Rewrite NonISODateAdd with new AOs

Author: sffc

spec.emu

@@ -902,20 +902,16 @@ contributors: Google, Ecma International
       <p>This definition supersedes the definition provided in <emu-xref href="#sec-temporal-nonisodateadd"></emu-xref>.</p>
       <p>It performs the following steps when called:</p>
       <emu-alg>
-        1. Let _calendarDate_ be CalendarISOToDate(_calendar_, _isoDate_).
-        1. Add _duration_.[[Years]] to _calendarDate_.
-        1. (This step only matters for lunisolar calendars.) If _calendarDate_.[[MonthCode]] is a leap month that doesn't exist in the year, then:
-          1. Set _calendarDate_ to another date according to the cultural conventions of that calendar's users. Of the currently supported calendars: if _calendar_ is *"chinese"* or *"dangi"*, change _calendarDate_.[[MonthCode]] to the same month code but without the *"L"*. If _calendar_ is *"hebrew"*, change _calendarDate_.[[MonthCode]] from *"M05L"* to *"M06"*.
-          1. Update _calendarDate_.[[Month]] accordingly.
-        1. Add _duration_.[[Months]] to _calendarDate_, balancing _calendarDate_ if it goes over a year boundary.
-        1. If the date described by _calendarDate_ does not exist, then
+        1. Let _yearMonth_ be RegulateNonISOYearMonth(_calendar_, _isoDate_, _years_).
+        1. Let _endOfMonth_ be BalanceNonISODate(_calendar_, _yearMonth_.[[Year]], _yearMonth_.[[Month]] + _months_ + 1, 0).
+        1. Let _baseDay_ be CalendarISOToDate(_calendar_, _isoDate_).[[Day]].
+        1. If _endOfMonth_.[[Day]] &lt; _baseDay_, then
           1. If _overflow_ is ~reject~, throw a *RangeError* exception.
-          1. If _calendarDate_.[[MonthCode]] is a valid month code for _calendarDate_.[[Year]], but the date described by _calendarDate_ does not exist, set _calendarDate_.[[Day]] to the closest day in the same month. If there are two equally-close dates in the same month, pick the later one.
-          1. (This step does not apply to any currently supported calendars.) If the date described by _calendarDate_ still does not exist, set _calendarDate_ to the closest date in the same year. If there are two equally-close dates in that year, pick the later one.
-        1. Add _duration_.[[Weeks]] and _duration_.[[Days]] to _calendarDate_, balancing _calendarDate_ if it goes over a month or year boundary.
-        1. Let _result_ be ? CalendarDateToISO(_calendar_, _calendarDate_, _overflow_).
-        1. If ISODateWithinLimits(_result_) is *false*, throw a *RangeError* exception.
-        1. Return _result_.
+          1. Let _regulatedDay_ be _endOfMonth_.[[Day]].
+        1. Else,
+          1. Let _regulatedDay_ be _baseDay_.
+        1. Let _balancedDate_ be BalanceNonISODate(_calendar_, _endOfMonth_.[[Year]], _endOfMonth_.[[Month]], _regulatedDay_ + 7 * _duration_.[[Weeks]] + _duration_.[[Days]]).
+        1. Return CalendarDateArithmeticalToISO(_balancedDate_.[[Year]], _balancedDate_.[[Month]], _balancedDate_.[[Day]]).
       </emu-alg>
     </emu-clause>
 
@@ -1014,6 +1010,27 @@ contributors: Google, Ecma International
       </emu-alg>
     </emu-clause>
 
+    <emu-clause id="sup-temporal-calendardatecodestoiso" type="implementation-defined abstract operation">
+      <h1>
+        CalendarDateArithmeticalToISO (
+          _calendar_: a calendar type that is not *"iso8601"*,
+          _year_: an integer,
+          _month_: an integer,
+          _day_: an integer,
+        ): either a normal completion containing an ISO Date Record or a throw completion
+      </h1>
+      <dl class="header">
+        <dt>description</dt>
+        <dd>
+          It returns an ISO Date Record that, when converted to a Calendar Date Record with _calendar_ (for example, with CalendarISOToDate), contains the given _year_, _month_, and _day_ values in its [[Year]], [[Month]], and [[Day]] fields. If this is not possible, a RangeError is thrown.
+        </dd>
+      </dl>
+      <p>It performs the following steps when called:</p>
+      <emu-alg>
+        Returns a calendar-dependent completion as described above.
+      </emu-alg>
+    </emu-clause>
+
     <emu-clause id="sup-temporal-calendardaysinmonth" type="implementation-defined abstract operation">
       <h1>
         CalendarDaysInMonth (