Editorial: Return ISO Date-Time Record from SystemDateTime

This avoids creation of an unobservable Temporal.PlainDateTime object, and
is also simpler to read.

See: #2949

polyfill/lib/now.mjs

@@ -2,26 +2,33 @@ import { ObjectDefineProperty, SymbolToStringTag } from './primordials.mjs';
 
 import * as ES from './ecmascript.mjs';
 import { GetIntrinsic } from './intrinsicclass.mjs';
-import { GetSlot, ISO_DATE_TIME } from './slots.mjs';
+
+function SystemDateTime(timeZone) {
+  return ES.GetISODateTimeFor(timeZone, ES.SystemUTCEpochNanoSeconds());
+}
 
 const instant = () => {
   const Instant = GetIntrinsic('%Temporal.Instant%');
   return new Instant(ES.SystemUTCEpochNanoSeconds());
 };
 const plainDateTimeISO = (temporalTimeZoneLike = ES.DefaultTimeZone()) => {
   const timeZone = ES.ToTemporalTimeZoneIdentifier(temporalTimeZoneLike);
-  const isoDateTime = ES.GetISODateTimeFor(timeZone, ES.SystemUTCEpochNanoSeconds());
+  const isoDateTime = SystemDateTime(timeZone);
   return ES.CreateTemporalDateTime(isoDateTime, 'iso8601');
 };
 const zonedDateTimeISO = (temporalTimeZoneLike = ES.DefaultTimeZone()) => {
   const timeZone = ES.ToTemporalTimeZoneIdentifier(temporalTimeZoneLike);
   return ES.CreateTemporalZonedDateTime(ES.SystemUTCEpochNanoSeconds(), timeZone, 'iso8601');
 };
 const plainDateISO = (temporalTimeZoneLike = ES.DefaultTimeZone()) => {
-  return ES.CreateTemporalDate(GetSlot(plainDateTimeISO(temporalTimeZoneLike), ISO_DATE_TIME).isoDate, 'iso8601');
+  const timeZone = ES.ToTemporalTimeZoneIdentifier(temporalTimeZoneLike);
+  const isoDateTime = SystemDateTime(timeZone);
+  return ES.CreateTemporalDate(isoDateTime.isoDate, 'iso8601');
 };
 const plainTimeISO = (temporalTimeZoneLike = ES.DefaultTimeZone()) => {
-  return ES.CreateTemporalTime(GetSlot(plainDateTimeISO(temporalTimeZoneLike), ISO_DATE_TIME).time);
+  const timeZone = ES.ToTemporalTimeZoneIdentifier(temporalTimeZoneLike);
+  const isoDateTime = SystemDateTime(timeZone);
+  return ES.CreateTemporalTime(isoDateTime.time);
 };
 const timeZoneId = () => {
   return ES.DefaultTimeZone();

spec/temporal.html

@@ -122,7 +122,8 @@ <h1>Temporal.Now.instant ( )</h1>
       <h1>Temporal.Now.plainDateTimeISO ( [ _temporalTimeZoneLike_ ] )</h1>
       <p>This function performs the following steps when called:</p>
       <emu-alg>
-        1. Return ? SystemDateTime(_temporalTimeZoneLike_).
+        1. Let _isoDateTime_ be ? SystemDateTime(_temporalTimeZoneLike_).
+        1. Return ! CreateTemporalDateTime(_isoDateTime_, *"iso8601"*).
       </emu-alg>
     </emu-clause>
 
@@ -138,17 +139,17 @@ <h1>Temporal.Now.zonedDateTimeISO ( [ _temporalTimeZoneLike_ ] )</h1>
       <h1>Temporal.Now.plainDateISO ( [ _temporalTimeZoneLike_ ] )</h1>
       <p>This function performs the following steps when called:</p>
       <emu-alg>
-        1. Let _dateTime_ be ? SystemDateTime(_temporalTimeZoneLike_).
-        1. Return ! CreateTemporalDate(_dateTime_.[[ISODateTime]].[[ISODate]], *"iso8601"*).
+        1. Let _isoDateTime_ be ? SystemDateTime(_temporalTimeZoneLike_).
+        1. Return ! CreateTemporalDate(_isoDateTime_.[[ISODate]], *"iso8601"*).
       </emu-alg>
     </emu-clause>
 
     <emu-clause id="sec-temporal.now.plaintimeiso">
       <h1>Temporal.Now.plainTimeISO ( [ _temporalTimeZoneLike_ ] )</h1>
       <p>This function performs the following steps when called:</p>
       <emu-alg>
-        1. Let _dateTime_ be ? SystemDateTime(_temporalTimeZoneLike_).
-        1. Return ! CreateTemporalTime(_dateTime_.[[ISODateTime]].[[Time]]).
+        1. Let _isoDateTime_ be ? SystemDateTime(_temporalTimeZoneLike_).
+        1. Return ! CreateTemporalTime(_isoDateTime_.[[Time]]).
       </emu-alg>
     </emu-clause>
   </emu-clause>
@@ -230,7 +231,7 @@ <h1>SystemInstant ( ): a Temporal.Instant</h1>
       <h1>
         SystemDateTime (
           _temporalTimeZoneLike_: an ECMAScript language value,
-        ): either a normal completion containing a Temporal.PlainDateTime or a throw completion
+        ): either a normal completion containing an ISO Date-Time Record or a throw completion
       </h1>
       <dl class="header">
         <dt>description</dt>
@@ -242,8 +243,7 @@ <h1>
         1. Else,
           1. Let _timeZone_ be ? ToTemporalTimeZoneIdentifier(_temporalTimeZoneLike_).
         1. Let _epochNs_ be SystemUTCEpochNanoseconds().
-        1. Let _isoDateTime_ be GetISODateTimeFor(_timeZone_, _epochNs_).
-        1. Return ! CreateTemporalDateTime(_isoDateTime_, *"iso8601"*).
+        1. Return GetISODateTimeFor(_timeZone_, _epochNs_).
       </emu-alg>
     </emu-clause>