Tests for computing PlainYearMonth addition and subtraction in correct calendar space

https://github.com/tc39/proposal-temporal/pull/2003 is a normative change
that reached consensus at the March 2022 TC39 plenary meeting. This adds
tests that verify the new spec text is implemented correctly, performing
arithmetic on a PlainYearMonth instance that would previously have thrown
an error if it was implemented as written.

test/built-ins/Temporal/PlainYearMonth/prototype/add/calendar-datefromfields-called.js

@@ -0,0 +1,147 @@
+// Copyright (C) 2022 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.add
+description: >
+  Calls calendar's dateFromFields method to obtain a start date for the
+  operation, based on the sign of the duration
+info: |
+  8. Let _fields_ be ? PrepareTemporalFields(_yearMonth_, _fieldNames_, «»).
+  9. Let _sign_ be ! DurationSign(_duration_.[[Years]], _duration_.[[Months]], _duration_.[[Weeks]], _balanceResult_.[[Days]], 0, 0, 0, 0, 0, 0).
+  10. If _sign_ < 0, then
+    a. Let _dayFromCalendar_ be ? CalendarDaysInMonth(_calendar_, _yearMonth_).
+    b. Let _day_ be ? ToPositiveInteger(_dayFromCalendar_).
+  11. Else,
+    a. Let _day_ be 1.
+  12. Perform ! CreateDataPropertyOrThrow(_fields_, *"day"*, _day_).
+  13. Let _date_ be ? DateFromFields(_calendar_, _fields_, *undefined*).
+includes: [deepEqual.js, temporalHelpers.js]
+features: [Temporal]
+---*/
+
+class CustomCalendar extends Temporal.Calendar {
+  constructor() {
+    super("iso8601");
+    this.dateFromFieldsCalls = [];
+  }
+  year(date) {
+    // years in this calendar start and end on the same day as ISO 8601 years
+    return date.getISOFields().isoYear;
+  }
+  month(date) {
+    // this calendar has 10 months of 36 days each, plus an 11th month of 5 or 6
+    const { isoYear, isoMonth, isoDay } = date.getISOFields();
+    const isoDate = new Temporal.PlainDate(isoYear, isoMonth, isoDay);
+    return Math.floor((isoDate.dayOfYear - 1) / 36) + 1;
+  }
+  monthCode(date) {
+    return "M" + this.month(date).toString().padStart(2, "0");
+  }
+  day(date) {
+    return (date.dayOfYear - 1) % 36 + 1;
+  }
+  daysInMonth(date) {
+    if (this.month(date) < 11) return 36;
+    return this.daysInYear(date) - 360;
+  }
+  _dateFromFieldsImpl({ year, month, monthCode, day }) {
+    if (year === undefined) throw new TypeError("year required");
+    if (month === undefined && monthCode === undefined) throw new TypeError("one of month or monthCode required");
+    if (month !== undefined && month < 1) throw new RangeError("month < 1");
+    if (day === undefined) throw new TypeError("day required");
+
+    if (monthCode !== undefined) {
+      const numberPart = +(monthCode.slice(1));
+      if ("M" + `${numberPart}`.padStart(2, "0") !== monthCode) throw new RangeError("invalid monthCode");
+      if (month === undefined) {
+        month = numberPart;
+      } else if (month !== numberPart) {
+        throw new RangeError("month and monthCode must match");
+      }
+    }
+
+    const isoDayOfYear = (month - 1) * 36 + day;
+    return new Temporal.PlainDate(year, 1, 1).add({ days: isoDayOfYear - 1 }).withCalendar(this);
+  }
+  dateFromFields(...args) {
+    this.dateFromFieldsCalls.push(args);
+    return this._dateFromFieldsImpl(...args);
+  }
+  yearMonthFromFields(fields, options) {
+    const { isoYear, isoMonth, isoDay } = this._dateFromFieldsImpl({ ...fields, day: 1 }, options).getISOFields();
+    return new Temporal.PlainYearMonth(isoYear, isoMonth, this, isoDay);
+  }
+  monthDayFromFields(fields, options) {
+    const { isoYear, isoMonth, isoDay } = this._dateFromFieldsImpl({ ...fields, year: 2000 }, options).getISOFields();
+    return new Temporal.PlainMonthDay(isoMonth, isoDay, this, isoYear);
+  }
+  dateAdd(date, duration, options) {
+    if (duration.months) throw new Error("adding months not implemented in this test");
+    return super.dateAdd(date, duration, options);
+  }
+  toString() {
+    return "thirty-six";
+  }
+}
+
+const calendar = new CustomCalendar();
+const month2 = Temporal.PlainYearMonth.from({ year: 2022, month: 2, calendar });
+const lessThanOneMonth = new Temporal.Duration(0, 0, 0, 35);
+const oneMonth = new Temporal.Duration(0, 0, 0, 36);
+
+calendar.dateFromFieldsCalls = [];
+TemporalHelpers.assertPlainYearMonth(
+  month2.add(lessThanOneMonth),
+  2022, 2, "M02",
+  "adding positive less than one month's worth of days yields the same month"
+);
+assert.sameValue(calendar.dateFromFieldsCalls.length, 1, "dateFromFields was called");
+assert.deepEqual(
+  calendar.dateFromFieldsCalls[0][0],
+  { year: 2022, month: 2, monthCode: "M02", day: 1 },
+  "first day of month 2 passed to dateFromFields when adding positive duration"
+);
+assert.sameValue(calendar.dateFromFieldsCalls[0][1], undefined, "undefined options passed");
+
+calendar.dateFromFieldsCalls = [];
+TemporalHelpers.assertPlainYearMonth(
+  month2.add(oneMonth),
+  2022, 3, "M03",
+  "adding positive one month's worth of days yields the following month"
+);
+assert.sameValue(calendar.dateFromFieldsCalls.length, 1, "dateFromFields was called");
+assert.deepEqual(
+  calendar.dateFromFieldsCalls[0][0],
+  { year: 2022, month: 2, monthCode: "M02", day: 1 },
+  "first day of month 2 passed to dateFromFields when adding positive duration"
+);
+assert.sameValue(calendar.dateFromFieldsCalls[0][1], undefined, "undefined options passed");
+
+calendar.dateFromFieldsCalls = [];
+TemporalHelpers.assertPlainYearMonth(
+  month2.add(lessThanOneMonth.negated()),
+  2022, 2, "M02",
+  "adding negative less than one month's worth of days yields the same month"
+);
+assert.sameValue(calendar.dateFromFieldsCalls.length, 1, "dateFromFields was called");
+assert.deepEqual(
+  calendar.dateFromFieldsCalls[0][0],
+  { year: 2022, month: 2, monthCode: "M02", day: 36 },
+  "last day of month 2 passed to dateFromFields when adding negative duration"
+);
+assert.sameValue(calendar.dateFromFieldsCalls[0][1], undefined, "undefined options passed");
+
+calendar.dateFromFieldsCalls = [];
+TemporalHelpers.assertPlainYearMonth(
+  month2.add(oneMonth.negated()),
+  2022, 1, "M01",
+  "adding negative one month's worth of days yields the previous month"
+);
+assert.sameValue(calendar.dateFromFieldsCalls.length, 1, "dateFromFields was called");
+assert.deepEqual(
+  calendar.dateFromFieldsCalls[0][0],
+  { year: 2022, month: 2, monthCode: "M02", day: 36 },
+  "last day of month 2 passed to dateFromFields when adding negative duration"
+);
+assert.sameValue(calendar.dateFromFieldsCalls[0][1], undefined, "undefined options passed");

test/built-ins/Temporal/PlainYearMonth/prototype/subtract/calendar-datefromfields-called.js

@@ -0,0 +1,147 @@
+// Copyright (C) 2022 Igalia, S.L. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-temporal.plainyearmonth.prototype.subtract
+description: >
+  Calls calendar's dateFromFields method to obtain a start date for the
+  operation, based on the sign of the duration
+info: |
+  9. Let _fields_ be ? PrepareTemporalFields(_yearMonth_, _fieldNames_, «»).
+  10. Let _sign_ be ! DurationSign(_duration_.[[Years]], _duration_.[[Months]], _duration_.[[Weeks]], _balanceResult_.[[Days]], 0, 0, 0, 0, 0, 0).
+  11. If _sign_ < 0, then
+    a. Let _dayFromCalendar_ be ? CalendarDaysInMonth(_calendar_, _yearMonth_).
+    b. Let _day_ be ? ToPositiveInteger(_dayFromCalendar_).
+  12. Else,
+    a. Let _day_ be 1.
+  13. Perform ! CreateDataPropertyOrThrow(_fields_, *"day"*, _day_).
+  14. Let _date_ be ? DateFromFields(_calendar_, _fields_, *undefined*).
+includes: [deepEqual.js, temporalHelpers.js]
+features: [Temporal]
+---*/
+
+class CustomCalendar extends Temporal.Calendar {
+  constructor() {
+    super("iso8601");
+    this.dateFromFieldsCalls = [];
+  }
+  year(date) {
+    // years in this calendar start and end on the same day as ISO 8601 years
+    return date.getISOFields().isoYear;
+  }
+  month(date) {
+    // this calendar has 10 months of 36 days each, plus an 11th month of 5 or 6
+    const { isoYear, isoMonth, isoDay } = date.getISOFields();
+    const isoDate = new Temporal.PlainDate(isoYear, isoMonth, isoDay);
+    return Math.floor((isoDate.dayOfYear - 1) / 36) + 1;
+  }
+  monthCode(date) {
+    return "M" + this.month(date).toString().padStart(2, "0");
+  }
+  day(date) {
+    return (date.dayOfYear - 1) % 36 + 1;
+  }
+  daysInMonth(date) {
+    if (this.month(date) < 11) return 36;
+    return this.daysInYear(date) - 360;
+  }
+  _dateFromFieldsImpl({ year, month, monthCode, day }) {
+    if (year === undefined) throw new TypeError("year required");
+    if (month === undefined && monthCode === undefined) throw new TypeError("one of month or monthCode required");
+    if (month !== undefined && month < 1) throw new RangeError("month < 1");
+    if (day === undefined) throw new TypeError("day required");
+
+    if (monthCode !== undefined) {
+      const numberPart = +(monthCode.slice(1));
+      if ("M" + `${numberPart}`.padStart(2, "0") !== monthCode) throw new RangeError("invalid monthCode");
+      if (month === undefined) {
+        month = numberPart;
+      } else if (month !== numberPart) {
+        throw new RangeError("month and monthCode must match");
+      }
+    }
+
+    const isoDayOfYear = (month - 1) * 36 + day;
+    return new Temporal.PlainDate(year, 1, 1).add({ days: isoDayOfYear - 1 }).withCalendar(this);
+  }
+  dateFromFields(...args) {
+    this.dateFromFieldsCalls.push(args);
+    return this._dateFromFieldsImpl(...args);
+  }
+  yearMonthFromFields(fields, options) {
+    const { isoYear, isoMonth, isoDay } = this._dateFromFieldsImpl({ ...fields, day: 1 }, options).getISOFields();
+    return new Temporal.PlainYearMonth(isoYear, isoMonth, this, isoDay);
+  }
+  monthDayFromFields(fields, options) {
+    const { isoYear, isoMonth, isoDay } = this._dateFromFieldsImpl({ ...fields, year: 2000 }, options).getISOFields();
+    return new Temporal.PlainMonthDay(isoMonth, isoDay, this, isoYear);
+  }
+  dateAdd(date, duration, options) {
+    if (duration.months) throw new Error("adding months not implemented in this test");
+    return super.dateAdd(date, duration, options);
+  }
+  toString() {
+    return "thirty-six";
+  }
+}
+
+const calendar = new CustomCalendar();
+const month2 = Temporal.PlainYearMonth.from({ year: 2022, month: 2, calendar });
+const lessThanOneMonth = new Temporal.Duration(0, 0, 0, 35);
+const oneMonth = new Temporal.Duration(0, 0, 0, 36);
+
+calendar.dateFromFieldsCalls = [];
+TemporalHelpers.assertPlainYearMonth(
+  month2.subtract(lessThanOneMonth),
+  2022, 2, "M02",
+  "subtracting positive less than one month's worth of days yields the same month"
+);
+assert.sameValue(calendar.dateFromFieldsCalls.length, 1, "dateFromFields was called");
+assert.deepEqual(
+  calendar.dateFromFieldsCalls[0][0],
+  { year: 2022, month: 2, monthCode: "M02", day: 36 },
+  "last day of month 2 passed to dateFromFields when subtracting positive duration"
+);
+assert.sameValue(calendar.dateFromFieldsCalls[0][1], undefined, "undefined options passed");
+
+calendar.dateFromFieldsCalls = [];
+TemporalHelpers.assertPlainYearMonth(
+  month2.subtract(oneMonth),
+  2022, 1, "M01",
+  "subtracting positive one month's worth of days yields the previous month"
+);
+assert.sameValue(calendar.dateFromFieldsCalls.length, 1, "dateFromFields was called");
+assert.deepEqual(
+  calendar.dateFromFieldsCalls[0][0],
+  { year: 2022, month: 2, monthCode: "M02", day: 36 },
+  "last day of month 2 passed to dateFromFields when subtracting positive duration"
+);
+assert.sameValue(calendar.dateFromFieldsCalls[0][1], undefined, "undefined options passed");
+
+calendar.dateFromFieldsCalls = [];
+TemporalHelpers.assertPlainYearMonth(
+  month2.subtract(lessThanOneMonth.negated()),
+  2022, 2, "M02",
+  "subtracting negative less than one month's worth of days yields the same month"
+);
+assert.sameValue(calendar.dateFromFieldsCalls.length, 1, "dateFromFields was called");
+assert.deepEqual(
+  calendar.dateFromFieldsCalls[0][0],
+  { year: 2022, month: 2, monthCode: "M02", day: 1 },
+  "first day of month 2 passed to dateFromFields when subtracting negative duration"
+);
+assert.sameValue(calendar.dateFromFieldsCalls[0][1], undefined, "undefined options passed");
+
+calendar.dateFromFieldsCalls = [];
+TemporalHelpers.assertPlainYearMonth(
+  month2.subtract(oneMonth.negated()),
+  2022, 3, "M03",
+  "subtracting negative one month's worth of days yields the following month"
+);
+assert.sameValue(calendar.dateFromFieldsCalls.length, 1, "dateFromFields was called");
+assert.deepEqual(
+  calendar.dateFromFieldsCalls[0][0],
+  { year: 2022, month: 2, monthCode: "M02", day: 1 },
+  "first day of month 2 passed to dateFromFields when subtracting negative duration"
+);
+assert.sameValue(calendar.dateFromFieldsCalls[0][1], undefined, "undefined options passed");