Use UTC instead of Etc/UTC when passing tz to dateutil rrule (#1414)

Fixes https://github.com/grafana/oncall-private/issues/1648

CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Fixed importing of global grafana styles ([672](https://github.com/grafana/oncall/issues/672))
 - Fixed UI permission related bug where Editors could not export their user iCal link
+- Fixed error when a shift is created using Etc/UTC as timezone
 
 ### Changed
 

engine/apps/schedules/models/custom_on_call_shift.py

@@ -588,6 +588,9 @@ class CustomOnCallShift(models.Model):
 
     def convert_dt_to_schedule_timezone(self, dt, time_zone):
         start_naive = dt.replace(tzinfo=None)
+        if time_zone and time_zone.lower() == "etc/utc":
+            # dateutil rrule breaks if Etc/UTC is given
+            time_zone = "UTC"
         return pytz.timezone(time_zone).localize(start_naive, is_dst=None)
 
     def get_rolling_users(self):

engine/apps/schedules/tests/test_custom_on_call_shift.py

@@ -1512,3 +1512,40 @@ def test_rolling_users_event_daily_by_day_start_none_convert_to_ical(
     ical_data = on_call_shift.convert_to_ical()
     # empty result since there is no event in the defined time range
     assert ical_data == ""
+
+
+@pytest.mark.django_db
+def test_etc_utc_timezone_convert_to_ical(
+    make_organization_and_user,
+    make_user_for_organization,
+    make_on_call_shift,
+):
+    organization, user_1 = make_organization_and_user()
+    user_2 = make_user_for_organization(organization)
+
+    date = timezone.now().replace(microsecond=0)
+    until = date + timezone.timedelta(days=30)
+
+    data = {
+        "priority_level": 1,
+        "start": date,
+        "rotation_start": date,
+        "duration": timezone.timedelta(seconds=10800),
+        "frequency": CustomOnCallShift.FREQUENCY_HOURLY,
+        "interval": 2,
+        "until": until,
+        "time_zone": "Etc/UTC",
+    }
+
+    on_call_shift = make_on_call_shift(
+        organization=organization, shift_type=CustomOnCallShift.TYPE_ROLLING_USERS_EVENT, **data
+    )
+    rolling_users = [[user_1], [user_2]]
+    on_call_shift.add_rolling_users(rolling_users)
+
+    ical_data = on_call_shift.convert_to_ical()
+    ical_rrule_until = on_call_shift.until.strftime("%Y%m%dT%H%M%S")
+    expected_rrule = f"RRULE:FREQ=HOURLY;UNTIL={ical_rrule_until}Z;INTERVAL=4;WKST=SU"
+
+    assert on_call_shift.event_interval == len(rolling_users) * data["interval"]
+    assert expected_rrule in ical_data