create a deployment check to ensure USE_TZ is enabled

Fixes #1086

modoboa/core/apps.py

@@ -29,6 +29,8 @@ class CoreConfig(AppConfig):
     def ready(self):
         load_core_settings()
 
+        # Import these to force registration of checks and signals
+        from . import checks  # noqa:F401
         from . import handlers
 
         signals.post_migrate.connect(handlers.create_local_config, sender=self)

modoboa/core/checks/__init__.py

@@ -0,0 +1,4 @@
+# -*- coding: utf-8 -*-
+
+# Import these to force registration of checks
+from . import settings_checks  # noqa:F401

modoboa/core/checks/settings_checks.py

@@ -0,0 +1,29 @@
+# -*- coding: utf-8 -*-
+
+from __future__ import unicode_literals
+
+from django.conf import settings
+from django.core.checks import Warning, register
+from django.utils.translation import ugettext as _
+
+
+W001 = Warning(
+    _("You have USE_TZ set to False, this may result in issues during "
+      "transitions between summer/winter time (ie the same local time occuring "
+      "twice due to clock change)."),
+    hint=_("Set `USE_TZ = True` in settings.py"),
+    id="modoboa.W001",
+)
+
+
+@register(deploy=True)
+def check_use_tz_enabled(app_configs, **kwargs):
+    """Ensure USE_TZ is enabled in settings.py
+
+    When USE_TZ is enabled all date/times are stored in UTC.
+    Fixes #1086 - https://github.com/modoboa/modoboa/issues/1086
+    """
+    errors = []
+    if not settings.USE_TZ:
+        errors.append(W001)
+    return errors

modoboa/core/tests/test_checks.py

@@ -0,0 +1,23 @@
+# -*- coding: utf-8 -*-
+
+from __future__ import unicode_literals
+
+from django.test import SimpleTestCase
+from django.test.utils import override_settings
+
+from ..checks import settings_checks
+
+
+class CheckSessionCookieSecureTest(SimpleTestCase):
+    @override_settings(USE_TZ=False)
+    def test_use_tz_false(self):
+        """If USE_TZ is off provide one warning."""
+        self.assertEqual(
+            settings_checks.check_use_tz_enabled(None),
+            [settings_checks.W001]
+        )
+
+    @override_settings(USE_TZ=True)
+    def test_use_tz_true(self):
+        """If USE_TZ is on, there's no warning about it."""
+        self.assertEqual(settings_checks.check_use_tz_enabled(None), [])