From ae2b7904b2fd5968472ea69986953ba77671d246 Mon Sep 17 00:00:00 2001
From: Philip Chimento <pchimento@igalia.com>
Date: Wed, 28 Oct 2020 15:51:43 -0700
Subject: [PATCH] Generalize DefaultTemporalLargestUnit

Per #980 it is a recognized operation to get the correct largestUnit value
corresponding with the largest non-zero unit in the duration. Generalize
this operation in the spec, in order to use in #857.
---
 polyfill/lib/duration.mjs   | 14 ++++----------
 polyfill/lib/ecmascript.mjs | 28 ++++++++++++++++++++++++++++
 spec/duration.html          | 27 +++++++++++++--------------
 3 files changed, 45 insertions(+), 24 deletions(-)

diff --git a/polyfill/lib/duration.mjs b/polyfill/lib/duration.mjs
index 8ef0d0c0b2..eaa1f71b60 100644
--- a/polyfill/lib/duration.mjs
+++ b/polyfill/lib/duration.mjs
@@ -357,8 +357,7 @@ export class Duration {
     let microseconds = GetSlot(this, MICROSECONDS);
     let nanoseconds = GetSlot(this, NANOSECONDS);
 
-    let defaultLargestUnit = 'nanoseconds';
-    for (const [prop, v] of Object.entries({
+    let defaultLargestUnit = ES.DefaultTemporalLargestUnit(
       years,
       months,
       weeks,
@@ -367,14 +366,9 @@ export class Duration {
       minutes,
       seconds,
       milliseconds,
-      microseconds
-    })) {
-      if (v !== 0) {
-        defaultLargestUnit = prop;
-        break;
-      }
-    }
-
+      microseconds,
+      nanoseconds
+    );
     options = ES.NormalizeOptionsObject(options);
     const smallestUnit = ES.ToSmallestTemporalDurationUnit(options, 'nanoseconds');
     defaultLargestUnit = ES.LargerOfTwoTemporalDurationUnits(defaultLargestUnit, smallestUnit);
diff --git a/polyfill/lib/ecmascript.mjs b/polyfill/lib/ecmascript.mjs
index eec8d5a64c..577c93ece0 100644
--- a/polyfill/lib/ecmascript.mjs
+++ b/polyfill/lib/ecmascript.mjs
@@ -731,6 +731,34 @@ export const ES = ObjectAssign({}, ES2020, {
       throw new RangeError(`largestUnit ${largestUnit} cannot be smaller than smallestUnit ${smallestUnit}`);
     }
   },
+  DefaultTemporalLargestUnit: (
+    years,
+    months,
+    weeks,
+    days,
+    hours,
+    minutes,
+    seconds,
+    milliseconds,
+    microseconds,
+    nanoseconds
+  ) => {
+    for (const [prop, v] of Object.entries({
+      years,
+      months,
+      weeks,
+      days,
+      hours,
+      minutes,
+      seconds,
+      milliseconds,
+      microseconds,
+      nanoseconds
+    })) {
+      if (v !== 0) return prop;
+    }
+    return 'nanoseconds';
+  },
   LargerOfTwoTemporalDurationUnits: (unit1, unit2) => {
     const validUnits = [
       'years',
diff --git a/spec/duration.html b/spec/duration.html
index 009c5822d6..9539541cee 100644
--- a/spec/duration.html
+++ b/spec/duration.html
@@ -399,7 +399,7 @@ <h1>Temporal.Duration.prototype.round ( _options_ )</h1>
         1. Perform ? RequireInternalSlot(_duration_, [[InitializedTemporalDuration]]).
         1. Set _options_ to ? NormalizeOptionsObject(_options_).
         1. Let _smallestUnit_ be ? ToSmallestTemporalDurationUnit(_options_, *"nanoseconds"*).
-        1. Let _defaultLargestUnit_ be ! DefaultTemporalLargestUnitForRounding(_duration_).
+        1. Let _defaultLargestUnit_ be ! DefaultTemporalLargestUnit(_duration_.[[Years]], _duration_.[[Months]], _duration_.[[Weeks]], _duration_.[[Days]], _duration_.[[Hours]], _duration_.[[Minutes]], _duration_.[[Seconds]], _duration_.[[Milliseconds]], _duration_.[[Microseconds]], _duration_.[[Nanoseconds]]).
         1. Set _defaultLargestUnit_ to ! LargerOfTwoTemporalDurationUnits(_defaultLargestUnit_, _smallestUnit_).
         1. Let _largestUnit_ be ? ToLargestTemporalUnit(_options_, _defaultLargestUnit_).
         1. Perform ? ValidateTemporalUnitRange(_largestUnit_, _smallestUnit_).
@@ -682,22 +682,21 @@ <h1>ValidateTemporalDuration ( _years_, _months_, _weeks_, _days_, _hours_, _min
       </emu-alg>
     </emu-clause>
 
-    <emu-clause id="sec-temporal-defaulttemporallargestunitforrounding" aoid="DefaultTemporalLargestUnitForRounding">
-      <h1>DefaultTemporalLargestUnitForRounding ( _duration_ )</h1>
+    <emu-clause id="sec-temporal-defaulttemporallargestunit" aoid="DefaultTemporalLargestUnit">
+      <h1>DefaultTemporalLargestUnit ( _years_, _months_, _weeks_, _days_, _hours_, _minutes_, _seconds_, _milliseconds_, _microseconds_, _nanoseconds_ )</h1>
       <p>
-        The abstract operation DefaultTemporalLargestUnitForRounding implements the logic used in the `Temporal.Duration.prototype.round()` method, where the `largestUnit` option, if not given explicitly, is set to the largest non-zero unit in the input Temporal.Duration.
+        The abstract operation DefaultTemporalLargestUnit implements the logic used in the `Temporal.Duration.prototype.round()` method and elsewhere, where the `largestUnit` option, if not given explicitly, is set to the largest non-zero unit in the input Temporal.Duration.
       </p>
       <emu-alg>
-        1. Assert: _duration_ has an [[InitializedTemporalDuration]] internal slot.
-        1. If _duration_.[[Years]] is not zero, return *"years"*.
-        1. If _duration_.[[Months]] is not zero, return *"months"*.
-        1. If _duration_.[[Weeks]] is not zero, return *"weeks"*.
-        1. If _duration_.[[Days]] is not zero, return *"days"*.
-        1. If _duration_.[[Hours]] is not zero, return *"hours"*.
-        1. If _duration_.[[Minutes]] is not zero, return *"minutes"*.
-        1. If _duration_.[[Seconds]] is not zero, return *"seconds"*.
-        1. If _duration_.[[Milliseconds]] is not zero, return *"milliseconds"*.
-        1. If _duration_.[[Microseconds]] is not zero, return *"microseconds"*.
+        1. If _years_ is not zero, return *"years"*.
+        1. If _months_ is not zero, return *"months"*.
+        1. If _weeks_ is not zero, return *"weeks"*.
+        1. If _days_ is not zero, return *"days"*.
+        1. If _hours_ is not zero, return *"hours"*.
+        1. If _minutes_ is not zero, return *"minutes"*.
+        1. If _seconds_ is not zero, return *"seconds"*.
+        1. If _milliseconds_ is not zero, return *"milliseconds"*.
+        1. If _microseconds_ is not zero, return *"microseconds"*.
         1. Return *"nanoseconds"*.
       </emu-alg>
     </emu-clause>