[1.7.x] Fixed #23365 -- Added support for timezone-aware datetimes to migrations.

Backport of a407b846b4 from master

django/db/migrations/questioner.py

@@ -5,7 +5,7 @@ import os
 import sys
 
 from django.apps import apps
-from django.utils import datetime_safe, six
+from django.utils import datetime_safe, six, timezone
 from django.utils.six.moves import input
 
 from .loader import MIGRATIONS_MODULE_NAME
@@ -108,7 +108,8 @@ class InteractiveMigrationQuestioner(MigrationQuestioner):
                 sys.exit(3)
             else:
                 print("Please enter the default value now, as valid Python")
-                print("The datetime module is available, so you can do e.g. datetime.date.today()")
+                print("The datetime and django.utils.timezone modules are "
+                      "available, so you can do e.g. timezone.now()")
                 while True:
                     if six.PY3:
                         # Six does not correctly abstract over the fact that
@@ -123,7 +124,7 @@ class InteractiveMigrationQuestioner(MigrationQuestioner):
                         sys.exit(1)
                     else:
                         try:
-                            return eval(code, {}, {"datetime": datetime_safe})
+                            return eval(code, {}, {"datetime": datetime_safe, "timezone": timezone})
                         except (SyntaxError, NameError) as e:
                             print("Invalid input: %s" % e)
         return None

django/db/migrations/writer.py

@@ -16,6 +16,7 @@ from django.db.migrations.loader import MigrationLoader
 from django.utils import datetime_safe, six
 from django.utils.encoding import force_text
 from django.utils.functional import Promise
+from django.utils.timezone import utc
 
 
 COMPILED_REGEX_TYPE = type(re.compile(''))
@@ -164,6 +165,20 @@ class MigrationWriter(object):
 
         return (MIGRATION_TEMPLATE % items).encode("utf8")
 
+    @staticmethod
+    def serialize_datetime(value):
+        """
+        Returns a serialized version of a datetime object that is valid,
+        executable python code. It converts timezone-aware values to utc with
+        an 'executable' utc representation of tzinfo.
+        """
+        if value.tzinfo is not None and value.tzinfo != utc:
+            value = value.astimezone(utc)
+        value_repr = repr(value).replace("<UTC>", "utc")
+        if isinstance(value, datetime_safe.datetime):
+            value_repr = "datetime.%s" % value_repr
+        return value_repr
+
     @property
     def filename(self):
         return "%s.py" % self.migration.name
@@ -267,12 +282,11 @@ class MigrationWriter(object):
             return "{%s}" % (", ".join("%s: %s" % (k, v) for k, v in strings)), imports
         # Datetimes
         elif isinstance(value, datetime.datetime):
+            value_repr = cls.serialize_datetime(value)
+            imports = ["import 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.")
-            value_repr = repr(value)
-            if isinstance(value, datetime_safe.datetime):
-                value_repr = "datetime.%s" % value_repr
-            return value_repr, set(["import datetime"])
+                imports.append("from django.utils.timezone import utc")
+            return value_repr, set(imports)
         # Dates
         elif isinstance(value, datetime.date):
             value_repr = repr(value)