'),
+  yo: () => void require('@formatjs/intl-pluralrules/locale-data/yo.js'),
+  zu: () => void require('@formatjs/intl-pluralrules/locale-data/zu.js'),
+} satisfies Record<SupportedLanguage, () => void>;
+
 export function loadNumberFormatLocaleData(language: SupportedLanguage): void {
   NUMBER_FORMAT_LOCALE_LOADERS[language]();
 }
 
 export function loadListFormatLocaleData(language: SupportedLanguage): void {
   LIST_FORMAT_LOCALE_LOADERS[language]();
 }
+
+export function loadPluralRulesLocaleData(language: SupportedLanguage): void {
+  PLURAL_RULES_LOCALE_LOADERS[language]();
+}

apps/mobile/src/lib/intl-cache-hermes-numberformat.test.ts

@@ -6,13 +6,12 @@ describe('Hermes NumberFormat compatibility', () => {
     vi.resetModules();
   });
 
-  it('polyfills currency parts and unit formatting when NumberFormat is missing', async () => {
+  it('polyfills currency parts and unit formatting when NumberFormat and PluralRules are missing', async () => {
     const nativeIntl = Intl;
     vi.stubGlobal('Intl', {
       Collator: nativeIntl.Collator,
       DateTimeFormat: nativeIntl.DateTimeFormat,
       getCanonicalLocales: nativeIntl.getCanonicalLocales,
-      PluralRules: nativeIntl.PluralRules,
     });
 
     const { prewarmIntl } = await import('./intl-cache');

apps/mobile/src/lib/intl-cache-hermes-surface.test.ts

@@ -0,0 +1,50 @@
+import { afterEach, describe, expect, it, vi } from 'vitest';
+
+// Hermes ships only these Intl members. Everything else must come from a polyfill.
+function stubHermesIntl(): void {
+  const nativeIntl = Intl;
+  vi.stubGlobal('Intl', {
+    Collator: nativeIntl.Collator,
+    DateTimeFormat: nativeIntl.DateTimeFormat,
+    getCanonicalLocales: nativeIntl.getCanonicalLocales,
+  });
+}
+
+describe('Hermes Intl surface', () => {
+  afterEach(() => {
+    vi.unstubAllGlobals();
+    vi.resetModules();
+  });
+
+  it('formats every supported language and pluralizes for i18next', async () => {
+    stubHermesIntl();
+    const { SUPPORTED_LANGUAGES } = await import('@/i18n/languages');
+    const { prewarmIntl, collator, dateTimeFormat } = await import('./intl-cache');
+    const format = await import('./format');
+    const { timeAgo } = await import('./utils');
+
+    for (const language of SUPPORTED_LANGUAGES) {
+      prewarmIntl(language);
+      expect(format.formatMoney(1234.5, language)).toBeTruthy();
+      expect(format.formatNumber(3, language)).toBeTruthy();
+      expect(format.formatPercent(0.5, language)).toBeTruthy();
+      expect(format.formatList(['a', 'b', 'c'], language)).toBeTruthy();
+      expect(format.formatDuration(3725, language)).toBeTruthy();
+      expect(format.formatFileSize(2048, language)).toBeTruthy();
+      expect(format.firstGrapheme('👍🏽x', language)).toBe('👍🏽');
+      expect(format.formatDate(new Date(0), language)).toBeTruthy();
+      expect(collator(language).compare('a', 'b')).toBeLessThan(0);
+      expect(dateTimeFormat(language, { hour: 'numeric' }).format(new Date(0))).toBeTruthy();
+      expect(timeAgo(new Date(Date.now() - 3 * 86_400_000), language)).toBeTruthy();
+    }
+
+    // i18next builds its own Intl.PluralRules; without the polyfill it silently
+    // falls back to English one/other and caches that per language.
+    const { i18n } = await import('@/i18n');
+    prewarmIntl('ru');
+    await i18n.changeLanguage('ru');
+    const few = i18n.t('prReview.hunkRows.fileLoadedCount', { count: 2, displayCount: '2' });
+    const many = i18n.t('prReview.hunkRows.fileLoadedCount', { count: 5, displayCount: '5' });
+    expect(few).not.toBe(many);
+  });
+});

apps/mobile/src/lib/intl-cache.ts

@@ -2,11 +2,16 @@ import { shouldPolyfill as shouldPolyfillDurationFormat } from '@formatjs/intl-d
 import { shouldPolyfill as shouldPolyfillListFormat } from '@formatjs/intl-listformat/should-polyfill.js';
 import { shouldPolyfill as shouldPolyfillLocale } from '@formatjs/intl-locale/should-polyfill.js';
 import { shouldPolyfill as shouldPolyfillNumberFormat } from '@formatjs/intl-numberformat/should-polyfill.js';
+import { shouldPolyfill as shouldPolyfillPluralRules } from '@formatjs/intl-pluralrules/should-polyfill.js';
 import { shouldPolyfill as shouldPolyfillRelativeTimeFormat } from '@formatjs/intl-relativetimeformat/should-polyfill.js';
 import { shouldPolyfill as shouldPolyfillSegmenter } from '@formatjs/intl-segmenter/should-polyfill.js';
 
 import { isSupportedLanguage, type SupportedLanguage } from '@/i18n/languages';
-import { loadListFormatLocaleData, loadNumberFormatLocaleData } from '@/lib/formatjs-locale-data';
+import {
+  loadListFormatLocaleData,
+  loadNumberFormatLocaleData,
+  loadPluralRulesLocaleData,
+} from '@/lib/formatjs-locale-data';
 import { RELATIVE_TIME_LOCALE_LOADERS } from '@/lib/relative-time-locales';
 
 /**
@@ -26,6 +31,7 @@ const durationFormats = new Map<string, Intl.DurationFormat>();
 const collators = new Map<string, Intl.Collator>();
 const segmenters = new Map<string, Intl.Segmenter>();
 let usesNumberFormatPolyfill = false;
+let usesPluralRulesPolyfill = false;
 let usesListFormatPolyfill = false;
 let usesRelativeTimePolyfill = false;
 let usesDurationFormatPolyfill = false;
@@ -54,8 +60,22 @@ function ensureLocale(): void {
   }
 }
 
+// Hermes ships without Intl.PluralRules, and the NumberFormat and
+// RelativeTimeFormat polyfills construct one.
+function ensurePluralRules(language: SupportedLanguage): void {
+  if (!usesPluralRulesPolyfill && shouldPolyfillPluralRules(language)) {
+    require('@formatjs/intl-pluralrules/polyfill-force.js');
+    usesPluralRulesPolyfill = true;
+  }
+  if (usesPluralRulesPolyfill) {
+    ensureLocale();
+    loadPluralRulesLocaleData(language);
+  }
+}
+
 function ensureNumberFormat(locale: string): void {
   const language = localeDataLanguage(locale);
+  ensurePluralRules(language);
   if (!usesNumberFormatPolyfill && shouldPolyfillNumberFormat(locale)) {
     require('@formatjs/intl-numberformat/polyfill-force.js');
     usesNumberFormatPolyfill = true;