[2.2.x] Fixed #30237 -- Made Authentication/SessionMiddleware and ModelBackend admin checks allow subclasses.

Backport of f976ab1b11 from master.

django/contrib/admin/checks.py

@@ -18,6 +18,7 @@ from django.template import engines
 from django.template.backends.django import DjangoTemplates
 from django.utils.deprecation import RemovedInDjango30Warning
 from django.utils.inspect import get_func_args
+from django.utils.module_loading import import_string
 
 
 def _issubclass(cls, classinfo):
@@ -31,6 +32,23 @@ def _issubclass(cls, classinfo):
         return False
 
 
+def _contains_subclass(class_path, candidate_paths):
+    """
+    Return whether or not a dotted class path (or a subclass of that class) is
+    found in a list of candidate paths.
+    """
+    cls = import_string(class_path)
+    for path in candidate_paths:
+        try:
+            candidate_cls = import_string(path)
+        except ImportError:
+            # ImportErrors are raised elsewhere.
+            continue
+        if _issubclass(candidate_cls, cls):
+            return True
+    return False
+
+
 def check_admin_app(app_configs, **kwargs):
     from django.contrib.admin.sites import all_sites
     errors = []
@@ -75,8 +93,7 @@ def check_dependencies(**kwargs):
     else:
         if ('django.contrib.auth.context_processors.auth'
                 not in django_templates_instance.context_processors and
-                'django.contrib.auth.backends.ModelBackend'
+                _contains_subclass('django.contrib.auth.backends.ModelBackend', settings.AUTHENTICATION_BACKENDS)):
-                in settings.AUTHENTICATION_BACKENDS):
             errors.append(checks.Error(
                 "'django.contrib.auth.context_processors.auth' must be "
                 "enabled in DjangoTemplates (TEMPLATES) if using the default "
@@ -91,15 +108,14 @@ 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 "
             "be in MIDDLEWARE in order to use the admin application.",
             id='admin.E408',
         ))
-    if ('django.contrib.messages.middleware.MessageMiddleware'
+    if not _contains_subclass('django.contrib.messages.middleware.MessageMiddleware', settings.MIDDLEWARE):
-            not in settings.MIDDLEWARE):
         errors.append(checks.Error(
             "'django.contrib.messages.middleware.MessageMiddleware' must "
             "be in MIDDLEWARE in order to use the admin application.",

tests/admin_checks/tests.py

@@ -1,7 +1,10 @@
 from django import forms
 from django.contrib import admin
 from django.contrib.admin import AdminSite
+from django.contrib.auth.backends import ModelBackend
+from django.contrib.auth.middleware import AuthenticationMiddleware
 from django.contrib.contenttypes.admin import GenericStackedInline
+from django.contrib.messages.middleware import MessageMiddleware
 from django.core import checks
 from django.test import SimpleTestCase, override_settings
 
@@ -37,6 +40,18 @@ class MyAdmin(admin.ModelAdmin):
         return ['error!']
 
 
+class AuthenticationMiddlewareSubclass(AuthenticationMiddleware):
+    pass
+
+
+class MessageMiddlewareSubclass(MessageMiddleware):
+    pass
+
+
+class ModelBackendSubclass(ModelBackend):
+    pass
+
+
 @override_settings(
     SILENCED_SYSTEM_CHECKS=['fields.W342'],  # ForeignKey(unique=True)
     INSTALLED_APPS=[
@@ -129,6 +144,27 @@ class SystemChecksTestCase(SimpleTestCase):
         with self.settings(AUTHENTICATION_BACKENDS=[]):
             self.assertEqual(admin.checks.check_dependencies(), expected[1:])
 
+    @override_settings(
+        AUTHENTICATION_BACKENDS=['admin_checks.tests.ModelBackendSubclass'],
+        TEMPLATES=[{
+            'BACKEND': 'django.template.backends.django.DjangoTemplates',
+            'DIRS': [],
+            'APP_DIRS': True,
+            'OPTIONS': {
+                'context_processors': ['django.contrib.messages.context_processors.messages'],
+            },
+        }],
+    )
+    def test_context_processor_dependencies_model_backend_subclass(self):
+        self.assertEqual(admin.checks.check_dependencies(), [
+            checks.Error(
+                "'django.contrib.auth.context_processors.auth' must be "
+                "enabled in DjangoTemplates (TEMPLATES) if using the default "
+                "auth backend in order to use the admin application.",
+                id='admin.E402',
+            ),
+        ])
+
     @override_settings(
         TEMPLATES=[
             {
@@ -169,6 +205,21 @@ class SystemChecksTestCase(SimpleTestCase):
         ]
         self.assertEqual(errors, expected)
 
+    @override_settings(MIDDLEWARE=[
+        'admin_checks.tests.AuthenticationMiddlewareSubclass',
+        'admin_checks.tests.MessageMiddlewareSubclass',
+    ])
+    def test_middleware_subclasses(self):
+        self.assertEqual(admin.checks.check_dependencies(), [])
+
+    @override_settings(MIDDLEWARE=[
+        'django.contrib.does.not.Exist',
+        'django.contrib.auth.middleware.AuthenticationMiddleware',
+        'django.contrib.messages.middleware.MessageMiddleware',
+    ])
+    def test_admin_check_ignores_import_error_in_middleware(self):
+        self.assertEqual(admin.checks.check_dependencies(), [])
+
     def test_custom_adminsite(self):
         class CustomAdminSite(admin.AdminSite):
             pass