feat(ivy): use i18n locale data to determine the plural form of ICU expressions (#29249)

Plural ICU expressions depend on the locale (different languages have different plural forms). Until now the locale was hard coded as `en-US`.
For compatibility reasons, if you use ivy with AOT and bootstrap your app with `bootstrapModule` then the `LOCALE_ID` token will be set automatically for ivy, which is then used to get the correct plural form.
If you use JIT, you need to define the `LOCALE_ID` provider on the module that you bootstrap.
For `TestBed` you can use either `configureTestingModule` or `overrideProvider` to define that provider.
If you don't use the compat mode and start your app with `renderComponent` you need to call `ɵsetLocaleId` manually to define the `LOCALE_ID` before bootstrap. We expect this to change once we start adding the new i18n APIs, so don't rely on this function (there's a reason why it's a private export).
PR Close #29249

packages/core/src/i18n/locale_data.ts

@@ -0,0 +1,38 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+/**
+ * This const is used to store the locale data registered with `registerLocaleData`
+ */
+export const LOCALE_DATA: {[localeId: string]: any} = {};
+
+/**
+ * Index of each type of locale data from the locale data array
+ */
+export enum LocaleDataIndex {
+  LocaleId = 0,
+  DayPeriodsFormat,
+  DayPeriodsStandalone,
+  DaysFormat,
+  DaysStandalone,
+  MonthsFormat,
+  MonthsStandalone,
+  Eras,
+  FirstDayOfWeek,
+  WeekendRange,
+  DateFormat,
+  TimeFormat,
+  DateTimeFormat,
+  NumberSymbols,
+  NumberFormats,
+  CurrencySymbol,
+  CurrencyName,
+  Currencies,
+  PluralCase,
+  ExtraData
+}

packages/core/src/i18n/locale_data_api.ts

@@ -0,0 +1,53 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {LOCALE_DATA, LocaleDataIndex} from './locale_data';
+import localeEn from './locale_en';
+
+/**
+ * Retrieves the plural function used by ICU expressions to determine the plural case to use
+ * for a given locale.
+ * @param locale A locale code for the locale format rules to use.
+ * @returns The plural function for the locale.
+ * @see `NgPlural`
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
+ */
+export function getLocalePluralCase(locale: string): (value: number) => number {
+  const data = findLocaleData(locale);
+  return data[LocaleDataIndex.PluralCase];
+}
+
+/**
+ * Finds the locale data for a given locale.
+ *
+ * @param locale The locale code.
+ * @returns The locale data.
+ * @see [Internationalization (i18n) Guide](https://angular.io/guide/i18n)
+ */
+export function findLocaleData(locale: string): any {
+  const normalizedLocale = locale.toLowerCase().replace(/_/g, '-');
+
+  let match = LOCALE_DATA[normalizedLocale];
+  if (match) {
+    return match;
+  }
+
+  // let's try to find a parent locale
+  const parentLocale = normalizedLocale.split('-')[0];
+  match = LOCALE_DATA[parentLocale];
+
+  if (match) {
+    return match;
+  }
+
+  if (parentLocale === 'en') {
+    return localeEn;
+  }
+
+  throw new Error(`Missing locale data for the locale "${locale}".`);
+}

packages/core/src/i18n/locale_en.ts

@@ -0,0 +1,41 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+// THIS CODE IS GENERATED - DO NOT MODIFY
+// See angular/tools/gulp-tasks/cldr/extract.js
+
+const u = undefined;
+
+function plural(n: number): number {
+  let i = Math.floor(Math.abs(n)), v = n.toString().replace(/^[^.]*\.?/, '').length;
+  if (i === 1 && v === 0) return 1;
+  return 5;
+}
+
+export default [
+  'en', [['a', 'p'], ['AM', 'PM'], u], [['AM', 'PM'], u, u],
+  [
+    ['S', 'M', 'T', 'W', 'T', 'F', 'S'], ['Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat'],
+    ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'],
+    ['Su', 'Mo', 'Tu', 'We', 'Th', 'Fr', 'Sa']
+  ],
+  u,
+  [
+    ['J', 'F', 'M', 'A', 'M', 'J', 'J', 'A', 'S', 'O', 'N', 'D'],
+    ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'],
+    [
+      'January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September',
+      'October', 'November', 'December'
+    ]
+  ],
+  u, [['B', 'A'], ['BC', 'AD'], ['Before Christ', 'Anno Domini']], 0, [6, 0],
+  ['M/d/yy', 'MMM d, y', 'MMMM d, y', 'EEEE, MMMM d, y'],
+  ['h:mm a', 'h:mm:ss a', 'h:mm:ss a z', 'h:mm:ss a zzzz'], ['{1}, {0}', u, '{1} \'at\' {0}', u],
+  ['.', ',', ';', '%', '+', '-', 'E', '×', '‰', '∞', 'NaN', ':'],
+  ['#,##0.###', '#,##0%', '¤#,##0.00', '#E0'], '$', 'US Dollar', {}, plural
+];

packages/core/src/i18n/localization.ts

@@ -0,0 +1,31 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {getLocalePluralCase} from './locale_data_api';
+
+/**
+ * Returns the plural case based on the locale
+ */
+export function getPluralCase(value: any, locale: string): string {
+  const plural = getLocalePluralCase(locale)(value);
+
+  switch (plural) {
+    case 0:
+      return 'zero';
+    case 1:
+      return 'one';
+    case 2:
+      return 'two';
+    case 3:
+      return 'few';
+    case 4:
+      return 'many';
+    default:
+      return 'other';
+  }
+}