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Normative: Fix intermediate value in ZonedDateTime difference #2760

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Normative: Fix intermediate value in ZonedDateTime difference #2760

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108 changes: 67 additions & 41 deletions polyfill/lib/ecmascript.mjs
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Original file line number Diff line number Diff line change
Expand Up @@ -3903,49 +3903,75 @@ export function DifferenceZonedDateTime(
const dtStart = precalculatedDtStart ?? GetPlainDateTimeFor(timeZoneRec, start, calendarRec.receiver);
const dtEnd = GetPlainDateTimeFor(timeZoneRec, end, calendarRec.receiver);

let { years, months, weeks } = DifferenceISODateTime(
GetSlot(dtStart, ISO_YEAR),
GetSlot(dtStart, ISO_MONTH),
GetSlot(dtStart, ISO_DAY),
GetSlot(dtStart, ISO_HOUR),
GetSlot(dtStart, ISO_MINUTE),
GetSlot(dtStart, ISO_SECOND),
GetSlot(dtStart, ISO_MILLISECOND),
GetSlot(dtStart, ISO_MICROSECOND),
GetSlot(dtStart, ISO_NANOSECOND),
GetSlot(dtEnd, ISO_YEAR),
GetSlot(dtEnd, ISO_MONTH),
GetSlot(dtEnd, ISO_DAY),
GetSlot(dtEnd, ISO_HOUR),
GetSlot(dtEnd, ISO_MINUTE),
GetSlot(dtEnd, ISO_SECOND),
GetSlot(dtEnd, ISO_MILLISECOND),
GetSlot(dtEnd, ISO_MICROSECOND),
GetSlot(dtEnd, ISO_NANOSECOND),
calendarRec,
largestUnit,
options
);
let intermediateNs = AddZonedDateTime(
start,
timeZoneRec,
calendarRec,
years,
months,
weeks,
0,
TimeDuration.ZERO,
dtStart
);
// may disambiguate
// Simulate moving ns1 as many years/months/weeks/days as possible without
// surpassing ns2. This value is stored in intermediateDateTime/intermediate.
// We do not literally move years/months/weeks/days with calendar arithmetic,
// but rather assume intermediateDateTime will have the same time-parts as
// dtStart and the date-parts from dtEnd, and move backward from there.
//
// This loop will run 3 times max:
// 1. initial run
// 2. backoff if the time-parts of intermediateDateTime have conflicting sign
// with overall diff direction, just like how DifferenceISODateTime works
// 3. backoff if intermediateDateTime fell into a DST gap and was pushed in a
// direction that would make the diff of the time-parts conflict with the
// sign of the overall direction. (Only possible when sign is +1, because
// a DST gap uses 'compatible' disambiguation resolution and can only move
// the intermediate forward)
//
// Credit to Adam Shaw for devising this algorithm.
const sign = nsDiff.lt(0) ? -1 : 1;
const maxTries = sign === 1 ? 3 : 2;
for (let dayCorrection = 0; dayCorrection < maxTries; dayCorrection++) {
const correctedEndDate = BalanceISODate(
GetSlot(dtEnd, ISO_YEAR),
GetSlot(dtEnd, ISO_MONTH),
GetSlot(dtEnd, ISO_DAY) - dayCorrection * sign
);

let norm = TimeDuration.fromEpochNsDiff(ns2, intermediateNs);
const intermediate = CreateTemporalZonedDateTime(intermediateNs, timeZoneRec.receiver, calendarRec.receiver);
let days;
({ norm, days } = NormalizedTimeDurationToDays(norm, intermediate, timeZoneRec));
// Incorporate time parts from dtStart
const intermediateDateTime = CreateTemporalDateTime(
correctedEndDate.year,
correctedEndDate.month,
correctedEndDate.day,
GetSlot(dtStart, ISO_HOUR),
GetSlot(dtStart, ISO_MINUTE),
GetSlot(dtStart, ISO_SECOND),
GetSlot(dtStart, ISO_MILLISECOND),
GetSlot(dtStart, ISO_MICROSECOND),
GetSlot(dtStart, ISO_NANOSECOND),
calendarRec.receiver
);
const intermediate = GetInstantFor(timeZoneRec, intermediateDateTime, 'compatible');
// may disambiguate
const intermediateNs = GetSlot(intermediate, EPOCHNANOSECONDS);

// Did intermediateNs surpass ns2?
const norm = TimeDuration.fromEpochNsDiff(ns2, intermediateNs);
const timeSign = norm.sign();
if (sign === 0 || timeSign == 0 || sign === timeSign) {
// sign of timeDuration now compatible with the overall sign

// Similar to what happens in DifferenceISODateTime with date parts only:
const date1 = TemporalDateTimeToDate(dtStart);
const date2 = TemporalDateTimeToDate(intermediateDateTime);
const dateLargestUnit = LargerOfTwoTemporalUnits('day', largestUnit);
const untilOptions = SnapshotOwnProperties(options, null);
untilOptions.largestUnit = dateLargestUnit;
const dateDifference = DifferenceDate(calendarRec, date1, date2, untilOptions);
const years = GetSlot(dateDifference, YEARS);
const months = GetSlot(dateDifference, MONTHS);
const weeks = GetSlot(dateDifference, WEEKS);
const days = GetSlot(dateDifference, DAYS);

CombineDateAndNormalizedTimeDuration(years, months, weeks, days, norm);
return { years, months, weeks, days, norm };
CombineDateAndNormalizedTimeDuration(years, months, weeks, days, norm);
return { years, months, weeks, days, norm };
}
// Else, keep backing off...
}
throw new RangeError(
`inconsistent return from calendar or time zone method: more than ${maxTries - 1} days correction needed`
);
}

export function GetDifferenceSettings(op, options, group, disallowed, fallbackSmallest, smallestLargestDefaultUnit) {
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27 changes: 21 additions & 6 deletions spec/zoneddatetime.html
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Expand Up @@ -1397,12 +1397,27 @@ <h1>
1. Let _startDateTime_ be _precalculatedPlainDateTime_.
1. Let _endInstant_ be ! CreateTemporalInstant(_ns2_).
1. Let _endDateTime_ be ? GetPlainDateTimeFor(_timeZoneRec_, _endInstant_, _calendarRec_.[[Receiver]]).
1. Let _dateDifference_ be ? DifferenceISODateTime(_startDateTime_.[[ISOYear]], _startDateTime_.[[ISOMonth]], _startDateTime_.[[ISODay]], _startDateTime_.[[ISOHour]], _startDateTime_.[[ISOMinute]], _startDateTime_.[[ISOSecond]], _startDateTime_.[[ISOMillisecond]], _startDateTime_.[[ISOMicrosecond]], _startDateTime_.[[ISONanosecond]], _endDateTime_.[[ISOYear]], _endDateTime_.[[ISOMonth]], _endDateTime_.[[ISODay]], _endDateTime_.[[ISOHour]], _endDateTime_.[[ISOMinute]], _endDateTime_.[[ISOSecond]], _endDateTime_.[[ISOMillisecond]], _endDateTime_.[[ISOMicrosecond]], _endDateTime_.[[ISONanosecond]], _calendarRec_, _largestUnit_, _options_).
1. Let _intermediateNs_ be ? AddZonedDateTime(_ns1_, _timeZoneRec_, _calendarRec_, _dateDifference_.[[Years]], _dateDifference_.[[Months]], _dateDifference_.[[Weeks]], 0, ZeroTimeDuration(), _startDateTime_).
1. Let _norm_ be NormalizedTimeDurationFromEpochNanosecondsDifference(_ns2_, _intermediateNs_).
1. Let _intermediate_ be ! CreateTemporalZonedDateTime(_intermediateNs_, _timeZoneRec_.[[Receiver]], _calendarRec_.[[Receiver]]).
1. Let _result_ be ? NormalizedTimeDurationToDays(_norm_, _intermediate_, _timeZoneRec_).
1. Return ! CreateNormalizedDurationRecord(_dateDifference_.[[Years]], _dateDifference_.[[Months]], _dateDifference_.[[Weeks]], _result_.[[Days]], _result_.[[Remainder]]).
1. If _ns2_ - _ns1_ &lt; 0, let _sign_ be -1; else let _sign_ be 1.
1. If _sign_ = 1, let _maxTries_ be 3; else let _maxTries_ be 2.
1. Let _dayCorrection_ be 0.
1. Repeat _maxTries_ times:
1. Let _correctedEndDate_ be BalanceISODate(_endDateTime_.[[ISOYear]], _endDateTime_.[[ISOMonth]], _endDateTime_.[[ISODay]] - _dayCorrection_ &times; _sign_).
1. Let _intermediateDateTime_ be ! CreateTemporalDateTime(_correctedEndDate_.[[Year]], _correctedEndDate_.[[Month]], _correctedEndDate_.[[Day]], _startDateTime_.[[ISOHour]], _startDateTime_.[[ISOMinute]], _startDateTime_.[[ISOSecond]], _startDateTime_.[[ISOMillisecond]], _startDateTime_.[[ISOMicrosecond]], _startDateTime_.[[ISONanosecond]], _calendarRec_.[[Receiver]]).
1. Let _intermediate_ be ? GetInstantFor(_timeZoneRec_, _intermediateDateTime_, *"compatible"*).
1. Let _intermediateNs_ be _intermediate_.[[Nanoseconds]].
1. Let _norm_ be NormalizedTimeDurationFromEpochNanosecondsDifference(_ns2_, _intermediateNs_).
1. Let _timeSign_ be NormalizedTimeDurationSign(_norm_).
1. If _sign_ = 0, or _timeSign_ = 0, or _sign_ = _timeSign_, then
1. Let _date1_ be ! CreateTemporalDate(_startDateTime_.[[ISOYear]], _startDateTime_.[[ISOMonth]], _startDateTime_.[[ISODay]], _calendarRec_.[[Receiver]]).
1. Let _date2_ be ! CreateTemporalDate(_correctedEndDate_.[[Year]], _correctedEndDate_.[[Month]], _correctedEndDate_.[[Day]], _calendarRec_.[[Receiver]]).
1. Let _dateLargestUnit_ be LargerOfTwoTemporalUnits(_largestUnit_, *"day"*).
1. Let _untilOptions_ be ? SnapshotOwnProperties(_options_, *null*).
1. Perform ! CreateDataPropertyOrThrow(_untilOptions_, *"largestUnit"*, _dateLargestUnit_).
1. Let _dateDifference_ be ? DifferenceDate(_calendarRec_, _date1_, _date2_, _untilOptions_).
1. Return ? CreateNormalizedDurationRecord(_dateDifference_.[[Years]], _dateDifference_.[[Months]], _dateDifference_.[[Weeks]], _dateDifference_.[[Days]], _norm_).
1. Set _dayCorrection_ to _dayCorrection_ + 1.
1. NOTE: This step is only reached when custom calendar or time zone methods return inconsistent values.
1. Throw a *RangeError* exception.
</emu-alg>
</emu-clause>

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