Normative: Look up time zone methods only once

Introduce a new spec type, Time Zone Record, which stores a time zone
object's getOffsetNanosecondsFor and getPossibleInstantsFor methods once
they have been observably looked up. The record is passed around into
abstract operations instead of the time zone object itself

Most API operations that do time zone calculations need to look up both
getOffsetNanosecondsFor and getPossibleInstantsFor unconditionally. Only
in the case where we convert a plain time to an exact time, it's possible
we only need to look up getPossibleInstantsFor, or neither (if the offset
is supplied.)

This is a large commit but most of it is mechanical replacement of
Temporal.TimeZone variables with Time Zone Record variables.

Author: ptomato

polyfill/lib/duration.mjs

@@ -15,7 +15,6 @@ import {
   NANOSECONDS,
   CALENDAR,
   INSTANT,
-  TIME_ZONE,
   CreateSlots,
   GetSlot,
   SetSlot
@@ -236,7 +235,7 @@ export class Duration {
     }
 
     let largestUnit = ES.GetTemporalUnit(roundTo, 'largestUnit', 'datetime', undefined, ['auto']);
-    let relativeTo = ES.ToRelativeTemporalObject(roundTo);
+    const { relativeTo, timeZoneRec } = ES.ToRelativeTemporalObject(roundTo);
     const roundingIncrement = ES.ToTemporalRoundingIncrement(roundTo);
     const roundingMode = ES.ToTemporalRoundingMode(roundTo, 'halfExpand');
     let smallestUnit = ES.GetTemporalUnit(roundTo, 'smallestUnit', 'datetime', undefined);
@@ -301,7 +300,12 @@ export class Duration {
     if (zonedRelativeTo && plainRelativeToWillBeUsed) {
       // Convert a ZonedDateTime relativeTo to PlainDate only if needed in one
       // of the operations below, because the conversion is user visible
-      plainRelativeTo = ES.ToTemporalDate(zonedRelativeTo);
+      const dt = ES.GetPlainDateTimeFor(
+        timeZoneRec,
+        GetSlot(zonedRelativeTo, INSTANT),
+        GetSlot(zonedRelativeTo, CALENDAR)
+      );
+      plainRelativeTo = ES.TemporalDateTimeToDate(dt);
     }
 
     ({ years, months, weeks, days } = ES.UnbalanceDurationRelative(
@@ -328,7 +332,8 @@ export class Duration {
         smallestUnit,
         roundingMode,
         plainRelativeTo,
-        zonedRelativeTo
+        zonedRelativeTo,
+        timeZoneRec
       ));
     if (zonedRelativeTo) {
       ({ years, months, weeks, days, hours, minutes, seconds, milliseconds, microseconds, nanoseconds } =
@@ -346,7 +351,8 @@ export class Duration {
           roundingIncrement,
           smallestUnit,
           roundingMode,
-          zonedRelativeTo
+          zonedRelativeTo,
+          timeZoneRec
         ));
     }
     ({ days, hours, minutes, seconds, milliseconds, microseconds, nanoseconds } = ES.BalanceDuration(
@@ -358,7 +364,8 @@ export class Duration {
       microseconds,
       nanoseconds,
       largestUnit,
-      zonedRelativeTo
+      zonedRelativeTo,
+      timeZoneRec
     ));
     ({ years, months, weeks, days } = ES.BalanceDurationRelative(
       years,
@@ -392,7 +399,7 @@ export class Duration {
     } else {
       totalOf = ES.GetOptionsObject(totalOf);
     }
-    const relativeTo = ES.ToRelativeTemporalObject(totalOf);
+    const { relativeTo, timeZoneRec } = ES.ToRelativeTemporalObject(totalOf);
     const unit = ES.GetTemporalUnit(totalOf, 'unit', 'datetime', ES.REQUIRED);
 
     let zonedRelativeTo = ES.IsTemporalZonedDateTime(relativeTo) ? relativeTo : undefined;
@@ -402,15 +409,20 @@ export class Duration {
     if (zonedRelativeTo !== undefined && plainRelativeToWillBeUsed) {
       // Convert a ZonedDateTime relativeTo to PlainDate only if needed in one
       // of the operations below, because the conversion is user visible
-      plainRelativeTo = ES.ToTemporalDate(zonedRelativeTo);
+      const dt = ES.GetPlainDateTimeFor(
+        timeZoneRec,
+        GetSlot(zonedRelativeTo, INSTANT),
+        GetSlot(zonedRelativeTo, CALENDAR)
+      );
+      plainRelativeTo = ES.TemporalDateTimeToDate(dt);
     }
 
     // Convert larger units down to days
     ({ years, months, weeks, days } = ES.UnbalanceDurationRelative(years, months, weeks, days, unit, plainRelativeTo));
     // If the unit we're totalling is smaller than `days`, convert days down to that unit.
     let intermediate;
     if (zonedRelativeTo) {
-      intermediate = ES.MoveRelativeZonedDateTime(zonedRelativeTo, years, months, weeks, 0);
+      intermediate = ES.MoveRelativeZonedDateTime(zonedRelativeTo, timeZoneRec, years, months, weeks, 0);
     }
     let balanceResult = ES.BalancePossiblyInfiniteDuration(
       days,
@@ -421,7 +433,8 @@ export class Duration {
       microseconds,
       nanoseconds,
       unit,
-      intermediate
+      intermediate,
+      timeZoneRec
     );
     if (balanceResult === 'positive overflow') {
       return Infinity;
@@ -445,7 +458,8 @@ export class Duration {
       unit,
       'trunc',
       plainRelativeTo,
-      zonedRelativeTo
+      zonedRelativeTo,
+      timeZoneRec
     );
     return total;
   }
@@ -532,19 +546,18 @@ export class Duration {
     ) {
       return 0;
     }
-    const relativeTo = ES.ToRelativeTemporalObject(options);
+    const { relativeTo, timeZoneRec } = ES.ToRelativeTemporalObject(options);
 
     const calendarUnitsPresent = y1 !== 0 || y2 !== 0 || mon1 !== 0 || mon2 !== 0 || w1 !== 0 || w2 !== 0;
 
     if (ES.IsTemporalZonedDateTime(relativeTo) && (calendarUnitsPresent || d1 != 0 || d2 !== 0)) {
       const instant = GetSlot(relativeTo, INSTANT);
-      const timeZone = GetSlot(relativeTo, TIME_ZONE);
       const calendar = GetSlot(relativeTo, CALENDAR);
-      const precalculatedDateTime = ES.GetPlainDateTimeFor(timeZone, instant, calendar);
+      const precalculatedDateTime = ES.GetPlainDateTimeFor(timeZoneRec, instant, calendar);
 
       const after1 = ES.AddZonedDateTime(
         instant,
-        timeZone,
+        timeZoneRec,
         calendar,
         y1,
         mon1,
@@ -560,7 +573,7 @@ export class Duration {
       );
       const after2 = ES.AddZonedDateTime(
         instant,
-        timeZone,
+        timeZoneRec,
         calendar,
         y2,
         mon2,