LibJS: Start implementing Temporal.PlainYearMonth

This commit adds the PlainYearMonth object itself, its constructor and
prototype (currently empty), and the CreateTemporalYearMonth and
ISOYearMonthWithinLimits abstract operations.

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

@@ -4,10 +4,29 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <LibJS/Runtime/AbstractOperations.h>
+#include <LibJS/Runtime/GlobalObject.h>
+#include <LibJS/Runtime/Temporal/PlainDate.h>
 #include <LibJS/Runtime/Temporal/PlainYearMonth.h>
+#include <LibJS/Runtime/Temporal/PlainYearMonthConstructor.h>
 
 namespace JS::Temporal {
 
+// 9 Temporal.PlainYearMonth Objects, https://tc39.es/proposal-temporal/#sec-temporal-plainyearmonth-objects
+PlainYearMonth::PlainYearMonth(i32 iso_year, u8 iso_month, u8 iso_day, Object& calendar, Object& prototype)
+    : Object(prototype)
+    , m_iso_year(iso_year)
+    , m_iso_month(iso_month)
+    , m_iso_day(iso_day)
+    , m_calendar(calendar)
+{
+}
+
+void PlainYearMonth::visit_edges(Visitor& visitor)
+{
+    visitor.visit(&m_calendar);
+}
+
 // 9.5.5 BalanceISOYearMonth ( year, month ), https://tc39.es/proposal-temporal/#sec-temporal-balanceisoyearmonth
 ISOYearMonth balance_iso_year_month(i32 year, i32 month)
 {
@@ -23,4 +42,68 @@ ISOYearMonth balance_iso_year_month(i32 year, i32 month)
     return ISOYearMonth { .year = year, .month = static_cast<u8>(month) };
 }
 
+// 9.5.4 ISOYearMonthWithinLimits ( year, month ), https://tc39.es/proposal-temporal/#sec-temporal-isoyearmonthwithinlimits
+bool iso_year_month_within_limits(i32 year, u8 month)
+{
+    // 1. Assert: year and month are integers.
+
+    // 2. If year < −271821 or year > 275760, then
+    if (year < -271821 || year > 275760) {
+        // a. Return false.
+        return false;
+    }
+
+    // 3. If year is −271821 and month < 4, then
+    if (year == -271821 && month < 4) {
+        // a. Return false.
+        return false;
+    }
+
+    // 4. If year is 275760 and month > 9, then
+    if (year == 275760 && month > 9) {
+        // a. Return false.
+        return false;
+    }
+
+    // 5. Return true.
+    return true;
+}
+
+// 9.5.7 CreateTemporalYearMonth ( isoYear, isoMonth, calendar, referenceISODay [ , newTarget ] ), https://tc39.es/proposal-temporal/#sec-temporal-createtemporalyearmonth
+PlainYearMonth* create_temporal_year_month(GlobalObject& global_object, i32 iso_year, u8 iso_month, Object& calendar, u8 reference_iso_day, FunctionObject* new_target)
+{
+    auto& vm = global_object.vm();
+
+    // 1. Assert: isoYear, isoMonth, and referenceISODay are integers.
+    // 2. Assert: Type(calendar) is Object.
+
+    // 3. If ! IsValidISODate(isoYear, isoMonth, referenceISODay) is false, throw a RangeError exception.
+    if (!is_valid_iso_date(iso_year, iso_month, reference_iso_day)) {
+        vm.throw_exception<RangeError>(global_object, ErrorType::TemporalInvalidPlainYearMonth);
+        return {};
+    }
+
+    // 4. If ! ISOYearMonthWithinLimits(isoYear, isoMonth) is false, throw a RangeError exception.
+    if (!iso_year_month_within_limits(iso_year, iso_month)) {
+        vm.throw_exception<RangeError>(global_object, ErrorType::TemporalInvalidPlainYearMonth);
+        return {};
+    }
+
+    // 5. If newTarget is not present, set it to %Temporal.PlainYearMonth%.
+    if (!new_target)
+        new_target = global_object.temporal_plain_year_month_constructor();
+
+    // 6. Let object be ? OrdinaryCreateFromConstructor(newTarget, "%Temporal.PlainYearMonth.prototype%", « [[InitializedTemporalYearMonth]], [[ISOYear]], [[ISOMonth]], [[ISODay]], [[Calendar]] »).
+    // 7. Set object.[[ISOYear]] to isoYear.
+    // 8. Set object.[[ISOMonth]] to isoMonth.
+    // 9. Set object.[[Calendar]] to calendar.
+    // 10. Set object.[[ISODay]] to referenceISODay.
+    auto* object = ordinary_create_from_constructor<PlainYearMonth>(global_object, *new_target, &GlobalObject::temporal_plain_year_month_prototype, iso_year, iso_month, reference_iso_day, calendar);
+    if (vm.exception())
+        return {};
+
+    // 11. Return object.
+    return object;
+}
+
 }