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

10 files changed, 223 insertions, 14 deletions

diff --git a/Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h b/Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h
index 7d74ae6959..1e1d5c3b13 100644
--- a/Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h
+++ b/Userland/Libraries/LibJS/Runtime/CommonPropertyNames.h
@@ -420,6 +420,7 @@ namespace JS {
     P(withPlainDate)                         \
     P(writable)                              \
     P(year)                                  \
+    P(yearMonthFromFields)                   \
     P(years)                                 \
     P(zonedDateTime)                         \
     P(zonedDateTimeISO)
diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.cpp b/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.cpp
index e3f4597060..13f291aee5 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.cpp
@@ -1,5 +1,6 @@
 /*
  * Copyright (c) 2021, Idan Horowitz <idan.horowitz@serenityos.org>
+ * Copyright (c) 2021, Linus Groh <linusg@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -714,6 +715,48 @@ Optional<ISODate> iso_date_from_fields(GlobalObject& global_object, Object& fiel
     return regulate_iso_date(global_object, year.as_double(), month, day.as_double(), *overflow);
 }
 
+// 12.1.39 ISOYearMonthFromFields ( fields, options ), https://tc39.es/proposal-temporal/#sec-temporal-isoyearmonthfromfields
+Optional<ISOYearMonth> iso_year_month_from_fields(GlobalObject& global_object, Object& fields, Object& options)
+{
+    auto& vm = global_object.vm();
+
+    // 1. Assert: Type(fields) is Object.
+
+    // 2. Let overflow be ? ToTemporalOverflow(options).
+    auto overflow = to_temporal_overflow(global_object, options);
+    if (vm.exception())
+        return {};
+
+    // 3. Set fields to ? PrepareTemporalFields(fields, « "month", "monthCode", "year" », «»).
+    auto* prepared_fields = prepare_temporal_fields(global_object, fields, { "month"sv, "monthCode"sv, "year"sv }, {});
+    if (vm.exception())
+        return {};
+
+    // 4. Let year be ? Get(fields, "year").
+    auto year = prepared_fields->get(vm.names.year);
+    if (vm.exception())
+        return {};
+
+    // 5. If year is undefined, throw a TypeError exception.
+    if (year.is_undefined()) {
+        vm.throw_exception<TypeError>(global_object, ErrorType::TemporalMissingRequiredProperty, vm.names.year.as_string());
+        return {};
+    }
+
+    // 6. Let month be ? ResolveISOMonth(fields).
+    auto month = resolve_iso_month(global_object, *prepared_fields);
+    if (vm.exception())
+        return {};
+
+    // 7. Let result be ? RegulateISOYearMonth(year, month, overflow).
+    auto result = regulate_iso_year_month(global_object, year.as_double(), month, *overflow);
+    if (vm.exception())
+        return {};
+
+    // 8. Return the new Record { [[Year]]: result.[[Year]], [[Month]]: result.[[Month]], [[ReferenceISODay]]: 1 }.
+    return ISOYearMonth { .year = result->year, .month = result->month, .reference_iso_day = 1 };
+}
+
 // 12.1.41 ISOYear ( temporalObject ), https://tc39.es/proposal-temporal/#sec-temporal-isoyear
 i32 iso_year(Object& temporal_object)
 {
diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.h b/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.h
index 653d37b175..162144f85c 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.h
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/Calendar.h
@@ -9,6 +9,7 @@
 
 #include <LibJS/Runtime/Object.h>
 #include <LibJS/Runtime/Temporal/PlainDate.h>
+#include <LibJS/Runtime/Temporal/PlainYearMonth.h>
 #include <LibJS/Runtime/Value.h>
 
 namespace JS::Temporal {
@@ -59,6 +60,7 @@ u8 to_iso_week_of_year(i32 year, u8 month, u8 day);
 String build_iso_month_code(u8 month);
 double resolve_iso_month(GlobalObject&, Object& fields);
 Optional<ISODate> iso_date_from_fields(GlobalObject&, Object& fields, Object& options);
+Optional<ISOYearMonth> iso_year_month_from_fields(GlobalObject&, Object& fields, Object& options);
 i32 iso_year(Object& temporal_object);
 u8 iso_month(Object& temporal_object);
 String iso_month_code(Object& temporal_object);
diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.cpp b/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.cpp
index ac01702ae7..ecdd4ad969 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.cpp
@@ -34,6 +34,7 @@ void CalendarPrototype::initialize(GlobalObject& global_object)
 
     u8 attr = Attribute::Writable | Attribute::Configurable;
     define_native_function(vm.names.dateFromFields, date_from_fields, 2, attr);
+    define_native_function(vm.names.yearMonthFromFields, year_month_from_fields, 2, attr);
     define_native_function(vm.names.year, year, 1, attr);
     define_native_function(vm.names.month, month, 1, attr);
     define_native_function(vm.names.monthCode, month_code, 1, attr);
@@ -107,6 +108,40 @@ JS_DEFINE_NATIVE_FUNCTION(CalendarPrototype::date_from_fields)
     return create_temporal_date(global_object, result->year, result->month, result->day, *calendar);
 }
 
+// 12.4.5 Temporal.Calendar.prototype.yearMonthFromFields ( fields, options ), https://tc39.es/proposal-temporal/#sec-temporal.calendar.prototype.yearmonthfromfields
+// NOTE: This is the minimum yearMonthFromFields implementation for engines without ECMA-402.
+JS_DEFINE_NATIVE_FUNCTION(CalendarPrototype::year_month_from_fields)
+{
+    // 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. If Type(fields) is not Object, throw a TypeError exception.
+    auto fields = vm.argument(0);
+    if (!fields.is_object()) {
+        vm.throw_exception<TypeError>(global_object, ErrorType::NotAnObject, fields.to_string_without_side_effects());
+        return {};
+    }
+
+    // 5. Set options to ? GetOptionsObject(options).
+    auto* options = get_options_object(global_object, vm.argument(1));
+    if (vm.exception())
+        return {};
+
+    // 6. Let result be ? ISOYearMonthFromFields(fields, options).
+    auto result = iso_year_month_from_fields(global_object, fields.as_object(), *options);
+    if (vm.exception())
+        return {};
+
+    // 7. Return ? CreateTemporalYearMonth(result.[[Year]], result.[[Month]], calendar, result.[[ReferenceISODay]]).
+    return create_temporal_year_month(global_object, result->year, result->month, *calendar, result->reference_iso_day);
+}
+
 // 12.4.9 Temporal.Calendar.prototype.year ( temporalDateLike ), https://tc39.es/proposal-temporal/#sec-temporal.calendar.prototype.year
 // NOTE: This is the minimum year implementation for engines without ECMA-402.
 JS_DEFINE_NATIVE_FUNCTION(CalendarPrototype::year)
diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.h b/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.h
index 7cee764bba..c4d5a0d494 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.h
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/CalendarPrototype.h
@@ -21,6 +21,7 @@ public:
 private:
     JS_DECLARE_NATIVE_FUNCTION(id_getter);
     JS_DECLARE_NATIVE_FUNCTION(date_from_fields);
+    JS_DECLARE_NATIVE_FUNCTION(year_month_from_fields);
     JS_DECLARE_NATIVE_FUNCTION(year);
     JS_DECLARE_NATIVE_FUNCTION(month);
     JS_DECLARE_NATIVE_FUNCTION(month_code);
diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/PlainDate.cpp b/Userland/Libraries/LibJS/Runtime/Temporal/PlainDate.cpp
index 83d1a660fb..0b71e50244 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/PlainDate.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/PlainDate.cpp
@@ -237,18 +237,18 @@ bool is_valid_iso_date(i32 year, u8 month, u8 day)
 }
 
 // 3.5.6 BalanceISODate ( year, month, day ), https://tc39.es/proposal-temporal/#sec-temporal-balanceisodate
-ISODate balance_iso_date(i32 year, i32 month, i32 day)
+ISODate balance_iso_date(double year_, double month_, double day)
 {
     // 1. Assert: year, month, and day are integers.
 
     // 2. Let balancedYearMonth be ! BalanceISOYearMonth(year, month).
-    auto balanced_year_month = balance_iso_year_month(year, month);
+    auto balanced_year_month = balance_iso_year_month(year_, month_);
 
     // 3. Set month to balancedYearMonth.[[Month]].
-    month = balanced_year_month.month;
+    auto month = balanced_year_month.month;
 
     // 4. Set year to balancedYearMonth.[[Year]].
-    year = balanced_year_month.year;
+    auto year = balanced_year_month.year;
 
     // 5. NOTE: To deal with negative numbers of days whose absolute value is greater than the number of days in a year, the following section subtracts years and adds days until the number of days is greater than −366 or −365.
 
diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/PlainDate.h b/Userland/Libraries/LibJS/Runtime/Temporal/PlainDate.h
index b0985fe52d..37489ee3b7 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/PlainDate.h
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/PlainDate.h
@@ -44,7 +44,7 @@ PlainDate* create_temporal_date(GlobalObject&, i32 iso_year, u8 iso_month, u8 is
 PlainDate* to_temporal_date(GlobalObject&, Value item, Object* options = nullptr);
 Optional<ISODate> regulate_iso_date(GlobalObject&, double year, double month, double day, String const& overflow);
 bool is_valid_iso_date(i32 year, u8 month, u8 day);
-ISODate balance_iso_date(i32 year, i32 month, i32 day);
+ISODate balance_iso_date(double year, double month, double day);
 i8 compare_iso_date(i32 year1, u8 month1, u8 day1, i32 year2, u8 month2, u8 day2);
 
 }
diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/PlainYearMonth.cpp b/Userland/Libraries/LibJS/Runtime/Temporal/PlainYearMonth.cpp
index 248aa43192..aa61eb9a4b 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/PlainYearMonth.cpp
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/PlainYearMonth.cpp
@@ -6,6 +6,7 @@
 
 #include <LibJS/Runtime/AbstractOperations.h>
 #include <LibJS/Runtime/GlobalObject.h>
+#include <LibJS/Runtime/Temporal/AbstractOperations.h>
 #include <LibJS/Runtime/Temporal/PlainDate.h>
 #include <LibJS/Runtime/Temporal/PlainYearMonth.h>
 #include <LibJS/Runtime/Temporal/PlainYearMonthConstructor.h>
@@ -28,19 +29,67 @@ 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)
+// 9.5.2 RegulateISOYearMonth ( year, month, overflow ), https://tc39.es/proposal-temporal/#sec-temporal-regulateisoyearmonth
+Optional<ISOYearMonth> regulate_iso_year_month(GlobalObject& global_object, double year, double month, String const& overflow)
 {
+    auto& vm = global_object.vm();
+
     // 1. Assert: year and month are integers.
+    VERIFY(year == trunc(year) && month == trunc(month));
+
+    // 2. Assert: overflow is either "constrain" or "reject".
+    // NOTE: Asserted by the VERIFY_NOT_REACHED at the end
+
+    // 3. If overflow is "constrain", then
+    if (overflow == "constrain"sv) {
+        // IMPLEMENTATION DEFINED: This is an optimization that allows us to treat `year` (a double) as normal integer from this point onwards.
+        // This does not change the exposed behaviour as the subsequent call to CreateTemporalYearMonth will check that its value is a valid ISO
+        // values (for years: -273975 - 273975) which is a subset of this check.
+        // If RegulateISOYearMonth is ever used outside ISOYearMonthFromFields, this may need to be changed.
+        if (!AK::is_within_range<i32>(year)) {
+            vm.throw_exception<RangeError>(global_object, ErrorType::TemporalInvalidPlainYearMonth);
+            return {};
+        }
+
+        // a. Return ! ConstrainISOYearMonth(year, month).
+        return constrain_iso_year_month(year, month);
+    }
 
-    // 2. Set year to year + floor((month - 1) / 12).
-    year += (month - 1) / 12;
+    // 4. If overflow is "reject", then
+    if (overflow == "reject"sv) {
+        // IMPLEMENTATION DEFINED: This is an optimization that allows us to treat these doubles as normal integers from this point onwards.
+        // This does not change the exposed behaviour as the call to IsValidISOMonth and subsequent call to CreateTemporalDateTime will check
+        // that these values are valid ISO values (for years: -273975 - 273975, for months: 1 - 12) all of which are subsets of this check.
+        if (!AK::is_within_range<i32>(year) || !AK::is_within_range<u8>(month)) {
+            vm.throw_exception<RangeError>(global_object, ErrorType::TemporalInvalidPlainYearMonth);
+            return {};
+        }
+
+        // a. If ! IsValidISOMonth(month) is false, throw a RangeError exception.
+        if (!is_valid_iso_month(month)) {
+            vm.throw_exception<RangeError>(global_object, ErrorType::TemporalInvalidPlainYearMonth);
+            return {};
+        }
+
+        // b. Return the new Record { [[Year]]: year, [[Month]]: month }.
+        return ISOYearMonth { .year = static_cast<i32>(year), .month = static_cast<u8>(month), .reference_iso_day = 0 };
+    }
 
-    // 3. Set month to (month − 1) modulo 12 + 1.
-    month = (month - 1) % 12 + 1;
+    VERIFY_NOT_REACHED();
+}
 
-    // 4. Return the new Record { [[Year]]: year, [[Month]]: month }.
-    return ISOYearMonth { .year = year, .month = static_cast<u8>(month) };
+// 9.5.3 IsValidISOMonth ( month ), https://tc39.es/proposal-temporal/#sec-temporal-isvalidisomonth
+bool is_valid_iso_month(u8 month)
+{
+    // 1. Assert: month is an integer.
+    // 2. If month < 1 or month > 12, then
+    if (month < 1 || month > 12) {
+        // a.Return false.
+        return false;
+    }
+
+    // 3. Return true.
+    return true;
 }
 
 // 9.5.4 ISOYearMonthWithinLimits ( year, month ), https://tc39.es/proposal-temporal/#sec-temporal-isoyearmonthwithinlimits
@@ -70,6 +119,36 @@ bool iso_year_month_within_limits(i32 year, u8 month)
     return true;
 }
 
+// 9.5.5 BalanceISOYearMonth ( year, month ), https://tc39.es/proposal-temporal/#sec-temporal-balanceisoyearmonth
+ISOYearMonth balance_iso_year_month(double year, double month)
+{
+    // 1. Assert: year and month are integers.
+    VERIFY(year == trunc(year) && month == trunc(month));
+
+    // 2. Set year to year + floor((month - 1) / 12).
+    year += floor((month - 1) / 12);
+
+    // 3. Set month to (month − 1) modulo 12 + 1.
+    month = fmod(month - 1, 12) + 1;
+
+    // 4. Return the new Record { [[Year]]: year, [[Month]]: month }.
+    return ISOYearMonth { .year = static_cast<i32>(year), .month = static_cast<u8>(month), .reference_iso_day = 0 };
+}
+
+// 9.5.6 ConstrainISOYearMonth ( year, month ), https://tc39.es/proposal-temporal/#sec-temporal-constrainisoyearmonth
+ISOYearMonth constrain_iso_year_month(double year, double month)
+{
+    // 1. Assert: year and month are integers.
+    VERIFY(year == trunc(year) && month == trunc(month));
+
+    // 2. Set month to ! ConstrainToRange(month, 1, 12).
+    month = constrain_to_range(month, 1, 12);
+
+    // 3. Return the Record { [[Year]]: year, [[Month]]: month }.
+    // NOTE: `year` is known to be in the i32 range.
+    return ISOYearMonth { .year = static_cast<i32>(year), .month = static_cast<u8>(month), .reference_iso_day = 0 };
+}
+
 // 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)
 {
diff --git a/Userland/Libraries/LibJS/Runtime/Temporal/PlainYearMonth.h b/Userland/Libraries/LibJS/Runtime/Temporal/PlainYearMonth.h
index 12160fd011..063cb6ec25 100644
--- a/Userland/Libraries/LibJS/Runtime/Temporal/PlainYearMonth.h
+++ b/Userland/Libraries/LibJS/Runtime/Temporal/PlainYearMonth.h
@@ -36,10 +36,14 @@ private:
 struct ISOYearMonth {
     i32 year;
     u8 month;
+    u8 reference_iso_day;
 };
 
-ISOYearMonth balance_iso_year_month(i32 year, i32 month);
+Optional<ISOYearMonth> regulate_iso_year_month(GlobalObject&, double year, double month, String const& overflow);
+bool is_valid_iso_month(u8 month);
 bool iso_year_month_within_limits(i32 year, u8 month);
+ISOYearMonth balance_iso_year_month(double year, double month);
+ISOYearMonth constrain_iso_year_month(double year, double month);
 PlainYearMonth* create_temporal_year_month(GlobalObject&, i32 iso_year, u8 iso_month, Object& calendar, u8 reference_iso_day, FunctionObject* new_target = nullptr);
 
 }
diff --git a/Userland/Libraries/LibJS/Tests/builtins/Temporal/Calendar/Calendar.prototype.yearMonthFromFields.js b/Userland/Libraries/LibJS/Tests/builtins/Temporal/Calendar/Calendar.prototype.yearMonthFromFields.js
new file mode 100644
index 0000000000..058a137cd7
--- /dev/null
+++ b/Userland/Libraries/LibJS/Tests/builtins/Temporal/Calendar/Calendar.prototype.yearMonthFromFields.js
@@ -0,0 +1,44 @@
+describe("correct behavior", () => {
+    test("length is 2", () => {
+        expect(Temporal.Calendar.prototype.yearMonthFromFields).toHaveLength(2);
+    });
+
+    test("basic functionality", () => {
+        const calendar = new Temporal.Calendar("iso8601");
+        const plainYearMonth = calendar.yearMonthFromFields({ year: 2021, month: 7 });
+        expect(plainYearMonth.calendar).toBe(calendar);
+        expect(plainYearMonth.year).toBe(2021);
+        expect(plainYearMonth.month).toBe(7);
+    });
+
+    test("with monthCode", () => {
+        const calendar = new Temporal.Calendar("iso8601");
+        const plainYearMonth = calendar.yearMonthFromFields({ year: 2021, monthCode: "M07" });
+        expect(plainYearMonth.calendar).toBe(calendar);
+        expect(plainYearMonth.year).toBe(2021);
+        expect(plainYearMonth.month).toBe(7);
+    });
+});
+
+describe("errors", () => {
+    test("first argument must be an object", () => {
+        const calendar = new Temporal.Calendar("iso8601");
+        expect(() => {
+            calendar.yearMonthFromFields(42);
+        }).toThrowWithMessage(TypeError, "42 is not an object");
+    });
+
+    test("year field is required", () => {
+        const calendar = new Temporal.Calendar("iso8601");
+        expect(() => {
+            calendar.yearMonthFromFields({ month: 7 });
+        }).toThrowWithMessage(TypeError, "Required property year is missing or undefined");
+    });
+
+    test("month or monthCode field is required", () => {
+        const calendar = new Temporal.Calendar("iso8601");
+        expect(() => {
+            calendar.yearMonthFromFields({ year: 2021 });
+        }).toThrowWithMessage(TypeError, "Required property month is missing or undefined");
+    });
+});