feat: 新增 PlainMonthDay 算术与 Instant 转换方法

Cargo.lock

@@ -1160,7 +1160,7 @@ dependencies = [
 
 [[package]]
 name = "oxide_builtins"
-version = "0.19.13"
+version = "0.19.14"
 dependencies = [
  "chrono",
  "fast-float",
@@ -1185,7 +1185,7 @@ dependencies = [
 
 [[package]]
 name = "oxide_bytecode"
-version = "0.19.13"
+version = "0.19.14"
 dependencies = [
  "num-bigint",
  "oxide_log",
@@ -1193,7 +1193,7 @@ dependencies = [
 
 [[package]]
 name = "oxide_cfg"
-version = "0.19.13"
+version = "0.19.14"
 dependencies = [
  "oxide_bytecode",
  "oxide_emit",
@@ -1204,7 +1204,7 @@ dependencies = [
 
 [[package]]
 name = "oxide_cli"
-version = "0.19.13"
+version = "0.19.14"
 dependencies = [
  "ansi_term",
  "bumpalo",
@@ -1228,7 +1228,7 @@ dependencies = [
 
 [[package]]
 name = "oxide_code_cache"
-version = "0.19.13"
+version = "0.19.14"
 dependencies = [
  "lru",
  "oxide_bytecode",
@@ -1237,7 +1237,7 @@ dependencies = [
 
 [[package]]
 name = "oxide_compiler"
-version = "0.19.13"
+version = "0.19.14"
 dependencies = [
  "oxide_bytecode",
  "oxide_cfg",
@@ -1258,7 +1258,7 @@ dependencies = [
 
 [[package]]
 name = "oxide_dce"
-version = "0.19.13"
+version = "0.19.14"
 dependencies = [
  "oxide_bytecode",
  "oxide_cfg",
@@ -1272,7 +1272,7 @@ dependencies = [
 
 [[package]]
 name = "oxide_emit"
-version = "0.19.13"
+version = "0.19.14"
 dependencies = [
  "num-bigint",
  "oxc_allocator",
@@ -1288,7 +1288,7 @@ dependencies = [
 
 [[package]]
 name = "oxide_engine"
-version = "0.19.13"
+version = "0.19.14"
 dependencies = [
  "oxide_bytecode",
  "oxide_compiler",
@@ -1300,7 +1300,7 @@ dependencies = [
 
 [[package]]
 name = "oxide_fold"
-version = "0.19.13"
+version = "0.19.14"
 dependencies = [
  "num-bigint",
  "oxide_bytecode",
@@ -1312,7 +1312,7 @@ dependencies = [
 
 [[package]]
 name = "oxide_ir"
-version = "0.19.13"
+version = "0.19.14"
 dependencies = [
  "oxide_bytecode",
  "oxide_log",
@@ -1321,7 +1321,7 @@ dependencies = [
 
 [[package]]
 name = "oxide_kernel"
-version = "0.19.13"
+version = "0.19.14"
 dependencies = [
  "bumpalo",
  "dashmap",
@@ -1335,7 +1335,7 @@ dependencies = [
 
 [[package]]
 name = "oxide_liveness"
-version = "0.19.13"
+version = "0.19.14"
 dependencies = [
  "oxide_bytecode",
  "oxide_cfg",
@@ -1347,7 +1347,7 @@ dependencies = [
 
 [[package]]
 name = "oxide_log"
-version = "0.19.13"
+version = "0.19.14"
 dependencies = [
  "tracing",
  "tracing-appender",
@@ -1356,11 +1356,11 @@ dependencies = [
 
 [[package]]
 name = "oxide_net"
-version = "0.19.13"
+version = "0.19.14"
 
 [[package]]
 name = "oxide_parser"
-version = "0.19.13"
+version = "0.19.14"
 dependencies = [
  "oxc_allocator",
  "oxc_ast",
@@ -1375,7 +1375,7 @@ dependencies = [
 
 [[package]]
 name = "oxide_regalloc"
-version = "0.19.13"
+version = "0.19.14"
 dependencies = [
  "oxide_bytecode",
  "oxide_cfg",
@@ -1391,7 +1391,7 @@ dependencies = [
 
 [[package]]
 name = "oxide_runtime_api"
-version = "0.19.13"
+version = "0.19.14"
 dependencies = [
  "num-bigint",
  "num-traits",
@@ -1404,7 +1404,7 @@ dependencies = [
 
 [[package]]
 name = "oxide_test262"
-version = "0.19.13"
+version = "0.19.14"
 dependencies = [
  "oxide_bytecode",
  "oxide_compiler",
@@ -1424,7 +1424,7 @@ dependencies = [
 
 [[package]]
 name = "oxide_types"
-version = "0.19.13"
+version = "0.19.14"
 dependencies = [
  "bumpalo",
  "dashmap",
@@ -1437,7 +1437,7 @@ dependencies = [
 
 [[package]]
 name = "oxide_vm"
-version = "0.19.13"
+version = "0.19.14"
 dependencies = [
  "bumpalo",
  "chrono",

Cargo.toml

@@ -25,7 +25,7 @@ members = [
 ]
 
 [workspace.package]
-version = "0.19.13"
+version = "0.19.14"
 edition = "2021"
 license = "MIT"
 rust-version = "1.80"

crates/oxide_builtins/src/temporal/instant.rs

@@ -2,6 +2,7 @@
 
 use chrono::Utc;
 use num_traits::ToPrimitive;
+use oxide_kernel::shape_forge::EMPTY_SHAPE_ID;
 use oxide_runtime_api::{to_number, to_string, NativeResult, ProtoKind, VmHost};
 use oxide_types::object::JsObject;
 use oxide_types::value::JsValue;
@@ -937,6 +938,71 @@ pub fn instant_to_zoned_date_time_iso<H: VmHost>(vm: &mut H, args: &[u8]) -> Nat
     make_zoned_date_time(vm, epoch_ns, &time_zone_id, "iso8601")
 }
 
+/// ToNumeric 语义的纪元纳秒取值：number 须为有限整数（否则 RangeError），
+/// BigInt 直读 i128；其余原始值 → TypeError。
+fn to_numeric_epoch_ns<H: VmHost>(vm: &mut H, value: JsValue) -> Result<i128, JsValue> {
+    if value.is_number() {
+        let number = to_number(value);
+        if !number.is_finite() || number.fract() != 0.0 {
+            return Err(crate::error::create_range_error(vm, "invalid epochNanoseconds"));
+        }
+        return Ok(number as i128);
+    }
+    if value.is_bigint() {
+        return Ok(vm.bigint_value(value).to_i128().unwrap_or(i128::MAX));
+    }
+    Err(crate::error::create_type_error(vm, "invalid epochNanoseconds"))
+}
+
+/// `Temporal.Instant.prototype.with(properties)`：properties.epochNanoseconds
+/// （number 或 BigInt）须过 Instant 范围，返回新 Instant；options 不读取。
+///
+/// # 步骤
+/// 1. receiver branding（TypeError）。
+/// 2. properties 非对象 → TypeError。
+/// 3. Get epochNanoseconds：undefined → TypeError；ToNumeric 取值。
+/// 4. 绝对值超 MAX_INSTANT_NS → RangeError；make_instant 重建。
+pub fn instant_with<H: VmHost>(vm: &mut H, args: &[u8]) -> NativeResult {
+    let ptr = native_try!(receiver_obj(vm, args));
+    let obj = unsafe { &*ptr };
+    native_try!(ensure_instant(vm, obj));
+    let properties = if args.len() < 2 { JsValue::undefined() } else { vm.reg(args[1]) };
+    if !properties.is_object() {
+        return NativeResult::Err(crate::error::create_type_error(vm, "properties must be an object"));
+    }
+    let pptr = properties.as_js_object_ptr();
+    if pptr.is_null() {
+        return NativeResult::Err(crate::error::create_type_error(vm, "properties must be an object"));
+    }
+    let properties_obj = unsafe { &*pptr };
+    let raw = native_try!(temporal_option_value(vm, properties_obj, properties, "epochNanoseconds"));
+    if raw.is_undefined() {
+        return NativeResult::Err(crate::error::create_type_error(vm, "epochNanoseconds is required"));
+    }
+    let epoch_ns = native_try!(to_numeric_epoch_ns(vm, raw));
+    if epoch_ns.unsigned_abs() > MAX_INSTANT_NS as u128 {
+        return NativeResult::Err(crate::error::create_range_error(vm, "Instant outside supported range"));
+    }
+    make_instant(vm, epoch_ns)
+}
+
+/// `Temporal.Instant.prototype.toDate()`：纪元纳秒按毫秒取整（floor）后
+/// 产出 Date 对象（同一时刻，亚毫秒精度丢失，与 epochMilliseconds getter 同口径）。
+pub fn instant_to_date<H: VmHost>(vm: &mut H, args: &[u8]) -> NativeResult {
+    let ptr = native_try!(receiver_obj(vm, args));
+    let obj = unsafe { &*ptr };
+    native_try!(ensure_instant(vm, obj));
+    let Some(epoch_ns) = get_instant_epoch_ns(obj) else {
+        return NativeResult::Err(crate::error::create_range_error(vm, "invalid Instant"));
+    };
+    let epoch_ms = epoch_ns.div_euclid(1_000_000) as f64;
+    let mut date =
+        JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::from_js_object(vm.builtin_proto(ProtoKind::DateProto)));
+    date.type_tag = JsObject::OBJ_TYPE_DATE;
+    date.set_prop_at(0, JsValue::float(epoch_ms));
+    NativeResult::Ok(JsValue::from_js_object(vm.alloc_object(date)))
+}
+
 /// `Temporal.Instant.prototype.valueOf()`：Temporal 对象禁止转原始值。
 pub fn instant_value_of<H: VmHost>(vm: &mut H, _args: &[u8]) -> NativeResult {
     NativeResult::Err(crate::error::create_type_error(vm, "Temporal.Instant has no valueOf"))

crates/oxide_builtins/src/temporal/plain_month_day.rs

@@ -6,12 +6,12 @@ use oxide_types::value::JsValue;
 
 use super::common::native_try;
 use super::{
-    calendar_annotation, days_from_civil, days_in_month_iso, ensure_plain_month_day, format_iso_year, get_calendar_id,
+    calendar_annotation, days_from_civil, days_in_month_iso, duration_like_values, ensure_plain_month_day,
-    get_double_prop, initialize_temporal_receiver, is_ctor_call, make_plain_date, make_plain_month_day,
+    format_iso_year, get_calendar_id, get_double_prop, initialize_temporal_receiver, is_ctor_call,
-    month_day_bag_calendar_id, read_iso2, receiver_obj, reject_partial_object_with_calendar_or_time_zone,
+    make_plain_date, make_plain_month_day, month_day_bag_calendar_id, parse_round_options, read_iso2, receiver_obj,
-    strip_iso_offset, temporal_calendar_id_strict, temporal_number_component, temporal_option_string,
+    reject_partial_object_with_calendar_or_time_zone, strip_iso_offset, temporal_calendar_id_strict,
-    temporal_option_value, temporal_overflow, temporal_to_show_calendar, valid_iso_date, valid_plain_time,
+    temporal_number_component, temporal_option_string, temporal_option_value, temporal_overflow,
-    ShowCalendar,
+    temporal_to_show_calendar, valid_iso_date, valid_plain_time, ShowCalendar,
 };
 
 /// 读 PlainMonthDay 的 月/日/参考年 三元组（槽 0-2），含 receiver 校验。
@@ -746,3 +746,109 @@ pub fn plain_month_day_to_plain_date<H: VmHost>(vm: &mut H, args: &[u8]) -> Nati
     let calendar = get_calendar_id(obj, 3);
     make_plain_date(vm, year, month, day, &calendar)
 }
+
+// ==================== PlainMonthDay add/subtract/round ====================
+
+/// `Temporal.PlainMonthDay.prototype.add/subtract(durationLike [, options])` 核心。
+///
+/// # 步骤
+/// 1. receiver branding（TypeError）。
+/// 2. ToTemporalDuration（串 / bag / 实例；TypeError、RangeError 各自语义）。
+/// 3. 读 overflow（缺省 constrain）。
+/// 4. years / weeks / days / 时间分量任一非零 → RangeError（PMD 无年与日分量）。
+/// 5. (年, 月) 按参考年（槽 2）折算绝对月数后平衡，日按 overflow 规整
+///    （constrain 钳到目标年月长，reject 非法即抛）。
+/// 6. 结果 (年, 月, 日) 过 ISODateWithinLimits（day 级）→ 越界 RangeError。
+///
+/// # 边界与副作用
+/// - 结果参考年为算术后的年，日历标识取自 receiver 槽 3。
+/// - subtract 与 add 共用本函数，sign 参数取反月分量。
+fn plain_month_day_apply_duration<H: VmHost>(vm: &mut H, args: &[u8], sign: i64) -> NativeResult {
+    let ptr = native_try!(receiver_obj(vm, args));
+    let obj = unsafe { &*ptr };
+    native_try!(ensure_plain_month_day(vm, obj));
+    let month = get_double_prop(obj, 0) as i64;
+    let day = get_double_prop(obj, 1) as i64;
+    let ref_year = get_double_prop(obj, 2) as i64;
+    let calendar = get_calendar_id(obj, 3);
+    let val = if args.len() > 1 { vm.reg(args[1]) } else { JsValue::undefined() };
+    let values = native_try!(duration_like_values(vm, val));
+    let constrain = native_try!(temporal_overflow(vm, args));
+    // PMD 无年分量：years 与 weeks/days/时间分量均须为零。
+    if values[0] != 0.0 || values[2..].iter().any(|value| *value != 0.0) {
+        return NativeResult::Err(crate::error::create_range_error(
+            vm,
+            "month-day cannot add years, weeks, days, or time units",
+        ));
+    }
+    // BalanceISOYearMonth：月折算绝对月数后平衡（days 恒 0，日不参与）。
+    let months = sign * values[1] as i64;
+    let absolute = ref_year * 12 + month - 1 + months;
+    let year = absolute.div_euclid(12);
+    let month = absolute.rem_euclid(12) + 1;
+    // RegulateISODate：constrain 钳日到目标年月长，reject 非法即抛。
+    let day = if constrain {
+        day.min(days_in_month_iso(year as i32, month as u32) as i64)
+    } else {
+        if !valid_iso_date(year as i32, month as u32, day as u32) {
+            return NativeResult::Err(crate::error::create_range_error(vm, "invalid ISO date"));
+        }
+        day
+    };
+    // ISODateWithinLimits（day 级）：-100_000_001..=100_000_000。
+    let day_count = days_from_civil(i128::from(year), i128::from(month), i128::from(day));
+    if !(-100_000_001..=100_000_000).contains(&day_count) {
+        return NativeResult::Err(crate::error::create_range_error(vm, "month-day is out of range"));
+    }
+    make_plain_month_day(vm, month as u32, day as u32, year as i32, &calendar)
+}
+
+/// `Temporal.PlainMonthDay.prototype.add(durationLike)`。
+pub fn plain_month_day_add<H: VmHost>(vm: &mut H, args: &[u8]) -> NativeResult {
+    plain_month_day_apply_duration(vm, args, 1)
+}
+
+/// `Temporal.PlainMonthDay.prototype.subtract(durationLike)`。
+pub fn plain_month_day_subtract<H: VmHost>(vm: &mut H, args: &[u8]) -> NativeResult {
+    plain_month_day_apply_duration(vm, args, -1)
+}
+
+/// `Temporal.PlainMonthDay.prototype.round(roundTo)`：smallestUnit 仅 "day"，
+/// 增量须为 1（日已是整数，舍入为恒等），日钳到参考年月长后过表示范围。
+///
+/// # 步骤
+/// 1. receiver 品牌校验；读槽 0-3 入本地（参考年与日历槽继承 receiver）。
+/// 2. roundTo 经 parse_round_options（undefined → TypeError；字符串简写；对象固定读序）。
+/// 3. smallestUnit 缺失 → RangeError；非 day → RangeError；增量 > 1 → RangeError。
+/// 4. 日钳到参考年月长（constrain 语义）；valid_iso_date 与 day 级表示范围检查。
+/// 5. make_plain_month_day 重建（参考年与日历槽继承 receiver）。
+pub fn plain_month_day_round<H: VmHost>(vm: &mut H, args: &[u8]) -> NativeResult {
+    let ptr = native_try!(receiver_obj(vm, args));
+    let obj = unsafe { &*ptr };
+    native_try!(ensure_plain_month_day(vm, obj));
+    let month = get_double_prop(obj, 0) as u32;
+    let day = get_double_prop(obj, 1) as u32;
+    let ref_year = get_double_prop(obj, 2) as i32;
+    let calendar = get_calendar_id(obj, 3);
+    let round_to = if args.len() > 1 { vm.reg(args[1]) } else { JsValue::undefined() };
+    let (increment, _mode, unit_value) = native_try!(parse_round_options(vm, round_to));
+    let Some(unit_value) = unit_value else {
+        return NativeResult::Err(crate::error::create_range_error(vm, "smallestUnit is required"));
+    };
+    if unit_value != "day" && unit_value != "days" {
+        return NativeResult::Err(crate::error::create_range_error(vm, "invalid smallest unit"));
+    }
+    if increment > 1 {
+        return NativeResult::Err(crate::error::create_range_error(vm, "invalid rounding increment"));
+    }
+    // 日已是整数且增量恒 1，舍入为恒等；钳到参考年月长。
+    let day = day.min(days_in_month_iso(ref_year, month));
+    if !valid_iso_date(ref_year, month, day) {
+        return NativeResult::Err(crate::error::create_range_error(vm, "month-day is out of range"));
+    }
+    let day_count = days_from_civil(i128::from(ref_year), i128::from(month), i128::from(day));
+    if !(-100_000_001..=100_000_000).contains(&day_count) {
+        return NativeResult::Err(crate::error::create_range_error(vm, "month-day is out of range"));
+    }
+    make_plain_month_day(vm, month, day, ref_year, &calendar)
+}

crates/oxide_vm/src/bindings/bind_temporal.rs

@@ -149,6 +149,8 @@ pub fn bind_temporal(env: BindEnv<'_>, global: &mut JsObject) {
             ),
             ("until", oxide_builtins::temporal::instant_until::<crate::vm::Vm> as *const (), 1),
             ("valueOf", oxide_builtins::temporal::instant_value_of::<crate::vm::Vm> as *const (), 0),
+            ("with", oxide_builtins::temporal::instant_with::<crate::vm::Vm> as *const (), 1),
+            ("toDate", oxide_builtins::temporal::instant_to_date::<crate::vm::Vm> as *const (), 0),
         ],
     );
     bind_well_known_data_property(
@@ -1063,6 +1065,13 @@ pub fn bind_temporal(env: BindEnv<'_>, global: &mut JsObject) {
                 oxide_builtins::temporal::plain_month_day_to_plain_date::<crate::vm::Vm> as *const (),
                 1,
             ),
+            ("add", oxide_builtins::temporal::plain_month_day_add::<crate::vm::Vm> as *const (), 1),
+            (
+                "subtract",
+                oxide_builtins::temporal::plain_month_day_subtract::<crate::vm::Vm> as *const (),
+                1,
+            ),
+            ("round", oxide_builtins::temporal::plain_month_day_round::<crate::vm::Vm> as *const (), 1),
         ],
     );
     bind_well_known_data_property(

crates/oxide_vm/tests/builtins_temporal_tests.rs

@@ -412,6 +412,61 @@ fn instant_from_invalid_throws_range_error() {
     assert_eq!(str_val(&vm, r), "RangeError");
 }
 
+#[test]
+fn instant_with_epoch_nanoseconds() {
+    let mut vm = Vm::new();
+    // with：epochNanoseconds 按 ToNumeric 取值（number 须有限整数、BigInt 直读）；
+    // 越界 → RangeError；缺失/非对象 → TypeError；非整数/NaN → RangeError；
+    // 边界值 ±MAX_INSTANT_NS 合法。
+    let r = eval(
+        &mut vm,
+        "(() => {
+           const kind = (fn) => { try { fn(); return 'no'; } catch (e) { return e.constructor.name; } };
+           const i = Temporal.Instant.fromEpochNanoseconds(0n);
+           return [
+             i.with({epochNanoseconds: 123456789n}).epochNanoseconds,
+             i.with({epochNanoseconds: 5000000}).epochNanoseconds,
+             kind(() => i.with({epochNanoseconds: 8640000000000000000001n})),
+             kind(() => i.with({epochNanoseconds: -8640000000000000000001n})),
+             i.with({epochNanoseconds: 8640000000000000000000n}).epochNanoseconds,
+             i.with({epochNanoseconds: -8640000000000000000000n}).epochNanoseconds,
+             kind(() => i.with({})),
+             kind(() => i.with(5)),
+             kind(() => i.with({epochNanoseconds: 1.5})),
+             kind(() => i.with({epochNanoseconds: NaN})),
+             kind(() => i.with({epochNanoseconds: '1'})),
+           ].join('|');
+         })()",
+    )
+    .unwrap();
+    assert_eq!(
+        str_val(&vm, r),
+        "123456789|5000000|RangeError|RangeError|8640000000000000000000|-8640000000000000000000|TypeError|TypeError|RangeError|RangeError|TypeError"
+    );
+}
+
+#[test]
+fn instant_to_date() {
+    let mut vm = Vm::new();
+    // toDate：纳秒按毫秒向下取整（与 epochMilliseconds getter 同口径），
+    // 负值向 -Inf 取整；结果是真实 Date（instanceof + getTime）。
+    let r = eval(
+        &mut vm,
+        "(() => {
+           const d = Temporal.Instant.fromEpochNanoseconds(1234567890123456789n).toDate();
+           return [
+             d instanceof Date,
+             d.getTime(),
+             Temporal.Instant.fromEpochNanoseconds(-1n).toDate().getTime(),
+             Temporal.Instant.fromEpochNanoseconds(-1000001n).toDate().getTime(),
+             Temporal.Instant.fromEpochNanoseconds(1000000000n).toDate().getTime(),
+           ].join('|');
+         })()",
+    )
+    .unwrap();
+    assert_eq!(str_val(&vm, r), "true|1234567890123|-1|-2|1000");
+}
+
 // -- Temporal.PlainDate --
 
 #[test]
@@ -3166,6 +3221,101 @@ fn plain_month_day_to_plain_date_matrix() {
     );
 }
 
+#[test]
+fn plain_month_day_add_balance_and_clamp() {
+    let mut vm = Vm::new();
+    // add：月按（参考年, 月）平衡，负年经 div_euclid 处理；日钳到目标年月长
+    // （constrain 缺省，reject 非法即抛）；years/weeks/days/时间分量 → RangeError；
+    // 无参 → TypeError；day 级表示范围 ±100_000_00x。
+    let r = eval(
+        &mut vm,
+        "(() => {
+           const kind = (fn) => { try { fn(); return 'no'; } catch (e) { return e.constructor.name; } };
+           const md = Temporal.PlainMonthDay.from('01-31');
+           return [
+             md.add('P1M').toString(),
+             kind(() => md.add('P1M', {overflow: 'reject'})),
+             Temporal.PlainMonthDay.from('02-29').add('P1M').toString(),
+             Temporal.PlainMonthDay.from('12-15').add('P1M').toString(),
+             Temporal.PlainMonthDay.from('01-15').add('P13M').toString(),
+             Temporal.PlainMonthDay.from('01-15').add({months: -1}).toString(),
+             new Temporal.PlainMonthDay(1, 15, 'iso8601', -1).add({months: -1}).toString(),
+             Temporal.PlainMonthDay.from('01-15').add({months: 1}).toString(),
+             kind(() => Temporal.PlainMonthDay.from('01-15').add('P1Y')),
+             kind(() => Temporal.PlainMonthDay.from('01-15').add('P1W')),
+             kind(() => Temporal.PlainMonthDay.from('01-15').add('P1D')),
+             kind(() => Temporal.PlainMonthDay.from('01-15').add('PT1H')),
+             kind(() => Temporal.PlainMonthDay.from('01-15').add()),
+             kind(() => new Temporal.PlainMonthDay(10, 31, 'iso8601', 275760).add('P1M')),
+           ].join('|');
+         })()",
+    )
+    .unwrap();
+    assert_eq!(
+        str_val(&vm, r),
+        "02-29|RangeError|03-29|01-15|02-15|12-15|12-15|02-15|RangeError|RangeError|RangeError|RangeError|TypeError|RangeError"
+    );
+}
+
+#[test]
+fn plain_month_day_subtract_balance_and_clamp() {
+    let mut vm = Vm::new();
+    // subtract：月分量反向（sign 取反）；日钳到目标年月长；
+    // years/weeks/days/时间分量 → RangeError；day 级表示范围下界。
+    let r = eval(
+        &mut vm,
+        "(() => {
+           const kind = (fn) => { try { fn(); return 'no'; } catch (e) { return e.constructor.name; } };
+           return [
+             Temporal.PlainMonthDay.from('03-31').subtract('P1M').toString(),
+             kind(() => Temporal.PlainMonthDay.from('03-31').subtract('P1M', {overflow: 'reject'})),
+             Temporal.PlainMonthDay.from('01-15').subtract('P13M').toString(),
+             new Temporal.PlainMonthDay(1, 15, 'iso8601', -1).subtract('P1M').toString(),
+             kind(() => Temporal.PlainMonthDay.from('01-15').subtract('P1Y')),
+             kind(() => Temporal.PlainMonthDay.from('01-15').subtract('P1D')),
+             kind(() => Temporal.PlainMonthDay.from('01-15').subtract('PT1H')),
+             kind(() => new Temporal.PlainMonthDay(3, 10, 'iso8601', -271821).subtract('P1M')),
+           ].join('|');
+         })()",
+    )
+    .unwrap();
+    assert_eq!(
+        str_val(&vm, r),
+        "02-29|RangeError|12-15|12-15|RangeError|RangeError|RangeError|RangeError"
+    );
+}
+
+#[test]
+fn plain_month_day_round_identity_and_validation() {
+    let mut vm = Vm::new();
+    // round：日已是整数且增量恒 1，舍入为恒等；日钳到参考年月长
+    // （from('02-31') 串路径不校验日，可造出超长按日）；smallestUnit 须 day
+    // （缺失/其他 → RangeError）；增量 > 1 → RangeError；非串/对象 → TypeError。
+    let r = eval(
+        &mut vm,
+        "(() => {
+           const kind = (fn) => { try { fn(); return 'no'; } catch (e) { return e.constructor.name; } };
+           const leap = Temporal.PlainMonthDay.from('02-29');
+           return [
+             leap.round('day').toString(),
+             leap.round({smallestUnit: 'days'}).toString(),
+             Temporal.PlainMonthDay.from('02-31').round('day').toString(),
+             kind(() => leap.round('month')),
+             kind(() => leap.round({})),
+             kind(() => leap.round({smallestUnit: 'day', roundingIncrement: 2})),
+             kind(() => leap.round(5)),
+             kind(() => leap.round()),
+             leap.round('day').day,
+           ].join('|');
+         })()",
+    )
+    .unwrap();
+    assert_eq!(
+        str_val(&vm, r),
+        "02-29|02-29|02-29|RangeError|RangeError|RangeError|TypeError|TypeError|29"
+    );
+}
+
 #[test]
 fn plain_year_month_from_string_matrix() {
     let mut vm = Vm::new();