Fix serialization of dates and times created by factory methods

CHANGELOG.md

@@ -8,6 +8,8 @@
 
 ### Fixed
 
+- Preserve valid serialization for dates and times created through standard-library factory methods.
+
 - Fix `item()` and `dumps()` writing a `datetime` whose UTC offset is not a whole number of minutes (e.g. the historical LMT offsets `zoneinfo` gives, such as `-00:44:30`) as invalid TOML like `1900-01-01T12:00:00Z:30`, which no parser accepts. Such a value is now written as the same instant in UTC; this also covers `DateTime.replace()` and `astimezone()`.
 - Allow `DateTime.astimezone()` to use the local timezone when no timezone argument is supplied, matching `datetime.datetime`.
 - Arithmetic and `replace()` results for `Integer`, `Float`, `String`, `DateTime`, `Date` and `Time` no longer share the original item's `Trivia`, so changing the result's comment or indentation no longer rewrites the item still stored in the document.

tests/test_temporal_factories.py

@@ -0,0 +1,92 @@
+from __future__ import annotations
+
+import sys
+
+from datetime import date
+from datetime import datetime
+from datetime import time
+from typing import Any
+
+import pytest
+
+from tomlkit import dumps
+from tomlkit import parse
+from tomlkit.items import Date
+from tomlkit.items import DateTime
+from tomlkit.items import Time
+
+
+def assert_temporal_round_trip(value: date | time, expected: date | time) -> None:
+    rendered = dumps({"value": value})
+    if sys.version_info >= (3, 11):
+        import tomllib
+
+        assert tomllib.loads(rendered) == {"value": expected}
+    assert parse(rendered).unwrap() == {"value": expected}
+
+
+@pytest.mark.parametrize(
+    "method, args",
+    [
+        ("fromisoformat", ("2026-11-09",)),
+        ("fromordinal", (date(2026, 11, 9).toordinal(),)),
+        ("fromtimestamp", (1720000000,)),
+        ("fromisocalendar", (2026, 46, 1)),
+    ],
+)
+def test_date_factories_serialize(method: str, args: tuple[Any, ...]) -> None:
+    value = getattr(Date, method)(*args)
+    expected = getattr(date, method)(*args)
+
+    assert isinstance(value, Date)
+    assert_temporal_round_trip(value, expected)
+
+
+def test_date_today_serializes() -> None:
+    before = date.today()
+    value = Date.today()
+    after = date.today()
+
+    assert isinstance(value, Date)
+    assert value.unwrap() in (before, after)
+    assert_temporal_round_trip(value, value.unwrap())
+
+
+@pytest.mark.parametrize(
+    "text",
+    [
+        "00:00:00",
+        "12:34",
+        "12:34:56",
+        "12:34:56.123456",
+        "12:34:56.000001",
+        "12:34:56+02:00",
+    ],
+)
+def test_time_fromisoformat_serializes(text: str) -> None:
+    value = Time.fromisoformat(text)
+    expected = time.fromisoformat(text)
+
+    assert isinstance(value, Time)
+    assert value.tzinfo == expected.tzinfo
+    assert_temporal_round_trip(value, expected.replace(tzinfo=None))
+
+
+@pytest.mark.parametrize(
+    "source",
+    [
+        "value = 2026-11-09 # date\n",
+        "value = 12:34:56.120000 # time\n",
+        "value = 12:34:56.000000 # whole second\n",
+    ],
+)
+def test_parsed_temporal_items_keep_original_format(source: str) -> None:
+    assert dumps(parse(source)) == source
+
+
+def test_datetime_factory_serialization_is_unchanged() -> None:
+    text = "2026-11-09T12:34:56.123456"
+    value = DateTime.fromisoformat(text)
+
+    assert isinstance(value, DateTime)
+    assert_temporal_round_trip(value, datetime.fromisoformat(text))

tomlkit/items.py

@@ -1302,7 +1302,7 @@ def __init__(
     ) -> None:
         super().__init__(trivia or Trivia())
 
-        self._raw = raw
+        self._raw = raw or date.isoformat(self)
 
     def unwrap(self) -> date:
         (year, month, day, _, _) = self._getstate()
@@ -1387,7 +1387,7 @@ def __init__(
     ) -> None:
         super().__init__(trivia or Trivia())
 
-        self._raw = raw
+        self._raw = raw or _format_time(self)
 
     def unwrap(self) -> time:
         (hour, minute, second, microsecond, tzinfo, _, _) = self._getstate()