Fixed #21954: Raise nice error when serializing datetimes with timezones

django/db/migrations/writer.py

@@ -212,7 +212,12 @@ class MigrationWriter(object):
                 strings.append((k_string, v_string))
             return "{%s}" % (", ".join("%s: %s" % (k, v) for k, v in strings)), imports
         # Datetimes
-        elif isinstance(value, (datetime.datetime, datetime.date)):
+        elif isinstance(value, datetime.datetime):
+            if value.tzinfo is not None:
+                raise ValueError("Cannot serialize datetime values with timezones. Either use a callable value for default or remove the timezone.")
+            return repr(value), set(["import datetime"])
+        # Dates
+        elif isinstance(value, datetime.date):
             return repr(value), set(["import datetime"])
         # Settings references
         elif isinstance(value, SettingsReference):

tests/migrations/test_writer.py

@@ -13,6 +13,7 @@ from django.conf import settings
 from django.utils import six
 from django.utils.deconstruct import deconstructible
 from django.utils.translation import ugettext_lazy as _
+from django.utils.timezone import get_default_timezone
 
 
 class WriterTests(TestCase):
@@ -78,6 +79,8 @@ class WriterTests(TestCase):
         self.assertSerializedEqual(datetime.datetime.today)
         self.assertSerializedEqual(datetime.date.today())
         self.assertSerializedEqual(datetime.date.today)
+        with self.assertRaises(ValueError):
+            self.assertSerializedEqual(datetime.datetime(2012, 1, 1, 1, 1, tzinfo=get_default_timezone()))
         # Classes
         validator = RegexValidator(message="hello")
         string, imports = MigrationWriter.serialize(validator)