Refs #26601 -- Added a warning if both MIDDLEWARE AND MIDDLEWARE_CLASSES are set.

django/core/checks/__init__.py

@@ -10,6 +10,7 @@ from .registry import Tags, register, run_checks, tag_exists
 # Import these to force registration of checks
 import django.core.checks.caches  # NOQA isort:skip
 import django.core.checks.compatibility.django_1_8_0  # NOQA isort:skip
+import django.core.checks.compatibility.django_1_10  # NOQA isort:skip
 import django.core.checks.database  # NOQA isort:skip
 import django.core.checks.model_checks  # NOQA isort:skip
 import django.core.checks.security.base  # NOQA isort:skip

django/core/checks/compatibility/django_1_10.py

@@ -0,0 +1,17 @@
+from __future__ import unicode_literals
+
+from django.conf import global_settings, settings
+
+from .. import Tags, Warning, register
+
+
+@register(Tags.compatibility)
+def check_duplicate_middleware_settings(app_configs, **kwargs):
+    if settings.MIDDLEWARE is not None and settings.MIDDLEWARE_CLASSES != global_settings.MIDDLEWARE_CLASSES:
+        return [Warning(
+            "The MIDDLEWARE_CLASSES setting is deprecated in Django 1.10 "
+            "and the MIDDLEWARE setting takes precedence. Since you've set "
+            "MIDDLEWARE, the value of MIDDLEWARE_CLASSES is ignored.",
+            id='1_10.W001',
+        )]
+    return []

docs/ref/checks.txt

@@ -266,6 +266,9 @@ that might occur as a result of a version upgrade.
   put the values of the following settings into your defaults ``TEMPLATES``
   dict: ``TEMPLATE_DIRS``, ``TEMPLATE_CONTEXT_PROCESSORS``, ``TEMPLATE_DEBUG``,
   ``TEMPLATE_LOADERS``, ``TEMPLATE_STRING_IF_INVALID``.
+* **1_10.W001**: The ``MIDDLEWARE_CLASSES`` setting is deprecated in Django
+  1.10  and the :setting:`MIDDLEWARE` setting takes precedence. Since you've
+  set ``MIDDLEWARE``, the value of ``MIDDLEWARE_CLASSES`` is ignored.
 
 Admin
 -----

tests/check_framework/tests_1_10_compatibility.py

@@ -0,0 +1,17 @@
+from django.core.checks.compatibility.django_1_10 import \
+    check_duplicate_middleware_settings
+from django.test import SimpleTestCase
+from django.test.utils import override_settings
+
+
+class CheckDuplicateMiddlwareSettingsTest(SimpleTestCase):
+
+    @override_settings(MIDDLEWARE=[], MIDDLEWARE_CLASSES=['django.middleware.common.CommonMiddleware'])
+    def test_duplicate_setting(self):
+        result = check_duplicate_middleware_settings(None)
+        self.assertEqual(result[0].id, '1_10.W001')
+
+    @override_settings(MIDDLEWARE=None)
+    def test_middleware_not_defined(self):
+        result = check_duplicate_middleware_settings(None)
+        self.assertEqual(len(result), 0)