LibJS: Implement Temporal.Now.plainDateTime()

Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h

@@ -284,6 +284,7 @@ namespace JS {
     P(parseInt)                              \
     P(plainDate)                             \
     P(plainDateISO)                          \
+    P(plainDateTime)                         \
     P(pop)                                   \
     P(pow)                                   \
     P(preventExtensions)                     \

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

@@ -34,6 +34,7 @@ void Now::initialize(GlobalObject& global_object)
     u8 attr = Attribute::Writable | Attribute::Configurable;
     define_native_function(vm.names.timeZone, time_zone, 0, attr);
     define_native_function(vm.names.instant, instant, 0, attr);
+    define_native_function(vm.names.plainDateTime, plain_date_time, 1, attr);
     define_native_function(vm.names.plainDate, plain_date, 1, attr);
     define_native_function(vm.names.plainDateISO, plain_date_iso, 0, attr);
 }
@@ -52,6 +53,16 @@ JS_DEFINE_NATIVE_FUNCTION(Now::instant)
     return system_instant(global_object);
 }
 
+// 2.1.3 Temporal.Now.plainDateTime ( calendar [ , temporalTimeZoneLike ] ), https://tc39.es/proposal-temporal/#sec-temporal.now.plaindatetime
+JS_DEFINE_NATIVE_FUNCTION(Now::plain_date_time)
+{
+    auto calendar = vm.argument(0);
+    auto temporal_time_zone_like = vm.argument(1);
+
+    // 1. Return ? SystemDateTime(temporalTimeZoneLike, calendar).
+    return system_date_time(global_object, temporal_time_zone_like, calendar);
+}
+
 // 2.1.7 Temporal.Now.plainDate ( calendar [ , temporalTimeZoneLike ] ), https://tc39.es/proposal-temporal/#sec-temporal.now.plaindate
 JS_DEFINE_NATIVE_FUNCTION(Now::plain_date)
 {

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

@@ -21,6 +21,7 @@ public:
 private:
     JS_DECLARE_NATIVE_FUNCTION(time_zone);
     JS_DECLARE_NATIVE_FUNCTION(instant);
+    JS_DECLARE_NATIVE_FUNCTION(plain_date_time);
     JS_DECLARE_NATIVE_FUNCTION(plain_date);
     JS_DECLARE_NATIVE_FUNCTION(plain_date_iso);
 };

Userland/Libraries/LibJS/Tests/builtins/Temporal/Now/Now.plainDateTime.js

@@ -0,0 +1,33 @@
+describe("correct behavior", () => {
+    test("length is 1", () => {
+        expect(Temporal.Now.plainDateTime).toHaveLength(1);
+    });
+
+    test("basic functionality", () => {
+        const calendar = new Temporal.Calendar("iso8601");
+        const plainDateTime = Temporal.Now.plainDateTime(calendar);
+        expect(plainDateTime).toBeInstanceOf(Temporal.PlainDateTime);
+        expect(plainDateTime.calendar).toBe(calendar);
+    });
+
+    test("custom time zone", () => {
+        const calendar = new Temporal.Calendar("iso8601");
+        const timeZone = {
+            getOffsetNanosecondsFor() {
+                return 86400000000000;
+            },
+        };
+        const plainDateTime = Temporal.Now.plainDateTime(calendar);
+        const plainDateTimeWithOffset = Temporal.Now.plainDateTime(calendar, timeZone);
+        // Yes, this will fail if a day, month, or year change happens between the above two lines :^)
+        // FIXME: enable these once the getters are implemented
+        // expect(plainDateTimeWithOffset.year).toBe(plainDateTime.year);
+        // expect(plainDateTimeWithOffset.month).toBe(plainDateTime.month);
+        // expect(plainDateTimeWithOffset.day).toBe(plainDateTime.day + 1);
+        // expect(plainDateTimeWithOffset.hour).not.toBe(plainDateTime.hour);
+        // expect(plainDateTimeWithOffset.minute).not.toBe(plainDateTime.minute);
+        // expect(plainDateTimeWithOffset.second).not.toBe(plainDateTime.second);
+        // expect(plainDateTimeWithOffset.millisecond).not.toBe(plainDateTime.millisecond);
+        // microsecond, and nanosecond not checked here as they could easily be the same for both
+    });
+});