fix: skip native Date fast paths when local timezone is overridden (#9669)

packages/@internationalized/date/src/conversion.ts

@@ -17,7 +17,7 @@ import {AnyCalendarDate, AnyDateTime, AnyTime, Calendar, DateFields, Disambiguat
 import {CalendarDate, CalendarDateTime, Time, ZonedDateTime} from './CalendarDate';
 import {constrain} from './manipulation';
 import {getExtendedYear, GregorianCalendar} from './calendars/GregorianCalendar';
-import {getLocalTimeZone, isEqualCalendar} from './queries';
+import {getLocalTimeZone, isEqualCalendar, isLocalTimeZoneOverridden} from './queries';
 import {Mutable} from './utils';
 
 export function epochFromDate(date: AnyDateTime): number {
@@ -42,7 +42,7 @@ export function getTimeZoneOffset(ms: number, timeZone: string): number {
   }
 
   // Fast path: for local timezone after 1970, use native Date.
-  if (ms > 0 && timeZone === getLocalTimeZone()) {
+  if (ms > 0 && timeZone === getLocalTimeZone() && !isLocalTimeZoneOverridden()) {
     return new Date(ms).getTimezoneOffset() * -60 * 1000;
   }
 
@@ -124,7 +124,7 @@ export function toAbsolute(date: CalendarDate | CalendarDateTime, timeZone: stri
   }
 
   // Fast path: if the time zone is the local timezone and disambiguation is compatible, use native Date.
-  if (timeZone === getLocalTimeZone() && disambiguation === 'compatible') {
+  if (timeZone === getLocalTimeZone() && disambiguation === 'compatible' && !isLocalTimeZoneOverridden()) {
     dateTime = toCalendar(dateTime, new GregorianCalendar());
 
     // Don't use Date constructor here because two-digit years are interpreted in the 20th century.

packages/@internationalized/date/src/index.ts

@@ -66,6 +66,7 @@ export {
   getLocalTimeZone,
   setLocalTimeZone,
   resetLocalTimeZone,
+  isLocalTimeZoneOverridden,
   startOfMonth,
   startOfWeek,
   startOfYear,

packages/@internationalized/date/src/queries.ts

@@ -130,6 +130,7 @@ export function getHoursInDay(a: CalendarDate, timeZone: string): number {
 }
 
 let localTimeZone: string | null = null;
+let localTimeZoneOverridden = false;
 
 /** Returns the time zone identifier for the current user. */
 export function getLocalTimeZone(): string {
@@ -143,11 +144,18 @@ export function getLocalTimeZone(): string {
 /** Sets the time zone identifier for the current user. */
 export function setLocalTimeZone(timeZone: string): void {
   localTimeZone = timeZone;
+  localTimeZoneOverridden = true;
 }
 
 /** Resets the time zone identifier for the current user. */
 export function resetLocalTimeZone(): void {
   localTimeZone = null;
+  localTimeZoneOverridden = false;
+}
+
+/** Returns whether the local time zone has been overridden via setLocalTimeZone. */
+export function isLocalTimeZoneOverridden(): boolean {
+  return localTimeZoneOverridden;
 }
 
 /** Returns the first date of the month for the given date. */

packages/@internationalized/date/tests/conversion.test.js

@@ -10,7 +10,7 @@
  * governing permissions and limitations under the License.
  */
 
-import {BuddhistCalendar, CalendarDate, CalendarDateTime, EthiopicAmeteAlemCalendar, EthiopicCalendar, GregorianCalendar, HebrewCalendar, IndianCalendar, IslamicCivilCalendar, IslamicTabularCalendar, IslamicUmalquraCalendar, JapaneseCalendar, PersianCalendar, TaiwanCalendar, Time, toCalendar, toCalendarDate, toCalendarDateTime, toTime, ZonedDateTime} from '..';
+import {BuddhistCalendar, CalendarDate, CalendarDateTime, EthiopicAmeteAlemCalendar, EthiopicCalendar, GregorianCalendar, HebrewCalendar, IndianCalendar, IslamicCivilCalendar, IslamicTabularCalendar, IslamicUmalquraCalendar, JapaneseCalendar, PersianCalendar, TaiwanCalendar, Time, toCalendar, toCalendarDate, toCalendarDateTime, toTime, ZonedDateTime, setLocalTimeZone, resetLocalTimeZone} from '..';
 import {Custom454Calendar} from './customCalendarImpl';
 import {fromAbsolute, possibleAbsolutes, toAbsolute, toDate} from '../src/conversion';
 
@@ -522,4 +522,28 @@ describe('CalendarDate conversion', function () {
       expect(toTime(dateTime)).toEqual(new Time(8, 23, 10, 80));
     });
   });
+
+  describe('setLocalTimeZone interaction with fast paths', function () {
+    afterEach(() => {
+      resetLocalTimeZone();
+    });
+
+    it('fromAbsolute should return the correct offset when local timezone is overridden', function () {
+      // Etc/GMT-10 means UTC+10
+      setLocalTimeZone('Etc/GMT-10');
+      let ms = Date.UTC(2020, 5, 15, 12, 0, 0); // 2020-06-15T12:00:00Z
+      let zdt = fromAbsolute(ms, 'Etc/GMT-10');
+      expect(zdt.hour).toBe(22); // 12:00 UTC + 10 = 22:00
+      expect(zdt.offset).toBe(10 * 60 * 60 * 1000);
+    });
+
+    it('toAbsolute should return the correct epoch when local timezone is overridden', function () {
+      // Etc/GMT-10 means UTC+10
+      setLocalTimeZone('Etc/GMT-10');
+      let date = new CalendarDateTime(2020, 6, 15, 22, 0, 0);
+      let ms = toAbsolute(date, 'Etc/GMT-10');
+      // 22:00 in UTC+10 = 12:00 UTC
+      expect(ms).toBe(Date.UTC(2020, 5, 15, 12, 0, 0));
+    });
+  });
 });

packages/@internationalized/date/tests/queries.test.js

@@ -32,6 +32,7 @@ import {
   maxDate,
   minDate,
   PersianCalendar,
+  isLocalTimeZoneOverridden,
   resetLocalTimeZone,
   setLocalTimeZone,
   startOfMonth,
@@ -371,4 +372,26 @@ describe('queries', function () {
       expect(getLocalTimeZone()).toBe(systemTimeZone);
     });
   });
+
+  describe('isLocalTimeZoneOverridden', function () {
+    afterEach(() => {
+      resetLocalTimeZone();
+    });
+
+    it('returns false by default', function () {
+      expect(isLocalTimeZoneOverridden()).toBe(false);
+    });
+
+    it('returns true after setLocalTimeZone', function () {
+      setLocalTimeZone('America/Denver');
+      expect(isLocalTimeZoneOverridden()).toBe(true);
+    });
+
+    it('returns false after resetLocalTimeZone', function () {
+      setLocalTimeZone('America/Denver');
+      expect(isLocalTimeZoneOverridden()).toBe(true);
+      resetLocalTimeZone();
+      expect(isLocalTimeZoneOverridden()).toBe(false);
+    });
+  });
 });