Preserve temporal serialization in reflected addition

CHANGELOG.md

@@ -8,6 +8,8 @@
 
 ### Fixed
 
+- Preserve date text and temporal trivia when adding a timedelta from the left to `Date` or `DateTime` values.
+
 - 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_items.py

@@ -874,6 +874,27 @@ def test_datetimes_behave_like_datetimes(tz_utc: tzinfo, tz_pst: tzinfo) -> None
     assert doc.as_string() == "dt = 2018-07-23T12:34:56-05:00"
 
 
+@pytest.mark.parametrize(
+    "literal", ["2024-02-28", "2024-02-28T10:00:00", "2024-02-28T10:00:00Z"]
+)
+@pytest.mark.parametrize("delta", [timedelta(days=1), timedelta(days=-1)])
+def test_reflected_temporal_addition_preserves_serialization(
+    literal: str, delta: timedelta
+) -> None:
+    doc = parse(f"when = {literal} # birthday\n")
+    value = doc["when"]
+    expected = value + delta
+
+    result = delta + value
+
+    assert type(result) is type(value)
+    assert result.unwrap() == expected.unwrap()
+    assert result.as_string() == expected.as_string()
+    assert result.trivia == expected.trivia
+    doc["when"] = result
+    assert parse(doc.as_string())["when"] == expected
+
+
 def test_datetime_astimezone_defaults_to_local_timezone() -> None:
     value = parse("time = 1979-05-27T07:32:00Z # birthday\n")["time"]
     expected = datetime(1979, 5, 27, 7, 32, tzinfo=timezone.utc).astimezone()

tomlkit/items.py

@@ -1207,6 +1207,8 @@ def __add__(self, other: timedelta) -> DateTime:
 
         return self._new(result)
 
+    __radd__ = __add__
+
     @overload  # type: ignore[override]
     def __sub__(self, other: timedelta) -> DateTime: ...
 
@@ -1327,6 +1329,8 @@ def __add__(self, other: timedelta) -> Date:
 
         return self._new(result)
 
+    __radd__ = __add__
+
     @overload  # type: ignore[override]
     def __sub__(self, other: timedelta) -> Date: ...