CalendarMonthDayToISOReferenceDate: Require "eraYear + year" and "month + monthCode" to be consistent?

[anba]

It'd be good to have more detailed information when built-in calendars need to check for consistent inputs:

// Which of these are errors?

// eraYear and year inconsistent when month is present.
Temporal.PlainMonthDay.from({calendar: "gregory", era: "ce", eraYear: 2023, year: 2022, month: 2, day: 30});

// eraYear and year inconsistent when monthCode is present.
Temporal.PlainMonthDay.from({calendar: "gregory", era: "ce", eraYear: 2023, year: 2022, monthCode: "M02", day: 30});

// month and monthCode inconsistent.
Temporal.PlainMonthDay.from({calendar: "gregory", month: 3, monthCode: "M02", day: 30});

[justingrant]

Meeting 2024-05-30: @gibson042 will PR a change to align behavior of non-ISO calendars to match behavior of ISO calendar, which would throw if month/monthCode or year/era/eraYear are present but inconsistent.

[ptomato]

@gibson042 Will you have time to pick this up in the near future or should I pick it up?

[gibson042]

I think this is already covered in the spec: CalendarResolveFields (emphasis mine)

The operation throws a TypeError exception if the fields of fields are internally inconsistent within the calendar or insufficient to identify a unique instance of type in the calendar. For example:

• If type is DATE or MONTH-DAY and DAY in the calendar has an interpretation analogous to ISO 8601 and fields.[[Day]] is UNSET.
• If MONTH and MONTH-CODE in the calendar have interpretations analogous to ISO 8601 and either the corresponding values for both are UNSET or neither value is UNSET but they do not identify the same month.
• If type is MONTH-DAY and fields.[[MonthCode]] is UNSET and a year cannot be determined from fields.
• If type is DATE or YEAR-MONTH and the calendar supports the usual partitioning of years into eras with their own year counting as represented by YEAR, ERA, and ERA-YEAR (as in the Gregorian or traditional Japanese calendars) and any of the following cases apply:
  • Each of fields.[[Year]], fields.[[Era]], and fields.[[EraYear]] is UNSET.
  • fields.[[Era]] is UNSET but fields.[[EraYear]] is not.
  • fields.[[EraYear]] is UNSET but fields.[[Era]] is not.
  • None of the three values are UNSET but fields.[[Era]] and fields.[[EraYear]] do not together identify the same year as fields.[[Year]].

But I've updated the polyfill accordingly in #2940. It's code that I haven't touched before, so I'd appreciate a thorough review for correctness and coverage.

[anba]

This part:

If type is DATE or YEAR-MONTH [...]

doesn't apply to the example, because Temporal.PlainMonthDay calls CalendarResolveFields with type = MONTH-DAY.

[gibson042]

Updated #2940 to correct that.