Normative: Separate zoned and plain operations in RoundDuration

This converts a ZonedDateTime relativeTo into a PlainDateTime relativeTo only when necessary, only after potentially throwing other errors, and only once. Previously, it could be converted up to a few separate times in each operation, such as UnbalanceDurationRelative, RoundDuration, and BalanceDurationRelative. Since the conversion is user-visible, we don't want to perform it when not necessary or perform it more times than necessary. Closes: #2247 Closes: #2529
tc39 · Aug 22, 2023 · 4b7e274 · 4b7e274
1 parent aaba929
commit 4b7e274
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Showing 4 changed files with 309 additions and 171 deletions.
diff --git a/polyfill/lib/duration.mjs b/polyfill/lib/duration.mjs
@@ -279,12 +279,15 @@ export class Duration {
     const maximum = maximumIncrements[smallestUnit];
     if (maximum !== undefined) ES.ValidateTemporalRoundingIncrement(roundingIncrement, maximum, false);
 
+    let zonedRelativeTo = ES.IsTemporalZonedDateTime(relativeTo) ? relativeTo : undefined;
+    let plainRelativeTo = ES.IsTemporalDate(relativeTo) ? relativeTo : undefined;
+
     const roundingGranularityIsNoop = smallestUnit === 'nanosecond' && roundingIncrement === 1;
     const balancingRequested = largestUnit !== existingLargestUnit;
     const calendarUnitsPresent = years !== 0 || months !== 0 || weeks !== 0;
     const timeUnitsOverflowWillOccur =
       minutes >= 60 || seconds >= 60 || milliseconds >= 1000 || microseconds >= 1000 || nanoseconds >= 1000;
-    const hoursToDaysConversionMayOccur = (days !== 0 && ES.IsTemporalZonedDateTime(relativeTo)) || hours >= 24;
+    const hoursToDaysConversionMayOccur = (days !== 0 && zonedRelativeTo) || hours >= 24;
     if (
       roundingGranularityIsNoop &&
       !balancingRequested &&
@@ -295,13 +298,27 @@ export class Duration {
       return new Duration(years, months, weeks, days, hours, minutes, seconds, milliseconds, microseconds, nanoseconds);
     }
 
+    const plainRelativeToWillBeUsed =
+      smallestUnit === 'year' ||
+      smallestUnit === 'month' ||
+      smallestUnit === 'week' ||
+      years !== 0 ||
+      months !== 0 ||
+      weeks !== 0 ||
+      days !== 0;
+    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);
+    }
+
     ({ years, months, weeks, days } = ES.UnbalanceDateDurationRelative(
       years,
       months,
       weeks,
       days,
       largestUnit,
-      relativeTo
+      plainRelativeTo
     ));
     ({ years, months, weeks, days, hours, minutes, seconds, milliseconds, microseconds, nanoseconds } =
       ES.RoundDuration(
@@ -318,9 +335,10 @@ export class Duration {
         roundingIncrement,
         smallestUnit,
         roundingMode,
-        relativeTo
+        plainRelativeTo,
+        zonedRelativeTo
       ));
-    if (ES.IsTemporalZonedDateTime(relativeTo)) {
+    if (zonedRelativeTo) {
       ({ years, months, weeks, days, hours, minutes, seconds, milliseconds, microseconds, nanoseconds } =
         ES.AdjustRoundedDurationDays(
           years,
@@ -336,7 +354,7 @@ export class Duration {
           roundingIncrement,
           smallestUnit,
           roundingMode,
-          relativeTo
+          zonedRelativeTo
         ));
       ({ days, hours, minutes, seconds, milliseconds, microseconds, nanoseconds } = ES.BalanceTimeDurationRelative(
         days,
@@ -347,7 +365,7 @@ export class Duration {
         microseconds,
         nanoseconds,
         largestUnit,
-        relativeTo
+        zonedRelativeTo
       ));
     } else {
       ({ days, hours, minutes, seconds, milliseconds, microseconds, nanoseconds } = ES.BalanceTimeDuration(
@@ -367,7 +385,7 @@ export class Duration {
       weeks,
       days,
       largestUnit,
-      relativeTo
+      plainRelativeTo
     ));
 
     return new Duration(years, months, weeks, days, hours, minutes, seconds, milliseconds, microseconds, nanoseconds);
@@ -396,12 +414,29 @@ export class Duration {
     const relativeTo = ES.ToRelativeTemporalObject(totalOf);
     const unit = ES.GetTemporalUnit(totalOf, 'unit', 'datetime', ES.REQUIRED);
 
+    let zonedRelativeTo = ES.IsTemporalZonedDateTime(relativeTo) ? relativeTo : undefined;
+    let plainRelativeTo = ES.IsTemporalDate(relativeTo) ? relativeTo : undefined;
+    const plainRelativeToWillBeUsed =
+      unit === 'year' || unit === 'month' || unit === 'week' || years !== 0 || months !== 0 || weeks !== 0;
+    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);
+    }
+
     // Convert larger units down to days
-    ({ years, months, weeks, days } = ES.UnbalanceDateDurationRelative(years, months, weeks, days, unit, relativeTo));
+    ({ years, months, weeks, days } = ES.UnbalanceDateDurationRelative(
+      years,
+      months,
+      weeks,
+      days,
+      unit,
+      plainRelativeTo
+    ));
     // If the unit we're totalling is smaller than `days`, convert days down to that unit.
     let balanceResult;
-    if (ES.IsTemporalZonedDateTime(relativeTo)) {
-      const intermediate = ES.MoveRelativeZonedDateTime(relativeTo, years, months, weeks, 0);
+    if (zonedRelativeTo) {
+      const intermediate = ES.MoveRelativeZonedDateTime(zonedRelativeTo, years, months, weeks, 0);
       balanceResult = ES.BalancePossiblyInfiniteTimeDurationRelative(
         days,
         hours,
@@ -446,7 +481,8 @@ export class Duration {
       1,
       unit,
       'trunc',
-      relativeTo
+      plainRelativeTo,
+      zonedRelativeTo
     );
     return total;
   }