Editorial: Make CreateTemporalDuration infallible in PlainYearMonth a…

…rithmetic

These operations cannot fail because they values they use as input already
come from valid durations (sometimes negated).

spec/plainyearmonth.html

@@ -263,7 +263,7 @@ <h1>Temporal.PlainYearMonth.prototype.add ( _temporalDurationLike_ [ , _options_
         1. Else,
           1. Let _day_ be 1.
         1. Let _date_ be ? CreateTemporalDate(_yearMonth_.[[ISOYear]], _yearMonth_.[[ISOMonth]], _day_, _calendar_).
-        1. Let _durationToAdd_ be ? CreateTemporalDuration(_duration_.[[Years]], _duration_.[[Months]], _duration_.[[Weeks]], _balanceResult_.[[Days]], 0, 0, 0, 0, 0, 0).
+        1. Let _durationToAdd_ be ! CreateTemporalDuration(_duration_.[[Years]], _duration_.[[Months]], _duration_.[[Weeks]], _balanceResult_.[[Days]], 0, 0, 0, 0, 0, 0).
         1. Let _optionsCopy_ be ! OrdinaryObjectCreate(%Object.prototype%).
         1. Let _entries_ be ? EnumerableOwnPropertyNames(_options_, ~key+value~).
         1. For each element _nextEntry_ of _entries_, do
@@ -295,7 +295,7 @@ <h1>Temporal.PlainYearMonth.prototype.subtract ( _temporalDurationLike_ [ , _opt
         1. Else,
           1. Let _day_ be 1.
         1. Let _date_ be ? CreateTemporalDate(_yearMonth_.[[ISOYear]], _yearMonth_.[[ISOMonth]], _day_, _calendar_).
-        1. Let _durationToAdd_ be ? CreateTemporalDuration(−_duration_.[[Years]], −_duration_.[[Months]], −_duration_.[[Weeks]], −_balanceResult_.[[Days]], 0, 0, 0, 0, 0, 0).
+        1. Let _durationToAdd_ be ! CreateTemporalDuration(−_duration_.[[Years]], −_duration_.[[Months]], −_duration_.[[Weeks]], −_balanceResult_.[[Days]], 0, 0, 0, 0, 0, 0).
         1. Let _optionsCopy_ be ! OrdinaryObjectCreate(%Object.prototype%).
         1. Let _entries_ be ? EnumerableOwnPropertyNames(_options_, ~key+value~).
         1. For each element _nextEntry_ of _entries_, do
@@ -335,9 +335,9 @@ <h1>Temporal.PlainYearMonth.prototype.until ( _other_ [ , _options_ ] )</h1>
         1. Let _untilOptions_ be ? MergeLargestUnitOption(_options_, _largestUnit_).
         1. Let _result_ be ? CalendarDateUntil(_calendar_, _thisDate_, _otherDate_, _untilOptions_).
         1. If _smallestUnit_ is *"month"* and _roundingIncrement_ = 1, then
-          1. Return ? CreateTemporalDuration(_result_.[[Years]], _result_.[[Months]], 0, 0, 0, 0, 0, 0, 0, 0).
+          1. Return ! CreateTemporalDuration(_result_.[[Years]], _result_.[[Months]], 0, 0, 0, 0, 0, 0, 0, 0).
         1. Let _result_ be ? RoundDuration(_result_.[[Years]], _result_.[[Months]], 0, 0, 0, 0, 0, 0, 0, 0, _roundingIncrement_, _smallestUnit_, _roundingMode_, _thisDate_).
-        1. Return ? CreateTemporalDuration(_result_.[[Years]], _result_.[[Months]], 0, 0, 0, 0, 0, 0, 0, 0).
+        1. Return ! CreateTemporalDuration(_result_.[[Years]], _result_.[[Months]], 0, 0, 0, 0, 0, 0, 0, 0).
       </emu-alg>
     </emu-clause>
 
@@ -371,9 +371,9 @@ <h1>Temporal.PlainYearMonth.prototype.since ( _other_ [ , _options_ ] )</h1>
         1. Let _untilOptions_ be ? MergeLargestUnitOption(_options_, _largestUnit_).
         1. Let _result_ be ? CalendarDateUntil(_calendar_, _thisDate_, _otherDate_, _untilOptions_).
         1. If _smallestUnit_ is *"month"* and _roundingIncrement_ = 1, then
-          1. Return ? CreateTemporalDuration(−_result_.[[Years]], −_result_.[[Months]], 0, 0, 0, 0, 0, 0, 0, 0).
+          1. Return ! CreateTemporalDuration(−_result_.[[Years]], −_result_.[[Months]], 0, 0, 0, 0, 0, 0, 0, 0).
         1. Let _result_ be ? RoundDuration(_result_.[[Years]], _result_.[[Months]], 0, 0, 0, 0, 0, 0, 0, 0, _roundingIncrement_, _smallestUnit_, _roundingMode_, _thisDate_).
-        1. Return ? CreateTemporalDuration(−_result_.[[Years]], −_result_.[[Months]], 0, 0, 0, 0, 0, 0, 0, 0).
+        1. Return ! CreateTemporalDuration(−_result_.[[Years]], −_result_.[[Months]], 0, 0, 0, 0, 0, 0, 0, 0).
       </emu-alg>
     </emu-clause>