LibJS: Add fast path TimeZone conversion to PlainDate#toZonedDateTime

This is a normative chane in the Temporal spec.

See: https://github.com/tc39/proposal-temporal/commit/fcab1af

1 files changed, 23 insertions, 13 deletions

diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/PlainDatePrototype.cpp b/Userland/Libraries/LibJS/Runtime/Temporal/PlainDatePrototype.cpp
index e2cbd780bf..2222b1eef1 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/PlainDatePrototype.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/PlainDatePrototype.cpp
@@ -525,23 +525,33 @@ JS_DEFINE_NATIVE_FUNCTION(PlainDatePrototype::to_zoned_date_time)
 
     // 3. If Type(item) is Object, then
     if (item.is_object()) {
-        // a. Let timeZoneLike be ? Get(item, "timeZone").
-        auto time_zone_like = TRY(item.as_object().get(vm.names.timeZone));
-
-        // b. If timeZoneLike is undefined, then
-        if (time_zone_like.is_undefined()) {
-            // i. Let timeZone be ? ToTemporalTimeZone(item).
-            time_zone = TRY(to_temporal_time_zone(vm, item));
+        // a. If item has an [[InitializedTemporalTimeZone]] internal slot, then
+        if (is<TimeZone>(item.as_object())) {
+            // i. Let timeZone be item.
+            time_zone = &item.as_object();
 
             // ii. Let temporalTime be undefined.
         }
-        // c. Else,
+        // b. Else,
         else {
-            // i. Let timeZone be ? ToTemporalTimeZone(timeZoneLike).
-            time_zone = TRY(to_temporal_time_zone(vm, time_zone_like));
-
-            // ii. Let temporalTime be ? Get(item, "plainTime").
-            temporal_time_value = TRY(item.as_object().get(vm.names.plainTime));
+            // i. Let timeZoneLike be ? Get(item, "timeZone").
+            auto time_zone_like = TRY(item.as_object().get(vm.names.timeZone));
+
+            // ii. If timeZoneLike is undefined, then
+            if (time_zone_like.is_undefined()) {
+                // 1. Let timeZone be ? ToTemporalTimeZone(item).
+                time_zone = TRY(to_temporal_time_zone(vm, item));
+
+                // 2. Let temporalTime be undefined.
+            }
+            // iii. Else,
+            else {
+                // 1. Let timeZone be ? ToTemporalTimeZone(timeZoneLike).
+                time_zone = TRY(to_temporal_time_zone(vm, time_zone_like));
+
+                // 2. Let temporalTime be ? Get(item, "plainTime").
+                temporal_time_value = TRY(item.as_object().get(vm.names.plainTime));
+            }
         }
     }
     // 4. Else,