LibJS: Implement Temporal.Duration.prototype.toString()

I hereby claim "implemented largest AO in LibJS ever" (450 lines). :^)

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

@@ -719,6 +719,21 @@ String format_seconds_string_part(u8 second, u16 millisecond, u16 microsecond, u
     return String::formatted("{}.{}", seconds_string, fraction_string);
 }
 
+// 13.28 Sign ( n ), https://tc39.es/proposal-temporal/#sec-temporal-sign
+double sign(double n)
+{
+    // 1. If n is NaN, n is +0𝔽, or n is −0𝔽, return n.
+    if (isnan(n) || n == 0)
+        return n;
+
+    // 2. If n < +0𝔽, return −1𝔽.
+    if (n < 0)
+        return -1;
+
+    // 3. Return 1𝔽.
+    return 1;
+}
+
 // 13.29 ConstrainToRange ( x, minimum, maximum ), https://tc39.es/proposal-temporal/#sec-temporal-constraintorange
 double constrain_to_range(double x, double minimum, double maximum)
 {

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

@@ -110,6 +110,7 @@ ThrowCompletionOr<Object*> merge_largest_unit_option(GlobalObject&, Object& opti
 Optional<u16> maximum_temporal_duration_rounding_increment(StringView unit);
 ThrowCompletionOr<void> reject_object_with_calendar_or_time_zone(GlobalObject&, Object&);
 String format_seconds_string_part(u8 second, u16 millisecond, u16 microsecond, u16 nanosecond, Variant<StringView, u8> const& precision);
+double sign(double);
 double constrain_to_range(double x, double minimum, double maximum);
 i64 round_number_to_increment(double, u64 increment, StringView rounding_mode);
 BigInt* round_number_to_increment(GlobalObject&, BigInt const&, u64 increment, StringView rounding_mode);

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

@@ -4,13 +4,18 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <AK/StringBuilder.h>
 #include <LibJS/Runtime/AbstractOperations.h>
 #include <LibJS/Runtime/Completion.h>
 #include <LibJS/Runtime/GlobalObject.h>
 #include <LibJS/Runtime/Object.h>
 #include <LibJS/Runtime/Temporal/AbstractOperations.h>
+#include <LibJS/Runtime/Temporal/Calendar.h>
 #include <LibJS/Runtime/Temporal/Duration.h>
 #include <LibJS/Runtime/Temporal/DurationConstructor.h>
+#include <LibJS/Runtime/Temporal/Instant.h>
+#include <LibJS/Runtime/Temporal/PlainDateTime.h>
+#include <LibJS/Runtime/Temporal/TimeZone.h>
 #include <LibJS/Runtime/Temporal/ZonedDateTime.h>
 
 namespace JS::Temporal {
@@ -436,6 +441,490 @@ ThrowCompletionOr<BalancedDuration> balance_duration(GlobalObject& global_object
     return BalancedDuration { .days = days, .hours = hours * sign, .minutes = minutes * sign, .seconds = seconds * sign, .milliseconds = milliseconds * sign, .microseconds = microseconds * sign, .nanoseconds = result_nanoseconds * sign };
 }
 
+// 7.5.16 MoveRelativeDate ( calendar, relativeTo, duration ), https://tc39.es/proposal-temporal/#sec-temporal-moverelativedate
+ThrowCompletionOr<MoveRelativeDateResult> move_relative_date(GlobalObject& global_object, Object& calendar, PlainDateTime& relative_to, Duration& duration)
+{
+    // 1. Assert: Type(relativeTo) is Object.
+    // 2. Assert: relativeTo has an [[InitializedTemporalDateTime]] internal slot.
+
+    // 3. Let options be ! OrdinaryObjectCreate(null).
+    auto* options = Object::create(global_object, nullptr);
+
+    // 4. Let later be ? CalendarDateAdd(calendar, relativeTo, duration, options).
+    auto* later = TRY(calendar_date_add(global_object, calendar, &relative_to, duration, options));
+
+    // FIXME: This cannot return an abrupt completion (spec issue, see https://github.com/tc39/proposal-temporal/pull/1909)
+    // 5. Let days be ? DaysUntil(relativeTo, later).
+    auto days = days_until(global_object, relative_to, *later);
+
+    // 6. Let dateTime be ? CreateTemporalDateTime(later.[[ISOYear]], later.[[ISOMonth]], later.[[ISODay]], relativeTo.[[ISOHour]], relativeTo.[[ISOMinute]], relativeTo.[[ISOSecond]], relativeTo.[[ISOMillisecond]], relativeTo.[[ISOMicrosecond]], relativeTo.[[ISONanosecond]], relativeTo.[[Calendar]]).
+    auto* date_time = TRY(create_temporal_date_time(global_object, later->iso_year(), later->iso_month(), later->iso_day(), relative_to.iso_hour(), relative_to.iso_minute(), relative_to.iso_second(), relative_to.iso_millisecond(), relative_to.iso_microsecond(), relative_to.iso_nanosecond(), relative_to.calendar()));
+
+    // 7. Return the Record { [[RelativeTo]]: dateTime, [[Days]]: days }.
+    return MoveRelativeDateResult { .relative_to = make_handle(date_time), .days = days };
+}
+
+// 7.5.17 MoveRelativeZonedDateTime ( zonedDateTime, years, months, weeks, days ), https://tc39.es/proposal-temporal/#sec-temporal-moverelativezoneddatetime
+ThrowCompletionOr<ZonedDateTime*> move_relative_zoned_date_time(GlobalObject& global_object, ZonedDateTime& zoned_date_time, double years, double months, double weeks, double days)
+{
+    // 1. Let intermediateNs be ? AddZonedDateTime(zonedDateTime.[[Nanoseconds]], zonedDateTime.[[TimeZone]], zonedDateTime.[[Calendar]], years, months, weeks, days, 0, 0, 0, 0, 0, 0).
+    auto* intermediate_ns = TRY(add_zoned_date_time(global_object, zoned_date_time.nanoseconds(), &zoned_date_time.time_zone(), zoned_date_time.calendar(), years, months, weeks, days, 0, 0, 0, 0, 0, 0));
+
+    // 2. Return ! CreateTemporalZonedDateTime(intermediateNs, zonedDateTime.[[TimeZone]], zonedDateTime.[[Calendar]]).
+    return MUST(create_temporal_zoned_date_time(global_object, *intermediate_ns, zoned_date_time.time_zone(), zoned_date_time.calendar()));
+}
+
+// 7.5.18 RoundDuration ( years, months, weeks, days, hours, minutes, seconds, milliseconds, microseconds, nanoseconds, increment, unit, roundingMode [ , relativeTo ] ), https://tc39.es/proposal-temporal/#sec-temporal-roundduration
+ThrowCompletionOr<RoundedDuration> round_duration(GlobalObject& global_object, double years, double months, double weeks, double days, double hours, double minutes, double seconds, double milliseconds, double microseconds, double nanoseconds, u32 increment, StringView unit, StringView rounding_mode, Object* relative_to_object)
+{
+    auto& vm = global_object.vm();
+
+    Object* calendar = nullptr;
+    double fractional_seconds = 0;
+
+    // 1. If relativeTo is not present, set relativeTo to undefined.
+    // NOTE: `relative_to_object`, `relative_to_date`, and `relative_to` in the various code paths below
+    // are all the same as far as the spec is concerned, but the latter two are more strictly typed for convenience.
+    // The `_date` suffix is used as relativeTo is guaranteed to be a PlainDateTime object or undefined after step 5
+    // (i.e. PlainDateTime*), but a PlainDate object is assigned in a couple of cases.
+    PlainDateTime* relative_to = nullptr;
+
+    // 2. Let years, months, weeks, days, hours, minutes, seconds, milliseconds, microseconds, nanoseconds, and increment each be the mathematical values of themselves.
+
+    // 3. If unit is "year", "month", or "week", and relativeTo is undefined, then
+    if (unit.is_one_of("year"sv, "month"sv, "week"sv) && !relative_to_object) {
+        // a. Throw a RangeError exception.
+        return vm.throw_completion<RangeError>(global_object, ErrorType::OptionIsNotValidValue, unit, "smallestUnit"sv);
+    }
+
+    // 4. Let zonedRelativeTo be undefined.
+    ZonedDateTime* zoned_relative_to = nullptr;
+
+    // 5. If relativeTo is not undefined, then
+    if (relative_to_object) {
+        // a. If relativeTo has an [[InitializedTemporalZonedDateTime]] internal slot, then
+        if (is<ZonedDateTime>(relative_to_object)) {
+            auto* relative_to_zoned_date_time = static_cast<ZonedDateTime*>(relative_to_object);
+
+            // i. Let instant be ! CreateTemporalInstant(relativeTo.[[Nanoseconds]]).
+            auto* instant = MUST(create_temporal_instant(global_object, relative_to_zoned_date_time->nanoseconds()));
+
+            // ii. Set zonedRelativeTo to relativeTo.
+            zoned_relative_to = relative_to_zoned_date_time;
+
+            // iii. Set relativeTo to ? BuiltinTimeZoneGetPlainDateTimeFor(relativeTo.[[TimeZone]], instant, relativeTo.[[Calendar]]).
+            relative_to = TRY(builtin_time_zone_get_plain_date_time_for(global_object, &relative_to_zoned_date_time->time_zone(), *instant, relative_to_zoned_date_time->calendar()));
+        }
+        // b. Else,
+        else {
+            // i. Assert: relativeTo has an [[InitializedTemporalDateTime]] internal slot.
+            VERIFY(is<PlainDateTime>(relative_to_object));
+
+            relative_to = static_cast<PlainDateTime*>(relative_to_object);
+        }
+
+        // c. Let calendar be relativeTo.[[Calendar]].
+        calendar = &relative_to->calendar();
+    }
+
+    // 6. If unit is one of "year", "month", "week", or "day", then
+    if (unit.is_one_of("year"sv, "month"sv, "week"sv, "day"sv)) {
+        auto* nanoseconds_bigint = js_bigint(vm, Crypto::SignedBigInteger::create_from((i64)nanoseconds));
+
+        // a. Let nanoseconds be ! TotalDurationNanoseconds(0, hours, minutes, seconds, milliseconds, microseconds, nanoseconds, 0).
+        nanoseconds_bigint = total_duration_nanoseconds(global_object, 0, hours, minutes, seconds, milliseconds, microseconds, *nanoseconds_bigint, 0);
+
+        // b. Let intermediate be undefined.
+        ZonedDateTime* intermediate = nullptr;
+
+        // c. If zonedRelativeTo is not undefined, then
+        if (zoned_relative_to) {
+            // i. Let intermediate be ? MoveRelativeZonedDateTime(zonedRelativeTo, years, months, weeks, days).
+            intermediate = TRY(move_relative_zoned_date_time(global_object, *zoned_relative_to, years, months, weeks, days));
+        }
+
+        // d. Let result be ? NanosecondsToDays(nanoseconds, intermediate).
+        auto result = TRY(nanoseconds_to_days(global_object, *nanoseconds_bigint, intermediate));
+
+        // e. Set days to days + result.[[Days]] + result.[[Nanoseconds]] / result.[[DayLength]].
+        days += result.days + result.nanoseconds.cell()->big_integer().divided_by(Crypto::UnsignedBigInteger::create_from((u64)result.day_length)).quotient.to_double();
+
+        // f. Set hours, minutes, seconds, milliseconds, microseconds, and nanoseconds to 0.
+        hours = 0;
+        minutes = 0;
+        seconds = 0;
+        milliseconds = 0;
+        microseconds = 0;
+        nanoseconds = 0;
+    }
+    // 7. Else,
+    else {
+        // a. Let fractionalSeconds be nanoseconds × 10^−9 + microseconds × 10^−6 + milliseconds × 10^−3 + seconds.
+        fractional_seconds = nanoseconds * 0.000000001 + microseconds * 0.000001 + milliseconds * 0.001 + seconds;
+    }
+
+    // 8. Let remainder be undefined.
+    double remainder = 0;
+
+    // 9. If unit is "year", then
+    if (unit == "year"sv) {
+        VERIFY(relative_to);
+
+        // a. Let yearsDuration be ? CreateTemporalDuration(years, 0, 0, 0, 0, 0, 0, 0, 0, 0).
+        auto* years_duration = TRY(create_temporal_duration(global_object, years, 0, 0, 0, 0, 0, 0, 0, 0, 0));
+
+        // b. Let dateAdd be ? GetMethod(calendar, "dateAdd").
+        auto* date_add = TRY(Value(calendar).get_method(global_object, vm.names.dateAdd));
+
+        // c. Let firstAddOptions be ! OrdinaryObjectCreate(null).
+        auto* first_add_options = Object::create(global_object, nullptr);
+
+        // d. Let yearsLater be ? CalendarDateAdd(calendar, relativeTo, yearsDuration, firstAddOptions, dateAdd).
+        auto* years_later = TRY(calendar_date_add(global_object, *calendar, relative_to, *years_duration, first_add_options, date_add));
+
+        // e. Let yearsMonthsWeeks be ? CreateTemporalDuration(years, months, weeks, 0, 0, 0, 0, 0, 0, 0).
+        auto* years_months_weeks = TRY(create_temporal_duration(global_object, years, months, weeks, 0, 0, 0, 0, 0, 0, 0));
+
+        // f. Let secondAddOptions be ! OrdinaryObjectCreate(null).
+        auto* second_add_options = Object::create(global_object, nullptr);
+
+        // g. Let yearsMonthsWeeksLater be ? CalendarDateAdd(calendar, relativeTo, yearsMonthsWeeks, secondAddOptions, dateAdd).
+        auto* years_months_weeks_later = TRY(calendar_date_add(global_object, *calendar, relative_to, *years_months_weeks, second_add_options, date_add));
+
+        // FIXME: This cannot return an abrupt completion (spec issue, see https://github.com/tc39/proposal-temporal/pull/1909)
+        // h. Let monthsWeeksInDays be ? DaysUntil(yearsLater, yearsMonthsWeeksLater).
+        auto months_weeks_in_days = days_until(global_object, *years_later, *years_months_weeks_later);
+
+        // i. Set relativeTo to yearsLater.
+        auto* relative_to_date = years_later;
+
+        // j. Let days be days + monthsWeeksInDays.
+        days += months_weeks_in_days;
+
+        // k. Let daysDuration be ? CreateTemporalDuration(0, 0, 0, days, 0, 0, 0, 0, 0, 0).
+        auto* days_duration = TRY(create_temporal_duration(global_object, 0, 0, 0, days, 0, 0, 0, 0, 0, 0));
+
+        // l. Let thirdAddOptions be ! OrdinaryObjectCreate(null).
+        auto* third_add_options = Object::create(global_object, nullptr);
+
+        // m. Let daysLater be ? CalendarDateAdd(calendar, relativeTo, daysDuration, thirdAddOptions, dateAdd).
+        auto* days_later = TRY(calendar_date_add(global_object, *calendar, relative_to_date, *days_duration, third_add_options, date_add));
+
+        // n. Let untilOptions be ! OrdinaryObjectCreate(null).
+        auto* until_options = Object::create(global_object, nullptr);
+
+        // o. Perform ! CreateDataPropertyOrThrow(untilOptions, "largestUnit", "year").
+        MUST(until_options->create_data_property_or_throw(vm.names.largestUnit, js_string(vm, "year"sv)));
+
+        // p. Let timePassed be ? CalendarDateUntil(calendar, relativeTo, daysLater, untilOptions).
+        auto* time_passed = TRY(calendar_date_until(global_object, *calendar, *relative_to_date, *days_later, *until_options));
+
+        // q. Let yearsPassed be timePassed.[[Years]].
+        auto years_passed = time_passed->years();
+
+        // r. Set years to years + yearsPassed.
+        years += years_passed;
+
+        // s. Let oldRelativeTo be relativeTo.
+        auto* old_relative_to_date = relative_to_date;
+
+        // t. Let yearsDuration be ? CreateTemporalDuration(yearsPassed, 0, 0, 0, 0, 0, 0, 0, 0, 0).
+        years_duration = TRY(create_temporal_duration(global_object, years_passed, 0, 0, 0, 0, 0, 0, 0, 0, 0));
+
+        // u. Let fourthAddOptions be ! OrdinaryObjectCreate(null).
+        auto* fourth_add_options = Object::create(global_object, nullptr);
+
+        // v. Set relativeTo to ? CalendarDateAdd(calendar, relativeTo, yearsDuration, fourthAddOptions, dateAdd).
+        relative_to_date = TRY(calendar_date_add(global_object, *calendar, relative_to_date, *years_duration, fourth_add_options, date_add));
+
+        // FIXME: This cannot return an abrupt completion (spec issue, see https://github.com/tc39/proposal-temporal/pull/1909)
+        // w. Let daysPassed be ? DaysUntil(oldRelativeTo, relativeTo).
+        auto days_passed = days_until(global_object, *old_relative_to_date, *relative_to_date);
+
+        // x. Set days to days - daysPassed.
+        days -= days_passed;
+
+        // y. Let sign be ! Sign(days).
+        auto sign = JS::Temporal::sign(days);
+
+        // z. If sign is 0, set sign to 1.
+        if (sign == 0)
+            sign = 1;
+
+        // aa. Let oneYear be ? CreateTemporalDuration(sign, 0, 0, 0, 0, 0, 0, 0, 0, 0).
+        auto* one_year = TRY(create_temporal_duration(global_object, sign, 0, 0, 0, 0, 0, 0, 0, 0, 0));
+
+        // ab. Set relativeTo to ! CreateTemporalDateTime(relativeTo.[[ISOYear]], relativeTo.[[ISOMonth]], relativeTo.[[ISODay]], 0, 0, 0, 0, 0, 0, relativeTo.[[Calendar]]).
+        relative_to = MUST(create_temporal_date_time(global_object, relative_to_date->iso_year(), relative_to_date->iso_month(), relative_to_date->iso_day(), 0, 0, 0, 0, 0, 0, relative_to->calendar()));
+
+        // ac. Let moveResult be ? MoveRelativeDate(calendar, relativeTo, oneYear).
+        auto move_result = TRY(move_relative_date(global_object, *calendar, *relative_to, *one_year));
+
+        // ad. Let oneYearDays be moveResult.[[Days]].
+        auto one_year_days = move_result.days;
+
+        // ae. Let fractionalYears be years + days / abs(oneYearDays).
+        auto fractional_years = years + days / fabs(one_year_days);
+
+        // af. Set years to ! RoundNumberToIncrement(fractionalYears, increment, roundingMode).
+        years = (double)round_number_to_increment(fractional_years, increment, rounding_mode);
+
+        // ag. Set remainder to fractionalYears - years.
+        remainder = fractional_years - years;
+
+        // ah. Set months, weeks, and days to 0.
+        months = 0;
+        weeks = 0;
+        days = 0;
+    }
+    // 10. Else if unit is "month", then
+    else if (unit == "month"sv) {
+        VERIFY(relative_to);
+
+        // a. Let yearsMonths be ? CreateTemporalDuration(years, months, 0, 0, 0, 0, 0, 0, 0, 0).
+        auto* years_months = TRY(create_temporal_duration(global_object, years, months, 0, 0, 0, 0, 0, 0, 0, 0));
+
+        // b. Let dateAdd be ? GetMethod(calendar, "dateAdd").
+        auto* date_add = TRY(Value(calendar).get_method(global_object, vm.names.dateAdd));
+
+        // c. Let firstAddOptions be ! OrdinaryObjectCreate(null).
+        auto* first_add_options = Object::create(global_object, nullptr);
+
+        // d. Let yearsMonthsLater be ? CalendarDateAdd(calendar, relativeTo, yearsMonths, firstAddOptions, dateAdd).
+        auto* years_months_later = TRY(calendar_date_add(global_object, *calendar, relative_to, *years_months, first_add_options, date_add));
+
+        // e. Let yearsMonthsWeeks be ? CreateTemporalDuration(years, months, weeks, 0, 0, 0, 0, 0, 0, 0).
+        auto* years_months_weeks = TRY(create_temporal_duration(global_object, years, months, weeks, 0, 0, 0, 0, 0, 0, 0));
+
+        // f. Let secondAddOptions be ! OrdinaryObjectCreate(null).
+        auto* seconds_add_options = Object::create(global_object, nullptr);
+
+        // g. Let yearsMonthsWeeksLater be ? CalendarDateAdd(calendar, relativeTo, yearsMonthsWeeks, secondAddOptions, dateAdd).
+        auto* years_months_weeks_later = TRY(calendar_date_add(global_object, *calendar, relative_to, *years_months_weeks, seconds_add_options, date_add));
+
+        // FIXME: This cannot return an abrupt completion (spec issue, see https://github.com/tc39/proposal-temporal/pull/1909)
+        // h. Let weeksInDays be ? DaysUntil(yearsMonthsLater, yearsMonthsWeeksLater).
+        auto weeks_in_days = days_until(global_object, *years_months_later, *years_months_weeks_later);
+
+        // i. Set relativeTo to yearsMonthsLater.
+        auto* relative_to_date = years_months_later;
+
+        // j. Let days be days + weeksInDays.
+        days += weeks_in_days;
+
+        // k. Let sign be ! Sign(days).
+        auto sign = JS::Temporal::sign(days);
+
+        // l. If sign is 0, set sign to 1.
+        if (sign == 0)
+            sign = 1;
+
+        // m. Let oneMonth be ? CreateTemporalDuration(0, sign, 0, 0, 0, 0, 0, 0, 0, 0).
+        auto* one_month = TRY(create_temporal_duration(global_object, 0, sign, 0, 0, 0, 0, 0, 0, 0, 0));
+
+        // n. Set relativeTo to ! CreateTemporalDateTime(relativeTo.[[ISOYear]], relativeTo.[[ISOMonth]], relativeTo.[[ISODay]], 0, 0, 0, 0, 0, 0, relativeTo.[[Calendar]]).
+        relative_to = MUST(create_temporal_date_time(global_object, relative_to_date->iso_year(), relative_to_date->iso_month(), relative_to_date->iso_day(), 0, 0, 0, 0, 0, 0, relative_to_date->calendar()));
+
+        // o. Let moveResult be ? MoveRelativeDate(calendar, relativeTo, oneMonth).
+        auto move_result = TRY(move_relative_date(global_object, *calendar, *relative_to, *one_month));
+
+        // p. Set relativeTo to moveResult.[[RelativeTo]].
+        relative_to = move_result.relative_to.cell();
+
+        // q. Let oneMonthDays be moveResult.[[Days]].
+        auto one_month_days = move_result.days;
+
+        // r. Repeat, while abs(days) ≥ abs(oneMonthDays),
+        while (fabs(days) >= fabs(one_month_days)) {
+            // i. Set months to months + sign.
+            months += sign;
+
+            // ii. Set days to days − oneMonthDays.
+            days -= one_month_days;
+
+            // iii. Set moveResult to ? MoveRelativeDate(calendar, relativeTo, oneMonth).
+            move_result = TRY(move_relative_date(global_object, *calendar, *relative_to, *one_month));
+
+            // iv. Set relativeTo to moveResult.[[RelativeTo]].
+            relative_to = move_result.relative_to.cell();
+
+            // v. Set oneMonthDays to moveResult.[[Days]].
+            one_month_days = move_result.days;
+        }
+
+        // s. Let fractionalMonths be months + days / abs(oneMonthDays).
+        auto fractional_months = months + days / fabs(one_month_days);
+
+        // t. Set months to ! RoundNumberToIncrement(fractionalMonths, increment, roundingMode).
+        months = (double)round_number_to_increment(fractional_months, increment, rounding_mode);
+
+        // u. Set remainder to fractionalMonths - months.
+        remainder = fractional_months - months;
+
+        // v. Set weeks and days to 0.
+        weeks = 0;
+        days = 0;
+    }
+    // 11. Else if unit is "week", then
+    else if (unit == "week"sv) {
+        VERIFY(relative_to);
+
+        // a. Let sign be ! Sign(days).
+        auto sign = JS::Temporal::sign(days);
+
+        // b. If sign is 0, set sign to 1.
+        if (sign == 0)
+            sign = 1;
+
+        // c. Let oneWeek be ? CreateTemporalDuration(0, 0, sign, 0, 0, 0, 0, 0, 0, 0).
+        auto* one_week = TRY(create_temporal_duration(global_object, 0, 0, sign, 0, 0, 0, 0, 0, 0, 0));
+
+        // d. Let moveResult be ? MoveRelativeDate(calendar, relativeTo, oneWeek).
+        auto move_result = TRY(move_relative_date(global_object, *calendar, *relative_to, *one_week));
+
+        // e. Set relativeTo to moveResult.[[RelativeTo]].
+        relative_to = move_result.relative_to.cell();
+
+        // f. Let oneWeekDays be moveResult.[[Days]].
+        auto one_week_days = move_result.days;
+
+        // g. Repeat, while abs(days) ≥ abs(oneWeekDays),
+        while (fabs(days) >= fabs(one_week_days)) {
+            // i. Set weeks to weeks + sign.
+            weeks += sign;
+
+            // ii. Set days to days − oneWeekDays.
+            days -= one_week_days;
+
+            // iii. Set moveResult to ? MoveRelativeDate(calendar, relativeTo, oneWeek).
+            move_result = TRY(move_relative_date(global_object, *calendar, *relative_to, *one_week));
+
+            // iv. Set relativeTo to moveResult.[[RelativeTo]].
+            relative_to = move_result.relative_to.cell();
+
+            // v. Set oneWeekDays to moveResult.[[Days]].
+            one_week_days = move_result.days;
+        }
+
+        // h. Let fractionalWeeks be weeks + days / abs(oneWeekDays).
+        auto fractional_weeks = weeks + days / fabs(one_week_days);
+
+        // i. Set weeks to ! RoundNumberToIncrement(fractionalWeeks, increment, roundingMode).
+        weeks = (double)round_number_to_increment(fractional_weeks, increment, rounding_mode);
+
+        // j. Set remainder to fractionalWeeks - weeks.
+        remainder = fractional_weeks - weeks;
+
+        // k. Set days to 0.
+        days = 0;
+    }
+    // 12. Else if unit is "day", then
+    else if (unit == "day"sv) {
+        // a. Let fractionalDays be days.
+        auto fractional_days = days;
+
+        // b. Set days to ! RoundNumberToIncrement(days, increment, roundingMode).
+        days = (double)round_number_to_increment(days, increment, rounding_mode);
+
+        // c. Set remainder to fractionalDays - days.
+        remainder = fractional_days - days;
+    }
+    // 13. Else if unit is "hour", then
+    else if (unit == "hour"sv) {
+        // a. Let fractionalHours be (fractionalSeconds / 60 + minutes) / 60 + hours.
+        auto fractional_hours = (fractional_seconds / 60 + minutes) / 60 + hours;
+
+        // b. Set hours to ! RoundNumberToIncrement(fractionalHours, increment, roundingMode).
+        hours = (double)round_number_to_increment(fractional_hours, increment, rounding_mode);
+
+        // c. Set remainder to fractionalHours - hours.
+        remainder = fractional_hours - days;
+
+        // d. Set minutes, seconds, milliseconds, microseconds, and nanoseconds to 0.
+        minutes = 0;
+        seconds = 0;
+        milliseconds = 0;
+        microseconds = 0;
+        nanoseconds = 0;
+    }
+    // 14. Else if unit is "minute", then
+    else if (unit == "minute"sv) {
+        // a. Let fractionalMinutes be fractionalSeconds / 60 + minutes.
+        auto fractional_minutes = fractional_seconds / 60 + minutes;
+
+        // b. Set minutes to ! RoundNumberToIncrement(fractionalMinutes, increment, roundingMode).
+        minutes = (double)round_number_to_increment(fractional_minutes, increment, rounding_mode);
+
+        // c. Set remainder to fractionalMinutes - minutes.
+        remainder = fractional_minutes - minutes;
+
+        // d. Set seconds, milliseconds, microseconds, and nanoseconds to 0.
+        seconds = 0;
+        milliseconds = 0;
+        microseconds = 0;
+        nanoseconds = 0;
+    }
+    // 15. Else if unit is "second", then
+    else if (unit == "second"sv) {
+        // a. Set seconds to ! RoundNumberToIncrement(fractionalSeconds, increment, roundingMode).
+        seconds = (double)round_number_to_increment(fractional_seconds, increment, rounding_mode);
+
+        // b. Set remainder to fractionalSeconds - seconds.
+        remainder = fractional_seconds - seconds;
+
+        // c. Set milliseconds, microseconds, and nanoseconds to 0.
+        milliseconds = 0;
+        microseconds = 0;
+        nanoseconds = 0;
+    }
+    // 16. Else if unit is "millisecond", then
+    else if (unit == "millisecond"sv) {
+        // a. Let fractionalMilliseconds be nanoseconds × 10^−6 + microseconds × 10^−3 + milliseconds.
+        auto fractional_milliseconds = nanoseconds * 0.000001 + microseconds * 0.001 + milliseconds;
+
+        // b. Set milliseconds to ! RoundNumberToIncrement(fractionalMilliseconds, increment, roundingMode).
+        milliseconds = (double)round_number_to_increment(fractional_milliseconds, increment, rounding_mode);
+
+        // c. Set remainder to fractionalMilliseconds - milliseconds.
+        remainder = fractional_milliseconds - milliseconds;
+
+        // d. Set microseconds and nanoseconds to 0.
+        microseconds = 0;
+        nanoseconds = 0;
+    }
+    // 17. Else if unit is "microsecond", then
+    else if (unit == "microsecond"sv) {
+        // a. Let fractionalMicroseconds be nanoseconds × 10^−3 + microseconds.
+        auto fractional_microseconds = nanoseconds * 0.001 + microseconds;
+
+        // b. Set microseconds to ! RoundNumberToIncrement(fractionalMicroseconds, increment, roundingMode).
+        microseconds = (double)round_number_to_increment(fractional_microseconds, increment, rounding_mode);
+
+        // c. Set remainder to fractionalMicroseconds - microseconds.
+        remainder = fractional_microseconds - microseconds;
+
+        // d. Set nanoseconds to 0.
+        nanoseconds = 0;
+    }
+    // 18. Else,
+    else {
+        // a. Assert: unit is "nanosecond".
+        VERIFY(unit == "nanosecond"sv);
+
+        // b. Set remainder to nanoseconds.
+        remainder = nanoseconds;
+
+        // c. Set nanoseconds to ! RoundNumberToIncrement(nanoseconds, increment, roundingMode).
+        nanoseconds = (double)round_number_to_increment(nanoseconds, increment, rounding_mode);
+
+        // d. Set remainder to remainder − nanoseconds.
+        remainder -= nanoseconds;
+    }
+
+    // Return the Record { [[Years]]: years, [[Months]]: months, [[Weeks]]: weeks, [[Days]]: days, [[Hours]]: hours, [[Minutes]]: minutes, [[Seconds]]: seconds, [[Milliseconds]]: milliseconds, [[Microseconds]]: microseconds, [[Nanoseconds]]: nanoseconds, [[Remainder]]: remainder }.
+    return RoundedDuration { .years = years, .months = months, .weeks = weeks, .days = days, .hours = hours, .minutes = minutes, .seconds = seconds, .milliseconds = milliseconds, .microseconds = microseconds, .nanoseconds = nanoseconds, .remainder = remainder };
+}
+
 // 7.5.20 ToLimitedTemporalDuration ( temporalDurationLike, disallowedFields ),https://tc39.es/proposal-temporal/#sec-temporal-tolimitedtemporalduration
 ThrowCompletionOr<TemporalDuration> to_limited_temporal_duration(GlobalObject& global_object, Value temporal_duration_like, Vector<StringView> const& disallowed_fields)
 {
@@ -479,4 +968,148 @@ ThrowCompletionOr<TemporalDuration> to_limited_temporal_duration(GlobalObject& g
     return duration;
 }
 
+// 7.5.21 TemporalDurationToString ( years, months, weeks, days, hours, minutes, seconds, milliseconds, microseconds, nanoseconds, precision ), https://tc39.es/proposal-temporal/#sec-temporal-temporaldurationtostring
+String temporal_duration_to_string(double years, double months, double weeks, double days, double hours, double minutes, double seconds, double milliseconds, double microseconds, double nanoseconds, Variant<StringView, u8> const& precision)
+{
+    // 1. Assert: precision is not "minute".
+    if (precision.has<StringView>())
+        VERIFY(precision.get<StringView>() != "minute"sv);
+
+    // 2. Set seconds to the mathematical value of seconds.
+    // 3. Set milliseconds to the mathematical value of milliseconds.
+    // 4. Set microseconds to the mathematical value of microseconds.
+    // 5. Set nanoseconds to the mathematical value of nanoseconds.
+
+    // 6. Let sign be ! DurationSign(years, months, weeks, days, hours, minutes, seconds, milliseconds, microseconds, nanoseconds).
+    auto sign = duration_sign(years, months, weeks, days, hours, minutes, seconds, milliseconds, microseconds, nanoseconds);
+
+    // 7. Set microseconds to microseconds + the integral part of nanoseconds / 1000.
+    microseconds += trunc(nanoseconds / 1000);
+
+    // 8. Set nanoseconds to remainder(nanoseconds, 1000).
+    nanoseconds = fmod(nanoseconds, 1000);
+
+    // 9. Set milliseconds to milliseconds + the integral part of microseconds / 1000.
+    milliseconds += trunc(microseconds / 1000);
+
+    // 10. Set microseconds to remainder(microseconds, 1000).
+    microseconds = fmod(microseconds, 1000);
+
+    // 11. Set seconds to seconds + the integral part of milliseconds / 1000.
+    seconds += trunc(milliseconds / 1000);
+
+    // 12. Set milliseconds to remainder(milliseconds, 1000).
+    milliseconds = fmod(milliseconds, 1000);
+
+    // 13. Let datePart be "".
+    StringBuilder date_part;
+
+    // 14. If years is not 0, then
+    if (years != 0) {
+        // a. Set datePart to the string concatenation of abs(years) formatted as a decimal number and the code unit 0x0059 (LATIN CAPITAL LETTER Y).
+        date_part.appendff("{}", fabs(years));
+        date_part.append('Y');
+    }
+
+    // 15. If months is not 0, then
+    if (months != 0) {
+        // a. Set datePart to the string concatenation of datePart, abs(months) formatted as a decimal number, and the code unit 0x004D (LATIN CAPITAL LETTER M).
+        date_part.appendff("{}", fabs(months));
+        date_part.append('M');
+    }
+
+    // 16. If weeks is not 0, then
+    if (weeks != 0) {
+        // a. Set datePart to the string concatenation of datePart, abs(weeks) formatted as a decimal number, and the code unit 0x0057 (LATIN CAPITAL LETTER W).
+        date_part.appendff("{}", fabs(weeks));
+        date_part.append('W');
+    }
+
+    // 17. If days is not 0, then
+    if (days != 0) {
+        // a. Set datePart to the string concatenation of datePart, abs(days) formatted as a decimal number, and the code unit 0x0044 (LATIN CAPITAL LETTER D).
+        date_part.appendff("{}", fabs(days));
+        date_part.append('D');
+    }
+
+    // 18. Let timePart be "".
+    StringBuilder time_part;
+
+    // 19. If hours is not 0, then
+    if (hours != 0) {
+        // a. Set timePart to the string concatenation of abs(hours) formatted as a decimal number and the code unit 0x0048 (LATIN CAPITAL LETTER H).
+        time_part.appendff("{}", fabs(hours));
+        time_part.append('H');
+    }
+
+    // 20. If minutes is not 0, then
+    if (minutes != 0) {
+        // a. Set timePart to the string concatenation of timePart, abs(minutes) formatted as a decimal number, and the code unit 0x004D (LATIN CAPITAL LETTER M).
+        time_part.appendff("{}", fabs(minutes));
+        time_part.append('M');
+    }
+
+    // 21. If any of seconds, milliseconds, microseconds, and nanoseconds are not 0; or years, months, weeks, days, hours, and minutes are all 0, then
+    if ((seconds != 0 || milliseconds != 0 || microseconds != 0 || nanoseconds != 0) || (years == 0 && months == 0 && weeks == 0 && days == 0 && hours == 0 && minutes == 0)) {
+        // a. Let fraction be abs(milliseconds) × 10^6 + abs(microseconds) × 10^3 + abs(nanoseconds).
+        auto fraction = fabs(milliseconds) * 1'000'000 + fabs(microseconds) * 1'000 + fabs(nanoseconds);
+
+        // b. Let decimalPart be fraction formatted as a nine-digit decimal number, padded to the left with zeroes if necessary.
+        // NOTE: padding with zeros leads to weird results when applied to a double. Not sure if that's a bug in AK/Format.h or if I'm doing this wrong.
+        auto decimal_part = String::formatted("{:09}", (u64)fraction);
+
+        // c. If precision is "auto", then
+        if (precision.has<StringView>() && precision.get<StringView>() == "auto"sv) {
+            // i. Set decimalPart to the longest possible substring of decimalPart starting at position 0 and not ending with the code unit 0x0030 (DIGIT ZERO).
+            // NOTE: trim() would keep the left-most 0.
+            while (decimal_part.ends_with('0'))
+                decimal_part = decimal_part.substring(0, decimal_part.length() - 1);
+        }
+        // d. Else if precision = 0, then
+        else if (precision.get<u8>() == 0) {
+            // i. Set decimalPart to "".
+            decimal_part = String::empty();
+        }
+        // e. Else,
+        else {
+            // i. Set decimalPart to the substring of decimalPart from 0 to precision.
+            decimal_part = decimal_part.substring(0, precision.get<u8>());
+        }
+
+        // f. Let secondsPart be abs(seconds) formatted as a decimal number.
+        StringBuilder seconds_part;
+        seconds_part.appendff("{}", fabs(seconds));
+
+        // g. If decimalPart is not "", then
+        if (!decimal_part.is_empty()) {
+            // i. Set secondsPart to the string-concatenation of secondsPart, the code unit 0x002E (FULL STOP), and decimalPart.
+            seconds_part.append('.');
+            seconds_part.append(decimal_part);
+        }
+
+        // h. Set timePart to the string concatenation of timePart, secondsPart, and the code unit 0x0053 (LATIN CAPITAL LETTER S).
+        time_part.append(seconds_part.string_view());
+        time_part.append('S');
+    }
+
+    // 22. Let signPart be the code unit 0x002D (HYPHEN-MINUS) if sign < 0, and otherwise the empty String.
+    auto sign_part = sign < 0 ? "-"sv : ""sv;
+
+    // 23. Let result be the string concatenation of signPart, the code unit 0x0050 (LATIN CAPITAL LETTER P) and datePart.
+    StringBuilder result;
+    result.append(sign_part);
+    result.append('P');
+    result.append(date_part.string_view());
+
+    // 24. If timePart is not "", then
+    if (!time_part.is_empty()) {
+        // a. Set result to the string concatenation of result, the code unit 0x0054 (LATIN CAPITAL LETTER T), and timePart.
+        result.append('T');
+        result.append(time_part.string_view());
+    }
+
+    // 25. Return result.
+    return result.to_string();
+}
+
 }

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

@@ -7,8 +7,12 @@
 #pragma once
 
 #include <AK/Optional.h>
+#include <LibJS/Heap/Handle.h>
 #include <LibJS/Runtime/Completion.h>
 #include <LibJS/Runtime/Object.h>
+#include <LibJS/Runtime/Temporal/PlainDate.h>
+#include <LibJS/Runtime/Temporal/PlainDateTime.h>
+#include <LibJS/Runtime/Temporal/ZonedDateTime.h>
 #include <LibJS/Runtime/VM.h>
 
 namespace JS::Temporal {
@@ -84,6 +88,27 @@ struct BalancedDuration {
     double nanoseconds;
 };
 
+// Used by MoveRelativeDate to temporarily hold values
+struct MoveRelativeDateResult {
+    Handle<PlainDateTime> relative_to;
+    double days;
+};
+
+// Used by RoundDuration to temporarily hold values
+struct RoundedDuration {
+    double years;
+    double months;
+    double weeks;
+    double days;
+    double hours;
+    double minutes;
+    double seconds;
+    double milliseconds;
+    double microseconds;
+    double nanoseconds;
+    double remainder;
+};
+
 // Table 7: Properties of a TemporalDurationLike, https://tc39.es/proposal-temporal/#table-temporal-temporaldurationlike-properties
 
 template<typename StructT, typename ValueT>
@@ -118,6 +143,24 @@ ThrowCompletionOr<Duration*> create_temporal_duration(GlobalObject&, double year
 Duration* create_negated_temporal_duration(GlobalObject& global_object, Duration const& duration);
 BigInt* total_duration_nanoseconds(GlobalObject&, double days, double hours, double minutes, double seconds, double milliseconds, double microseconds, BigInt const& nanoseconds, double offset_shift);
 ThrowCompletionOr<BalancedDuration> balance_duration(GlobalObject&, double days, double hours, double minutes, double seconds, double milliseconds, double microseconds, BigInt const& nanoseconds, String const& largest_unit, Object* relative_to = nullptr);
+ThrowCompletionOr<MoveRelativeDateResult> move_relative_date(GlobalObject&, Object& calendar, PlainDateTime& relative_to, Duration& duration);
+ThrowCompletionOr<ZonedDateTime*> move_relative_zoned_date_time(GlobalObject&, ZonedDateTime&, double years, double months, double weeks, double days);
+ThrowCompletionOr<RoundedDuration> round_duration(GlobalObject&, double years, double months, double weeks, double days, double hours, double minutes, double seconds, double milliseconds, double microseconds, double nanoseconds, u32 increment, StringView unit, StringView rounding_mode, Object* relative_to_object = nullptr);
 ThrowCompletionOr<TemporalDuration> to_limited_temporal_duration(GlobalObject&, Value temporal_duration_like, Vector<StringView> const& disallowed_fields);
+String temporal_duration_to_string(double years, double months, double weeks, double days, double hours, double minutes, double seconds, double milliseconds, double microseconds, double nanoseconds, Variant<StringView, u8> const& precision);
+
+// 7.5.15 DaysUntil ( earlier, later ), https://tc39.es/proposal-temporal/#sec-temporal-daysuntil
+template<typename EarlierObjectType, typename LaterObjectType>
+double days_until(GlobalObject& global_object, EarlierObjectType& earlier, LaterObjectType& later)
+{
+    // 1. Assert: earlier and later both have [[ISOYear]], [[ISOMonth]], and [[ISODay]] internal slots.
+    // NOTE: We could enforce this via concepts, but the compiler would complain anyway if either of the types doesn't have the methods used below.
+
+    // 2. Let difference be ! DifferenceISODate(earlier.[[ISOYear]], earlier.[[ISOMonth]], earlier.[[ISODay]], later.[[ISOYear]], later.[[ISOMonth]], later.[[ISODay]], "day").
+    auto difference = difference_iso_date(global_object, earlier.iso_year(), earlier.iso_month(), earlier.iso_day(), later.iso_year(), later.iso_month(), later.iso_day(), "day"sv);
+
+    // 3. Return difference.[[Days]].
+    return difference.days;
+}
 
 }

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

@@ -6,6 +6,7 @@
 
 #include <AK/TypeCasts.h>
 #include <LibJS/Runtime/GlobalObject.h>
+#include <LibJS/Runtime/Temporal/AbstractOperations.h>
 #include <LibJS/Runtime/Temporal/Duration.h>
 #include <LibJS/Runtime/Temporal/DurationPrototype.h>
 #include <math.h>
@@ -44,6 +45,7 @@ void DurationPrototype::initialize(GlobalObject& global_object)
     define_native_function(vm.names.with, with, 1, attr);
     define_native_function(vm.names.negated, negated, 0, attr);
     define_native_function(vm.names.abs, abs, 0, attr);
+    define_native_function(vm.names.toString, to_string, 0, attr);
     define_native_function(vm.names.valueOf, value_of, 0, attr);
 }
 
@@ -282,6 +284,33 @@ JS_DEFINE_NATIVE_FUNCTION(DurationPrototype::abs)
     return TRY(create_temporal_duration(global_object, fabs(duration->years()), fabs(duration->months()), fabs(duration->weeks()), fabs(duration->days()), fabs(duration->hours()), fabs(duration->minutes()), fabs(duration->seconds()), fabs(duration->milliseconds()), fabs(duration->microseconds()), fabs(duration->nanoseconds())));
 }
 
+// 7.3.22 Temporal.Duration.prototype.toString ( [ options ] ), https://tc39.es/proposal-temporal/#sec-temporal.duration.prototype.tostring
+JS_DEFINE_NATIVE_FUNCTION(DurationPrototype::to_string)
+{
+    // 1. Let duration be the this value.
+    // 2. Perform ? RequireInternalSlot(duration, [[InitializedTemporalDuration]]).
+    auto* duration = TRY(typed_this_object(global_object));
+
+    // 3. Set options to ? GetOptionsObject(options).
+    auto* options = TRY(get_options_object(global_object, vm.argument(0)));
+
+    // 4. Let precision be ? ToSecondsStringPrecision(options).
+    auto precision = TRY(to_seconds_string_precision(global_object, *options));
+
+    // 5. If precision.[[Unit]] is "minute", throw a RangeError exception.
+    if (precision.unit == "minute"sv)
+        return vm.throw_completion<RangeError>(global_object, ErrorType::OptionIsNotValidValue, "minute"sv, "smallestUnit"sv);
+
+    // 6. Let roundingMode be ? ToTemporalRoundingMode(options, "trunc").
+    auto rounding_mode = TRY(to_temporal_rounding_mode(global_object, *options, "trunc"sv));
+
+    // 7. Let result be ? RoundDuration(duration.[[Years]], duration.[[Months]], duration.[[Weeks]], duration.[[Days]], duration.[[Hours]], duration.[[Minutes]], duration.[[Seconds]], duration.[[Milliseconds]], duration.[[Microseconds]], duration.[[Nanoseconds]], precision.[[Increment]], precision.[[Unit]], roundingMode).
+    auto result = TRY(round_duration(global_object, duration->years(), duration->months(), duration->weeks(), duration->days(), duration->hours(), duration->minutes(), duration->seconds(), duration->milliseconds(), duration->microseconds(), duration->nanoseconds(), precision.increment, precision.unit, rounding_mode));
+
+    // 8. Return ! TemporalDurationToString(result.[[Years]], result.[[Months]], result.[[Weeks]], result.[[Days]], result.[[Hours]], result.[[Minutes]], result.[[Seconds]], result.[[Milliseconds]], result.[[Microseconds]], result.[[Nanoseconds]], precision.[[Precision]]).
+    return js_string(vm, temporal_duration_to_string(result.years, result.months, result.weeks, result.days, result.hours, result.minutes, result.seconds, result.milliseconds, result.microseconds, result.nanoseconds, precision.precision));
+}
+
 // 7.3.25 Temporal.Duration.prototype.valueOf ( ), https://tc39.es/proposal-temporal/#sec-temporal.duration.prototype.valueof
 JS_DEFINE_NATIVE_FUNCTION(DurationPrototype::value_of)
 {

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

@@ -35,6 +35,7 @@ private:
     JS_DECLARE_NATIVE_FUNCTION(with);
     JS_DECLARE_NATIVE_FUNCTION(negated);
     JS_DECLARE_NATIVE_FUNCTION(abs);
+    JS_DECLARE_NATIVE_FUNCTION(to_string);
     JS_DECLARE_NATIVE_FUNCTION(value_of);
 };
 

Userland/Libraries/LibJS/Tests/builtins/Temporal/Duration/Duration.prototype.toString.js

@@ -0,0 +1,94 @@
+describe("correct behavior", () => {
+    test("length is 0", () => {
+        expect(Temporal.Duration.prototype.toString).toHaveLength(0);
+    });
+
+    test("basic functionality", () => {
+        const values = [
+            [[0], "PT0S"],
+            [[1], "P1Y"],
+            [[0, 1], "P1M"],
+            [[0, 0, 1], "P1W"],
+            [[0, 0, 0, 1], "P1D"],
+            [[0, 0, 0, 0, 1], "PT1H"],
+            [[0, 0, 0, 0, 0, 1], "PT1M"],
+            [[0, 0, 0, 0, 0, 0, 1], "PT1S"],
+            [[0, 0, 0, 0, 0, 0, 0, 1], "PT0.001S"],
+            [[0, 0, 0, 0, 0, 0, 0, 0, 1], "PT0.000001S"],
+            [[0, 0, 0, 0, 0, 0, 0, 0, 0, 1], "PT0.000000001S"],
+            [[1, 2], "P1Y2M"],
+            [[1, 2, 3], "P1Y2M3W"],
+            [[1, 2, 3, 4], "P1Y2M3W4D"],
+            [[1, 2, 3, 4, 5], "P1Y2M3W4DT5H"],
+            [[1, 2, 3, 4, 5, 6], "P1Y2M3W4DT5H6M"],
+            [[1, 2, 3, 4, 5, 6, 7], "P1Y2M3W4DT5H6M7S"],
+            [[1, 2, 3, 4, 5, 6, 7, 8], "P1Y2M3W4DT5H6M7.008S"],
+            [[1, 2, 3, 4, 5, 6, 7, 8, 9], "P1Y2M3W4DT5H6M7.008009S"],
+            [[1, 2, 3, 4, 5, 6, 7, 8, 9, 10], "P1Y2M3W4DT5H6M7.00800901S"],
+            [
+                [100, 200, 300, 400, 500, 600, 700, 800, 900, 1000],
+                "P100Y200M300W400DT500H600M700.800901S",
+            ],
+            [[-1], "-P1Y"],
+        ];
+        for (const [args, expected] of values) {
+            expect(new Temporal.Duration(...args).toString()).toBe(expected);
+        }
+    });
+
+    test("smallestUnit option", () => {
+        const values = [
+            ["second", "P1Y2M3W4DT5H6M7S"],
+            ["millisecond", "P1Y2M3W4DT5H6M7.008S"],
+            ["microsecond", "P1Y2M3W4DT5H6M7.008010S"],
+            ["nanosecond", "P1Y2M3W4DT5H6M7.008010000S"],
+        ];
+        for (const [smallestUnit, expected] of values) {
+            expect(
+                new Temporal.Duration(1, 2, 3, 4, 5, 6, 7, 8, 10).toString({ smallestUnit })
+            ).toBe(expected);
+        }
+    });
+
+    test("fractionalSecondDigits option", () => {
+        const values = [
+            [0, "P1Y2M3W4DT5H6M7S"],
+            [1, "P1Y2M3W4DT5H6M7.0S"],
+            [2, "P1Y2M3W4DT5H6M7.00S"],
+            [3, "P1Y2M3W4DT5H6M7.008S"],
+            [4, "P1Y2M3W4DT5H6M7.0080S"],
+            [5, "P1Y2M3W4DT5H6M7.00801S"],
+            [6, "P1Y2M3W4DT5H6M7.008010S"],
+            [7, "P1Y2M3W4DT5H6M7.0080100S"],
+            [8, "P1Y2M3W4DT5H6M7.00801000S"],
+            [9, "P1Y2M3W4DT5H6M7.008010000S"],
+        ];
+        for (const [fractionalSecondDigits, expected] of values) {
+            expect(
+                new Temporal.Duration(1, 2, 3, 4, 5, 6, 7, 8, 10).toString({
+                    fractionalSecondDigits,
+                })
+            ).toBe(expected);
+        }
+    });
+});
+
+describe("errors", () => {
+    test("this value must be a Temporal.Duration object", () => {
+        expect(() => {
+            Temporal.Duration.prototype.toString.call("foo");
+        }).toThrowWithMessage(TypeError, "Not an object of type Temporal.Duration");
+    });
+
+    test("disallowed smallestUnit option values", () => {
+        const values = ["year", "month", "week", "day", "hour", "minute"];
+        for (const smallestUnit of values) {
+            expect(() => {
+                new Temporal.Duration(0).toString({ smallestUnit });
+            }).toThrowWithMessage(
+                RangeError,
+                `${smallestUnit} is not a valid value for option smallestUnit`
+            );
+        }
+    });
+});