Fixed #29695 -- Added system checks for admin's app dependencies and TEMPLATES setting.

4 files changed, 182 insertions, 38 deletions

diff --git a/django/contrib/admin/checks.py b/django/contrib/admin/checks.py
index fbc8d50693..d129acb124 100644
--- a/django/contrib/admin/checks.py
+++ b/django/contrib/admin/checks.py
@@ -14,7 +14,8 @@ from django.db.models.expressions import Combinable, F, OrderBy
 from django.forms.models import (
     BaseModelForm, BaseModelFormSet, _get_foreign_key,
 )
-from django.template.engine import Engine
+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
 
@@ -31,38 +32,68 @@ def check_dependencies(**kwargs):
     """
     Check that the admin's dependencies are correctly installed.
     """
+    if not apps.is_installed('django.contrib.admin'):
+        return []
     errors = []
-    # contrib.contenttypes must be installed.
-    if not apps.is_installed('django.contrib.contenttypes'):
-        missing_app = checks.Error(
-            "'django.contrib.contenttypes' must be in INSTALLED_APPS in order "
-            "to use the admin application.",
-            id="admin.E401",
-        )
-        errors.append(missing_app)
-    # The auth context processor must be installed if using the default
-    # authentication backend.
-    try:
-        default_template_engine = Engine.get_default()
-    except Exception:
-        # Skip this non-critical check:
-        # 1. if the user has a non-trivial TEMPLATES setting and Django
-        #    can't find a default template engine
-        # 2. if anything goes wrong while loading template engines, in
-        #    order to avoid raising an exception from a confusing location
-        # Catching ImproperlyConfigured suffices for 1. but 2. requires
-        # catching all exceptions.
-        pass
+    app_dependencies = (
+        ('django.contrib.contenttypes', 401),
+        ('django.contrib.auth', 405),
+        ('django.contrib.messages', 406),
+        ('django.contrib.sessions', 407),
+    )
+    for app_name, error_code in app_dependencies:
+        if not apps.is_installed(app_name):
+            errors.append(checks.Error(
+                "'%s' must be in INSTALLED_APPS in order to use the admin "
+                "application." % app_name,
+                id='admin.E%d' % error_code,
+            ))
+    for engine in engines.all():
+        if isinstance(engine, DjangoTemplates):
+            django_templates_instance = engine.engine
+            break
+    else:
+        django_templates_instance = None
+    if not django_templates_instance:
+        errors.append(checks.Error(
+            "A 'django.template.backends.django.DjangoTemplates' instance "
+            "must be configured in TEMPLATES in order to use the admin "
+            "application.",
+            id='admin.E403',
+        ))
     else:
         if ('django.contrib.auth.context_processors.auth'
-                not in default_template_engine.context_processors and
-                'django.contrib.auth.backends.ModelBackend' in settings.AUTHENTICATION_BACKENDS):
-            missing_template = checks.Error(
-                "'django.contrib.auth.context_processors.auth' must be in "
-                "TEMPLATES in order to use the admin application.",
-                id="admin.E402"
-            )
-            errors.append(missing_template)
+                not in django_templates_instance.context_processors and
+                'django.contrib.auth.backends.ModelBackend'
+                in settings.AUTHENTICATION_BACKENDS):
+            errors.append(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',
+            ))
+        if ('django.contrib.messages.context_processors.messages'
+                not in django_templates_instance.context_processors):
+            errors.append(checks.Error(
+                "'django.contrib.messages.context_processors.messages' must "
+                "be enabled in DjangoTemplates (TEMPLATES) in order to use "
+                "the admin application.",
+                id='admin.E404',
+            ))
+    if ('django.contrib.auth.middleware.AuthenticationMiddleware'
+            not in 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'
+            not in settings.MIDDLEWARE):
+        errors.append(checks.Error(
+            "'django.contrib.messages.middleware.MessageMiddleware' must "
+            "be in MIDDLEWARE in order to use the admin application.",
+            id='admin.E409',
+        ))
     return errors
 
 
diff --git a/docs/ref/checks.txt b/docs/ref/checks.txt
index ee16ebde54..a84d9b60b6 100644
--- a/docs/ref/checks.txt
+++ b/docs/ref/checks.txt
@@ -624,7 +624,26 @@ The following checks are performed on the default
 * **admin.E401**: :mod:`django.contrib.contenttypes` must be in
   :setting:`INSTALLED_APPS` in order to use the admin application.
 * **admin.E402**: :mod:`django.contrib.auth.context_processors.auth`
-  must be in :setting:`TEMPLATES` in order to use the admin application.
+  must be enabled in :class:`~django.template.backends.django.DjangoTemplates`
+  (:setting:`TEMPLATES`) if using the default auth backend in order to use the
+  admin application.
+* **admin.E403**: A :class:`django.template.backends.django.DjangoTemplates`
+  instance must be configured in :setting:`TEMPLATES` in order to use the
+  admin application.
+* **admin.E404**: ``django.contrib.messages.context_processors.messages``
+  must be enabled in :class:`~django.template.backends.django.DjangoTemplates`
+  (:setting:`TEMPLATES`) in order to use the admin application.
+* **admin.E405**: :mod:`django.contrib.auth` must be in
+  :setting:`INSTALLED_APPS` in order to use the admin application.
+* **admin.E406**: :mod:`django.contrib.messages` must be in
+  :setting:`INSTALLED_APPS` in order to use the admin application.
+* **admin.E407**: :mod:`django.contrib.sessions` must be in
+  :setting:`INSTALLED_APPS` in order to use the admin application.
+* **admin.E408**:
+  :class:`django.contrib.auth.middleware.AuthenticationMiddleware` must be in
+  :setting:`MIDDLEWARE` in order to use the admin application.
+* **admin.E409**: :class:`django.contrib.messages.middleware.MessageMiddleware`
+  must be in :setting:`MIDDLEWARE` in order to use the admin application.
 
 ``auth``
 --------
diff --git a/tests/admin_checks/tests.py b/tests/admin_checks/tests.py
index a968cd5ba3..d5661a137d 100644
--- a/tests/admin_checks/tests.py
+++ b/tests/admin_checks/tests.py
@@ -43,6 +43,8 @@ class MyAdmin(admin.ModelAdmin):
         'django.contrib.admin',
         'django.contrib.auth',
         'django.contrib.contenttypes',
+        'django.contrib.sessions',
+        'django.contrib.messages',
         'admin_checks',
     ],
 )
@@ -58,20 +60,42 @@ class SystemChecksTestCase(SimpleTestCase):
             admin.site.unregister(Song)
 
     @override_settings(INSTALLED_APPS=['django.contrib.admin'])
-    def test_contenttypes_dependency(self):
+    def test_apps_dependencies(self):
         errors = admin.checks.check_dependencies()
         expected = [
             checks.Error(
                 "'django.contrib.contenttypes' must be in "
                 "INSTALLED_APPS in order to use the admin application.",
                 id="admin.E401",
+            ),
+            checks.Error(
+                "'django.contrib.auth' must be in INSTALLED_APPS in order "
+                "to use the admin application.",
+                id='admin.E405',
+            ),
+            checks.Error(
+                "'django.contrib.messages' must be in INSTALLED_APPS in order "
+                "to use the admin application.",
+                id='admin.E406',
+            ),
+            checks.Error(
+                "'django.contrib.sessions' must be in INSTALLED_APPS in order "
+                "to use the admin application.",
+                id='admin.E407',
             )
         ]
         self.assertEqual(errors, expected)
 
     @override_settings(TEMPLATES=[])
     def test_no_template_engines(self):
-        self.assertEqual(admin.checks.check_dependencies(), [])
+        self.assertEqual(admin.checks.check_dependencies(), [
+            checks.Error(
+                "A 'django.template.backends.django.DjangoTemplates' "
+                "instance must be configured in TEMPLATES in order to use "
+                "the admin application.",
+                id='admin.E403',
+            )
+        ])
 
     @override_settings(
         TEMPLATES=[{
@@ -83,13 +107,64 @@ class SystemChecksTestCase(SimpleTestCase):
             },
         }],
     )
-    def test_auth_contextprocessor_dependency(self):
+    def test_context_processor_dependencies(self):
+        expected = [
+            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',
+            ),
+            checks.Error(
+                "'django.contrib.messages.context_processors.messages' must "
+                "be enabled in DjangoTemplates (TEMPLATES) in order to use "
+                "the admin application.",
+                id='admin.E404',
+            )
+        ]
+        self.assertEqual(admin.checks.check_dependencies(), expected)
+        # The first error doesn't happen if
+        # 'django.contrib.auth.backends.ModelBackend' isn't in
+        # AUTHENTICATION_BACKENDS.
+        with self.settings(AUTHENTICATION_BACKENDS=[]):
+            self.assertEqual(admin.checks.check_dependencies(), expected[1:])
+
+    @override_settings(
+        TEMPLATES=[
+            {
+                'BACKEND': 'django.template.backends.jinja2.Jinja2',
+                'DIRS': [],
+                'APP_DIRS': True,
+            },
+            {
+                'BACKEND': 'django.template.backends.django.DjangoTemplates',
+                'DIRS': [],
+                'APP_DIRS': True,
+                'OPTIONS': {
+                    'context_processors': [
+                        'django.contrib.auth.context_processors.auth',
+                        'django.contrib.messages.context_processors.messages',
+                    ],
+                },
+            },
+        ],
+    )
+    def test_several_templates_backends(self):
+        self.assertEqual(admin.checks.check_dependencies(), [])
+
+    @override_settings(MIDDLEWARE=[])
+    def test_middleware_dependencies(self):
         errors = admin.checks.check_dependencies()
         expected = [
             checks.Error(
-                "'django.contrib.auth.context_processors.auth' must be in "
-                "TEMPLATES in order to use the admin application.",
-                id="admin.E402",
+                "'django.contrib.auth.middleware.AuthenticationMiddleware' "
+                "must be in MIDDLEWARE in order to use the admin application.",
+                id='admin.E408',
+            ),
+            checks.Error(
+                "'django.contrib.messages.middleware.MessageMiddleware' "
+                "must be in MIDDLEWARE in order to use the admin application.",
+                id='admin.E409',
             )
         ]
         self.assertEqual(errors, expected)
diff --git a/tests/admin_scripts/tests.py b/tests/admin_scripts/tests.py
index c1d8baef6b..c60194fe72 100644
--- a/tests/admin_scripts/tests.py
+++ b/tests/admin_scripts/tests.py
@@ -1172,9 +1172,28 @@ class ManageCheck(AdminScriptTestCase):
                 'django.contrib.admin.apps.SimpleAdminConfig',
                 'django.contrib.auth',
                 'django.contrib.contenttypes',
+                'django.contrib.messages',
+                'django.contrib.sessions',
             ],
             sdict={
-                'DEBUG': True
+                'DEBUG': True,
+                'MIDDLEWARE': [
+                    'django.contrib.messages.middleware.MessageMiddleware',
+                    'django.contrib.auth.middleware.AuthenticationMiddleware',
+                ],
+                'TEMPLATES': [
+                    {
+                        'BACKEND': 'django.template.backends.django.DjangoTemplates',
+                        'DIRS': [],
+                        'APP_DIRS': True,
+                        'OPTIONS': {
+                            'context_processors': [
+                                'django.contrib.auth.context_processors.auth',
+                                'django.contrib.messages.context_processors.messages',
+                            ],
+                        },
+                    },
+                ],
             }
         )
         args = ['check']