LibJS: Implement Temporal.ZonedDateTime.prototype.startOfDay

Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h

@@ -416,6 +416,7 @@ namespace JS {
     P(source)                                \
     P(splice)                                \
     P(sqrt)                                  \
+    P(startOfDay)                            \
     P(startsWith)                            \
     P(status)                                \
     P(sticky)                                \

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

@@ -65,6 +65,7 @@ void ZonedDateTimePrototype::initialize(GlobalObject& global_object)
 
     u8 attr = Attribute::Writable | Attribute::Configurable;
     define_native_function(vm.names.valueOf, value_of, 0, attr);
+    define_native_function(vm.names.startOfDay, start_of_day, 0, attr);
     define_native_function(vm.names.toInstant, to_instant, 0, attr);
     define_native_function(vm.names.toPlainDate, to_plain_date, 0, attr);
     define_native_function(vm.names.toPlainTime, to_plain_time, 0, attr);
@@ -708,6 +709,35 @@ JS_DEFINE_NATIVE_FUNCTION(ZonedDateTimePrototype::value_of)
     return vm.throw_completion<TypeError>(global_object, ErrorType::Convert, "Temporal.ZonedDateTime", "a primitive value");
 }
 
+// 6.3.45 Temporal.ZonedDateTime.prototype.startOfDay ( ), https://tc39.es/proposal-temporal/#sec-temporal.zoneddatetime.prototype.startofday
+JS_DEFINE_NATIVE_FUNCTION(ZonedDateTimePrototype::start_of_day)
+{
+    // 1. Let zonedDateTime be the this value.
+    // 2. Perform ? RequireInternalSlot(zonedDateTime, [[InitializedTemporalZonedDateTime]]).
+    auto* zoned_date_time = TRY(typed_this_object(global_object));
+
+    // 3. Let timeZone be zonedDateTime.[[TimeZone]].
+    auto& time_zone = zoned_date_time->time_zone();
+
+    // 4. Let calendar be zonedDateTime.[[Calendar]].
+    auto& calendar = zoned_date_time->calendar();
+
+    // 5. Let instant be ! CreateTemporalInstant(zonedDateTime.[[Nanoseconds]]).
+    auto* instant = MUST(create_temporal_instant(global_object, zoned_date_time->nanoseconds()));
+
+    // 6. Let temporalDateTime be ? BuiltinTimeZoneGetPlainDateTimeFor(timeZone, instant, calendar).
+    auto* temporal_date_time = TRY(builtin_time_zone_get_plain_date_time_for(global_object, &time_zone, *instant, calendar));
+
+    // 7. Let startDateTime be ? CreateTemporalDateTime(temporalDateTime.[[ISOYear]], temporalDateTime.[[ISOMonth]], temporalDateTime.[[ISODay]], 0, 0, 0, 0, 0, 0, calendar).
+    auto* start_date_time = TRY(create_temporal_date_time(global_object, temporal_date_time->iso_year(), temporal_date_time->iso_month(), temporal_date_time->iso_day(), 0, 0, 0, 0, 0, 0, calendar));
+
+    // 8. Let startInstant be ? BuiltinTimeZoneGetInstantFor(timeZone, startDateTime, "compatible").
+    auto* start_instant = TRY(builtin_time_zone_get_instant_for(global_object, &time_zone, *start_date_time, "compatible"sv));
+
+    // 9. Return ! CreateTemporalZonedDateTime(startInstant.[[Nanoseconds]], timeZone, calendar).
+    return MUST(create_temporal_zoned_date_time(global_object, start_instant->nanoseconds(), time_zone, calendar));
+}
+
 // 6.3.46 Temporal.ZonedDateTime.prototype.toInstant ( ), https://tc39.es/proposal-temporal/#sec-temporal.zoneddatetime.prototype.toinstant
 JS_DEFINE_NATIVE_FUNCTION(ZonedDateTimePrototype::to_instant)
 {

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

@@ -50,6 +50,7 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(era_getter);
     JS_DECLARE_NATIVE_FUNCTION(era_year_getter);
     JS_DECLARE_NATIVE_FUNCTION(value_of);
+    JS_DECLARE_NATIVE_FUNCTION(start_of_day);
     JS_DECLARE_NATIVE_FUNCTION(to_instant);
     JS_DECLARE_NATIVE_FUNCTION(to_plain_date);
     JS_DECLARE_NATIVE_FUNCTION(to_plain_time);

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

@@ -0,0 +1,45 @@
+describe("correct behavior", () => {
+    test("length is 0", () => {
+        expect(Temporal.ZonedDateTime.prototype.startOfDay).toHaveLength(0);
+    });
+
+    test("basic functionality", () => {
+        const plainDateTime = new Temporal.PlainDateTime(2021, 11, 3, 20, 9, 45, 100, 200, 300);
+        const timeZone = new Temporal.TimeZone("UTC");
+        const zonedDateTime = plainDateTime.toZonedDateTime(timeZone);
+        const startOfDayZonedDateTime = zonedDateTime.startOfDay();
+
+        expect(startOfDayZonedDateTime.epochNanoseconds).toBe(1635897600000000000n);
+        expect(startOfDayZonedDateTime.epochMicroseconds).toBe(1635897600000000n);
+        expect(startOfDayZonedDateTime.epochMilliseconds).toBe(1635897600000);
+        expect(startOfDayZonedDateTime.epochSeconds).toBe(1635897600);
+        expect(startOfDayZonedDateTime.year).toBe(2021);
+        expect(startOfDayZonedDateTime.month).toBe(11);
+        expect(startOfDayZonedDateTime.monthCode).toBe("M11");
+        expect(startOfDayZonedDateTime.day).toBe(3);
+        expect(startOfDayZonedDateTime.hour).toBe(0);
+        expect(startOfDayZonedDateTime.minute).toBe(0);
+        expect(startOfDayZonedDateTime.second).toBe(0);
+        expect(startOfDayZonedDateTime.millisecond).toBe(0);
+        expect(startOfDayZonedDateTime.microsecond).toBe(0);
+        expect(startOfDayZonedDateTime.nanosecond).toBe(0);
+        expect(startOfDayZonedDateTime.dayOfWeek).toBe(3);
+        expect(startOfDayZonedDateTime.dayOfYear).toBe(307);
+        expect(startOfDayZonedDateTime.weekOfYear).toBe(44);
+        expect(startOfDayZonedDateTime.hoursInDay).toBe(24);
+        expect(startOfDayZonedDateTime.daysInWeek).toBe(7);
+        expect(startOfDayZonedDateTime.daysInYear).toBe(365);
+        expect(startOfDayZonedDateTime.monthsInYear).toBe(12);
+        expect(startOfDayZonedDateTime.inLeapYear).toBeFalse();
+        expect(startOfDayZonedDateTime.offset).toBe("+00:00");
+        expect(startOfDayZonedDateTime.offsetNanoseconds).toBe(0);
+    });
+});
+
+describe("errors", () => {
+    test("this value must be a Temporal.ZonedDateTime object", () => {
+        expect(() => {
+            Temporal.ZonedDateTime.prototype.startOfDay.call("foo");
+        }).toThrowWithMessage(TypeError, "Not an object of type Temporal.ZonedDateTime");
+    });
+});