From 9f3d0cda54c902bf6e9d6749649fc565b5d73f6e Mon Sep 17 00:00:00 2001
From: PerryLink <255665900+PerryLink@users.noreply.github.com>
Date: Tue, 20 Oct 2026 11:25:59 +0000
Subject: [PATCH] feat: map es_US in the dayjs and date-fns adapters
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The `es_US` picker locale means Spanish for the US: Spanish month and weekday
names with Sunday as the first day of the week.

Day.js has an `es-us` locale, but `localeMap` had no `es_US` entry, so
`parseLocale('es_US')` fell back to `es` — Spanish, but Monday first. The
picker's `lang.locale` stays in the underscore form because it is shared with
the other adapters, so the mapping belongs here.

The date-fns adapter had the same gap the other way round: it resolved `es_US`
to `es`, which also starts the week on Monday, and date-fns ships no es-US
locale. `es_US` now returns the Spanish locale with `weekStartsOn: 0`.

Adds a test per adapter: Spanish month and weekday names, Sunday first.
---
 src/generate/dateFns.ts | 12 ++++++++++++
 src/generate/dayjs.ts   |  1 +
 tests/generate.spec.tsx | 22 ++++++++++++++++++++++
 3 files changed, 35 insertions(+)

diff --git a/src/generate/dateFns.ts b/src/generate/dateFns.ts
index c1c97d91c..6076f4160 100644
--- a/src/generate/dateFns.ts
+++ b/src/generate/dateFns.ts
@@ -31,7 +31,19 @@ import {
 import * as locales from 'date-fns/locale';
 import type { GenerateConfig } from '.';
 
+// date-fns has no es-US locale and its `es` locale starts the week on Monday.
+// The `es_US` picker locale means Spanish with the US week start, so keep the
+// Spanish formatting and override the first day of the week.
+const esUS: Locale = {
+  ...locales.es,
+  options: { ...locales.es.options, weekStartsOn: 0 },
+};
+
 const getLocale = (locale: string): Locale => {
+  if (locale === 'es_US') {
+    return esUS;
+  }
+
   return (
     locales[locale] || locales[locale.replace(/_/g, '')] || locales[locale.replace(/_.*$/g, '')]
   );
diff --git a/src/generate/dayjs.ts b/src/generate/dayjs.ts
index a4fa37804..1fa2f8536 100644
--- a/src/generate/dayjs.ts
+++ b/src/generate/dayjs.ts
@@ -39,6 +39,7 @@ const localeMap: IlocaleMapObject = {
   // el_GR:
   en_GB: 'en-gb',
   en_US: 'en',
+  es_US: 'es-us',
   // es_ES:
   // et_EE:
   // fa_IR:
diff --git a/tests/generate.spec.tsx b/tests/generate.spec.tsx
index f0a7aed60..c555e7b15 100644
--- a/tests/generate.spec.tsx
+++ b/tests/generate.spec.tsx
@@ -9,6 +9,7 @@ import { getMoment } from './util/commonUtil';
 import 'dayjs/locale/zh-cn';
 import 'dayjs/locale/ko';
 import 'dayjs/locale/fr';
+import 'dayjs/locale/es-us';
 import type { GenerateConfig } from '../src/generate';
 
 describe('Picker.Generate', () => {
@@ -415,3 +416,24 @@ describe('Generate:date-fns', () => {
     expect(dateFnsGenerateConfig.getMinute(parsed)).toEqual(30);
   });
 });
+
+
+describe('Generate: es_US', () => {
+  it('dayjs keeps the US week start and formats in Spanish', () => {
+    expect(dayjsGenerateConfig.locale.getWeekFirstDay('es_US')).toEqual(0);
+
+    const date = dayjsGenerateConfig.locale.parse('es_US', '2018-01-15', ['YYYY-MM-DD'])!;
+
+    expect(dayjsGenerateConfig.locale.format('es_US', date, 'MMMM')).toEqual('enero');
+    expect(dayjsGenerateConfig.locale.format('es_US', date, 'dddd')).toEqual('lunes');
+  });
+
+  it('date-fns keeps the US week start and formats in Spanish', () => {
+    expect(dateFnsGenerateConfig.locale.getWeekFirstDay('es_US')).toEqual(0);
+
+    const date = new Date(2018, 0, 15);
+
+    expect(dateFnsGenerateConfig.locale.format('es_US', date, 'MMMM')).toEqual('enero');
+    expect(dateFnsGenerateConfig.locale.format('es_US', date, 'EEEE')).toEqual('lunes');
+  });
+});