Check if module path is superclass of required classes for admin

django/contrib/admin/checks.py

@@ -15,6 +15,7 @@
 )
 from django.template import engines
 from django.template.backends.django import DjangoTemplates
+from django.utils.module_loading import import_string
 
 
 def _issubclass(cls, classinfo):
@@ -28,6 +29,22 @@ def _issubclass(cls, classinfo):
         return False
 
 
+def _contains_subclass(subclass_path, candidate_paths):
+    """
+    Check if dotted subclass module path is found among a list of candidate
+    paths.
+    """
+    subclass = import_string(subclass_path)
+    for path in candidate_paths:
+        try:
+            candidate_cls = import_string(path)
+        except ImportError:
+            continue
+        if _issubclass(candidate_cls, subclass):
+            return True
+    return False
+
+
 def check_admin_app(app_configs, **kwargs):
     from django.contrib.admin.sites import all_sites
     errors = []
@@ -70,10 +87,8 @@ def check_dependencies(**kwargs):
             id='admin.E403',
         ))
     else:
-        if ('django.contrib.auth.context_processors.auth'
-                not in django_templates_instance.context_processors and
-                'django.contrib.auth.backends.ModelBackend'
-                in settings.AUTHENTICATION_BACKENDS):
+        if ('django.contrib.auth.context_processors.auth' not in django_templates_instance.context_processors and
+                _contains_subclass('django.contrib.auth.backends.ModelBackend', settings.AUTHENTICATION_BACKENDS)):
             errors.append(checks.Error(
                 "'django.contrib.auth.context_processors.auth' must be "
                 "enabled in DjangoTemplates (TEMPLATES) if using the default "
@@ -88,17 +103,16 @@ def check_dependencies(**kwargs):
                 "the admin application.",
                 id='admin.E404',
             ))
-    if ('django.contrib.auth.middleware.AuthenticationMiddleware'
-            not in settings.MIDDLEWARE):
+
+    if not _contains_subclass('django.contrib.auth.middleware.AuthenticationMiddleware', settings.MIDDLEWARE):
         errors.append(checks.Error(
-            "'django.contrib.auth.middleware.AuthenticationMiddleware' must "
+            "'django.contrib.auth.middleware.AuthenticationMiddleware' (or a subclass) must "
             "be in MIDDLEWARE in order to use the admin application.",
             id='admin.E408',
         ))
-    if ('django.contrib.messages.middleware.MessageMiddleware'
-            not in settings.MIDDLEWARE):
+    if not _contains_subclass('django.contrib.messages.middleware.MessageMiddleware', settings.MIDDLEWARE):
         errors.append(checks.Error(
-            "'django.contrib.messages.middleware.MessageMiddleware' must "
+            "'django.contrib.messages.middleware.MessageMiddleware' (or a subclass) must "
             "be in MIDDLEWARE in order to use the admin application.",
             id='admin.E409',
         ))

tests/admin_checks/tests.py

@@ -1,6 +1,7 @@
 from django import forms
 from django.contrib import admin
 from django.contrib.admin import AdminSite
+from django.contrib.auth.middleware import AuthenticationMiddleware
 from django.contrib.contenttypes.admin import GenericStackedInline
 from django.core import checks
 from django.test import SimpleTestCase, override_settings
@@ -37,6 +38,10 @@ def check(self, **kwargs):
         return ['error!']
 
 
+class MyAuthMiddleware(AuthenticationMiddleware):
+    pass
+
+
 @override_settings(
     SILENCED_SYSTEM_CHECKS=['fields.W342'],  # ForeignKey(unique=True)
     INSTALLED_APPS=[
@@ -157,18 +162,25 @@ def test_middleware_dependencies(self):
         errors = admin.checks.check_dependencies()
         expected = [
             checks.Error(
-                "'django.contrib.auth.middleware.AuthenticationMiddleware' "
+                "'django.contrib.auth.middleware.AuthenticationMiddleware' (or a subclass) "
                 "must be in MIDDLEWARE in order to use the admin application.",
                 id='admin.E408',
             ),
             checks.Error(
-                "'django.contrib.messages.middleware.MessageMiddleware' "
+                "'django.contrib.messages.middleware.MessageMiddleware' (or a subclass) "
                 "must be in MIDDLEWARE in order to use the admin application.",
                 id='admin.E409',
             )
         ]
         self.assertEqual(errors, expected)
 
+    @override_settings(MIDDLEWARE=[
+        'admin_checks.tests.MyAuthMiddleware',
+        'django.contrib.messages.middleware.MessageMiddleware',
+    ])
+    def test_subclass_middleware_dependencies(self):
+        self.assertEqual(admin.checks.check_dependencies(), [])
+
     def test_custom_adminsite(self):
         class CustomAdminSite(admin.AdminSite):
             pass