From 780c2408df19a8e345ccf243fc8977928656dd21 Mon Sep 17 00:00:00 2001
From: Frazer McLean <frazer@frazermclean.co.uk>
Date: Tue, 11 Nov 2025 18:50:55 +0100
Subject: [PATCH] DateTime.combine should default to time.tzinfo

---
 src/datetype/__init__.py           |  6 +++++-
 src/datetype/test/test_datetype.py | 29 +++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/src/datetype/__init__.py b/src/datetype/__init__.py
index 8a9c680..c56063b 100644
--- a/src/datetype/__init__.py
+++ b/src/datetype/__init__.py
@@ -39,6 +39,8 @@
 AnyDateTime = TypeVar("AnyDateTime", bound="DateTime[Optional[_tzinfo]]")
 AnyTime = TypeVar("AnyTime", bound="Time[Optional[_tzinfo]]")
 
+_missing = object()
+
 if sys.version_info >= (3, 9):
 
     class _IsoCalendarDate(NamedTuple):
@@ -513,8 +515,10 @@ def combine(
             cls,
             date: Date,
             time: Time[Optional[_tzinfo]],
-            tzinfo: Optional[_tzinfo] = None,
+            tzinfo: Optional[_tzinfo] = _missing,  # type: ignore[assignment]
         ) -> DateTime[Optional[_tzinfo]]:
+            if tzinfo is _missing:
+                tzinfo = time.tzinfo
             return _datetime.combine(
                 concrete(date), concrete(time), tzinfo
             )  # type:ignore[return-value]
diff --git a/src/datetype/test/test_datetype.py b/src/datetype/test/test_datetype.py
index 6d42cbd..1a73dd5 100644
--- a/src/datetype/test/test_datetype.py
+++ b/src/datetype/test/test_datetype.py
@@ -12,6 +12,7 @@
     aware,
     naive,
     DateTime,
+    date_only,
 )
 
 TEST_DATA = (Path(__file__) / "..").resolve()
@@ -109,3 +110,31 @@ def test_differing_zone_subtract(self) -> None:
 
         self.assertEqual(dtzi - dttz, timedelta(0))
         self.assertEqual(dttz - dtzi, timedelta(0))
+
+    def test_combine(self) -> None:
+        from zoneinfo import ZoneInfo
+
+        d = date_only(date(2025, 2, 13))
+        aware_time = aware(
+            time(hour=15, minute=35, second=13, tzinfo=timezone.utc), timezone
+        )
+        naive_time = naive(time(hour=15, minute=35, second=13))
+
+        combined_aware: DateTime[timezone] = DateTime.combine(d, aware_time)
+        combined_naive: DateTime[None] = DateTime.combine(d, naive_time)
+
+        self.assertIsInstance(combined_naive, NaiveDateTime)
+        self.assertIsInstance(combined_aware, AwareDateTime)
+        self.assertIs(combined_aware.tzinfo, timezone.utc)
+
+        zi = ZoneInfo("Europe/Berlin")
+
+        adt_zi: DateTime[ZoneInfo] = DateTime.combine(d, aware_time, zi)
+        self.assertIsInstance(adt_zi, AwareDateTime)
+        adt_naive: DateTime[None] = DateTime.combine(d, aware_time, tzinfo=None)
+        self.assertIsInstance(adt_naive, NaiveDateTime)
+
+        ndt_zi: DateTime[ZoneInfo] = DateTime.combine(d, naive_time, zi)
+        self.assertIsInstance(ndt_zi, AwareDateTime)
+        ndt_naive: DateTime[None] = DateTime.combine(d, naive_time, tzinfo=None)
+        self.assertIsInstance(ndt_naive, NaiveDateTime)