Avoid infinite loop in CalendarIntervalTrigger with UTC timezone (#898)

Fixes #897.

docs/versionhistory.rst

@@ -20,6 +20,7 @@ APScheduler, see the :doc:`migration section <migration>`.
 - Fixed JSON serialization of triggers that had been used at least once
 - Fixed dialect name checks in the SQLAlchemy job store
 - Fixed JSON and CBOR serializers unable to serialize enums
+- Fixed infinite loop in CalendarIntervalTrigger with UTC timezone (PR by unights)
 
 **4.0.0a4**
 

src/apscheduler/triggers/calendarinterval.py

@@ -118,7 +118,7 @@ def next(self) -> datetime | None:
             next_time = datetime.fromtimestamp(timestamp, self.timezone)
 
             # Check if the time is off due to normalization and a forward DST shift
-            if next_time.time() != self._time:
+            if next_time.timetz() != self._time:
                 previous_date = next_time.date()
             else:
                 self._last_fire_date = next_date

tests/conftest.py

@@ -29,6 +29,11 @@ def timezone() -> ZoneInfo:
     return ZoneInfo("Europe/Berlin")
 
 
+@pytest.fixture(scope="session")
+def utc_timezone() -> ZoneInfo:
+    return ZoneInfo("UTC")
+
+
 @pytest.fixture(
     params=[
         pytest.param(PickleSerializer, id="pickle"),

tests/triggers/test_calendarinterval.py

@@ -100,3 +100,10 @@ def test_repr(timezone, serializer):
         "time='03:00:08', start_date='2016-03-05', end_date='2020-12-25', "
         "timezone='Europe/Berlin')"
     )
+
+
+def test_utc_timezone(utc_timezone):
+    trigger = CalendarIntervalTrigger(
+        days=1, hour=1, start_date=date(2016, 3, 31), timezone=utc_timezone
+    )
+    assert trigger.next() == datetime(2016, 3, 31, 1, tzinfo=utc_timezone)