LibJS: Implement Temporal.PlainDate.prototype.toPlainMonthDay()

Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h

@@ -392,6 +392,7 @@ namespace JS {
     P(toLowerCase)                           \
     P(toPlainDate)                           \
     P(toPlainDateTime)                       \
+    P(toPlainMonthDay)                       \
     P(toPlainTime)                           \
     P(toPlainYearMonth)                      \
     P(toString)                              \

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

@@ -447,6 +447,36 @@ PlainYearMonth* year_month_from_fields(GlobalObject& global_object, Object& cale
     return static_cast<PlainYearMonth*>(year_month_object);
 }
 
+// 12.1.26 MonthDayFromFields ( calendar, fields [ , options ] ), https://tc39.es/proposal-temporal/#sec-temporal-monthdayfromfields
+PlainMonthDay* month_day_from_fields(GlobalObject& global_object, Object& calendar, Object& fields, Object* options)
+{
+    auto& vm = global_object.vm();
+
+    // 1. Assert: Type(calendar) is Object.
+    // 2. Assert: Type(fields) is Object.
+    // 3. If options is not present, then
+    //     a. Set options to undefined.
+    // 4. Else,
+    //     a. Assert: Type(options) is Object.
+
+    // 5. Let monthDay be ? Invoke(calendar, "monthDayFromFields", « fields, options »).
+    auto month_day = Value(&calendar).invoke(global_object, vm.names.monthDayFromFields, &fields, options ?: js_undefined());
+    if (vm.exception())
+        return {};
+
+    // 6. Perform ? RequireInternalSlot(monthDay, [[InitializedTemporalMonthDay]]).
+    auto* month_day_object = month_day.to_object(global_object);
+    if (!month_day_object)
+        return {};
+    if (!is<PlainMonthDay>(month_day_object)) {
+        vm.throw_exception<TypeError>(global_object, ErrorType::NotA, "Temporal.PlainMonthDay");
+        return {};
+    }
+
+    // 7. Return monthDay.
+    return static_cast<PlainMonthDay*>(month_day_object);
+}
+
 // 12.1.28 CalendarEquals ( one, two ), https://tc39.es/proposal-temporal/#sec-temporal-calendarequals
 bool calendar_equals(GlobalObject& global_object, Object& one, Object& two)
 {

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

@@ -51,6 +51,7 @@ Object* to_temporal_calendar_with_iso_default(GlobalObject&, Value);
 Object* get_temporal_calendar_with_iso_default(GlobalObject&, Object&);
 PlainDate* date_from_fields(GlobalObject&, Object& calendar, Object& fields, Object& options);
 PlainYearMonth* year_month_from_fields(GlobalObject&, Object& calendar, Object& fields, Object* options = nullptr);
+PlainMonthDay* month_day_from_fields(GlobalObject& global_object, Object& calendar, Object& fields, Object* options = nullptr);
 bool calendar_equals(GlobalObject&, Object& one, Object& two);
 Object* consolidate_calendars(GlobalObject&, Object& one, Object& two);
 bool is_iso_leap_year(i32 year);

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

@@ -11,6 +11,7 @@
 #include <LibJS/Runtime/Temporal/Calendar.h>
 #include <LibJS/Runtime/Temporal/PlainDate.h>
 #include <LibJS/Runtime/Temporal/PlainDatePrototype.h>
+#include <LibJS/Runtime/Temporal/PlainMonthDay.h>
 #include <LibJS/Runtime/Temporal/PlainYearMonth.h>
 
 namespace JS::Temporal {
@@ -46,6 +47,7 @@ void PlainDatePrototype::initialize(GlobalObject& global_object)
 
     u8 attr = Attribute::Writable | Attribute::Configurable;
     define_native_function(vm.names.toPlainYearMonth, to_plain_year_month, 0, attr);
+    define_native_function(vm.names.toPlainMonthDay, to_plain_month_day, 0, attr);
     define_native_function(vm.names.getISOFields, get_iso_fields, 0, attr);
     define_native_function(vm.names.withCalendar, with_calendar, 1, attr);
     define_native_function(vm.names.equals, equals, 1, attr);
@@ -296,6 +298,32 @@ JS_DEFINE_NATIVE_FUNCTION(PlainDatePrototype::to_plain_year_month)
     return year_month_from_fields(global_object, calendar, *fields);
 }
 
+// 3.3.17 Temporal.PlainDate.prototype.toPlainMonthDay ( ), https://tc39.es/proposal-temporal/#sec-temporal.plaindate.prototype.toplainmonthday
+JS_DEFINE_NATIVE_FUNCTION(PlainDatePrototype::to_plain_month_day)
+{
+    // 1. Let temporalDate be the this value.
+    // 2. Perform ? RequireInternalSlot(temporalDate, [[InitializedTemporalDate]]).
+    auto* temporal_date = typed_this(global_object);
+    if (vm.exception())
+        return {};
+
+    // 3. Let calendar be temporalDate.[[Calendar]].
+    auto& calendar = temporal_date->calendar();
+
+    // 4. Let fieldNames be ? CalendarFields(calendar, « "day", "monthCode" »).
+    auto field_names = calendar_fields(global_object, calendar, { "day"sv, "monthCode"sv });
+    if (vm.exception())
+        return {};
+
+    // 5. Let fields be ? PrepareTemporalFields(temporalDate, fieldNames, «»).
+    auto* fields = prepare_temporal_fields(global_object, *temporal_date, field_names, {});
+    if (vm.exception())
+        return {};
+
+    // 6. Return ? MonthDayFromFields(calendar, fields).
+    return month_day_from_fields(global_object, calendar, *fields);
+}
+
 // 3.3.18 Temporal.PlainDate.prototype.getISOFields ( ), https://tc39.es/proposal-temporal/#sec-temporal.plaindate.prototype.getisofields
 JS_DEFINE_NATIVE_FUNCTION(PlainDatePrototype::get_iso_fields)
 {

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

@@ -33,6 +33,7 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(months_in_year_getter);
     JS_DECLARE_NATIVE_FUNCTION(in_leap_year_getter);
     JS_DECLARE_NATIVE_FUNCTION(to_plain_year_month);
+    JS_DECLARE_NATIVE_FUNCTION(to_plain_month_day);
     JS_DECLARE_NATIVE_FUNCTION(get_iso_fields);
     JS_DECLARE_NATIVE_FUNCTION(with_calendar);
     JS_DECLARE_NATIVE_FUNCTION(equals);

Userland/Libraries/LibJS/Tests/builtins/Temporal/PlainDate/PlainDate.prototype.toPlainMonthDay.js

@@ -0,0 +1,15 @@
+describe("correct behavior", () => {
+    test("length is 0", () => {
+        expect(Temporal.PlainDate.prototype.toPlainMonthDay).toHaveLength(0);
+    });
+
+    test("basic functionality", () => {
+        const plainDate = new Temporal.PlainDate(2021, 7, 6);
+        const plainMonthDay = plainDate.toPlainMonthDay();
+        expect(plainMonthDay.calendar).toBe(plainDate.calendar);
+        expect(plainMonthDay.monthCode).toBe("M07");
+        expect(plainMonthDay.day).toBe(6);
+        const fields = plainMonthDay.getISOFields();
+        expect(fields.isoYear).toBe(1972);
+    });
+});