Fix caldav calendars with custom timezones (#84955)

* Fix caldav calendars with custom timezones

* Revert whitespace change

homeassistant/components/caldav/calendar.py

@@ -1,7 +1,7 @@
 """Support for WebDav Calendar."""
 from __future__ import annotations
 
-from datetime import datetime, timedelta
+from datetime import date, datetime, timedelta
 import logging
 import re
 
@@ -185,8 +185,8 @@ class WebDavCalendarData:
             event_list.append(
                 CalendarEvent(
                     summary=self.get_attr_value(vevent, "summary") or "",
-                    start=vevent.dtstart.value,
+                    start=self.to_local(vevent.dtstart.value),
-                    end=self.get_end_date(vevent),
+                    end=self.to_local(self.get_end_date(vevent)),
                     location=self.get_attr_value(vevent, "location"),
                     description=self.get_attr_value(vevent, "description"),
                 )
@@ -269,8 +269,8 @@ class WebDavCalendarData:
         )
         self.event = CalendarEvent(
             summary=summary,
-            start=vevent.dtstart.value,
+            start=self.to_local(vevent.dtstart.value),
-            end=self.get_end_date(vevent),
+            end=self.to_local(self.get_end_date(vevent)),
             location=self.get_attr_value(vevent, "location"),
             description=self.get_attr_value(vevent, "description"),
         )
@@ -308,15 +308,23 @@ class WebDavCalendarData:
     def to_datetime(obj):
         """Return a datetime."""
         if isinstance(obj, datetime):
-            if obj.tzinfo is None:
+            return WebDavCalendarData.to_local(obj)
-                # floating value, not bound to any time zone in particular
-                # represent same time regardless of which time zone is currently being observed
-                return obj.replace(tzinfo=dt.DEFAULT_TIME_ZONE)
-            return obj
         return dt.dt.datetime.combine(obj, dt.dt.time.min).replace(
             tzinfo=dt.DEFAULT_TIME_ZONE
         )
 
+    @staticmethod
+    def to_local(obj: datetime | date) -> datetime | date:
+        """Return a datetime as a local datetime, leaving dates unchanged.
+
+        This handles giving floating times a timezone for comparison
+        with all day events and dropping the custom timezone object
+        used by the caldav client and dateutil so the datetime can be copied.
+        """
+        if isinstance(obj, datetime):
+            return dt.as_local(obj)
+        return obj
+
     @staticmethod
     def get_attr_value(obj, attribute):
         """Return the value of the attribute if defined."""

tests/components/caldav/test_calendar.py

@@ -226,6 +226,35 @@ DTEND:20151127T003000Z
 RRULE:FREQ=HOURLY;INTERVAL=1;COUNT=12
 END:VEVENT
 END:VCALENDAR
+""",
+    """BEGIN:VCALENDAR
+VERSION:2.0
+PRODID:-//Global Corp.//CalDAV Client//EN
+BEGIN:VTIMEZONE
+TZID:Europe/London
+BEGIN:STANDARD
+DTSTART:19961027T020000
+RRULE:FREQ=YEARLY;BYMONTH=10;BYDAY=-1SU
+TZNAME:GMT
+TZOFFSETFROM:+0100
+TZOFFSETTO:+0000
+END:STANDARD
+BEGIN:DAYLIGHT
+DTSTART:19810329T010000
+RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=-1SU
+TZNAME:BST
+TZOFFSETFROM:+0000
+TZOFFSETTO:+0100
+END:DAYLIGHT
+END:VTIMEZONE
+BEGIN:VEVENT
+UID:15
+DTSTAMP:20221125T000000Z
+DTSTART;TZID=Europe/London:20221127T000000
+DTEND;TZID=Europe/London:20221127T003000
+SUMMARY:Event with a provided Timezone
+END:VEVENT
+END:VCALENDAR
 """,
 ]
 
@@ -929,7 +958,7 @@ async def test_get_events(hass, calendar, get_api_events):
     await hass.async_block_till_done()
 
     events = await get_api_events("calendar.private")
-    assert len(events) == 15
+    assert len(events) == 16
     assert calendar.call