Chinese calendar until throws "mixed-sign values not allowed as duration fields" RangeError

[justingrant]

Clearly this is a polyfill bug, but not sure if it reflects an underlying spec issue. Note that 2001 is a leap year in the chinese calendar that has an M04L leap month, so month 6 in 2001 is M05 while month 6 in 2000 is M06.

// 2001 is a leap year
Temporal.PlainDate.from({ year: 2001, month: 6, day: 1, calendar: 'chinese' })
  .since({ year: 2000, month: 6, day: 1, calendar: 'chinese' }, { largestUnit: 'year' })

It throws a RangeError:

ecmascript.mjs:3324 Uncaught RangeError: mixed-sign values not allowed as duration fields
    at Object.RejectDuration (ecmascript.mjs:3324:54)
    at new Duration (duration.mjs:47:8)
    at Calendar.dateUntil (calendar.mjs:165:12)
    at Object.Call (Call.js:19:9)
    at Object.CalendarDateUntil (ecmascript.mjs:1601:23)
    at Object.DifferenceTemporalPlainDate (ecmascript.mjs:3716:45)
    at Temporal.PlainDate.since (plaindate.mjs:136:15)
    at <anonymous>:2:4

[gibson042]

This is probably not a spec bug because non-ISO-8601 comparisons are implementation-defined, but if you can reproduce this with e.g. a leap day then a spec issue is more likely.

[justingrant]

if you can reproduce this with e.g. a leap day then a spec issue is more likely.

The problem turned out to be caused by a case that can never happen in the ISO calendar: when calculating the number of years between two dates where the years are different, the monthCodes are different, but the month is the same in both because the later date was after a leap month.

So not a spec issue (until non-ISO math is specified, of course!).

Fix available in #2539.