Refactor calendars to eliminate multiple parent classes

We had originally decided to go with a scheme where the value of the [[Identifier]] internal slot determines the behaviour of the calendar methods, and there are not individual parent classes for each built-in calendar. This implements that scheme. Merges most of the spec text of ISO8601Calendar into Calendar. Closes: #847 See: #300
tc39 · Nov 16, 2020 · ce22f7b · ce22f7b
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diff --git a/docs/calendar.md b/docs/calendar.md
@@ -41,11 +41,15 @@ date.withCalendar(calendar).add({ months: 1 });
 For specialized applications where you need to do calculations in a calendar system that is not supported by Intl, you can implement a custom calendar.
 There are two ways to do this.
 
-The recommended way is to create a class inheriting from `Temporal.Calendar`, call `super()` in the constructor with a calendar identifier string, and implement all the members except `id`, `toString()`, and `fields()`, which are optional.
-If you don't implement the optional members, then the base class's default implementations will be used.
+The recommended way is to create a class inheriting from `Temporal.Calendar`.
+You must use one of the built-in calendars as the "base calendar".
+In the class's constructor, call `super()` with the identifier of the base calendar.
+The class must override `toString()` to return its own identifier.
+Overriding all the other members is optional.
+If you don't override the optional members, then they will behave as in the base calendar.
 
 The other, more difficult, way to create a custom calendar is to create a plain object implementing the `Temporal.Calendar` protocol, without subclassing.
-The object must implement all of the `Temporal.Calendar` methods except for `fields()`.
+The object must implement all of the `Temporal.Calendar` methods except for `id` and `fields()`.
 Any object with the required methods will return the correct output from any Temporal property or method.
 However, most other code will assume that custom calendars act like built-in `Temporal.Calendar` objects.
 To interoperate with libraries or other code that you didn't write, then you should implement the `id` property and the `fields()` method as well.

diff --git a/polyfill/lib/calendar.mjs b/polyfill/lib/calendar.mjs
diff --git a/polyfill/lib/ecmascript.mjs b/polyfill/lib/ecmascript.mjs
@@ -21,7 +21,6 @@ import ToPrimitive from 'es-abstract/2020/ToPrimitive.js';
 import ToString from 'es-abstract/2020/ToString.js';
 import Type from 'es-abstract/2020/Type.js';
 
-import { GetISO8601Calendar } from './calendar.mjs';
 import { GetIntrinsic } from './intrinsicclass.mjs';
 import {
   GetSlot,
@@ -677,7 +676,7 @@ export const ES = ObjectAssign({}, ES2020, {
     if (ES.Type(relativeTo) === 'Object') {
       if (ES.IsTemporalZonedDateTime(relativeTo) || ES.IsTemporalDateTime(relativeTo)) return relativeTo;
       calendar = relativeTo.calendar;
-      if (calendar === undefined) calendar = GetISO8601Calendar();
+      if (calendar === undefined) calendar = ES.GetISO8601Calendar();
       calendar = ES.ToTemporalCalendar(calendar);
       const fieldNames = ES.CalendarFields(calendar, [
         'day',
@@ -721,7 +720,7 @@ export const ES = ObjectAssign({}, ES2020, {
         offset
       } = ES.ParseISODateTime(ES.ToString(relativeTo), { zoneRequired: false }));
       if (ianaName) timeZone = ianaName;
-      if (!calendar) calendar = GetISO8601Calendar();
+      if (!calendar) calendar = ES.GetISO8601Calendar();
       calendar = ES.ToTemporalCalendar(calendar);
     }
     if (timeZone) {
@@ -764,7 +763,7 @@ export const ES = ObjectAssign({}, ES2020, {
       return new TemporalTime(hour, minute, second, millisecond, microsecond, nanosecond);
     }
     let { year, month, day, hour, minute, second, millisecond, microsecond, nanosecond, calendar } = props;
-    if (!calendar) calendar = new (GetIntrinsic('%Temporal.ISO8601Calendar%'))();
+    if (!calendar) calendar = ES.GetISO8601Calendar();
     const DATE_ONLY = new RegExp(`^${PARSE.datesplit.source}$`);
     const match = DATE_ONLY.exec(str);
     if (match) {
@@ -972,15 +971,15 @@ export const ES = ObjectAssign({}, ES2020, {
     if (ES.Type(item) === 'Object') {
       if (ES.IsTemporalDate(item)) return item;
       let calendar = item.calendar;
-      if (calendar === undefined) calendar = new (GetIntrinsic('%Temporal.ISO8601Calendar%'))();
+      if (calendar === undefined) calendar = ES.GetISO8601Calendar();
       calendar = ES.ToTemporalCalendar(calendar);
       const fieldNames = ES.CalendarFields(calendar, ['day', 'month', 'year']);
       const fields = ES.ToTemporalDateFields(item, fieldNames);
       return ES.DateFromFields(calendar, fields, constructor, overflow);
     }
     let { year, month, day, calendar } = ES.ParseTemporalDateString(ES.ToString(item));
     ({ year, month, day } = ES.RegulateDate(year, month, day, overflow));
-    if (calendar === undefined) calendar = new (GetIntrinsic('%Temporal.ISO8601Calendar%'))();
+    if (calendar === undefined) calendar = ES.GetISO8601Calendar();
     calendar = ES.ToTemporalCalendar(calendar);
     let result = new constructor(year, month, day, calendar);
     if (!ES.IsTemporalDate(result)) throw new TypeError('invalid result');
@@ -1010,7 +1009,7 @@ export const ES = ObjectAssign({}, ES2020, {
       if (ES.IsTemporalDateTime(item)) return item;
 
       calendar = item.calendar;
-      if (calendar === undefined) calendar = new (GetIntrinsic('%Temporal.ISO8601Calendar%'))();
+      if (calendar === undefined) calendar = ES.GetISO8601Calendar();
       calendar = ES.ToTemporalCalendar(calendar);
 
       const fieldNames = ES.CalendarFields(calendar, ['day', 'month', 'year']);
@@ -1039,7 +1038,7 @@ export const ES = ObjectAssign({}, ES2020, {
         nanosecond,
         calendar
       } = ES.ParseTemporalDateTimeString(ES.ToString(item)));
-      if (calendar === undefined) calendar = new (GetIntrinsic('%Temporal.ISO8601Calendar%'))();
+      if (calendar === undefined) calendar = ES.GetISO8601Calendar();
       calendar = ES.ToTemporalCalendar(calendar);
     }
     const result = new constructor(
@@ -1113,7 +1112,7 @@ export const ES = ObjectAssign({}, ES2020, {
     if (ES.Type(item) === 'Object') {
       if (ES.IsTemporalMonthDay(item)) return item;
       let calendar = item.calendar;
-      if (calendar === undefined) calendar = new (GetIntrinsic('%Temporal.ISO8601Calendar%'))();
+      if (calendar === undefined) calendar = ES.GetISO8601Calendar();
       calendar = ES.ToTemporalCalendar(calendar);
       const fieldNames = ES.CalendarFields(calendar, ['day', 'month']);
       const fields = ES.ToTemporalMonthDayFields(item, fieldNames);
@@ -1122,7 +1121,7 @@ export const ES = ObjectAssign({}, ES2020, {
 
     let { month, day, referenceISOYear, calendar } = ES.ParseTemporalMonthDayString(ES.ToString(item));
     ({ month, day } = ES.RegulateMonthDay(month, day, overflow));
-    if (calendar === undefined) calendar = new (GetIntrinsic('%Temporal.ISO8601Calendar%'))();
+    if (calendar === undefined) calendar = ES.GetISO8601Calendar();
     calendar = ES.ToTemporalCalendar(calendar);
     if (referenceISOYear === undefined) referenceISOYear = 1972;
     let result = new constructor(month, day, calendar, referenceISOYear);
@@ -1133,7 +1132,7 @@ export const ES = ObjectAssign({}, ES2020, {
     if (ES.Type(item) === 'Object') {
       if (ES.IsTemporalTime(item)) return item;
       let calendar = item.calendar;
-      if (calendar === undefined) calendar = new (GetIntrinsic('%Temporal.ISO8601Calendar%'))();
+      if (calendar === undefined) calendar = ES.GetISO8601Calendar();
       calendar = ES.ToTemporalCalendar(calendar);
       const fieldNames = ES.CalendarFields(calendar, [
         'hour',
@@ -1159,7 +1158,7 @@ export const ES = ObjectAssign({}, ES2020, {
       nanosecond,
       overflow
     ));
-    if (calendar === undefined) calendar = new (GetIntrinsic('%Temporal.ISO8601Calendar%'))();
+    if (calendar === undefined) calendar = ES.GetISO8601Calendar();
     calendar = ES.ToTemporalCalendar(calendar);
     let result = new constructor(hour, minute, second, millisecond, microsecond, nanosecond, calendar);
     if (!ES.IsTemporalTime(result)) throw new TypeError('invalid result');
@@ -1169,7 +1168,7 @@ export const ES = ObjectAssign({}, ES2020, {
     if (ES.Type(item) === 'Object') {
       if (ES.IsTemporalYearMonth(item)) return item;
       let calendar = item.calendar;
-      if (calendar === undefined) calendar = new (GetIntrinsic('%Temporal.ISO8601Calendar%'))();
+      if (calendar === undefined) calendar = ES.GetISO8601Calendar();
       calendar = ES.ToTemporalCalendar(calendar);
       const fieldNames = ES.CalendarFields(calendar, ['month', 'year']);
       const fields = ES.ToTemporalYearMonthFields(item, fieldNames);
@@ -1178,7 +1177,7 @@ export const ES = ObjectAssign({}, ES2020, {
 
     let { year, month, referenceISODay = 1, calendar } = ES.ParseTemporalYearMonthString(ES.ToString(item));
     ({ year, month } = ES.RegulateYearMonth(year, month, overflow));
-    if (calendar === undefined) calendar = new (GetIntrinsic('%Temporal.ISO8601Calendar%'))();
+    if (calendar === undefined) calendar = ES.GetISO8601Calendar();
     calendar = ES.ToTemporalCalendar(calendar);
     let result = new constructor(year, month, calendar, referenceISODay);
     if (!ES.IsTemporalYearMonth(result)) throw new TypeError('invalid result');
@@ -1258,7 +1257,7 @@ export const ES = ObjectAssign({}, ES2020, {
     if (ES.Type(item) === 'Object') {
       if (ES.IsTemporalZonedDateTime(item)) return item;
       calendar = item.calendar;
-      if (calendar === undefined) calendar = new (GetIntrinsic('%Temporal.ISO8601Calendar%'))();
+      if (calendar === undefined) calendar = ES.GetISO8601Calendar();
       calendar = ES.ToTemporalCalendar(calendar);
       const fieldNames = ES.CalendarFields(calendar, ['day', 'month', 'year']);
       const fields = ES.ToTemporalZonedDateTimeFields(item, fieldNames);
@@ -1294,7 +1293,7 @@ export const ES = ObjectAssign({}, ES2020, {
       } = ES.ParseTemporalZonedDateTimeString(ES.ToString(item)));
       if (!ianaName) throw new RangeError('time zone ID required in brackets');
       timeZone = ES.TimeZoneFrom(ianaName);
-      if (!calendar) calendar = new (GetIntrinsic('%Temporal.ISO8601Calendar%'))();
+      if (!calendar) calendar = ES.GetISO8601Calendar();
       calendar = ES.ToTemporalCalendar(calendar);
     }
     let offsetNs = null;
@@ -1319,6 +1318,10 @@ export const ES = ObjectAssign({}, ES2020, {
     return result;
   },
 
+  GetISO8601Calendar: () => {
+    const TemporalCalendar = GetIntrinsic('%Temporal.Calendar%');
+    return new TemporalCalendar('iso8601');
+  },
   CalendarFrom: (calendarLike) => {
     const TemporalCalendar = GetIntrinsic('%Temporal.Calendar%');
     let from = TemporalCalendar.from;

diff --git a/polyfill/lib/instant.mjs b/polyfill/lib/instant.mjs
@@ -1,6 +1,5 @@
 /* global __debug__ */
 
-import { GetISO8601Calendar } from './calendar.mjs';
 import { ES } from './ecmascript.mjs';
 import { DateTimeFormat } from './intl.mjs';
 import { GetIntrinsic, MakeIntrinsicClass } from './intrinsicclass.mjs';
@@ -259,7 +258,7 @@ export class Instant {
       }
     }
     const timeZone = ES.ToTemporalTimeZone(item);
-    const calendar = GetISO8601Calendar();
+    const calendar = ES.GetISO8601Calendar();
     const TemporalZonedDateTime = GetIntrinsic('%Temporal.ZonedDateTime%');
     return new TemporalZonedDateTime(GetSlot(this, EPOCHNANOSECONDS), timeZone, calendar);
   }

diff --git a/polyfill/lib/now.mjs b/polyfill/lib/now.mjs
@@ -1,4 +1,3 @@
-import { GetISO8601Calendar } from './calendar.mjs';
 import { ES } from './ecmascript.mjs';
 import { GetIntrinsic } from './intrinsicclass.mjs';
 
@@ -27,7 +26,7 @@ function plainDateTime(calendarLike, temporalTimeZoneLike = timeZone()) {
 }
 function plainDateTimeISO(temporalTimeZoneLike = timeZone()) {
   const timeZone = ES.ToTemporalTimeZone(temporalTimeZoneLike);
-  const calendar = GetISO8601Calendar();
+  const calendar = ES.GetISO8601Calendar();
   const inst = instant();
   return ES.GetTemporalDateTimeFor(timeZone, inst, calendar);
 }
@@ -39,7 +38,7 @@ function zonedDateTime(calendarLike, temporalTimeZoneLike = timeZone()) {
 }
 function zonedDateTimeISO(temporalTimeZoneLike = timeZone()) {
   const timeZone = ES.ToTemporalTimeZone(temporalTimeZoneLike);
-  const calendar = GetISO8601Calendar();
+  const calendar = ES.GetISO8601Calendar();
   const ZonedDateTime = GetIntrinsic('%Temporal.ZonedDateTime%');
   return new ZonedDateTime(ES.SystemUTCEpochNanoSeconds(), timeZone, calendar);
 }

diff --git a/polyfill/lib/plaindate.mjs b/polyfill/lib/plaindate.mjs
@@ -1,6 +1,5 @@
 /* global __debug__ */
 
-import { GetISO8601Calendar } from './calendar.mjs';
 import { ES } from './ecmascript.mjs';
 import { DateTimeFormat } from './intl.mjs';
 import { GetIntrinsic, MakeIntrinsicClass } from './intrinsicclass.mjs';
@@ -34,7 +33,7 @@ function TemporalDateToString(date, showCalendar = 'auto') {
 }
 
 export class PlainDate {
-  constructor(isoYear, isoMonth, isoDay, calendar = GetISO8601Calendar()) {
+  constructor(isoYear, isoMonth, isoDay, calendar = ES.GetISO8601Calendar()) {
     isoYear = ES.ToInteger(isoYear);
     isoMonth = ES.ToInteger(isoMonth);
     isoDay = ES.ToInteger(isoDay);

diff --git a/polyfill/lib/plaindatetime.mjs b/polyfill/lib/plaindatetime.mjs
@@ -1,6 +1,5 @@
 /* global __debug__ */
 
-import { GetISO8601Calendar } from './calendar.mjs';
 import { ES } from './ecmascript.mjs';
 import { DateTimeFormat } from './intl.mjs';
 import { GetIntrinsic, MakeIntrinsicClass } from './intrinsicclass.mjs';
@@ -75,7 +74,7 @@ export class PlainDateTime {
     millisecond = 0,
     microsecond = 0,
     nanosecond = 0,
-    calendar = GetISO8601Calendar()
+    calendar = ES.GetISO8601Calendar()
   ) {
     isoYear = ES.ToInteger(isoYear);
     isoMonth = ES.ToInteger(isoMonth);

diff --git a/polyfill/lib/plainmonthday.mjs b/polyfill/lib/plainmonthday.mjs
@@ -1,6 +1,5 @@
 /* global __debug__ */
 
-import { GetISO8601Calendar } from './calendar.mjs';
 import { ES } from './ecmascript.mjs';
 import { DateTimeFormat } from './intl.mjs';
 import { GetIntrinsic, MakeIntrinsicClass } from './intrinsicclass.mjs';
@@ -24,7 +23,7 @@ function MonthDayToString(monthDay, showCalendar = 'auto') {
 }
 
 export class PlainMonthDay {
-  constructor(isoMonth, isoDay, calendar = GetISO8601Calendar(), referenceISOYear = 1972) {
+  constructor(isoMonth, isoDay, calendar = ES.GetISO8601Calendar(), referenceISOYear = 1972) {
     isoMonth = ES.ToInteger(isoMonth);
     isoDay = ES.ToInteger(isoDay);
     calendar = ES.ToTemporalCalendar(calendar);

diff --git a/polyfill/lib/plaintime.mjs b/polyfill/lib/plaintime.mjs
@@ -1,6 +1,5 @@
 /* global __debug__ */
 
-import { GetISO8601Calendar } from './calendar.mjs';
 import { ES } from './ecmascript.mjs';
 import { DateTimeFormat } from './intl.mjs';
 import { GetIntrinsic, MakeIntrinsicClass } from './intrinsicclass.mjs';
@@ -63,7 +62,7 @@ export class PlainTime {
     isoMillisecond = 0,
     isoMicrosecond = 0,
     isoNanosecond = 0,
-    calendar = GetISO8601Calendar()
+    calendar = ES.GetISO8601Calendar()
   ) {
     isoHour = ES.ToInteger(isoHour);
     isoMinute = ES.ToInteger(isoMinute);

diff --git a/polyfill/lib/plainyearmonth.mjs b/polyfill/lib/plainyearmonth.mjs
@@ -1,6 +1,5 @@
 /* global __debug__ */
 
-import { GetISO8601Calendar } from './calendar.mjs';
 import { ES } from './ecmascript.mjs';
 import { DateTimeFormat } from './intl.mjs';
 import { GetIntrinsic, MakeIntrinsicClass } from './intrinsicclass.mjs';
@@ -24,7 +23,7 @@ function YearMonthToString(yearMonth, showCalendar = 'auto') {
 }
 
 export class PlainYearMonth {
-  constructor(isoYear, isoMonth, calendar = GetISO8601Calendar(), referenceISODay = 1) {
+  constructor(isoYear, isoMonth, calendar = ES.GetISO8601Calendar(), referenceISODay = 1) {
     isoYear = ES.ToInteger(isoYear);
     isoMonth = ES.ToInteger(isoMonth);
     calendar = ES.ToTemporalCalendar(calendar);

diff --git a/polyfill/lib/timezone.mjs b/polyfill/lib/timezone.mjs
@@ -1,6 +1,5 @@
 /* global __debug__ */
 
-import { GetISO8601Calendar } from './calendar.mjs';
 import { ES } from './ecmascript.mjs';
 import { GetIntrinsic, MakeIntrinsicClass, DefineIntrinsic } from './intrinsicclass.mjs';
 import {
@@ -62,7 +61,7 @@ export class TimeZone {
     const offsetNs = ES.GetOffsetNanosecondsFor(this, instant);
     return ES.FormatTimeZoneOffsetString(offsetNs);
   }
-  getPlainDateTimeFor(instant, calendar = GetISO8601Calendar()) {
+  getPlainDateTimeFor(instant, calendar = ES.GetISO8601Calendar()) {
     instant = ES.ToTemporalInstant(instant, GetIntrinsic('%Temporal.Instant%'));
     calendar = ES.ToTemporalCalendar(calendar);
 

diff --git a/polyfill/lib/zoneddatetime.mjs b/polyfill/lib/zoneddatetime.mjs
@@ -1,6 +1,5 @@
 /* global __debug__ */
 
-import { GetISO8601Calendar } from './calendar.mjs';
 import { ES } from './ecmascript.mjs';
 import { DateTimeFormat } from './intl.mjs';
 import { GetIntrinsic, MakeIntrinsicClass } from './intrinsicclass.mjs';
@@ -29,7 +28,7 @@ const ArrayPrototypePush = Array.prototype.push;
 const ObjectAssign = Object.assign;
 
 export class ZonedDateTime {
-  constructor(epochNanoseconds, timeZone, calendar = GetISO8601Calendar()) {
+  constructor(epochNanoseconds, timeZone, calendar = ES.GetISO8601Calendar()) {
     epochNanoseconds = ES.ToBigInt(epochNanoseconds);
     timeZone = ES.ToTemporalTimeZone(timeZone);
     calendar = ES.ToTemporalCalendar(calendar);

diff --git a/polyfill/test/regex.mjs b/polyfill/test/regex.mjs
@@ -1,5 +1,5 @@
 import Demitasse from '@pipobscure/demitasse';
-const { describe, it, report } = Demitasse;
+const { after, before, describe, it, report } = Demitasse;
 
 import Pretty from '@pipobscure/demitasse-pretty';
 const { reporter } = Pretty;
@@ -649,30 +649,35 @@ describe('fromString regex', () => {
   });
 
   describe('calendar ID', () => {
-    function makeCustomCalendar(id) {
-      return class extends Temporal.Calendar {
-        constructor() {
-          super(id);
-        }
+    let oldTemporalCalendarFrom = Temporal.Calendar.from;
+    let fromCalledWith;
+    before(() => {
+      Temporal.Calendar.from = function (item) {
+        fromCalledWith = item;
+        return new Temporal.Calendar('iso8601');
       };
+    });
+    function testCalendarID(id) {
+      return Temporal.PlainDateTime.from(`1970-01-01T00:00[c=${id}]`);
     }
     describe('valid', () => {
       ['aaa', 'aaa-aaa', 'eightZZZ', 'eightZZZ-eightZZZ'].forEach((id) => {
         it(id, () => {
-          const Custom = makeCustomCalendar(id);
-          const calendar = new Custom();
-          equal(calendar.id, id);
+          testCalendarID(id);
+          equal(fromCalledWith, id);
         });
       });
     });
     describe('not valid', () => {
       ['a', 'a-a', 'aa', 'aa-aa', 'foo_', 'foo.', 'ninechars', 'ninechars-ninechars'].forEach((id) => {
         it(id, () => {
-          const Custom = makeCustomCalendar(id);
-          throws(() => new Custom(), RangeError);
+          throws(() => testCalendarID(id), RangeError);
         });
       });
     });
+    after(() => {
+      Temporal.Calendar.from = oldTemporalCalendarFrom;
+    });
   });
 });