LibJS: Implement Temporal.PlainDateTime.prototype.toPlainDate()

Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h

@@ -348,6 +348,7 @@ namespace JS {
     P(toLocaleString)                        \
     P(toLocaleTimeString)                    \
     P(toLowerCase)                           \
+    P(toPlainDate)                           \
     P(toString)                              \
     P(toTemporalInstant)                     \
     P(toTimeString)                          \

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

@@ -5,6 +5,7 @@
  */
 
 #include <LibJS/Runtime/GlobalObject.h>
+#include <LibJS/Runtime/Temporal/PlainDate.h>
 #include <LibJS/Runtime/Temporal/PlainDateTime.h>
 #include <LibJS/Runtime/Temporal/PlainDateTimePrototype.h>
 
@@ -29,6 +30,7 @@ void PlainDateTimePrototype::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.toPlainDate, to_plain_date, 0, attr);
 }
 
 static PlainDateTime* typed_this(GlobalObject& global_object)
@@ -65,4 +67,17 @@ JS_DEFINE_NATIVE_FUNCTION(PlainDateTimePrototype::value_of)
     return {};
 }
 
+// 5.3.37 Temporal.PlainDateTime.prototype.toPlainDate ( ), https://tc39.es/proposal-temporal/#sec-temporal.plaindatetime.prototype.toplaindate
+JS_DEFINE_NATIVE_FUNCTION(PlainDateTimePrototype::to_plain_date)
+{
+    // 1. Let dateTime be the this value.
+    // 2. Perform ? RequireInternalSlot(dateTime, [[InitializedTemporalDateTime]]).
+    auto* date_time = typed_this(global_object);
+    if (vm.exception())
+        return {};
+
+    // 3. Return ? CreateTemporalDate(dateTime.[[ISOYear]], dateTime.[[ISOMonth]], dateTime.[[ISODay]], dateTime.[[Calendar]]).
+    return create_temporal_date(global_object, date_time->iso_year(), date_time->iso_month(), date_time->iso_day(), date_time->calendar());
+}
+
 }

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

@@ -21,6 +21,7 @@ public:
 private:
     JS_DECLARE_NATIVE_FUNCTION(calendar_getter);
     JS_DECLARE_NATIVE_FUNCTION(value_of);
+    JS_DECLARE_NATIVE_FUNCTION(to_plain_date);
 };
 
 }

Userland/Libraries/LibJS/Tests/builtins/Temporal/PlainDateTime/PlainDateTime.prototype.toPlainDate.js

@@ -0,0 +1,11 @@
+describe("normal behavior", () => {
+    test("length is 0", () => {
+        expect(Temporal.PlainDateTime.prototype.toPlainDate).toHaveLength(0);
+    });
+
+    test("basic functionality", () => {
+        const plainDateTime = new Temporal.PlainDateTime(2021, 7, 23, 0, 32, 18, 123, 456, 789);
+        const plainDate = plainDateTime.toPlainDate();
+        expect(plainDate.equals(new Temporal.PlainDate(2021, 7, 23))).toBeTrue();
+    });
+});