Normative: Validate required methods of TimeZone protocol

Checking whether an object implements the TimeZone protocol is now done by means of HasProperty operations for each of the required methods unless the object already has the TimeZone brand. Discussion: #2104 (comment) See: #2104
tc39 · Apr 10, 2023 · 9852b94 · 9852b94
1 parent f431988
commit 9852b94
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Showing 2 changed files with 29 additions and 3 deletions.
diff --git a/polyfill/lib/ecmascript.mjs b/polyfill/lib/ecmascript.mjs
@@ -1956,11 +1956,15 @@ export const ES = ObjectAssign({}, ES2022, {
     return result;
   },
 
+  ObjectImplementsTemporalTimeZoneProtocol: (object) => {
+    if (ES.IsTemporalTimeZone(object)) return true;
+    return 'getOffsetNanosecondsFor' in object && 'getPossibleInstantsFor' in object && 'id' in object;
+  },
   ToTemporalTimeZoneSlotValue: (temporalTimeZoneLike) => {
     if (ES.Type(temporalTimeZoneLike) === 'Object') {
       if (ES.IsTemporalZonedDateTime(temporalTimeZoneLike)) return GetSlot(temporalTimeZoneLike, TIME_ZONE);
-      if (ES.IsTemporalCalendar(temporalTimeZoneLike)) {
-        throw new RangeError('Expected a time zone object but received a Temporal.Calendar');
+      if (!ES.ObjectImplementsTemporalTimeZoneProtocol(temporalTimeZoneLike)) {
+        throw new TypeError('expected a Temporal.TimeZone or object implementing the Temporal.TimeZone protocol');
       }
       return temporalTimeZoneLike;
     }

diff --git a/spec/timezone.html b/spec/timezone.html
@@ -546,6 +546,28 @@ <h1>FormatISOTimeZoneOffsetString ( _offsetNanoseconds_ )</h1>
       </emu-alg>
     </emu-clause>
 
+    <emu-clause id="sec-temporal-objectimplementstemporaltimezoneprotocol" type="abstract operation">
+      <h1>
+        ObjectImplementsTemporalTimeZoneProtocol (
+          _object_: an Object,
+        ): either a normal completion containing a Boolean, or a throw completion
+      </h1>
+      <dl class="header">
+        <dt>description</dt>
+        <dd>
+          It determines whether the given _object_ is a Temporal.TimeZone instance or implements the required methods from the Temporal.TimeZone protocol.
+          For ordinary objects, and some exotic objects, this operation is infallible and will always return a normal completion.
+          However, if _object_ is a Proxy or has one in its prototype chain, user code may be called.
+        </dd>
+      </dl>
+      <emu-alg>
+        1. If _object_ has an [[InitializedTemporalTimeZone]] internal slot, return *true*.
+        1. For each property key _key_ of « *"getOffsetNanosecondsFor"*, *"getPossibleInstantsFor"*, *"id"* », do
+          1. If ? HasProperty(_object_, _key_) is *false*, return *false*.
+        1. Return *true*.
+      </emu-alg>
+    </emu-clause>
+
     <emu-clause id="sec-temporal-totemporaltimezoneslotvalue" type="abstract operation">
       <h1>
         ToTemporalTimeZoneSlotValue (
@@ -560,7 +582,7 @@ <h1>
         1. If Type(_temporalTimeZoneLike_) is Object, then
           1. If _temporalTimeZoneLike_ has an [[InitializedTemporalZonedDateTime]] internal slot, then
             1. Return _temporalTimeZoneLike_.[[TimeZone]].
-          1. If _temporalTimeZoneLike_ has an [[InitializedTemporalCalendar]] internal slot, throw a *RangeError* exception.
+          1. If ? ObjectImplementsTemporalTimeZoneProtocol(_temporalTimeZoneLike_) is *false*, throw a *TypeError* exception.
           1. Return _temporalTimeZoneLike_.
         1. Let _identifier_ be ? ToString(_temporalTimeZoneLike_).
         1. Let _parseResult_ be ? ParseTemporalTimeZoneString(_identifier_).