fix(datetime): month picker no longer gives duplicate months on ios 1…

…4 and older (#24792)

resolves #24663

core/src/components/datetime/test/format.spec.ts

@@ -27,6 +27,11 @@ describe('generateDayAriaLabel()', () => {
 
     expect(generateDayAriaLabel('en-US', false, reference)).toEqual('Monday, May 31');
   });
+  it('should return Saturday, April 1', () => {
+    const reference = { month: 4, day: 1, year: 2006 };
+
+    expect(generateDayAriaLabel('en-US', false, reference)).toEqual('Saturday, April 1');
+  });
 });
 
 describe('getMonthAndDay()', () => {
@@ -37,6 +42,14 @@ describe('getMonthAndDay()', () => {
   it('should return mar, 11 may', () => {
     expect(getMonthAndDay('es-ES', { month: 5, day: 11, year: 2021 })).toEqual('mar, 11 may');
   });
+
+  it('should return Sat, Apr 1', () => {
+    expect(getMonthAndDay('en-US', { month: 4, day: 1, year: 2006 })).toEqual('Sat, Apr 1');
+  });
+
+  it('should return sáb, 1 abr', () => {
+    expect(getMonthAndDay('es-ES', { month: 4, day: 1, year: 2006 })).toEqual('sáb, 1 abr');
+  });
 })
 
 describe('getFormattedHour()', () => {
@@ -63,7 +76,15 @@ describe('getMonthAndYear()', () => {
     expect(getMonthAndYear('en-US', { month: 5, day: 11, year: 2021 })).toEqual('May 2021');
   });
 
-  it('should return mar, 11 may', () => {
+  it('should return mayo de 2021', () => {
     expect(getMonthAndYear('es-ES', { month: 5, day: 11, year: 2021 })).toEqual('mayo de 2021');
   });
+
+  it('should return April 2006', () => {
+    expect(getMonthAndYear('en-US', { month: 4, day: 1, year: 2006 })).toEqual('April 2006');
+  });
+
+  it('should return abril de 2006', () => {
+    expect(getMonthAndYear('es-ES', { month: 4, day: 1, year: 2006 })).toEqual('abril de 2006');
+  });
 })

core/src/components/datetime/utils/data.ts

@@ -282,19 +282,44 @@ export const getPickerMonths = (
     }
 
     processedMonths.forEach(processedMonth => {
-      const date = new Date(`${processedMonth}/1/${year}`);
+      const date = new Date(`${processedMonth}/1/${year} GMT+0000`);
 
-      const monthString = new Intl.DateTimeFormat(locale, { month: 'long' }).format(date);
+      const monthString = new Intl.DateTimeFormat(locale, { month: 'long', timeZone: 'UTC' }).format(date);
       months.push({ text: monthString, value: processedMonth });
     });
   } else {
     const maxMonth = maxParts && maxParts.year === year ? maxParts.month : 12;
     const minMonth = minParts && minParts.year === year ? minParts.month : 1;
 
     for (let i = minMonth; i <= maxMonth; i++) {
-      const date = new Date(`${i}/1/${year}`);
 
-      const monthString = new Intl.DateTimeFormat(locale, { month: 'long' }).format(date);
+      /**
+       *
+       * There is a bug on iOS 14 where
+       * Intl.DateTimeFormat takes into account
+       * the local timezone offset when formatting dates.
+       *
+       * Forcing the timezone to 'UTC' fixes the issue. However,
+       * we should keep this workaround as it is safer. In the event
+       * this breaks in another browser, we will not be impacted
+       * because all dates will be interpreted in UTC.
+       *
+       * Example:
+       * new Intl.DateTimeFormat('en-US', { month: 'long' }).format(new Date('Sat Apr 01 2006 00:00:00 GMT-0400 (EDT)')) // "March"
+       * new Intl.DateTimeFormat('en-US', { month: 'long', timeZone: 'UTC' }).format(new Date('Sat Apr 01 2006 00:00:00 GMT-0400 (EDT)')) // "April"
+       *
+       * In certain timezones, iOS 14 shows the wrong
+       * date for .toUTCString(). To combat this, we
+       * force all of the timezones to GMT+0000 (UTC).
+       *
+       * Example:
+       * Time Zone: Central European Standard Time
+       * new Date('1/1/1992').toUTCString() // "Tue, 31 Dec 1991 23:00:00 GMT"
+       * new Date('1/1/1992 GMT+0000').toUTCString() // "Wed, 01 Jan 1992 00:00:00 GMT"
+       */
+      const date = new Date(`${i}/1/${year} GMT+0000`);
+
+      const monthString = new Intl.DateTimeFormat(locale, { month: 'long', timeZone: 'UTC' }).format(date);
       months.push({ text: monthString, value: i });
     }
   }

core/src/components/datetime/utils/format.ts

@@ -56,9 +56,9 @@ export const generateDayAriaLabel = (locale: string, today: boolean, refParts: D
   /**
    * MM/DD/YYYY will return midnight in the user's timezone.
    */
-  const date = new Date(`${refParts.month}/${refParts.day}/${refParts.year}`);
+  const date = new Date(`${refParts.month}/${refParts.day}/${refParts.year} GMT+0000`);
 
-  const labelString = new Intl.DateTimeFormat(locale, { weekday: 'long', month: 'long', day: 'numeric' }).format(date);
+  const labelString = new Intl.DateTimeFormat(locale, { weekday: 'long', month: 'long', day: 'numeric', timeZone: 'UTC' }).format(date);
 
   /**
    * If date is today, prepend "Today" so screen readers indicate
@@ -72,8 +72,8 @@ export const generateDayAriaLabel = (locale: string, today: boolean, refParts: D
  * Used for the header in MD mode.
  */
 export const getMonthAndDay = (locale: string, refParts: DatetimeParts) => {
-  const date = new Date(`${refParts.month}/${refParts.day}/${refParts.year}`);
-  return new Intl.DateTimeFormat(locale, { weekday: 'short', month: 'short', day: 'numeric' }).format(date);
+  const date = new Date(`${refParts.month}/${refParts.day}/${refParts.year} GMT+0000`);
+  return new Intl.DateTimeFormat(locale, { weekday: 'short', month: 'short', day: 'numeric', timeZone: 'UTC' }).format(date);
 }
 
 /**
@@ -83,6 +83,6 @@ export const getMonthAndDay = (locale: string, refParts: DatetimeParts) => {
  * Example: May 2021
  */
 export const getMonthAndYear = (locale: string, refParts: DatetimeParts) => {
-  const date = new Date(`${refParts.month}/${refParts.day}/${refParts.year}`);
-  return new Intl.DateTimeFormat(locale, { month: 'long', year: 'numeric' }).format(date);
+  const date = new Date(`${refParts.month}/${refParts.day}/${refParts.year} GMT+0000`);
+  return new Intl.DateTimeFormat(locale, { month: 'long', year: 'numeric', timeZone: 'UTC' }).format(date);
 }