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// |reftest| shell-option(--enable-temporal) skip-if(!this.hasOwnProperty('Temporal')||!xulRuntime.shell) -- Temporal is not enabled unconditionally, requires shell-options
// Copyright (C) 2025 Igalia, S.L. All rights reserved.
// This code is governed by the BSD license found in the LICENSE file.
/*---
esid: sec-temporal.plainyearmonth.from
description: Test remapping behaviour of regnal eras
info: |
CalendarYearMonthFromFields:
1. Perform ? CalendarResolveFields(_calendar_, _fields_, ~year-month~).
2. Let _firstDayIndex_ be the 1-based index of the first day of the month
described by _fields_ (i.e., 1 unless the month's first day is skipped by
this calendar.)
3. Set _fields_.[[Day]] to _firstDayIndex_.
4. Let result be ? CalendarDateToISO(_calendar_, _fields_, _overflow_).
CalendarResolveFields:
When the fields of _fields_ are inconsistent with respect to a non-unset
_fields_.[[Era]], it is recommended that _fields_.[[Era]] and
_fields_.[[EraYear]] be updated to resolve the inconsistency by lenient
interpretation of out-of-bounds values (rather than throwing a *RangeError*),
which is particularly useful for consistent interpretation of dates in
calendars with regnal eras.
includes: [temporalHelpers.js]
features: [Temporal]
---*/
// Based on a test originally by André Bargull <andre.bargull@gmail.com>
// Notes:
// - "heisei" era started January 8, 1989.
// - "reiwa" era started May 1, 2019.
for (const overflow of ["constrain", "reject"]) {
function test(fields) {
return Temporal.PlainYearMonth.from({ ...fields, calendar: "japanese" }, { overflow });
}
// Reiwa era started in month 5 of the year, so the era of month 1 is remapped
// to be the correct one for the month.
TemporalHelpers.assertPlainYearMonth(
test({ era: "reiwa", eraYear: 1, monthCode: "M01" }),
2019, 1, "M01",
"Reiwa 1 before May is mapped to Heisei 31",
"heisei", 31, /* reference day = */ 1
);
// Reiwa era started on the first day of the month, so the reference day 1
// does not need remapping.
TemporalHelpers.assertPlainYearMonth(
test({ era: "reiwa", eraYear: 1, monthCode: "M05" }),
2019, 5, "M05",
"reference day is 1",
"reiwa", 1, /* reference day = */ 1
);
// Heisei era started on the eighth day of the month, but PlainYearMonth
// references the first day of the month. So the era is remapped to be the
// correct one for the reference day.
TemporalHelpers.assertPlainYearMonth(
test({ era: "heisei", eraYear: 1, monthCode: "M01" }),
1989, 1, "M01",
"01-01 Heisei 1 is remapped to 01-01 Showa 64",
"showa", 64, /* reference day = */ 1
);
// Era year past the end of the Heisei era is remapped to Reiwa era
TemporalHelpers.assertPlainYearMonth(
test({ era: "heisei", eraYear: 37, monthCode: "M04" }),
2025, 4, "M04",
"Heisei 37 is remapped to Reiwa 7",
"reiwa", 7, /* reference day = */ 1
);
// Zero year in a 1-based era is remapped to the previous era
TemporalHelpers.assertPlainYearMonth(
test({ era: "reiwa", eraYear: 0, monthCode: "M04" }),
2018, 4, "M04",
"Reiwa 0 is remapped to Heisei 30",
"heisei", 30, /* reference day = */ 1
);
// Negative year in a forwards-counting era is remapped to the previous era
TemporalHelpers.assertPlainYearMonth(
test({ era: "reiwa", eraYear: -20, monthCode: "M04" }),
1998, 4, "M04",
"Reiwa -20 is remapped to Heisei 10",
"heisei", 10, /* reference day = */ 1
);
// Test the last two things for Gregorian eras as well
function testGregorian(fields) {
return Temporal.PlainYearMonth.from({ ...fields, calendar: "gregory" }, { overflow });
}
TemporalHelpers.assertPlainYearMonth(
testGregorian({ era: "ce", eraYear: 0, monthCode: "M04" }),
0, 4, "M04",
"0 CE is remapped to 1 BCE",
"bce", 1, /* reference day = */ 1
);
TemporalHelpers.assertPlainYearMonth(
testGregorian({ era: "ce", eraYear: -20, monthCode: "M04" }),
-20, 4, "M04",
"-20 CE is remapped to 21 BCE",
"bce", 21, /* reference day = */ 1
);
// Zero year in a backwards-counting era is remapped to the next era
TemporalHelpers.assertPlainYearMonth(
testGregorian({ era: "bce", eraYear: 0, monthCode: "M04" }),
1, 4, "M04",
"0 BCE is remapped to 1 CE",
"ce", 1, /* reference day = */ 1
);
// Negative year in a backwards-counting era is remapped to the next era
TemporalHelpers.assertPlainYearMonth(
testGregorian({ era: "bce", eraYear: -20, monthCode: "M04" }),
21, 4, "M04",
"-20 BCE is remapped to 21 CE",
"ce", 21, /* reference day = */ 1
);
}
reportCompare(0, 0);