Editorial: Remove duplicate steps in UnbalanceDateDurationRelative

polyfill/lib/ecmascript.mjs

@@ -3445,14 +3445,18 @@ export function BalanceTimeDurationRelative(
 export function UnbalanceDateDurationRelative(years, months, weeks, days, largestUnit, plainRelativeTo, calendarRec) {
   // calendarRec must have looked up dateAdd and dateUntil
   const TemporalDuration = GetIntrinsic('%Temporal.Duration%');
+  const defaultLargestUnit = DefaultTemporalLargestUnit(years, months, weeks, days, 0, 0, 0, 0, 0, 0);
+  const effectiveLargestUnit = LargerOfTwoTemporalUnits(largestUnit, 'day');
+  if (LargerOfTwoTemporalUnits(defaultLargestUnit, effectiveLargestUnit) === effectiveLargestUnit) {
+    // no-op
+    return { years, months, weeks, days };
+  }
+  if (!calendarRec) throw new RangeError(`a starting point is required for ${largestUnit}s balancing`);
 
-  switch (largestUnit) {
+  switch (effectiveLargestUnit) {
     case 'year':
-      // no-op
-      return { years, months, weeks, days };
+      throw new Error('assert not reached');
     case 'month': {
-      if (years === 0) return { years: 0, months, weeks, days };
-      if (!calendarRec) throw new RangeError('a starting point is required for months balancing');
       // balance years down to months
       const later = CalendarDateAdd(calendarRec, plainRelativeTo, new TemporalDuration(years));
       const untilOptions = ObjectCreate(null);
@@ -3462,17 +3466,13 @@ export function UnbalanceDateDurationRelative(years, months, weeks, days, larges
       return { years: 0, months: months + yearsInMonths, weeks, days };
     }
     case 'week': {
-      if (years === 0 && months === 0) return { years: 0, months: 0, weeks, days };
-      if (!calendarRec) throw new RangeError('a starting point is required for weeks balancing');
       // balance years and months down to days
       const later = CalendarDateAdd(calendarRec, plainRelativeTo, new TemporalDuration(years, months));
       const yearsMonthsInDays = DaysUntil(plainRelativeTo, later);
       return { years: 0, months: 0, weeks, days: days + yearsMonthsInDays };
     }
     default: {
       // largestUnit is "day", or any time unit
-      if (years === 0 && months === 0 && weeks === 0) return { years: 0, months: 0, weeks: 0, days };
-      if (!calendarRec) throw new RangeError('a starting point is required for balancing calendar units');
       // balance years, months, and weeks down to days
       const later = CalendarDateAdd(calendarRec, plainRelativeTo, new TemporalDuration(years, months, weeks));
       const yearsMonthsWeeksInDays = DaysUntil(plainRelativeTo, later);

spec/duration.html

@@ -1739,13 +1739,15 @@ <h1>
       </dl>
       <emu-alg>
         1. Assert: If _plainRelativeTo_ is not *undefined*, _calendarRec_ is not *undefined*.
-        1. If _largestUnit_ is *"year"*, then
+        1. Let _defaultLargestUnit_ be DefaultTemporalLargestUnit(_years_, _months_, _weeks_, _days_, 0, 0, 0, 0, 0).
+        1. Let _effectiveLargestUnit_ be LargerOfTwoTemporalUnits(_largestUnit_, *"day"*).
+        1. If _effectiveLargestUnit_ is LargerOfTwoTemporalUnits(_defaultLargestUnit_, _effectiveLargestUnit_), then
           1. Return ! CreateDateDurationRecord(_years_, _months_, _weeks_, _days_).
-        1. If _largestUnit_ is *"month"*, then
-          1. If _years_ = 0, return ! CreateDateDurationRecord(0, _months_, _weeks_, _days_).
-          1. If _calendarRec_ is *undefined*, then
-            1. Throw a *RangeError* exception.
-          1. Assert: CalendarMethodsRecordHasLookedUp(_calendarRec_, ~date-add~) is *true*.
+        1. Assert: _effectiveLargestUnit_ is not *"year"*.
+        1. If _calendarRec_ is *undefined*, then
+          1. Throw a *RangeError* exception.
+        1. Assert: CalendarMethodsRecordHasLookedUp(_calendarRec_, ~date-add~) is *true*.
+        1. If _effectiveLargestUnit_ is *"month"*, then
           1. Assert: CalendarMethodsRecordHasLookedUp(_calendarRec_, ~date-until~) is *true*.
           1. Let _yearsDuration_ be ! CreateTemporalDuration(_years_, 0, 0, 0, 0, 0, 0, 0, 0, 0).
           1. Let _later_ be ? CalendarDateAdd(_calendarRec_, _plainRelativeTo_, _yearsDuration_).
@@ -1754,24 +1756,16 @@ <h1>
           1. Let _untilResult_ be ? CalendarDateUntil(_calendarRec_, _plainRelativeTo_, _later_, _untilOptions_).
           1. Let _yearsInMonths_ be _untilResult_.[[Months]].
           1. Return ? CreateDateDurationRecord(0, _months_ + _yearsInMonths_, _weeks_, _days_).
-        1. If _largestUnit_ is *"week"*, then
-          1. If _years_ = 0 and _months_ = 0, return ! CreateDateDurationRecord(0, 0, _weeks_, _days_).
-          1. If _calendarRec_ is *undefined*, then
-            1. Throw a *RangeError* exception.
-          1. Assert: CalendarMethodsRecordHasLookedUp(_calendarRec_, ~date-add~) is *true*.
+        1. If _effectiveLargestUnit_ is *"week"*, then
           1. Let _yearsMonthsDuration_ be ! CreateTemporalDuration(_years_, _months_, 0, 0, 0, 0, 0, 0, 0, 0).
           1. Let _later_ be ? CalendarDateAdd(_calendarRec_, _plainRelativeTo_, _yearsMonthsDuration_).
           1. Let _yearsMonthsInDays_ be DaysUntil(_plainRelativeTo_, _later_).
-          1. Return ? CreateDateDurationRecord(0, 0, _weeks_, _days_ + _yearsMonthsInDays_).
+          1. Return ! CreateDateDurationRecord(0, 0, _weeks_, _days_ + _yearsMonthsInDays_).
         1. NOTE: _largestUnit_ can be any time unit as well as *"day"*.
-        1. If _years_ = 0, and _months_ = 0, and _weeks_ = 0, return ! CreateDateDurationRecord(0, 0, 0, _days_).
-        1. If _calendarRec_ is *undefined*, then
-          1. Throw a *RangeError* exception.
-        1. Assert: CalendarMethodsRecordHasLookedUp(_calendarRec_, ~date-add~) is *true*.
         1. Let _yearsMonthsWeeksDuration_ be ! CreateTemporalDuration(_years_, _months_, _weeks_, 0, 0, 0, 0, 0, 0, 0).
         1. Let _later_ be ? CalendarDateAdd(_calendarRec_, _plainRelativeTo_, _yearsMonthsWeeksDuration_).
         1. Let _yearsMonthsWeeksInDays_ be DaysUntil(_plainRelativeTo_, _later_).
-        1. Return ? CreateDateDurationRecord(0, 0, 0, _days_ + _yearsMonthsWeeksInDays_).
+        1. Return ! CreateDateDurationRecord(0, 0, 0, _days_ + _yearsMonthsWeeksInDays_).
       </emu-alg>
     </emu-clause>