Editorial: Refactor ISODateSurpasses parallel to NonISODateSurpasses

See tc39/proposal-intl-era-monthcode#101. This
changes the general outline of ISODateSurpasses so that it parallels
the outline of NonISODateSurpasses in the Intl Era Monthcode proposal as
proposed in the PR.

Also refactors the polyfill code, but keeps the optimizations we already
had regarding not passing weeks and days to ISODateSurpasses and not
(yet) adapting the polyfill code to use this algorithm in non-ISO8601
calculations.

Author: ptomato

polyfill/lib/calendar.mjs

@@ -132,19 +132,27 @@ function calendarDateWeekOfYear(id, isoDate) {
   return { week: woy, year: yow };
 }
 
-function ISODateSurpasses(sign, baseDate, isoDate2, years, months) {
-  const yearMonth = ES.BalanceISOYearMonth(baseDate.year + years, baseDate.month + months);
-  let y1 = yearMonth.year;
-  let m1 = yearMonth.month;
-  let d1 = baseDate.day;
-  if (y1 !== isoDate2.year) {
-    if (sign * (y1 - isoDate2.year) > 0) return true;
-  } else if (m1 !== isoDate2.month) {
-    if (sign * (m1 - isoDate2.month) > 0) return true;
-  } else if (d1 !== isoDate2.day) {
-    if (sign * (d1 - isoDate2.day) > 0) return true;
+function CompareSurpasses(sign, year, month, day, target) {
+  if (year !== target.year) {
+    if (sign * (year - target.year) > 0) return true;
+  } else if (month !== target.month) {
+    // Skip the monthCode case that is in the spec, as we are currently not
+    // using this operation in non-iso8601 calculations
+    if (sign * (month - target.month) > 0) return true;
+  } else if (day !== target.day) {
+    if (sign * (day - target.day) > 0) return true;
   }
-  return false;
+}
+
+function ISODateSurpasses(sign, baseDate, isoDate2, years, months) {
+  const y0 = baseDate.year + years;
+  if (CompareSurpasses(sign, y0, baseDate.month, baseDate.day, isoDate2)) return true;
+  if (months === 0) return false;
+  const m0 = baseDate.month + months;
+  const monthsAdded = ES.BalanceISOYearMonth(y0, m0);
+  return CompareSurpasses(sign, monthsAdded.year, monthsAdded.month, baseDate.day, isoDate2);
+  // Skip the weeks and days addition in the spec, as we currently optimize that
+  // out in iso8601 date difference calculation
 }
 
 function addDaysISO(isoDate, days) {

spec/plaindate.html

@@ -691,6 +691,38 @@ <h1>
       </emu-alg>
     </emu-clause>
 
+    <emu-clause id="sec-temporal-comparesurpasses" type="abstract operation">
+      <h1>
+        CompareSurpasses (
+          _sign_: -1 or 1,
+          _year_: an integer,
+          _monthOrCode_: an integer or a month code,
+          _day_: an integer,
+          _target_: a Calendar Fields Record,
+        ): a Boolean
+      </h1>
+      <dl class="header">
+        <dt>description</dt>
+        <dd>
+          The return value indicates whether the calendar date formed by _year_, _monthOrCode_, and _day_, which need not exist, surpasses _target_ in the direction denoted by _sign_.
+        </dd>
+      </dl>
+      <emu-alg>
+        1. If _year_ ≠ _target_.[[Year]], then
+          1. If _sign_ × (_year_ - _target_.[[Year]]) > 0, return *true*.
+        1. Else if _monthOrCode_ is a month code and _monthOrCode_ is not _target_.[[MonthCode]], then
+          1. If _sign_ > 0, then
+            1. If _monthOrCode_ is lexicographically greater than _target_.[[MonthCode]], return *true*.
+          1. Else,
+            1. If _target_.[[MonthCode]] is lexicographically greater than _monthOrCode_, return *true*.
+        1. Else if _monthOrCode_ is an integer and _monthOrCode_ ≠ _target_.[[Month]], then
+          1. If _sign_ × (_monthOrCode_ - _target_.[[Month]]) > 0, return *true*.
+        1. Else if _day_ ≠ _target_.[[Day]], then
+          1. If _sign_ × (_day_ - _target_.[[Day]]) > 0, return *true*.
+        1. Return *false*.
+      </emu-alg>
+    </emu-clause>
+
     <emu-clause id="sec-temporal-isodatesurpasses" type="abstract operation">
       <h1>
         ISODateSurpasses (
@@ -712,24 +744,19 @@ <h1>
         </dd>
       </dl>
       <emu-alg>
-        1. Let _yearMonth_ be BalanceISOYearMonth(_baseDate_.[[Year]] + _years_, _baseDate_.[[Month]] + _months_).
-        1. If _weeks_ is not 0 or _days_ is not 0, then
-          1. Let _regulatedDate_ be ! RegulateISODate(_yearMonth_.[[Year]], _yearMonth_.[[Month]], _baseDate_.[[Day]], ~constrain~).
-          1. Let _balancedDate_ be BalanceISODate(_regulatedDate_.[[Year]], _regulatedDate_.[[Month]], _regulatedDate_.[[Day]] + 7 * _weeks_ + _days_).
-          1. Let _y1_ be _balancedDate_.[[Year]].
-          1. Let _m1_ be _balancedDate_.[[Month]].
-          1. Let _d1_ be _balancedDate_.[[Day]].
-        1. Else,
-          1. Let _y1_ be _yearMonth_.[[Year]].
-          1. Let _m1_ be _yearMonth_.[[Month]].
-          1. Let _d1_ be _baseDate_.[[Day]].
-        1. If _y1_ ≠ _isoDate2_.[[Year]], then
-          1. If _sign_ × (_y1_ - _isoDate2_.[[Year]]) > 0, return *true*.
-        1. Else if _m1_ ≠ _isoDate2_.[[Month]], then
-          1. If _sign_ × (_m1_ - _isoDate2_.[[Month]]) > 0, return *true*.
-        1. Else if _d1_ ≠ _isoDate2_.[[Day]], then
-          1. If _sign_ × (_d1_ - _isoDate2_.[[Day]]) > 0, return *true*.
-        1. Return *false*.
+        1. Let _parts_ be CalendarISOToDate(*"iso8601"*, _baseDate_).
+        1. Let _target_ be CalendarISOToDate(*"iso8601"*, _isoDate2_).
+        1. Let _y0_ be _parts_.[[Year]] + _years_.
+        1. If CompareSurpasses(_sign_, _y0_, _parts_.[[MonthCode]], _parts_.[[Day]], _target_) is *true*, return *true*.
+        1. If _months_ = 0, return *false*.
+        1. Let _m0_ be _parts_.[[Month]] + _months_.
+        1. Let _monthsAdded_ be BalanceISOYearMonth(_y0_, _m0_).
+        1. If CompareSurpasses(_sign_, _monthsAdded_.[[Year]], _monthsAdded_.[[Month]], _parts_.[[Day]], _target_) is *true*, return *true*.
+        1. If _weeks_ = 0 and _days_ = 0, return *false*.
+        1. Let _regulatedDate_ be ! RegulateISODate(_monthsAdded_.[[Year]], _monthsAdded_.[[Month]], _parts_.[[Day]], ~constrain~).
+        1. Let _daysInWeek_ be 7.
+        1. Let _balancedDate_ be BalanceISODate(_regulatedDate_.[[Year]], _regulatedDate_.[[Month]], _regulatedDate_.[[Day]] + _daysInWeek_ * _weeks_ + _days_).
+        1. Return CompareSurpasses(_sign_, _balancedDate_.[[Year]], _balancedDate_.[[Month]], _balancedDate_.[[Day]], _target_).
       </emu-alg>
       <emu-note>
         <p>This operation intentionally uses overflow ~constrain~ when regulating the year-month. As a result, adding the duration returned by `.since` or `.until` to _baseDate_ may cause a *RangeError* exception when _overflow_ is ~reject~.</p>