Normative: Remove Plain/ZonedDateTime to PlainYearMonth/MonthDay APIs

Closes: #2848

docs/plaindatetime.md

@@ -986,29 +986,23 @@ If the result is earlier or later than the range that `Temporal.ZonedDateTime` c
 
 **Returns:** a `Temporal.PlainDate` object that is the same as the date portion of `datetime`.
 
-### datetime.**toPlainYearMonth**() : Temporal.PlainYearMonth
-
-**Returns:** a `Temporal.PlainYearMonth` object that is the same as the year and month of `datetime`.
-
-### datetime.**toPlainMonthDay**() : Temporal.PlainMonthDay
-
-**Returns:** a `Temporal.PlainMonthDay` object that is the same as the month and day of `datetime`.
-
 ### datetime.**toPlainTime**() : Temporal.PlainTime
 
 **Returns:** a `Temporal.PlainTime` object that is the same as the wall-clock time portion of `datetime`.
 
-The above four methods can be used to convert `Temporal.PlainDateTime` into a `Temporal.PlainDate`, `Temporal.PlainYearMonth`, `Temporal.PlainMonthDay`, or `Temporal.PlainTime` respectively.
+The above two methods can be used to convert `Temporal.PlainDateTime` into a `Temporal.PlainDate` or `Temporal.PlainTime` respectively.
 The converted object carries a copy of all the relevant fields of `datetime` (for example, in `toPlainDate()`, the `year`, `month`, and `day` properties are copied.)
 
+To convert to `Temporal.PlainYearMonth` or `Temporal.PlainMonthDay`, first use `toPlainDate()` and go from there.
+
 Usage example:
 
 ```javascript
 dt = Temporal.PlainDateTime.from('1995-12-07T03:24:30.000003500');
 dt.toPlainDate(); // => 1995-12-07
-dt.toPlainYearMonth(); // => 1995-12
-dt.toPlainMonthDay(); // => 12-07
 dt.toPlainTime(); // => 03:24:30.0000035
+dt.toPlainDate().toPlainYearMonth(); // => 1995-12
+dt.toPlainDate().toPlainMonthDay(); // => 12-07
 ```
 
 ### datetime.**getCalendar**(): object

docs/zoneddatetime.md

@@ -1355,27 +1355,21 @@ Use `Temporal.ZonedDateTime.compare()` for this, or `zonedDateTime.equals()` for
 > However, unless you perform those operations across a time zone offset transition, it's impossible to notice the difference.
 > Therefore, be very careful when performing this conversion because subsequent results may look correct most of the time while failing around time zone transitions like when DST starts or ends.
 
-### zonedDateTime.**toPlainYearMonth**() : Temporal.PlainYearMonth
-
-**Returns:** a `Temporal.PlainYearMonth` object that is the same as the year and month of `zonedDateTime`.
-
-### zonedDateTime.**toPlainMonthDay**() : Temporal.PlainMonthDay
-
-**Returns:** a `Temporal.PlainMonthDay` object that is the same as the month and day of `zonedDateTime`.
-
-The above six methods can be used to convert `Temporal.ZonedDateTime` into a `Temporal.Instant`, `Temporal.PlainDate`, `Temporal.PlainTime`, `Temporal.PlainDateTime`, `Temporal.PlainYearMonth`, or `Temporal.PlainMonthDay` respectively.
+The above four methods can be used to convert `Temporal.ZonedDateTime` into a `Temporal.Instant`, `Temporal.PlainDate`, `Temporal.PlainTime`, or `Temporal.PlainDateTime`, respectively.
 The converted object carries a copy of all the relevant data of `zonedDateTime` (for example, in `toPlainDate()`, the `year`, `month`, and `day` properties are the same.)
 
+To convert to `Temporal.PlainYearMonth` or `Temporal.PlainMonthDay`, first use `toPlainDate()` and go from there.
+
 Usage example:
 
 ```javascript
 zdt = Temporal.ZonedDateTime.from('1995-12-07T03:24:30+02:00[Africa/Johannesburg]');
 zdt.toInstant(); // => 1995-12-07T01:24:30Z
 zdt.toPlainDateTime(); // => 1995-12-07T03:24:30
 zdt.toPlainDate(); // => 1995-12-07
-zdt.toPlainYearMonth(); // => 1995-12
-zdt.toPlainMonthDay(); // => 12-07
 zdt.toPlainTime(); // => 03:24:30
+zdt.toPlainDate().toPlainYearMonth(); // => 1995-12
+zdt.toPlainDate().toPlainMonthDay(); // => 12-07
 ```
 
 ### zonedDateTime.**getCalendar**(): object

polyfill/index.d.ts

@@ -960,8 +960,6 @@ export namespace Temporal {
     ): Temporal.PlainDateTime;
     toZonedDateTime(tzLike: TimeZoneLike, options?: ToInstantOptions): Temporal.ZonedDateTime;
     toPlainDate(): Temporal.PlainDate;
-    toPlainYearMonth(): Temporal.PlainYearMonth;
-    toPlainMonthDay(): Temporal.PlainMonthDay;
     toPlainTime(): Temporal.PlainTime;
     getISOFields(): PlainDateTimeISOFields;
     toLocaleString(locales?: string | string[], options?: Intl.DateTimeFormatOptions): string;
@@ -1306,8 +1304,6 @@ export namespace Temporal {
     toInstant(): Temporal.Instant;
     toPlainDateTime(): Temporal.PlainDateTime;
     toPlainDate(): Temporal.PlainDate;
-    toPlainYearMonth(): Temporal.PlainYearMonth;
-    toPlainMonthDay(): Temporal.PlainMonthDay;
     toPlainTime(): Temporal.PlainTime;
     getISOFields(): ZonedDateTimeISOFields;
     toLocaleString(locales?: string | string[], options?: Intl.DateTimeFormatOptions): string;

polyfill/lib/plaindatetime.mjs

@@ -379,18 +379,6 @@ export class PlainDateTime {
     if (!ES.IsTemporalDateTime(this)) throw new TypeError('invalid receiver');
     return ES.TemporalDateTimeToDate(this);
   }
-  toPlainYearMonth() {
-    if (!ES.IsTemporalDateTime(this)) throw new TypeError('invalid receiver');
-    const calendarRec = new CalendarMethodRecord(GetSlot(this, CALENDAR), ['fields', 'yearMonthFromFields']);
-    const fields = ES.PrepareCalendarFields(calendarRec, this, ['monthCode', 'year'], [], []);
-    return ES.CalendarYearMonthFromFields(calendarRec, fields);
-  }
-  toPlainMonthDay() {
-    if (!ES.IsTemporalDateTime(this)) throw new TypeError('invalid receiver');
-    const calendarRec = new CalendarMethodRecord(GetSlot(this, CALENDAR), ['fields', 'monthDayFromFields']);
-    const fields = ES.PrepareCalendarFields(calendarRec, this, ['day', 'monthCode'], [], []);
-    return ES.CalendarMonthDayFromFields(calendarRec, fields);
-  }
   toPlainTime() {
     if (!ES.IsTemporalDateTime(this)) throw new TypeError('invalid receiver');
     return ES.TemporalDateTimeToTime(this);

polyfill/lib/zoneddatetime.mjs

@@ -557,20 +557,6 @@ export class ZonedDateTime {
     if (!ES.IsTemporalZonedDateTime(this)) throw new TypeError('invalid receiver');
     return dateTime(this);
   }
-  toPlainYearMonth() {
-    if (!ES.IsTemporalZonedDateTime(this)) throw new TypeError('invalid receiver');
-    const calendarRec = new CalendarMethodRecord(GetSlot(this, CALENDAR), ['fields', 'yearMonthFromFields']);
-    const dt = dateTime(this);
-    const fields = ES.PrepareCalendarFields(calendarRec, dt, ['monthCode', 'year'], [], []);
-    return ES.CalendarYearMonthFromFields(calendarRec, fields);
-  }
-  toPlainMonthDay() {
-    if (!ES.IsTemporalZonedDateTime(this)) throw new TypeError('invalid receiver');
-    const calendarRec = new CalendarMethodRecord(GetSlot(this, CALENDAR), ['fields', 'monthDayFromFields']);
-    const dt = dateTime(this);
-    const fields = ES.PrepareCalendarFields(calendarRec, dt, ['day', 'monthCode'], [], []);
-    return ES.CalendarMonthDayFromFields(calendarRec, fields);
-  }
   getISOFields() {
     if (!ES.IsTemporalZonedDateTime(this)) throw new TypeError('invalid receiver');
     const timeZoneRec = new TimeZoneMethodRecord(GetSlot(this, TIME_ZONE), ['getOffsetNanosecondsFor']);

spec/plaindatetime.html

@@ -672,36 +672,6 @@ <h1>Temporal.PlainDateTime.prototype.toPlainDate ( )</h1>
       </emu-alg>
     </emu-clause>
 
-    <emu-clause id="sec-temporal.plaindatetime.prototype.toplainyearmonth">
-      <h1>Temporal.PlainDateTime.prototype.toPlainYearMonth ( )</h1>
-      <p>
-        This method performs the following steps when called:
-      </p>
-      <emu-alg>
-        1. Let _dateTime_ be the *this* value.
-        1. Perform ? RequireInternalSlot(_dateTime_, [[InitializedTemporalDateTime]]).
-        1. Let _calendarRec_ be ? CreateCalendarMethodsRecord(_dateTime_.[[Calendar]], « ~fields~, ~year-month-from-fields~ »).
-        1. Let _fields_ be ? PrepareCalendarFields(_calendarRec_, _dateTime_, « *"monthCode"*, *"year"* », «», «»).
-        1. Return ? CalendarYearMonthFromFields(_calendarRec_, _fields_).
-        1. NOTE: The call to CalendarYearMonthFromFields is necessary in order to create a PlainYearMonth object with the [[ISOYear]], [[ISOMonth]], and [[ISODay]] internal slots set correctly.
-      </emu-alg>
-    </emu-clause>
-
-    <emu-clause id="sec-temporal.plaindatetime.prototype.toplainmonthday">
-      <h1>Temporal.PlainDateTime.prototype.toPlainMonthDay ( )</h1>
-      <p>
-        This method performs the following steps when called:
-      </p>
-      <emu-alg>
-        1. Let _dateTime_ be the *this* value.
-        1. Perform ? RequireInternalSlot(_dateTime_, [[InitializedTemporalDateTime]]).
-        1. Let _calendarRec_ be ? CreateCalendarMethodsRecord(_dateTime_.[[Calendar]], « ~fields~, ~month-day-from-fields~ »).
-        1. Let _fields_ be ? PrepareCalendarFields(_calendarRec_, _dateTime_, « *"day"*, *"monthCode"* », «», «»).
-        1. Return ? CalendarMonthDayFromFields(_calendarRec_, _fields_).
-        1. NOTE: The call to CalendarMonthDayFromFields is necessary in order to create a PlainMonthDay object with the [[ISOYear]], [[ISOMonth]], and [[ISODay]] internal slots set correctly.
-      </emu-alg>
-    </emu-clause>
-
     <emu-clause id="sec-temporal.plaindatetime.prototype.toplaintime">
       <h1>Temporal.PlainDateTime.prototype.toPlainTime ( )</h1>
       <p>

spec/zoneddatetime.html

@@ -934,42 +934,6 @@ <h1>Temporal.ZonedDateTime.prototype.toPlainDateTime ( )</h1>
       </emu-alg>
     </emu-clause>
 
-    <emu-clause id="sec-temporal.zoneddatetime.prototype.toplainyearmonth">
-      <h1>Temporal.ZonedDateTime.prototype.toPlainYearMonth ( )</h1>
-      <p>
-        This method performs the following steps when called:
-      </p>
-      <emu-alg>
-        1. Let _zonedDateTime_ be the *this* value.
-        1. Perform ? RequireInternalSlot(_zonedDateTime_, [[InitializedTemporalZonedDateTime]]).
-        1. Let _calendarRec_ be ? CreateCalendarMethodsRecord(_zonedDateTime_.[[Calendar]], « ~fields~, ~year-month-from-fields~ »).
-        1. Let _timeZoneRec_ be ? CreateTimeZoneMethodsRecord(_zonedDateTime_.[[TimeZone]], « ~get-offset-nanoseconds-for~ »).
-        1. Let _instant_ be ! CreateTemporalInstant(_zonedDateTime_.[[Nanoseconds]]).
-        1. Let _temporalDateTime_ be ? GetPlainDateTimeFor(_timeZoneRec_, _instant_, _calendarRec_.[[Receiver]]).
-        1. Let _fields_ be ? PrepareCalendarFields(_calendarRec_, _temporalDateTime_, « *"monthCode"*, *"year"* », «», «»).
-        1. Return ? CalendarYearMonthFromFields(_calendarRec_, _fields_).
-        1. NOTE: The call to CalendarYearMonthFromFields is necessary in order to create a PlainYearMonth object with the [[ISOYear]], [[ISOMonth]], and [[ISODay]] internal slots set correctly.
-      </emu-alg>
-    </emu-clause>
-
-    <emu-clause id="sec-temporal.zoneddatetime.prototype.toplainmonthday">
-      <h1>Temporal.ZonedDateTime.prototype.toPlainMonthDay ( )</h1>
-      <p>
-        This method performs the following steps when called:
-      </p>
-      <emu-alg>
-        1. Let _zonedDateTime_ be the *this* value.
-        1. Perform ? RequireInternalSlot(_zonedDateTime_, [[InitializedTemporalZonedDateTime]]).
-        1. Let _calendarRec_ be ? CreateCalendarMethodsRecord(_zonedDateTime_.[[Calendar]], « ~fields~, ~month-day-from-fields~ »).
-        1. Let _timeZoneRec_ be ? CreateTimeZoneMethodsRecord(_zonedDateTime_.[[TimeZone]], « ~get-offset-nanoseconds-for~ »).
-        1. Let _instant_ be ! CreateTemporalInstant(_zonedDateTime_.[[Nanoseconds]]).
-        1. Let _temporalDateTime_ be ? GetPlainDateTimeFor(_timeZoneRec_, _instant_, _calendarRec_.[[Receiver]]).
-        1. Let _fields_ be ? PrepareCalendarFields(_calendarRec_, _temporalDateTime_, « *"day"*, *"monthCode"* », «», «»).
-        1. Return ? CalendarMonthDayFromFields(_calendarRec_, _fields_).
-        1. NOTE: The call to CalendarMonthDayFromFields is necessary in order to create a PlainMonthDay object with the [[ISOYear]], [[ISOMonth]], and [[ISODay]] internal slots set correctly.
-      </emu-alg>
-    </emu-clause>
-
     <emu-clause id="sec-temporal.zoneddatetime.prototype.getisofields">
       <h1>Temporal.ZonedDateTime.prototype.getISOFields ( )</h1>
       <p>