Normative: Changes to AddDurationToYearMonth

polyfill/lib/ecmascript.mjs

@@ -1715,6 +1715,25 @@ export function CalendarDateAdd(calendar, isoDate, dateDuration, overflow) {
   return result;
 }
 
+function CalendarDateLastDayOfMonth(calendar, isoDate) {
+  if (calendar === 'iso8601') {
+    let maxDay = ISODaysInMonth(isoDate.year, isoDate.month);
+    return { year: isoDate.year, month: isoDate.month, day: maxDay };
+  }
+  let previousIsoDate = isoDate;
+  let nextIsoDate = isoDate;
+  let calendarDate = calendarImplForID(calendar).isoToDate(nextIsoDate, { year: true, month: true, day: true });
+  let initialMonth = calendarDate.month;
+  while (calendarDate.month === initialMonth) {
+    previousIsoDate = nextIsoDate;
+    // If the date overflows the maxium range, an exception will be thrown,
+    // which is the desired behavior
+    nextIsoDate = CalendarDateAdd(calendar, nextIsoDate, { days: 1 }, 'constrain');
+    calendarDate = calendarImplForID(calendar).isoToDate(nextIsoDate, { year: true, month: true, day: true });
+  }
+  return previousIsoDate;
+}
+
 export function CalendarDateUntil(calendar, isoDate, isoOtherDate, largestUnit) {
   return calendarImplForID(calendar).dateUntil(isoDate, isoOtherDate, largestUnit);
 }
@@ -4129,23 +4148,35 @@ export function AddDurationToTime(operation, temporalTime, durationLike) {
 export function AddDurationToYearMonth(operation, yearMonth, durationLike, options) {
   let duration = ToTemporalDuration(durationLike);
   if (operation === 'subtract') duration = CreateNegatedTemporalDuration(duration);
+  const sign = DurationSign(duration);
+  duration = ToDateDurationRecordWithoutTime(duration);
   const resolvedOptions = GetOptionsObject(options);
   const overflow = GetTemporalOverflowOption(resolvedOptions);
-  const sign = DurationSign(duration);
-
+  const durationYearsMonthsOnly = AdjustDateDurationRecord(duration, 0, 0);
+  const durationWithoutYearsMonths = {
+    years: 0,
+    months: 0,
+    weeks: duration.weeks,
+    days: duration.days
+  };
   const calendar = GetSlot(yearMonth, CALENDAR);
   const fields = ISODateToFields(calendar, GetSlot(yearMonth, ISO_DATE), 'year-month');
   fields.day = 1;
   let startDate = CalendarDateFromFields(calendar, fields, 'constrain');
-  if (sign < 0) {
-    const nextMonth = CalendarDateAdd(calendar, startDate, { months: 1 }, 'constrain');
-    startDate = BalanceISODate(nextMonth.year, nextMonth.month, nextMonth.day - 1);
-  }
-  const durationToAdd = ToDateDurationRecordWithoutTime(duration);
   RejectDateRange(startDate);
-  const addedDate = CalendarDateAdd(calendar, startDate, durationToAdd, overflow);
+  const dateWithYearMonthAdded = CalendarDateAdd(calendar, startDate, durationYearsMonthsOnly, overflow);
+  let addedDate;
+  if (!(durationWithoutYearsMonths.weeks === 0 && durationWithoutYearsMonths.days === 0)) {
+    if (sign < 0) {
+      startDate = CalendarDateLastDayOfMonth(calendar, dateWithYearMonthAdded);
+    } else {
+      startDate = dateWithYearMonthAdded;
+    }
+    addedDate = CalendarDateAdd(calendar, startDate, durationWithoutYearsMonths, overflow);
+  } else {
+    addedDate = dateWithYearMonthAdded;
+  }
   const addedDateFields = ISODateToFields(calendar, addedDate, 'year-month');
-
   const isoDate = CalendarYearMonthFromFields(calendar, addedDateFields, overflow);
   return CreateTemporalYearMonth(isoDate, calendar);
 }

spec/calendar.html

@@ -595,6 +595,49 @@ <h1>
       </emu-alg>
     </emu-clause>
 
+    <emu-clause id="sec-temporal-nonisodatelastdayofmonth" type="implementation-defined abstract operation">
+      <h1>
+        NonISODateLastDayOfMonth (
+          _calendar_: a calendar type that is not *"iso8601"*,
+          _year_: an integer,
+          _month_: an integer between 1 and 13 (inclusive),
+        ): an ISO Date Record
+      </h1>
+      <dl class="header">
+        <dt>description</dt>
+        <dd>
+          The operation performs implementation-defined processing to determine the last day of the month denoted by _year_ and _month_. It returns an ISO Date Record representing a date in the reckoning of _calendar_ that has the the same year and month as _year_ and _month_, and the day set to the last day of _month_.
+        </dd>
+      </dl>
+    </emu-clause>
+
+    <emu-clause id="sec-temporal-calendardatelastdayofmonth" type="abstract operation">
+      <h1>
+        CalendarDateLastDayOfMonth (
+          _calendar_: a calendar type,
+          _isoDate_: an ISO Date Record,
+        ): an ISO Date Record
+      </h1>
+      <dl class="header">
+        <dt>description</dt>
+        <dd>
+          It determines the last day in the month _isoMonth_ of the year _isoYear_ using the years, months
+          and weeks reckoning of _calendar_, and returns an ISO Date Record with the same year and month
+          as _isoDate_, and the day set to the last day in the month.
+        </dd>
+      </dl>
+      <emu-alg>
+        1. If _calendar_ is *"iso8601"*, then
+          1. If _isoDate_.[[Year]] equals 275760 and _isoDate_.[[Month]] equals 9, then
+            1. Let _maxDay_ be 13.
+          1. Else,
+            1. Let _maxDay_ be ISODaysInMonth(_isoDate_.[[Year]], _isoDate_.[[Month]]).
+          1. Return CreateISODateRecord(_isoDate_.[[Year]], _isoDate_.[[Month]], _maxDay_).
+        1. Else,
+          1. Return NonISODateLastDayOfMonth(_calendar_, _isoDate_.[[Year]], _isoDate_.[[Month]]).
+      </emu-alg>
+    </emu-clause>
+
     <emu-clause id="sec-temporal-nonisodateuntil" type="implementation-defined abstract operation">
       <h1>
         NonISODateUntil (

spec/plainyearmonth.html

@@ -639,22 +639,27 @@ <h1>
       <emu-alg>
         1. Let _duration_ be ? ToTemporalDuration(_temporalDurationLike_).
         1. If _operation_ is ~subtract~, set _duration_ to CreateNegatedTemporalDuration(_duration_).
+        1. Let _sign_ be DurationSign(_duration_).
+        1. Set _duration_ to ToDateDurationRecordWithoutTime(_duration_).
         1. Let _resolvedOptions_ be ? GetOptionsObject(_options_).
         1. Let _overflow_ be ? GetTemporalOverflowOption(_resolvedOptions_).
-        1. Let _sign_ be DurationSign(_duration_).
+        1. Let _durationYearsMonthsOnly_ be ! AdjustDateDurationRecord(_duration_, 0, 0).
+        1. Let _durationWithoutYearsMonths_ be ? CreateDateDurationRecord(0, 0, _duration_.[[Weeks]], _duration_.[[Days]]).
         1. Let _calendar_ be _yearMonth_.[[Calendar]].
         1. Let _fields_ be ISODateToFields(_calendar_, _yearMonth_.[[ISODate]], ~year-month~).
         1. Set _fields_.[[Day]] to 1.
         1. Let _intermediateDate_ be ? CalendarDateFromFields(_calendar_, _fields_, ~constrain~).
-        1. If _sign_ &lt; 0, then
-          1. Let _oneMonthDuration_ be ! CreateDateDurationRecord(0, 1, 0, 0).
-          1. Let _nextMonth_ be ? CalendarDateAdd(_calendar_, _intermediateDate_, _oneMonthDuration_, ~constrain~).
-          1. Let _date_ be BalanceISODate(_nextMonth_.[[Year]], _nextMonth_.[[Month]], _nextMonth_.[[Day]] - 1).
-          1. Assert: ISODateWithinLimits(_date_) is *true*.
+        1. If IsValidISODate(_intermediateDate_.[[Year]], _intermediateDate_.[[Month]], _intermediateDate_.[[Day]]) is *false*, throw a *RangeError* exception.
+        1. Let _dateWithYearMonthAdded_ be ? CalendarDateAdd(_calendar_, _intermediateDate_, _durationYearsMonthsOnly_, _overflow_).
+        1. Let _addedDate_ be ~unset~.
+        1. If _durationWithoutYearsMonths_.[[Weeks]] is not equal to 0 or _durationWithoutYearsMonths_.[[Days]] is not equal to 0, then
+          1. If _sign_ &lt; 0, then
+            1. Set _intermediateDate_ to CalendarDateLastDayOfMonth(_calendar_, _dateWithYearMonthAdded_).
+          1. Else,
+            1. Set _intermediateDate_ to _dateWithYearMonthAdded_.
+          1. Set _addedDate_ to ? CalendarDateAdd(_calendar_, _intermediateDate_, _durationWithoutYearsMonths_, _overflow_).
         1. Else,
-          1. Let _date_ be _intermediateDate_.
-        1. Let _durationToAdd_ be ToDateDurationRecordWithoutTime(_duration_).
-        1. Let _addedDate_ be ? CalendarDateAdd(_calendar_, _date_, _durationToAdd_, _overflow_).
+          1. Set _addedDate_ to _dateWithYearMonthAdded_.
         1. Let _addedDateFields_ be ISODateToFields(_calendar_, _addedDate_, ~year-month~).
         1. Let _isoDate_ be ? CalendarYearMonthFromFields(_calendar_, _addedDateFields_, _overflow_).
         1. Return ! CreateTemporalYearMonth(_isoDate_, _calendar_).