LibJS: Implement Temporal.Calendar.prototype.fields()

Author: https://github.com/linusg
Commit: https://github.com/SerenityOS/serenity/commit/c1ffc171345
Pull-request: https://github.com/SerenityOS/serenity/pull/9459

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

@@ -5,6 +5,7 @@
  */
 
 #include <AK/TypeCasts.h>
+#include <LibJS/Runtime/Array.h>
 #include <LibJS/Runtime/GlobalObject.h>
 #include <LibJS/Runtime/Temporal/AbstractOperations.h>
 #include <LibJS/Runtime/Temporal/Calendar.h>
@@ -47,6 +48,7 @@ void CalendarPrototype::initialize(GlobalObject& global_object)
     define_native_function(vm.names.daysInYear, days_in_year, 1, attr);
     define_native_function(vm.names.monthsInYear, months_in_year, 1, attr);
     define_native_function(vm.names.inLeapYear, in_leap_year, 1, attr);
+    define_native_function(vm.names.fields, fields, 1, attr);
     define_native_function(vm.names.toString, to_string, 0, attr);
     define_native_function(vm.names.toJSON, to_json, 0, attr);
 }
@@ -446,6 +448,30 @@ JS_DEFINE_NATIVE_FUNCTION(CalendarPrototype::in_leap_year)
     return Value(is_iso_leap_year(iso_year(temporal_date_like.as_object())));
 }
 
+// 12.4.21 Temporal.Calendar.prototype.fields ( fields ), https://tc39.es/proposal-temporal/#sec-temporal.calendar.prototype.fields
+// NOTE: This is the minimum fields implementation for engines without ECMA-402.
+JS_DEFINE_NATIVE_FUNCTION(CalendarPrototype::fields)
+{
+    auto fields = vm.argument(0);
+
+    // 1. Let calendar be the this value.
+    // 2. Perform ? RequireInternalSlot(calendar, [[InitializedTemporalCalendar]]).
+    auto* calendar = typed_this(global_object);
+    if (vm.exception())
+        return {};
+
+    // 3. Assert: calendar.[[Identifier]] is "iso8601".
+    VERIFY(calendar->identifier() == "iso8601"sv);
+
+    // 4. Let fieldNames be ? IterableToListOfType(fields, « String »).
+    auto field_names = iterable_to_list_of_type(global_object, fields, { OptionType::String });
+    if (vm.exception())
+        return {};
+
+    // 5. Return ! CreateArrayFromList(fieldNames).
+    return Array::create_from(global_object, field_names);
+}
+
 // 12.4.23 Temporal.Calendar.prototype.toString ( ), https://tc39.es/proposal-temporal/#sec-temporal.calendar.prototype.tostring
 JS_DEFINE_NATIVE_FUNCTION(CalendarPrototype::to_string)
 {

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

@@ -34,6 +34,7 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(days_in_year);
     JS_DECLARE_NATIVE_FUNCTION(months_in_year);
     JS_DECLARE_NATIVE_FUNCTION(in_leap_year);
+    JS_DECLARE_NATIVE_FUNCTION(fields);
     JS_DECLARE_NATIVE_FUNCTION(to_string);
     JS_DECLARE_NATIVE_FUNCTION(to_json);
 };

Userland/Libraries/LibJS/Tests/builtins/Temporal/Calendar/Calendar.prototype.fields.js

@@ -0,0 +1,30 @@
+describe("correct behavior", () => {
+    test("length is 1", () => {
+        expect(Temporal.Calendar.prototype.fields).toHaveLength(1);
+    });
+
+    test("basic functionality", () => {
+        const calendar = new Temporal.Calendar("iso8601");
+        const array = ["foo", "bar", "baz"];
+        const fields = calendar.fields(array);
+        expect(fields).toEqual(array);
+        expect(fields).not.toBe(array);
+    });
+});
+
+describe("errors", () => {
+    test("this value must be a Temporal.Calendar object", () => {
+        expect(() => {
+            Temporal.Calendar.prototype.fields.call("foo");
+        }).toThrowWithMessage(TypeError, "Not a Temporal.Calendar");
+    });
+
+    test("iterator values must be strings", () => {
+        const calendar = new Temporal.Calendar("iso8601");
+        for (const value of [123, null, undefined, true, {}]) {
+            expect(() => {
+                calendar.fields([value]);
+            }).toThrowWithMessage(TypeError, "FIXME: Add a string for this error.");
+        }
+    });
+});