When making datetimes aware, use the active timezone if it exists. Fixes #2850.

rest_framework/fields.py

@@ -13,6 +13,7 @@ from django.core.exceptions import ValidationError as DjangoValidationError
 from django.core.exceptions import ObjectDoesNotExist
 from django.core.validators import RegexValidator, ip_address_validators
 from django.forms import ImageField as DjangoImageField
+from django.forms.utils import from_current_timezone
 from django.utils import six, timezone
 from django.utils.dateparse import parse_date, parse_datetime, parse_time
 from django.utils.encoding import is_protected_type, smart_text
@@ -903,7 +904,12 @@ class DateTimeField(Field):
         When `self.default_timezone` is not `None`, always return aware datetimes.
         """
         if (self.default_timezone is not None) and not timezone.is_aware(value):
-            return timezone.make_aware(value, self.default_timezone)
+            # If a timezone is active, we want to use it, but if not we want to use the timezone
+            # specified for this field over the system's default timezone.
+            if hasattr(timezone._active, 'value'):
+                return from_current_timezone(value)
+            else:
+                return timezone.make_aware(value, self.default_timezone)
         elif (self.default_timezone is None) and timezone.is_aware(value):
             return timezone.make_naive(value, timezone.UTC())
         return value

tests/test_fields.py

@@ -4,6 +4,7 @@ from decimal import Decimal
 
 import django
 import pytest
+from django.test.utils import override_settings
 from django.utils import timezone
 
 import rest_framework
@@ -848,6 +849,40 @@ class TestNoOutputFormatDateField(FieldValues):
     field = serializers.DateField(format=None)
 
 
+class FakeTimezone(datetime.tzinfo):
+
+    def __repr__(self):
+        return "<FakeTimezone>"
+
+    def utcoffset(self, dt):
+        return datetime.timedelta(1)
+
+    def tzname(self, dt):
+        return "FakeTimezone"
+
+    def dst(self, dt):
+        return datetime.timedelta(1)
+
+
+class TestAwareDateTimeField:
+
+    @override_settings(USE_TZ=True)
+    def test_with_timezone_active(self):
+        naive_now = timezone.make_naive(timezone.now())
+        timezone.activate(FakeTimezone())
+        field = serializers.DateTimeField(default_timezone=timezone.UTC())
+        aware_now = field.enforce_timezone(naive_now)
+        assert aware_now.tzname() == 'FakeTimezone'
+        timezone.deactivate()
+
+    @override_settings(USE_TZ=True)
+    def test_without_timezone_active(self):
+        naive_now = timezone.make_naive(timezone.now())
+        field = serializers.DateTimeField(default_timezone=timezone.UTC())
+        aware_now = field.enforce_timezone(naive_now)
+        assert aware_now.tzname() == 'UTC'
+
+
 class TestDateTimeField(FieldValues):
     """
     Valid and invalid values for `DateTimeField`.