Temporal: Remove BigInt arithmetic and loops in BalanceDurationRelative

A few results change because the algorithm previously used for rounding
didn't always add duration units to dates in RFC 5545 order, and we also
introduce a special case for rounding with largestUnit years or months and
smallestUnit weeks.

test/built-ins/Temporal/Duration/prototype/round/calendar-dateadd-called-with-options-undefined.js

@@ -20,13 +20,11 @@ const relativeTo = new Temporal.ZonedDateTime(0n, timeZone, calendar);
 //   RoundDuration ->
 //     MoveRelativeZonedDateTime -> AddZonedDateTime -> calendar.dateAdd()
 //     MoveRelativeDate -> calendar.dateAdd()
-//   BalanceDurationRelative ->
-//     MoveRelativeDate -> calendar.dateAdd() (2x)
-//     calendar.dateAdd()
+//   BalanceDateDurationRelative -> calendar.dateAdd()
 
 const instance1 = new Temporal.Duration(1, 1, 1, 1, 1);
 instance1.round({ smallestUnit: "weeks", relativeTo });
-assert.sameValue(calendar.dateAddCallCount, 5, "rounding with calendar smallestUnit");
+assert.sameValue(calendar.dateAddCallCount, 3, "rounding with calendar smallestUnit");
 
 // Rounding with a non-default largestUnit to cover the path in
 // UnbalanceDurationRelative where larger units are converted into smaller
@@ -37,8 +35,7 @@ assert.sameValue(calendar.dateAddCallCount, 5, "rounding with calendar smallestU
 //   UnbalanceDurationRelative -> MoveRelativeDate -> calendar.dateAdd()
 //   RoundDuration ->
 //     MoveRelativeDate -> calendar.dateAdd() (5x)
-//   BalanceDurationRelative
-//     MoveRelativeDate -> calendar.dateAdd()
+//   BalanceDateDurationRelative -> calendar.dateAdd()
 //   MoveRelativeZonedDateTime -> AddZonedDateTime -> calendar.dateAdd()
 
 calendar.dateAddCallCount = 0;
@@ -52,12 +49,10 @@ assert.sameValue(calendar.dateAddCallCount, 8, "rounding with non-default larges
 // Duration.round() ->
 //   RoundDuration ->
 //     MoveRelativeZonedDateTime -> AddZonedDateTime -> calendar.dateAdd()
-//   BalanceDurationRelative ->
-//     MoveRelativeDate -> calendar.dateAdd() (2x)
-//     calendar.dateAdd()
+//   BalanceDateDurationRelative -> calendar.dateAdd()
 
 calendar.dateAddCallCount = 0;
 
 const instance3 = new Temporal.Duration(1, 1, 1, 1, 1);
 instance3.round({ smallestUnit: "days", relativeTo });
-assert.sameValue(calendar.dateAddCallCount, 4, "rounding with days smallestUnit");
+assert.sameValue(calendar.dateAddCallCount, 2, "rounding with days smallestUnit");

test/built-ins/Temporal/Duration/prototype/round/calendar-dateuntil-called-with-singular-largestunit.js

@@ -74,8 +74,8 @@ features: [Temporal]
 // should result in one call to dateUntil() originating from
 // AdjustRoundedDurationDays, with largestUnit equal to the largest unit in
 // the duration higher than "day".
-// Additionally one call with largestUnit: "month" in BalanceDurationRelative
-// when the largestUnit given to round() is "year".
+// Additionally one call in BalanceDateDurationRelative with the same
+// largestUnit.
 // Other calls have largestUnit: "day" so the difference is taken in ISO
 // calendar space.
 
@@ -99,9 +99,9 @@ TemporalHelpers.checkCalendarDateUntilLargestUnitSingular(
     duration.round({ largestUnit, roundingIncrement: 2, roundingMode: 'ceil', relativeTo });
   },
   {
-    years: ["year", "month"],
-    months: ["month"],
-    weeks: ["week"],
+    years: ["year", "year"],
+    months: ["month", "month"],
+    weeks: ["week", "week"],
     days: [],
     hours: [],
     minutes: [],
@@ -122,9 +122,9 @@ TemporalHelpers.checkCalendarDateUntilLargestUnitSingular(
     duration.round({ largestUnit, relativeTo });
   },
   {
-    years: ["month", "month", "month", "month", "month", "month"],
-    months: ["month"],
-    weeks: [],
+    years: ["year"],
+    months: ["month", "month"],
+    weeks: ["week"],
     days: [],
     hours: [],
     minutes: [],
@@ -147,8 +147,8 @@ TemporalHelpers.checkCalendarDateUntilLargestUnitSingular(
     duration.round({ largestUnit, smallestUnit: largestUnit, relativeTo });
   }, {
     years: ["year"],
-    months: [],
-    weeks: [],
+    months: ["month"],
+    weeks: ["week"],
     days: []
   }
 );

test/built-ins/Temporal/Duration/prototype/round/calendar-possibly-required.js

@@ -45,8 +45,8 @@ assert.throws(
   "rounding a week Duration fails without largest/smallest unit"
 );
 
-TemporalHelpers.assertDuration(duration3.round(relativeToYears), 0, 0, 5, 0, 0, 0, 0, 0, 0, 0, "round week duration to years");
-TemporalHelpers.assertDuration(duration3.round(relativeToMonths), 0, 0, 5, 0, 0, 0, 0, 0, 0, 0, "round week duration to months");
+TemporalHelpers.assertDuration(duration3.round(relativeToYears), 0, 1, 0, 4, 0, 0, 0, 0, 0, 0, "round week duration to years");
+TemporalHelpers.assertDuration(duration3.round(relativeToMonths), 0, 1, 0, 4, 0, 0, 0, 0, 0, 0, "round week duration to months");
 TemporalHelpers.assertDuration(duration3.round(relativeToWeeks), 0, 0, 5, 0, 0, 0, 0, 0, 0, 0, "round week duration to weeks");
 TemporalHelpers.assertDuration(duration3.round(relativeToDays), 0, 0, 0, 35, 0, 0, 0, 0, 0, 0, "round week duration to days");
 

test/built-ins/Temporal/Duration/prototype/round/dateuntil-field.js

@@ -4,8 +4,8 @@
 /*---
 esid: sec-temporal.duration.prototype.round
 description: >
-    When consulting calendar.dateUntil() to calculate the number of months in a
-    year, the months property is not accessed on the result Duration
+    When consulting calendar.dateUntil() to balance or unbalance a duration, no
+    properties are accessed on the result Duration
 includes: [compareArray.js, temporalHelpers.js]
 features: [Temporal]
 ---*/
@@ -16,36 +16,23 @@ class CalendarDateUntilObservable extends Temporal.Calendar {
   dateUntil(...args) {
     actual.push("call dateUntil");
     const returnValue = super.dateUntil(...args);
+    TemporalHelpers.observeProperty(actual, returnValue, "years", Infinity);
     TemporalHelpers.observeProperty(actual, returnValue, "months", Infinity);
+    TemporalHelpers.observeProperty(actual, returnValue, "weeks", Infinity);
+    TemporalHelpers.observeProperty(actual, returnValue, "days", Infinity);
     return returnValue;
   }
 }
 
 const calendar = new CalendarDateUntilObservable("iso8601");
 const relativeTo = new Temporal.PlainDate(2018, 10, 12, calendar);
 
-// One path, through UnbalanceDateDurationRelative, calls dateUntil()
-
-const expected1 = [
-  "call dateUntil",
+const expected = [
+  "call dateUntil",  // UnbalanceDateDurationRelative
+  "call dateUntil",  // BalanceDateDurationRelative
 ];
 
 const years = new Temporal.Duration(2);
-const result1 = years.round({ largestUnit: "months", relativeTo });
-TemporalHelpers.assertDuration(result1, 0, 24, 0, 0, 0, 0, 0, 0, 0, 0, "result");
-assert.compareArray(actual, expected1, "operations");
-
-// There is a second path, through BalanceDurationRelative, that calls
-// dateUntil() in a loop for each year in the duration plus one extra time
-
-actual.splice(0); // reset calls for next test
-const expected2 = [
-  "call dateUntil",
-  "call dateUntil",
-  "call dateUntil",
-];
-
-const months = new Temporal.Duration(0, 24);
-const result2 = months.round({ largestUnit: "years", relativeTo });
-TemporalHelpers.assertDuration(result2, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, "result");
-assert.compareArray(actual, expected2, "operations");
+const result = years.round({ largestUnit: "months", relativeTo });
+TemporalHelpers.assertDuration(result, 0, 24, 0, 0, 0, 0, 0, 0, 0, 0, "result");
+assert.compareArray(actual, expected, "operations");

test/built-ins/Temporal/Duration/prototype/round/february-leap-year.js

@@ -10,8 +10,8 @@ features: [Temporal]
 
 // Based on a test case by André Bargull <andre.bargull@gmail.com>
 
-// Note: February in a leap year.
-const relativeTo = new Temporal.PlainDate(1972, 2, 1);
+// Note: One day after February in a leap year.
+const relativeTo = new Temporal.PlainDate(1972, 3, 1);
 
 const options = {
   largestUnit: "years",

test/built-ins/Temporal/Duration/prototype/round/order-of-operations.js

@@ -139,10 +139,8 @@ const expectedOpsForYearRounding = expectedOpsForPlainRelativeTo.concat([
   "call options.relativeTo.calendar.dateAdd",    // 7.s MoveRelativeDate
   "call options.relativeTo.calendar.dateAdd",    // 7.y MoveRelativeDate
   // BalanceDateDurationRelative
-  "call options.relativeTo.calendar.dateAdd",    // 11.c MoveRelativeDate
-  "call options.relativeTo.calendar.dateAdd",    // 11.g MoveRelativeDate
-  "call options.relativeTo.calendar.dateAdd",    // 11.k
-  "call options.relativeTo.calendar.dateUntil",  // 11.p
+  "call options.relativeTo.calendar.dateAdd",    // 9.c
+  "call options.relativeTo.calendar.dateUntil",  // 9.d
 ]);
 const instanceYears = new Temporal.Duration(1, 12, 0, 0, /* hours = */ 2400);
 instanceYears.round(createOptionsObserver({ smallestUnit: "years", relativeTo: plainRelativeTo }));
@@ -159,8 +157,9 @@ const expectedOpsForMonthRounding = expectedOpsForPlainRelativeTo.concat([
   "call options.relativeTo.calendar.dateAdd",    // 10.e
   "call options.relativeTo.calendar.dateAdd",    // 10.k MoveRelativeDate
 ], Array(2).fill("call options.relativeTo.calendar.dateAdd"), [ // 2× 10.n.iii MoveRelativeDate
-  // BalanceDurationRelative
-  "call options.relativeTo.calendar.dateAdd",
+  // BalanceDateDurationRelative
+  "call options.relativeTo.calendar.dateAdd",    // 10.d
+  "call options.relativeTo.calendar.dateUntil",  // 10.e
 ]);
 const instance2 = new Temporal.Duration(1, 0, 0, 62);
 instance2.round(createOptionsObserver({ largestUnit: "months", smallestUnit: "months", relativeTo: plainRelativeTo }));
@@ -174,8 +173,9 @@ const expectedOpsForWeekRounding = expectedOpsForPlainRelativeTo.concat([
   // RoundDuration
   "call options.relativeTo.calendar.dateAdd",  // 11.d MoveRelativeDate
 ], Array(58).fill("call options.relativeTo.calendar.dateAdd"), [  // 58× 11.g.iii MoveRelativeDate (52 + 4 + 2)
-  // BalanceDurationRelative
-  "call options.relativeTo.calendar.dateAdd",  // 12.c
+  // BalanceDateDurationRelative
+  "call options.relativeTo.calendar.dateAdd",    // 16
+  "call options.relativeTo.calendar.dateUntil",  // 17
 ]);
 const instance3 = new Temporal.Duration(1, 1, 0, 15);
 instance3.round(createOptionsObserver({ largestUnit: "weeks", smallestUnit: "weeks", relativeTo: plainRelativeTo }));
@@ -191,14 +191,10 @@ instance4.round(createOptionsObserver({ largestUnit: "days", smallestUnit: "days
 assert.compareArray(actual, expectedOpsForDayRounding, "order of operations with largestUnit = smallestUnit = days");
 actual.splice(0);  // clear
 
-// code path through BalanceDurationRelative balancing from days up to years:
+// code path through BalanceDateDurationRelative balancing from days up to years:
 const expectedOpsForDayToYearBalancing = expectedOpsForPlainRelativeTo.concat([
-  "call options.relativeTo.calendar.dateAdd",    // 10.b MoveRelativeDate
-  "call options.relativeTo.calendar.dateAdd",    // 10.e.iv MoveRelativeDate
-  "call options.relativeTo.calendar.dateAdd",    // 10.f MoveRelativeDate
-  "call options.relativeTo.calendar.dateAdd",    // 10.i.iv MoveRelativeDate
-  "call options.relativeTo.calendar.dateAdd",    // 10.j
-  "call options.relativeTo.calendar.dateUntil",  // 10.n
+  // BalanceDateDurationRelative
+  "call options.relativeTo.calendar.dateUntil",  // 9.d
 ]);
 const instance5 = new Temporal.Duration(0, 0, 0, 0, /* hours = */ 396 * 24);
 instance5.round(createOptionsObserver({ largestUnit: "years", smallestUnit: "days", relativeTo: plainRelativeTo }));
@@ -211,33 +207,27 @@ const expectedOpsForMonthToYearBalancing = expectedOpsForPlainRelativeTo.concat(
   "call options.relativeTo.calendar.dateAdd",    // 10.c
   "call options.relativeTo.calendar.dateAdd",    // 10.e
   "call options.relativeTo.calendar.dateAdd",    // 10.k MoveRelativeDate
-  // BalanceDurationRelative
-  "call options.relativeTo.calendar.dateAdd",    // 10.b MoveRelativeDate
-  "call options.relativeTo.calendar.dateAdd",    // 10.f MoveRelativeDate
-  "call options.relativeTo.calendar.dateAdd",    // 10.j
-  "call options.relativeTo.calendar.dateUntil",  // 10.n
-  "call options.relativeTo.calendar.dateAdd",    // 10.p.iv
-  "call options.relativeTo.calendar.dateUntil",  // 10.p.vii
+  // BalanceDateDurationRelative
+  "call options.relativeTo.calendar.dateAdd",    // 9.c
+  "call options.relativeTo.calendar.dateUntil",  // 9.d
 ]);
 const instance6 = new Temporal.Duration(0, 12);
 instance6.round(createOptionsObserver({ largestUnit: "years", smallestUnit: "months", relativeTo: plainRelativeTo }));
 assert.compareArray(actual, expectedOpsForMonthToYearBalancing, "order of operations with largestUnit = years, smallestUnit = months");
 actual.splice(0); // clear
 
 const expectedOpsForDayToMonthBalancing = expectedOpsForPlainRelativeTo.concat([
-  // BalanceDurationRelative
-  "call options.relativeTo.calendar.dateAdd",    // 11.b MoveRelativeDate
-  "call options.relativeTo.calendar.dateAdd",    // 11.e.iv MoveRelativeDate
+  // BalanceDateDurationRelative
+  "call options.relativeTo.calendar.dateUntil",  // 10.e
 ]);
 const instance7 = new Temporal.Duration(0, 0, 0, 0, /* hours = */ 32 * 24);
 instance7.round(createOptionsObserver({ largestUnit: "months", smallestUnit: "days", relativeTo: plainRelativeTo }));
 assert.compareArray(actual, expectedOpsForDayToMonthBalancing, "order of operations with largestUnit = months, smallestUnit = days");
 actual.splice(0); // clear
 
 const expectedOpsForDayToWeekBalancing = expectedOpsForPlainRelativeTo.concat([
-  // BalanceDurationRelative
-  "call options.relativeTo.calendar.dateAdd",  // 12.c MoveRelativeDate
-  "call options.relativeTo.calendar.dateAdd",  // 12.f.iv MoveRelativeDate
+  // BalanceDateDurationRelative
+  "call options.relativeTo.calendar.dateUntil",  // 17
 ]);
 const instance8 = new Temporal.Duration(0, 0, 0, 0, /* hours = */ 8 * 24);
 instance8.round(createOptionsObserver({ largestUnit: "weeks", smallestUnit: "days", relativeTo: plainRelativeTo }));
@@ -403,10 +393,8 @@ const expectedOpsForYearRoundingZoned = expectedOpsForZonedRelativeTo.concat([
   "call options.relativeTo.calendar.dateAdd",    // 7.s MoveRelativeDate
   "call options.relativeTo.calendar.dateAdd",    // 7.y MoveRelativeDate
   // BalanceDateDurationRelative
-  "call options.relativeTo.calendar.dateAdd",    // 11.c MoveRelativeDate
-  "call options.relativeTo.calendar.dateAdd",    // 11.g MoveRelativeDate
-  "call options.relativeTo.calendar.dateAdd",    // 11.k
-  "call options.relativeTo.calendar.dateUntil",  // 11.p
+  "call options.relativeTo.calendar.dateAdd",    // 9.c
+  "call options.relativeTo.calendar.dateUntil",  // 9.d
 ]);
 instanceYears.round(createOptionsObserver({ smallestUnit: "years", relativeTo: zonedRelativeTo }));
 assert.compareArray(
@@ -431,12 +419,35 @@ const expectedOpsForUnbalanceRoundBalance = expectedOpsForZonedRelativeTo.concat
   // RoundDuration
   "call options.relativeTo.calendar.dateAdd",  // 8.g MoveRelativeDate
   // BalanceDateDurationRelative
-  "call options.relativeTo.calendar.dateAdd",  // 13.c MoveRelativeDate
+  "call options.relativeTo.calendar.dateAdd",    // 10.d
+  "call options.relativeTo.calendar.dateUntil",  // 10.e
 ]);
-new Temporal.Duration(0, 1, 1).round(createOptionsObserver({ largestUnit: "months", smallestUnit: "weeks", relativeTo: zonedRelativeTo }));
+new Temporal.Duration(0, 1, 1).round(createOptionsObserver({ largestUnit: "years", smallestUnit: "weeks", relativeTo: zonedRelativeTo }));
 assert.compareArray(
   actual,
   expectedOpsForUnbalanceRoundBalance,
+  "order of operations with largestUnit = years, smallestUnit = weeks, and ZonedDateTime relativeTo"
+);
+actual.splice(0); // clear
+
+// code path that skips user code calls in BalanceDateDurationRelative due to
+// special case for largestUnit months and smallestUnit weeks
+const expectedOpsForWeeksSpecialCase = expectedOpsForZonedRelativeTo.concat([
+  // ToTemporalDate
+  "call options.relativeTo.timeZone.getOffsetNanosecondsFor",
+  // lookup in Duration.p.round
+  "get options.relativeTo.calendar.dateAdd",
+  "get options.relativeTo.calendar.dateUntil",
+  // RoundDuration → MoveRelativeZonedDateTime → AddZonedDateTime
+  "call options.relativeTo.calendar.dateAdd",
+  "call options.relativeTo.timeZone.getPossibleInstantsFor",   // 13. GetInstantFor
+  // RoundDuration
+  "call options.relativeTo.calendar.dateAdd",  // 14.p MoveRelativeDate
+]);
+new Temporal.Duration(0, 1, 1).round(createOptionsObserver({ largestUnit: "months", smallestUnit: "weeks", relativeTo: zonedRelativeTo }));
+assert.compareArray(
+  actual,
+  expectedOpsForWeeksSpecialCase,
   "order of operations with largestUnit = months, smallestUnit = weeks, and ZonedDateTime relativeTo"
 );
 actual.splice(0); // clear