difference: throw out-of-order; zap Time 12h limit

Fixes tc39#663. Changes `difference()` to throw if `other`is
larger than `this`. Goal is encourage feedback about long-term solution:
option 1 - previous behavior: `difference()` returns an absolute value
option 2 - behavior in this commit: throw if other is larger
option 3 - negative durations (tc39#558)

Tests are updated to make it easy to choose any of the three options.
Tests for option 1 are commented out in case we want to revert.
The rest of test changes were reversing arguments so that choosing any
of the options will break few tests.

Because `difference` is now unidirectional, it doesn't make sense to
restrict `Time.prototype.difference` to 12 hours max. Fixes tc39#597.

docs/absolute.md

@@ -296,7 +296,7 @@ Temporal.now.absolute().minus(oneDay);
 **Returns:** a `Temporal.Duration` representing the difference between `absolute` and `other`.
 
 This method computes the difference between the two times represented by `absolute` and `other`, and returns it as a `Temporal.Duration` object.
-The difference is always positive, no matter the order of `absolute` and `other`, because `Temporal.Duration` objects cannot represent negative durations.
+A `RangeError` will be thrown if `other` is later than `absolute`, because `Temporal.Duration` objects cannot represent negative durations.
 
 The `largestUnit` option controls how the resulting duration is expressed.
 The returned `Temporal.Duration` object will not have any nonzero fields that are larger than the unit in `largestUnit`.
@@ -312,25 +312,25 @@ Example usage:
 ```js
 startOfMoonMission = Temporal.Absolute.from('1969-07-16T13:32:00Z');
 endOfMoonMission = Temporal.Absolute.from('1969-07-24T16:50:35Z');
-missionLength = startOfMoonMission.difference(endOfMoonMission, { largestUnit: 'days' });
-  // => P8DT3H18M35S
-endOfMoonMission.difference(startOfMoonMission, { largestUnit: 'days' });
+missionLength = endOfMoonMission.difference(startOfMoonMission, { largestUnit: 'days' });
   // => P8DT3H18M35S
+startOfMoonMission.difference(endOfMoonMission, { largestUnit: 'days' });
+  // => throws RangeError
 missionLength.toLocaleString();
   // example output: '8 days 3 hours 18 minutes 35 seconds'
 
 // A billion (10^9) seconds since the epoch in different units
 epoch = new Temporal.Absolute(0n);
 billion = Temporal.Absolute.fromEpochSeconds(1e9);
-epoch.difference(billion);  // => PT1000000000S
-epoch.difference(billion, { largestUnit: 'hours' })  // => PT277777H46M40S
-epoch.difference(billion, { largestUnit: 'days' })  // => P11574DT1H46M40S
+billion.difference(epoch);  // => PT1000000000S
+billion.difference(epoch, { largestUnit: 'hours' })  // => PT277777H46M40S
+billion.difference(epoch, { largestUnit: 'days' })  // => P11574DT1H46M40S
 
 // If you really need to calculate the difference between two Absolutes
 // in years, you can eliminate the ambiguity by choosing your starting
 // point explicitly. For example, using the corresponding UTC date:
 utc = Temporal.TimeZone.from('UTC');
-epoch.inTimeZone(utc).difference(billion.inTimeZone(utc), { largestUnit: 'years' });
+billion.inTimeZone(utc).difference(epoch.inTimeZone(utc), { largestUnit: 'years' });
   // => P31Y8M8DT1H46M40S
 ```
 

docs/calendar.md

@@ -257,12 +257,12 @@ For example:
 ```javascript
 d1 = Temporal.Date.from('2020-07-29').withCalendar('chinese');
 d2 = Temporal.Date.from('2020-08-29').withCalendar('chinese');
-d1.difference(d2, { largestUnit: 'months' })  // => P1M2D
+d2.difference(d1, { largestUnit: 'months' })  // => P1M2D
 
 // same result, but calling the method directly:
 Temporal.Calendar.from('chinese').difference(
-    Temporal.Date.from('2020-07-29'),
     Temporal.Date.from('2020-08-29'),
+    Temporal.Date.from('2020-07-29'),
     { largestUnit: 'months' }
 )  // => P1M2D
 ```

docs/cookbook/futureDateForm.js

@@ -14,8 +14,8 @@ function englishPlural(n, singular, plural) {
 if (futuredateParam !== null) {
   const futureDate = Temporal.Date.from(futuredateParam);
   const today = Temporal.now.date();
-  const until = today.difference(futureDate, { largestUnit: 'days' });
-  const untilMonths = today.difference(futureDate, { largestUnit: 'months' });
+  const until = futureDate.difference(today, { largestUnit: 'days' });
+  const untilMonths = futureDate.difference(today, { largestUnit: 'months' });
 
   const dayString = englishPlural(until.days, 'day', 'days');
   const monthString =

docs/cookbook/getElapsedDurationSinceInstant.mjs

@@ -14,7 +14,7 @@
  */
 function getElapsedDurationSinceInstant(then, now, largestUnit = 'days') {
   const sign = Temporal.Absolute.compare(now, then) < 0 ? '-' : '+';
-  const duration = now.difference(then, { largestUnit });
+  const duration = sign === '-' ? then.difference(now, { largestUnit }) : now.difference(then, { largestUnit });
   return { sign, duration };
 }
 

docs/cookbook/getTripDurationInHrMinSec.mjs

@@ -9,7 +9,7 @@
 function getTripDurationInHrMinSec(parseableDeparture, parseableArrival) {
   const departure = Temporal.Absolute.from(parseableDeparture);
   const arrival = Temporal.Absolute.from(parseableArrival);
-  return departure.difference(arrival, { largestUnit: 'hours' });
+  return arrival.difference(departure, { largestUnit: 'hours' });
 }
 
 const flightTime = getTripDurationInHrMinSec(

docs/date.md

@@ -338,7 +338,7 @@ date.minus({ months: 1 }, { disambiguation: 'reject' })  // => throws
 **Returns:** a `Temporal.Duration` representing the difference between `date` and `other`.
 
 This method computes the difference between the two dates represented by `date` and `other`, and returns it as a `Temporal.Duration` object.
-The difference is always positive, no matter the order of `date` and `other`, because `Temporal.Duration` objects cannot represent negative durations.
+A `RangeError` will be thrown if `other` is later than `date`, because `Temporal.Duration` objects cannot represent negative durations.
 
 The `largestUnit` option controls how the resulting duration is expressed.
 The returned `Temporal.Duration` object will not have any nonzero fields that are larger than the unit in `largestUnit`.
@@ -351,10 +351,11 @@ Unlike other Temporal types, hours and lower are not allowed, because the data m
 
 Usage example:
 ```javascript
-date = Temporal.Date.from('2006-08-24');
-other = Temporal.Date.from('2019-01-31');
+date = Temporal.Date.from('2019-01-31');
+other = Temporal.Date.from('2006-08-24');
 date.difference(other)                            // => P4543D
 date.difference(other, { largestUnit: 'years' })  // => P12Y5M7D
+other.difference(date, { largestUnit: 'years' })  // => throws RangeError
 
 // If you really need to calculate the difference between two Dates in
 // hours, you can eliminate the ambiguity by explicitly choosing the

docs/datetime.md

@@ -394,7 +394,7 @@ dt.minus({ months: 1 })  // => throws
 **Returns:** a `Temporal.Duration` representing the difference between `datetime` and `other`.
 
 This method computes the difference between the two times represented by `datetime` and `other`, and returns it as a `Temporal.Duration` object.
-The difference is always positive, no matter the order of `datetime` and `other`, because `Temporal.Duration` objects cannot represent negative durations.
+A `RangeError` will be thrown if `other` is later than `datetime`, because `Temporal.Duration` objects cannot represent negative durations.
 
 The `largestUnit` option controls how the resulting duration is expressed.
 The returned `Temporal.Duration` object will not have any nonzero fields that are larger than the unit in `largestUnit`.
@@ -408,15 +408,16 @@ Usage example:
 ```javascript
 dt1 = Temporal.DateTime.from('1995-12-07T03:24:30.000003500');
 dt2 = Temporal.DateTime.from('2019-01-31T15:30');
-dt1.difference(dt2);                            // =>    P8456DT12H5M29.999996500S
-dt1.difference(dt2), { largestUnit: 'years' })  // => P23Y1M24DT12H5M29.999996500S
+dt2.difference(dt1);                            // =>    P8456DT12H5M29.999996500S
+dt2.difference(dt1), { largestUnit: 'years' })  // => P23Y1M24DT12H5M29.999996500S
+dt1.difference(dt2), { largestUnit: 'years' })  // => throws RangeError
 
 // Months and years can be different lengths
 [jan1, feb1, mar1] = [1, 2, 3].map(month => Temporal.DateTime.from({year: 2020, month, day: 1}));
-jan1.difference(feb1);                             // => P31D
-jan1.difference(feb1, { largestUnit: 'months' });  // => P1M
-feb1.difference(mar1);                             // => P29D
-feb1.difference(mar1, { largestUnit: 'months' });  // => P1M
+feb1.difference(jan1);                             // => P31D
+feb1.difference(jan1, { largestUnit: 'months' });  // => P1M
+mar1.difference(feb1);                             // => P29D
+mar1.difference(feb1, { largestUnit: 'months' });  // => P1M
 ```
 
 ### datetime.**equals**(_other_: Temporal.DateTime) : boolean

docs/time.md

@@ -245,23 +245,21 @@ time.minus({ minutes: 5, nanoseconds: 800 })  // => 19:34:09.068345405
 **Returns:** a `Temporal.Duration` representing the difference between `time` and `other`.
 
 This method computes the difference between the two times represented by `time` and `other`, and returns it as a `Temporal.Duration` object.
-The difference is always positive, and always 12 hours or less, no matter the order of `time` and `other`, because `Temporal.Duration` objects cannot represent negative durations.
+A `RangeError` will be thrown if `other` is later than `time`, because `Temporal.Duration` objects cannot represent negative durations.
 
 The `largestUnit` parameter controls how the resulting duration is expressed.
 The returned `Temporal.Duration` object will not have any nonzero fields that are larger than the unit in `largestUnit`.
-A difference of two hours will become 7200 seconds when `largestUnit` is `"seconds"`, for example.
-However, a difference of 30 seconds will still be 30 seconds even if `largestUnit` is `"hours"`.
+A difference of two hours will become 7200 seconds when `largestUnit` is `'seconds'`, for example.
+However, a difference of 30 seconds will still be 30 seconds even if `largestUnit` is `'hours'`.
 
-The default largest unit in the result is technically days, for consistency with other Temporal types' `difference` methods.
-However, since this method never returns any duration longer than 12 hours, largest units of years, months, or days, are by definition treated as hours.
+The default largest unit in the result is technically `'days'`, for consistency with other Temporal types' `difference` methods.
+However, since time differences are always shorter than one day, largest units of `'years'`, `'months'`, or `'days'` are treated as `'hours'`.
 
 Usage example:
 ```javascript
-time = Temporal.Time.from('19:39:09.068346205');
-time.difference(Temporal.Time.from('20:13:20.971398099'))  // => PT34M11.903051894S
-
-// The difference is always less than 12 hours, crossing midnight if needed
-Temporal.Time.from('01:00').difference(Temporal.Time.from('23:00'))  // => P2H
+time = Temporal.Time.from('20:13:20.971398099');
+time.difference(Temporal.Time.from('19:39:09.068346205'))  // => PT34M11.903051894S
+time.difference(Temporal.Time.from('22:39:09.068346205'))  // => throws RangeError
 ```
 
 ### time.**equals**(_other_: Temporal.Time) : boolean

docs/yearmonth.md

@@ -284,7 +284,7 @@ ym.minus({years: 20, months: 4})  // => 1999-02
 **Returns:** a `Temporal.Duration` representing the difference between `yearMonth` and `other`.
 
 This method computes the difference between the two months represented by `yearMonth` and `other`, and returns it as a `Temporal.Duration` object.
-The difference is always positive, no matter the order of `yearMonth` and `other`, because `Temporal.Duration` objects cannot represent negative durations.
+A `RangeError` will be thrown if `other` is later than `yearMonth`, because `Temporal.Duration` objects cannot represent negative durations.
 
 The `largestUnit` option controls how the resulting duration is expressed.
 The returned `Temporal.Duration` object will not have any nonzero fields that are larger than the unit in `largestUnit`.
@@ -299,6 +299,7 @@ ym = Temporal.YearMonth.from('2019-06');
 other = Temporal.YearMonth.from('2006-08');
 ym.difference(other)                             // => P12Y10M
 ym.difference(other, { largestUnit: 'months' })  // => P154M
+other.difference(ym, { largestUnit: 'months' })  // => throws RangeError
 
 // If you really need to calculate the difference between two YearMonths
 // in days, you can eliminate the ambiguity by explicitly choosing the

polyfill/lib/absolute.mjs

@@ -95,9 +95,10 @@ export class Absolute {
     if (!ES.IsTemporalAbsolute(other)) throw new TypeError('invalid Absolute object');
     const largestUnit = ES.ToLargestTemporalUnit(options, 'seconds', ['years', 'months', 'weeks']);
 
-    const [one, two] = [this, other].sort(Absolute.compare);
-    const onens = GetSlot(one, EPOCHNANOSECONDS);
-    const twons = GetSlot(two, EPOCHNANOSECONDS);
+    const comparison = Absolute.compare(this, other);
+    if (comparison < 0) throw new RangeError('other instance cannot be larger than `this`');
+    const onens = GetSlot(other, EPOCHNANOSECONDS);
+    const twons = GetSlot(this, EPOCHNANOSECONDS);
     const diff = twons.minus(onens);
 
     const ns = +diff.mod(1e3);

polyfill/lib/date.mjs

@@ -126,8 +126,9 @@ export class Date {
     if (!ES.IsTemporalDate(this)) throw new TypeError('invalid receiver');
     if (!ES.IsTemporalDate(other)) throw new TypeError('invalid Date object');
     const largestUnit = ES.ToLargestTemporalUnit(options, 'days', ['hours', 'minutes', 'seconds']);
-    const [smaller, larger] = [this, other].sort(Date.compare);
-    const { years, months, weeks, days } = ES.DifferenceDate(smaller, larger, largestUnit);
+    const comparison = Date.compare(this, other);
+    if (comparison < 0) throw new RangeError('other instance cannot be larger than `this`');
+    const { years, months, weeks, days } = ES.DifferenceDate(other, this, largestUnit);
     const Duration = GetIntrinsic('%Temporal.Duration%');
     return new Duration(years, months, weeks, days, 0, 0, 0, 0, 0, 0);
   }

polyfill/lib/datetime.mjs

@@ -239,12 +239,13 @@ export class DateTime {
     if (!ES.IsTemporalDateTime(this)) throw new TypeError('invalid receiver');
     if (!ES.IsTemporalDateTime(other)) throw new TypeError('invalid DateTime object');
     const largestUnit = ES.ToLargestTemporalUnit(options, 'days');
-    const [smaller, larger] = [this, other].sort(DateTime.compare);
+    const comparison = DateTime.compare(this, other);
+    if (comparison < 0) throw new RangeError('other instance cannot be larger than `this`');
     let { deltaDays, hours, minutes, seconds, milliseconds, microseconds, nanoseconds } = ES.DifferenceTime(
-      smaller,
-      larger
+      other,
+      this
     );
-    let { year, month, day } = larger;
+    let { year, month, day } = this;
     day += deltaDays;
     ({ year, month, day } = ES.BalanceDate(year, month, day));
 
@@ -253,7 +254,7 @@ export class DateTime {
       dateLargestUnit = largestUnit;
     }
 
-    let { years, months, weeks, days } = ES.DifferenceDate(smaller, { year, month, day }, dateLargestUnit);
+    let { years, months, weeks, days } = ES.DifferenceDate(other, { year, month, day }, dateLargestUnit);
 
     ({ days, hours, minutes, seconds, milliseconds, microseconds, nanoseconds } = ES.BalanceDuration(
       days,

polyfill/lib/time.mjs

@@ -168,8 +168,10 @@ export class Time {
     if (!ES.IsTemporalTime(this)) throw new TypeError('invalid receiver');
     if (!ES.IsTemporalTime(other)) throw new TypeError('invalid Time object');
     const largestUnit = ES.ToLargestTemporalUnit(options, 'hours');
-    const [earlier, later] = [this, other].sort(Time.compare);
-    let { hours, minutes, seconds, milliseconds, microseconds, nanoseconds } = ES.DifferenceTime(earlier, later);
+    const comparison = Time.compare(this, other);
+    if (comparison < 0) throw new RangeError('other instance cannot be larger than `this`');
+    let { hours, minutes, seconds, milliseconds, microseconds, nanoseconds } = ES.DifferenceTime(other, this);
+    /*
     if (hours >= 12) {
       hours = 24 - hours;
       minutes *= -1;
@@ -178,6 +180,7 @@ export class Time {
       microseconds *= -1;
       nanoseconds *= -1;
     }
+    */
     ({ hours, minutes, seconds, milliseconds, microseconds, nanoseconds } = ES.BalanceDuration(
       0,
       hours,

polyfill/lib/yearmonth.mjs

@@ -100,9 +100,10 @@ export class YearMonth {
     if (!ES.IsTemporalYearMonth(this)) throw new TypeError('invalid receiver');
     if (!ES.IsTemporalYearMonth(other)) throw new TypeError('invalid YearMonth object');
     const largestUnit = ES.ToLargestTemporalUnit(options, 'years', ['weeks', 'days', 'hours', 'minutes', 'seconds']);
-    const [one, two] = [this, other].sort(YearMonth.compare);
-    let years = two.year - one.year;
-    let months = two.month - one.month;
+    const comparison = YearMonth.compare(this, other);
+    if (comparison < 0) throw new RangeError('other instance cannot be larger than `this`');
+    let years = this.year - other.year;
+    let months = this.month - other.month;
     if (months < 0) {
       years -= 1;
       months += 12;

polyfill/test/absolute.mjs

@@ -423,9 +423,10 @@ describe('Absolute', () => {
   describe('Absolute.difference works', () => {
     const earlier = Absolute.from('1976-11-18T15:23:30.123456789Z');
     const later = Absolute.from('2019-10-29T10:46:38.271986102Z');
-    const diff = earlier.difference(later);
-    it(`(${earlier}).difference(${later}) == (${later}).difference(${earlier})`, () =>
-      equal(`${later.difference(earlier)}`, `${diff}`));
+    const diff = later.difference(earlier);
+    // it(`(${earlier}).difference(${later}) == (${later}).difference(${earlier})`, () =>
+    //  equal(`${later.difference(earlier)}`, `${diff}`));
+    it('throws if out of order', () => throws(() => earlier.difference(later), RangeError));
     it(`(${earlier}).plus(${diff}) == (${later})`, () => assert(earlier.plus(diff).equals(later)));
     it(`(${later}).minus(${diff}) == (${earlier})`, () => assert(later.minus(diff).equals(earlier)));
     it("doesn't cast argument", () => {

polyfill/test/date.mjs

@@ -162,7 +162,8 @@ describe('Date', () => {
       equal(duration.nanoseconds, 0);
     });
     it('date.difference({ year: 2019, month: 11, day: 18 }, { largestUnit: "years" })', () => {
-      const duration = date.difference(Date.from({ year: 2019, month: 11, day: 18 }), { largestUnit: 'years' });
+      const later = Date.from({ year: 2019, month: 11, day: 18 });
+      const duration = later.difference(date, { largestUnit: 'years' });
       equal(duration.years, 43);
       equal(duration.months, 0);
       equal(duration.weeks, 0);
@@ -182,12 +183,12 @@ describe('Date', () => {
       const date1 = Date.from('2019-01-01');
       const date2 = Date.from('2019-02-01');
       const date3 = Date.from('2019-03-01');
-      equal(`${date1.difference(date2)}`, 'P31D');
-      equal(`${date2.difference(date3)}`, 'P28D');
+      equal(`${date2.difference(date1)}`, 'P31D');
+      equal(`${date3.difference(date2)}`, 'P28D');
 
       const date4 = Date.from('2020-02-01');
       const date5 = Date.from('2020-03-01');
-      equal(`${date4.difference(date5)}`, 'P29D');
+      equal(`${date5.difference(date4)}`, 'P29D');
     });
     it('takes days per year into account', () => {
       const date1 = Date.from('2019-01-01');
@@ -196,10 +197,10 @@ describe('Date', () => {
       const date4 = Date.from('2020-06-01');
       const date5 = Date.from('2021-01-01');
       const date6 = Date.from('2021-06-01');
-      equal(`${date1.difference(date3)}`, 'P365D');
-      equal(`${date3.difference(date5)}`, 'P366D');
-      equal(`${date2.difference(date4)}`, 'P366D');
-      equal(`${date4.difference(date6)}`, 'P365D');
+      equal(`${date3.difference(date1)}`, 'P365D');
+      equal(`${date5.difference(date3)}`, 'P366D');
+      equal(`${date4.difference(date2)}`, 'P366D');
+      equal(`${date6.difference(date4)}`, 'P365D');
     });
     const feb20 = Date.from('2020-02-01');
     const feb21 = Date.from('2021-02-01');

polyfill/test/datetime.mjs

@@ -300,9 +300,12 @@ describe('DateTime', () => {
     const earlier = DateTime.from('1976-11-18T15:23:30.123456789');
     const later = DateTime.from('2019-10-29T10:46:38.271986102');
     ['years', 'months', 'weeks', 'days', 'hours', 'minutes', 'seconds'].forEach((largestUnit) => {
-      const diff = earlier.difference(later, { largestUnit });
+      const diff = later.difference(earlier, { largestUnit });
+      /*
       it(`(${earlier}).difference(${later}, ${largestUnit}) == (${later}).difference(${earlier}, ${largestUnit})`, () =>
         equal(`${later.difference(earlier, { largestUnit })}`, `${diff}`));
+      */
+      it('throws if out of order', () => throws(() => earlier.difference(later), RangeError));
       it(`(${earlier}).plus(${diff}) == (${later})`, () => earlier.plus(diff).equals(later));
       it(`(${later}).minus(${diff}) == (${earlier})`, () => later.minus(diff).equals(earlier));
     });