LibJS: Implement Temporal.PlainDate.prototype.era

Author: https://github.com/linusg
Commit: https://github.com/SerenityOS/serenity/commit/6f7d6d917e6
Pull-request: https://github.com/SerenityOS/serenity/pull/9647
Reviewed-by: https://github.com/IdanHo ✅

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

@@ -288,6 +288,30 @@ Value calendar_in_leap_year(GlobalObject& global_object, Object& calendar, Objec
     return Value(&calendar).invoke(global_object, vm.names.inLeapYear, &date_like);
 }
 
+// 15.6.1.2 CalendarEra ( calendar, dateLike ), https://tc39.es/proposal-temporal/#sec-temporal-calendarera
+Value calendar_era(GlobalObject& global_object, Object& calendar, Object& date_like)
+{
+    auto& vm = global_object.vm();
+
+    // 1. Assert: Type(calendar) is Object.
+
+    // 2. Let result be ? Invoke(calendar, "era", « dateLike »).
+    auto result = Value(&calendar).invoke(global_object, vm.names.era, &date_like);
+    if (vm.exception())
+        return {};
+
+    // 3. If result is not undefined, set result to ? ToString(result).
+    if (!result.is_undefined()) {
+        auto result_string = result.to_string(global_object);
+        if (vm.exception())
+            return {};
+        result = js_string(vm, move(result_string));
+    }
+
+    // 4. Return result.
+    return result;
+}
+
 // 12.1.21 ToTemporalCalendar ( temporalCalendarLike ), https://tc39.es/proposal-temporal/#sec-temporal-totemporalcalendar
 Object* to_temporal_calendar(GlobalObject& global_object, Value temporal_calendar_like)
 {

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

@@ -46,6 +46,7 @@ Value calendar_days_in_month(GlobalObject&, Object& calendar, Object& date_like)
 Value calendar_days_in_year(GlobalObject&, Object& calendar, Object& date_like);
 Value calendar_months_in_year(GlobalObject&, Object& calendar, Object& date_like);
 Value calendar_in_leap_year(GlobalObject&, Object& calendar, Object& date_like);
+Value calendar_era(GlobalObject&, Object& calendar, Object& date_like);
 Object* to_temporal_calendar(GlobalObject&, Value);
 Object* to_temporal_calendar_with_iso_default(GlobalObject&, Value);
 Object* get_temporal_calendar_with_iso_default(GlobalObject&, Object&);

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

@@ -46,6 +46,7 @@ void PlainDatePrototype::initialize(GlobalObject& global_object)
     define_native_accessor(vm.names.daysInYear, days_in_year_getter, {}, Attribute::Configurable);
     define_native_accessor(vm.names.monthsInYear, months_in_year_getter, {}, Attribute::Configurable);
     define_native_accessor(vm.names.inLeapYear, in_leap_year_getter, {}, Attribute::Configurable);
+    define_native_accessor(vm.names.era, era_getter, {}, Attribute::Configurable);
 
     u8 attr = Attribute::Writable | Attribute::Configurable;
     define_native_function(vm.names.toPlainYearMonth, to_plain_year_month, 0, attr);
@@ -278,6 +279,22 @@ JS_DEFINE_NATIVE_FUNCTION(PlainDatePrototype::in_leap_year_getter)
     return Value(calendar_in_leap_year(global_object, calendar, *temporal_date));
 }
 
+// 15.6.5.2 get Temporal.PlainDate.prototype.era, https://tc39.es/proposal-temporal/#sec-get-temporal.plaindate.prototype.era
+JS_DEFINE_NATIVE_FUNCTION(PlainDatePrototype::era_getter)
+{
+    // 1. Let plainDate be the this value.
+    // 2. Perform ? RequireInternalSlot(plainDate, [[InitializedTemporalDate]]).
+    auto* plain_date = typed_this(global_object);
+    if (vm.exception())
+        return {};
+
+    // 3. Let calendar be plainDate.[[Calendar]].
+    auto& calendar = plain_date->calendar();
+
+    // 4. Return ? CalendarEra(calendar, plainDate).
+    return calendar_era(global_object, calendar, *plain_date);
+}
+
 // 3.3.16 Temporal.PlainDate.prototype.toPlainYearMonth ( ), https://tc39.es/proposal-temporal/#sec-temporal.plaindate.prototype.toplainyearmonth
 JS_DEFINE_NATIVE_FUNCTION(PlainDatePrototype::to_plain_year_month)
 {

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

@@ -32,6 +32,7 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(days_in_year_getter);
     JS_DECLARE_NATIVE_FUNCTION(months_in_year_getter);
     JS_DECLARE_NATIVE_FUNCTION(in_leap_year_getter);
+    JS_DECLARE_NATIVE_FUNCTION(era_getter);
     JS_DECLARE_NATIVE_FUNCTION(to_plain_year_month);
     JS_DECLARE_NATIVE_FUNCTION(to_plain_month_day);
     JS_DECLARE_NATIVE_FUNCTION(get_iso_fields);

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

@@ -0,0 +1,24 @@
+describe("correct behavior", () => {
+    test("basic functionality", () => {
+        const plainDate = new Temporal.PlainDate(2021, 7, 6);
+        expect(plainDate.era).toBeUndefined();
+    });
+
+    test("calendar with custom era function", () => {
+        const calendar = {
+            era() {
+                return "foo";
+            },
+        };
+        const plainDate = new Temporal.PlainDate(2021, 7, 6, calendar);
+        expect(plainDate.era).toBe("foo");
+    });
+});
+
+describe("errors", () => {
+    test("this value must be a Temporal.PlainDate object", () => {
+        expect(() => {
+            Reflect.get(Temporal.PlainDate.prototype, "era", "foo");
+        }).toThrowWithMessage(TypeError, "Not a Temporal.PlainDate");
+    });
+});