Document the tzinfo parameter of TruncDate/TruncTime as unsupported

Add the same exception raising from TruncDate to TruncTime and add
tests for both functions.

Author: timgraham

django_mongodb_backend/functions.py

@@ -248,6 +248,9 @@ def trunc_date(self, compiler, connection):
 
 
 def trunc_time(self, compiler, connection):
+    tzname = self.get_tzname()
+    if tzname and tzname != "UTC":
+        raise NotSupportedError(f"TruncTime with tzinfo ({tzname}) isn't supported on MongoDB.")
     lhs_mql = process_lhs(self, compiler, connection)
     return {
         "$dateFromString": {

docs/source/topics/known-issues.rst

@@ -74,6 +74,11 @@ Database functions
     :class:`~django.db.models.functions.SHA512`
   - :class:`~django.db.models.functions.Sign`
 
+- The ``tzinfo`` parameter of the
+  :class:`~django.db.models.functions.TruncDate` and
+  :class:`~django.db.models.functions.TruncTime` database functions isn't
+  supported.
+
 Transaction management
 ======================
 

tests/db_functions_/models.py

@@ -0,0 +1,5 @@
+from django.db import models
+
+
+class DTModel(models.Model):
+    start_datetime = models.DateTimeField(null=True, blank=True)

tests/db_functions_/test_datetime.py

@@ -0,0 +1,26 @@
+from zoneinfo import ZoneInfo
+
+from django.db import NotSupportedError
+from django.db.models.functions import TruncDate, TruncTime
+from django.test import TestCase, override_settings
+
+from .models import DTModel
+
+
+@override_settings(USE_TZ=True)
+class TruncTests(TestCase):
+    melb = ZoneInfo("Australia/Melbourne")
+
+    def test_truncdate_tzinfo(self):
+        msg = "TruncDate with tzinfo (Australia/Melbourne) isn't supported on MongoDB."
+        with self.assertRaisesMessage(NotSupportedError, msg):
+            DTModel.objects.annotate(
+                melb_date=TruncDate("start_datetime", tzinfo=self.melb),
+            ).get()
+
+    def test_trunctime_tzinfo(self):
+        msg = "TruncTime with tzinfo (Australia/Melbourne) isn't supported on MongoDB."
+        with self.assertRaisesMessage(NotSupportedError, msg):
+            DTModel.objects.annotate(
+                melb_date=TruncTime("start_datetime", tzinfo=self.melb),
+            ).get()