fix: clamp the displayed month when the navigation range changes

[nahuelsoria]

Closes #2912.

The problem

When endMonth (or startMonth) changes to a range that no longer contains the month being displayed, the month grid and the dropdowns disappear.

getDisplayMonths breaks out of its loop as soon as the first month is past calendarEndMonth, so it returns an empty array and nothing is rendered:

for (let i = 0; i < numberOfMonths; i++) {
  const month = dateLib.addMonths(firstDisplayedMonth, i);
  if (calendarEndMonth && month > calendarEndMonth) break;
  months.push(month);
}

The displayed month is clamped to the navigation range by getInitialMonth, but that only happens when the calendar mounts (and when the time zone changes). The month stored by useControlledValue is then left out of range.

Worth noting: this does not reproduce when month is controlled, because in that case initialMonth is recomputed on every render and the clamping is applied again. The uncontrolled case was the one drifting out of range.

The fix

Clamp the displayed month to the navigation range on every render, reusing the existing getInitialMonth logic so the rule lives in one place:

const displayMonth = getInitialMonth(
  { ...props, month: firstMonth },
  navStart,
  navEnd,
  dateLib,
);

displayMonth then feeds getDisplayMonths, getPreviousMonth and getNextMonth, so the grid, the dropdowns and the navigation buttons all stay consistent with the new range. This matches the behaviour suggested in the issue: the calendar switches to the closest month it can display. No state is written, so no extra render and no onMonthChange is fired.

Tests

Three tests in DayPicker.test.tsx covering endMonth narrowing, startMonth moving forward, and numberOfMonths={2}. They fail on main and pass with the fix.

Verification

• pnpm test: 221 suites, 1087 tests passing
• pnpm test:tz: 3 passing
• pnpm typecheck and biome check: clean
• Same results on main before the change, so no regressions

[changeset-bot]

🦋 Changeset detected

Latest commit: 5ef25b1

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 7 packages

Name	Type
@daypicker/buddhist	Patch
@daypicker/ethiopic	Patch
@daypicker/hebrew	Patch
@daypicker/hijri	Patch
@daypicker/persian	Patch
@daypicker/react	Patch
react-day-picker	Patch

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