LibJS: Implement Temporal.ZonedDateTime.prototype.daysInMonth

Author: https://github.com/linusg
Commit: https://github.com/SerenityOS/serenity/commit/6007fc48041
Pull-request: https://github.com/SerenityOS/serenity/pull/9213
Reviewed-by: https://github.com/IdanHo ✅

Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTimePrototype.cpp

@@ -50,6 +50,7 @@ void ZonedDateTimePrototype::initialize(GlobalObject& global_object)
     define_native_accessor(vm.names.dayOfYear, day_of_year_getter, {}, Attribute::Configurable);
     define_native_accessor(vm.names.weekOfYear, week_of_year_getter, {}, Attribute::Configurable);
     define_native_accessor(vm.names.daysInWeek, days_in_week_getter, {}, Attribute::Configurable);
+    define_native_accessor(vm.names.daysInMonth, days_in_month_getter, {}, Attribute::Configurable);
 }
 
 static ZonedDateTime* typed_this(GlobalObject& global_object)
@@ -539,4 +540,31 @@ JS_DEFINE_NATIVE_FUNCTION(ZonedDateTimePrototype::days_in_week_getter)
     return calendar_days_in_week(global_object, calendar, *temporal_date_time);
 }
 
+// 6.3.24 get Temporal.ZonedDateTime.prototype.daysInMonth, https://tc39.es/proposal-temporal/#sec-get-temporal.zoneddatetime.prototype.daysinmonth
+JS_DEFINE_NATIVE_FUNCTION(ZonedDateTimePrototype::days_in_month_getter)
+{
+    // 1. Let zonedDateTime be the this value.
+    // 2. Perform ? RequireInternalSlot(zonedDateTime, [[InitializedTemporalZonedDateTime]]).
+    auto* zoned_date_time = typed_this(global_object);
+    if (vm.exception())
+        return {};
+
+    // 3. Let timeZone be zonedDateTime.[[TimeZone]].
+    auto& time_zone = zoned_date_time->time_zone();
+
+    // 4. Let instant be ! CreateTemporalInstant(zonedDateTime.[[Nanoseconds]]).
+    auto* instant = create_temporal_instant(global_object, zoned_date_time->nanoseconds());
+
+    // 5. Let calendar be zonedDateTime.[[Calendar]].
+    auto& calendar = zoned_date_time->calendar();
+
+    // 6. Let temporalDateTime be ? BuiltinTimeZoneGetPlainDateTimeFor(timeZone, instant, calendar).
+    auto* temporal_date_time = builtin_time_zone_get_plain_date_time_for(global_object, &time_zone, *instant, calendar);
+    if (vm.exception())
+        return {};
+
+    // 7. Return ? CalendarDaysInMonth(calendar, temporalDateTime).
+    return calendar_days_in_month(global_object, calendar, *temporal_date_time);
+}
+
 }

Userland/Libraries/LibJS/Runtime/Temporal/ZonedDateTimePrototype.h

@@ -39,6 +39,7 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(day_of_year_getter);
     JS_DECLARE_NATIVE_FUNCTION(week_of_year_getter);
     JS_DECLARE_NATIVE_FUNCTION(days_in_week_getter);
+    JS_DECLARE_NATIVE_FUNCTION(days_in_month_getter);
 };
 
 }

Userland/Libraries/LibJS/Tests/builtins/Temporal/ZonedDateTime/ZonedDateTime.prototype.daysInMonth.js

@@ -0,0 +1,15 @@
+describe("correct behavior", () => {
+    test("basic functionality", () => {
+        const timeZone = new Temporal.TimeZone("UTC");
+        const zonedDateTime = new Temporal.ZonedDateTime(1625614921000000000n, timeZone);
+        expect(zonedDateTime.daysInMonth).toBe(31);
+    });
+});
+
+test("errors", () => {
+    test("this value must be a Temporal.ZonedDateTime object", () => {
+        expect(() => {
+            Reflect.get(Temporal.ZonedDateTime.prototype, "daysInMonth", "foo");
+        }).toThrowWithMessage(TypeError, "Not a Temporal.ZonedDateTime");
+    });
+});