LibJS: Implement Temporal.Calendar.prototype.inLeapYear

Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h

@@ -219,6 +219,7 @@ namespace JS {
     P(indexOf)                               \
     P(indices)                               \
     P(info)                                  \
+    P(inLeapYear)                            \
     P(input)                                 \
     P(instant)                               \
     P(is)                                    \

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

@@ -42,6 +42,7 @@ void CalendarPrototype::initialize(GlobalObject& global_object)
     define_native_function(vm.names.daysInMonth, days_in_month, 1, attr);
     define_native_function(vm.names.daysInYear, days_in_year, 1, attr);
     define_native_function(vm.names.monthsInYear, months_in_year, 1, attr);
+    define_native_function(vm.names.inLeapYear, in_leap_year, 1, attr);
     define_native_function(vm.names.toString, to_string, 0, attr);
     define_native_function(vm.names.toJSON, to_json, 0, attr);
 }
@@ -385,6 +386,33 @@ JS_DEFINE_NATIVE_FUNCTION(CalendarPrototype::months_in_year)
     return Value(12);
 }
 
+// 12.4.20 Temporal.Calendar.prototype.inLeapYear ( temporalDateLike ), https://tc39.es/proposal-temporal/#sec-temporal.calendar.prototype.inleapyear
+// NOTE: This is the minimum inLeapYear implementation for engines without ECMA-402.
+JS_DEFINE_NATIVE_FUNCTION(CalendarPrototype::in_leap_year)
+{
+    // 1. Let calendar be the this value.
+    // 2. Perform ? RequireInternalSlot(calendar, [[InitializedTemporalCalendar]]).
+    auto* calendar = typed_this(global_object);
+    if (vm.exception())
+        return {};
+
+    // 3. Assert: calendar.[[Identifier]] is "iso8601".
+    VERIFY(calendar->identifier() == "iso8601"sv);
+
+    auto temporal_date_like = vm.argument(0);
+    // 4. If Type(temporalDateLike) is not Object or temporalDateLike does not have an [[InitializedTemporalDate]] or [[InitializedTemporalYearMonth]] internal slot, then
+    // TODO PlainYearMonth objects
+    if (!temporal_date_like.is_object() || !is<PlainDate>(temporal_date_like.as_object())) {
+        // a. Set temporalDateLike to ? ToTemporalDate(temporalDateLike).
+        temporal_date_like = to_temporal_date(global_object, temporal_date_like);
+        if (vm.exception())
+            return {};
+    }
+
+    // 5. Return ! IsISOLeapYear(temporalDateLike.[[ISOYear]]).
+    return Value(is_iso_leap_year(iso_year(temporal_date_like.as_object())));
+}
+
 // 12.4.23 Temporal.Calendar.prototype.toString ( ), https://tc39.es/proposal-temporal/#sec-temporal.calendar.prototype.tostring
 JS_DEFINE_NATIVE_FUNCTION(CalendarPrototype::to_string)
 {

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

@@ -32,6 +32,7 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(days_in_month);
     JS_DECLARE_NATIVE_FUNCTION(days_in_year);
     JS_DECLARE_NATIVE_FUNCTION(months_in_year);
+    JS_DECLARE_NATIVE_FUNCTION(in_leap_year);
     JS_DECLARE_NATIVE_FUNCTION(to_string);
     JS_DECLARE_NATIVE_FUNCTION(to_json);
 };

Userland/Libraries/LibJS/Tests/builtins/Temporal/Calendar/Calendar.prototype.inLeapYear.js

@@ -0,0 +1,13 @@
+describe("correct behavior", () => {
+    test("length is 1", () => {
+        expect(Temporal.Calendar.prototype.inLeapYear).toHaveLength(1);
+    });
+
+    test("basic functionality", () => {
+        const calendar = new Temporal.Calendar("iso8601");
+        const date = new Temporal.PlainDate(2021, 7, 23);
+        expect(calendar.inLeapYear(date)).toBeFalse();
+        const leapDate = new Temporal.PlainDate(2020, 7, 23);
+        expect(calendar.inLeapYear(leapDate)).toBeTrue();
+    });
+});