[pickers] Fix DateCalendar timezone management (@LukasTy)

packages/x-date-pickers-pro/src/DateRangeCalendar/timezone.DateRangeCalendar.test.tsx

@@ -0,0 +1,41 @@
+import * as React from 'react';
+import { expect } from 'chai';
+import { screen, fireEvent } from '@mui/internal-test-utils';
+import { describeAdapters } from 'test/utils/pickers';
+import { DateRangeCalendar } from './DateRangeCalendar';
+
+describe('<DateRangeCalendar /> - Timezone', () => {
+  describeAdapters('Timezone prop', DateRangeCalendar, ({ adapter, render }) => {
+    if (!adapter.isTimezoneCompatible) {
+      return;
+    }
+
+    it('should correctly render month days when timezone changes', () => {
+      function DateCalendarWithControlledTimezone() {
+        const [timezone, setTimezone] = React.useState('Europe/Paris');
+        return (
+          <React.Fragment>
+            <DateRangeCalendar timezone={timezone} calendars={1} />
+            <button onClick={() => setTimezone('America/New_York')}>Switch timezone</button>
+          </React.Fragment>
+        );
+      }
+      render(<DateCalendarWithControlledTimezone />);
+
+      expect(
+        screen.getAllByRole('gridcell', {
+          name: (_, element) => element.nodeName === 'BUTTON',
+        }).length,
+      ).to.equal(30);
+
+      fireEvent.click(screen.getByRole('button', { name: 'Switch timezone' }));
+
+      // the amount of rendered days should remain the same after changing timezone
+      expect(
+        screen.getAllByRole('gridcell', {
+          name: (_, element) => element.nodeName === 'BUTTON',
+        }).length,
+      ).to.equal(30);
+    });
+  });
+});

packages/x-date-pickers/src/DateCalendar/DayCalendar.tsx

@@ -533,9 +533,8 @@ export function DayCalendar<TDate>(inProps: DayCalendarProps<TDate>) {
   ]);
 
   const weeksToDisplay = React.useMemo(() => {
-    const currentMonthWithTimezone = utils.setTimezone(currentMonth, timezone);
-    const toDisplay = utils.getWeekArray(currentMonthWithTimezone);
-    let nextMonth = utils.addMonths(currentMonthWithTimezone, 1);
+    const toDisplay = utils.getWeekArray(currentMonth);
+    let nextMonth = utils.addMonths(currentMonth, 1);
     while (fixedWeekNumber && toDisplay.length < fixedWeekNumber) {
       const additionalWeeks = utils.getWeekArray(nextMonth);
       const hasCommonWeek = utils.isSameDay(
@@ -552,7 +551,7 @@ export function DayCalendar<TDate>(inProps: DayCalendarProps<TDate>) {
       nextMonth = utils.addMonths(nextMonth, 1);
     }
     return toDisplay;
-  }, [currentMonth, fixedWeekNumber, utils, timezone]);
+  }, [currentMonth, fixedWeekNumber, utils]);
 
   return (
     <PickersCalendarDayRoot role="grid" aria-labelledby={gridLabelId} className={classes.root}>

packages/x-date-pickers/src/DateCalendar/tests/timezone.DateCalendar.test.tsx

@@ -29,6 +29,49 @@ describe('<DateCalendar /> - Timezone', () => {
       expect(actualDate).toEqualDateTime(expectedDate);
     });
 
+    it('should use "default" timezone for onChange when provided', () => {
+      const onChange = spy();
+      const value = adapter.date('2022-04-25T15:30');
+
+      render(<DateCalendar value={value} onChange={onChange} timezone="default" />);
+
+      fireEvent.click(screen.getByRole('gridcell', { name: '25' }));
+      const expectedDate = adapter.setDate(value, 25);
+
+      // Check the `onChange` value (uses timezone prop)
+      const actualDate = onChange.lastCall.firstArg;
+      expect(adapter.getTimezone(actualDate)).to.equal(adapter.lib === 'dayjs' ? 'UTC' : 'system');
+      expect(actualDate).toEqualDateTime(expectedDate);
+    });
+
+    it('should correctly render month days when timezone changes', () => {
+      function DateCalendarWithControlledTimezone() {
+        const [timezone, setTimezone] = React.useState('Europe/Paris');
+        return (
+          <React.Fragment>
+            <DateCalendar timezone={timezone} />
+            <button onClick={() => setTimezone('America/New_York')}>Switch timezone</button>
+          </React.Fragment>
+        );
+      }
+      render(<DateCalendarWithControlledTimezone />);
+
+      expect(
+        screen.getAllByRole('gridcell', {
+          name: (_, element) => element.nodeName === 'BUTTON',
+        }).length,
+      ).to.equal(30);
+
+      fireEvent.click(screen.getByRole('button', { name: 'Switch timezone' }));
+
+      // the amount of rendered days should remain the same after changing timezone
+      expect(
+        screen.getAllByRole('gridcell', {
+          name: (_, element) => element.nodeName === 'BUTTON',
+        }).length,
+      ).to.equal(30);
+    });
+
     TIMEZONE_TO_TEST.forEach((timezone) => {
       describe(`Timezone: ${timezone}`, () => {
         it('should use timezone prop for onChange when no value is provided', () => {

packages/x-date-pickers/src/DateCalendar/useCalendarState.tsx

@@ -42,6 +42,7 @@ export const createCalendarStateReducer =
     action:
       | ReducerAction<'finishMonthSwitchingAnimation'>
       | ReducerAction<'changeMonth', ChangeMonthPayload<TDate>>
+      | ReducerAction<'changeMonthTimezone', { newTimezone: string }>
       | ReducerAction<'changeFocusedDay', ChangeFocusedDayPayload<TDate>>,
   ): CalendarState<TDate> => {
     switch (action.type) {
@@ -53,6 +54,21 @@ export const createCalendarStateReducer =
           isMonthSwitchingAnimating: !reduceAnimations,
         };
 
+      case 'changeMonthTimezone': {
+        const newTimezone = action.newTimezone;
+        if (utils.getTimezone(state.currentMonth) === newTimezone) {
+          return state;
+        }
+        let newCurrentMonth = utils.setTimezone(state.currentMonth, newTimezone);
+        if (utils.getMonth(newCurrentMonth) !== utils.getMonth(state.currentMonth)) {
+          newCurrentMonth = utils.setMonth(newCurrentMonth, utils.getMonth(state.currentMonth));
+        }
+        return {
+          ...state,
+          currentMonth: newCurrentMonth,
+        };
+      }
+
       case 'finishMonthSwitchingAnimation':
         return {
           ...state,
@@ -156,7 +172,9 @@ export const useCalendarState = <TDate extends unknown>(params: UseCalendarState
         granularity: SECTION_TYPE_GRANULARITY.day,
       });
     },
-    [], // eslint-disable-line react-hooks/exhaustive-deps
+    // We want the `referenceDate` to update on prop and `timezone` change (https://github.com/mui/mui-x/issues/10804)
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+    [referenceDateProp, timezone],
   );
 
   const [calendarState, dispatch] = React.useReducer(reducerFn, {
@@ -166,6 +184,15 @@ export const useCalendarState = <TDate extends unknown>(params: UseCalendarState
     slideDirection: 'left',
   });
 
+  // Ensure that `calendarState.currentMonth` timezone is updated when `referenceDate` (or timezone changes)
+  // https://github.com/mui/mui-x/issues/10804
+  React.useEffect(() => {
+    dispatch({
+      type: 'changeMonthTimezone',
+      newTimezone: utils.getTimezone(referenceDate),
+    });
+  }, [referenceDate, utils]);
+
   const handleChangeMonth = React.useCallback(
     (payload: ChangeMonthPayload<TDate>) => {
       dispatch({