Fixed #27829 -- Deprecated settings.DEFAULT_CONTENT_TYPE.

django/conf/__init__.py

@@ -9,9 +9,11 @@ a list of all possible variables.
 import importlib
 import os
 import time
+import warnings
 
 from django.conf import global_settings
 from django.core.exceptions import ImproperlyConfigured
+from django.utils.deprecation import RemovedInDjango30Warning
 from django.utils.functional import LazyObject, empty
 
 ENVIRONMENT_VARIABLE = "DJANGO_SETTINGS_MODULE"
@@ -128,6 +130,9 @@ class Settings:
         if not self.SECRET_KEY:
             raise ImproperlyConfigured("The SECRET_KEY setting must not be empty.")
 
+        if self.is_overridden('DEFAULT_CONTENT_TYPE'):
+            warnings.warn('The DEFAULT_CONTENT_TYPE setting is deprecated.', RemovedInDjango30Warning)
+
         if hasattr(time, 'tzset') and self.TIME_ZONE:
             # When we can, attempt to validate the timezone. If we can't find
             # this file, no check happens and it's harmless.
@@ -173,6 +178,8 @@ class UserSettingsHolder:
 
     def __setattr__(self, name, value):
         self._deleted.discard(name)
+        if name == 'DEFAULT_CONTENT_TYPE':
+            warnings.warn('The DEFAULT_CONTENT_TYPE setting is deprecated.', RemovedInDjango30Warning)
         super().__setattr__(name, value)
 
     def __delattr__(self, name):

docs/internals/deprecation.txt

@@ -19,6 +19,8 @@ details on these changes.
 
 * ``django.shortcuts.render_to_response()`` will be removed.
 
+* The ``DEFAULT_CONTENT_TYPE`` setting will be removed.
+
 .. _deprecation-removed-in-2.1:
 
 2.1

docs/ref/settings.txt

@@ -1140,6 +1140,11 @@ Default content type to use for all ``HttpResponse`` objects, if a MIME type
 isn't manually specified. Used with :setting:`DEFAULT_CHARSET` to construct
 the ``Content-Type`` header.
 
+.. deprecated:: 2.0
+
+    This setting is deprecated because it doesn't interact well with
+    third-party apps and is obsolete since HTML5 has mostly superseded XHTML.
+
 .. setting:: DEFAULT_EXCEPTION_REPORTER_FILTER
 
 ``DEFAULT_EXCEPTION_REPORTER_FILTER``

docs/releases/2.0.txt

@@ -301,6 +301,10 @@ Miscellaneous
   :func:`django.shortcuts.render`. ``render()`` takes the same arguments
   except that is also requires a ``request``.
 
+* The ``DEFAULT_CONTENT_TYPE`` setting is deprecated. It doesn't interact well
+  well with third-party apps and is obsolete since HTML5 has mostly superseded
+  XHTML.
+
 .. _removed-features-2.0:
 
 Features removed in 2.0

tests/view_tests/tests/test_default_content_type.py

@@ -0,0 +1,44 @@
+import sys
+from types import ModuleType
+
+from django.conf import Settings
+from django.test import SimpleTestCase, ignore_warnings
+from django.utils.deprecation import RemovedInDjango30Warning
+
+
+class DefaultContentTypeTests(SimpleTestCase):
+    msg = 'The DEFAULT_CONTENT_TYPE setting is deprecated.'
+
+    @ignore_warnings(category=RemovedInDjango30Warning)
+    def test_default_content_type_is_text_html(self):
+        """
+        Content-Type of the default error responses is text/html. Refs #20822.
+        """
+        with self.settings(DEFAULT_CONTENT_TYPE='text/xml'):
+            response = self.client.get('/raises400/')
+            self.assertEqual(response['Content-Type'], 'text/html')
+
+            response = self.client.get('/raises403/')
+            self.assertEqual(response['Content-Type'], 'text/html')
+
+            response = self.client.get('/nonexistent_url/')
+            self.assertEqual(response['Content-Type'], 'text/html')
+
+            response = self.client.get('/server_error/')
+            self.assertEqual(response['Content-Type'], 'text/html')
+
+    def test_override_settings_warning(self):
+        with self.assertRaisesMessage(RemovedInDjango30Warning, self.msg):
+            with self.settings(DEFAULT_CONTENT_TYPE='text/xml'):
+                pass
+
+    def test_settings_init_warning(self):
+        settings_module = ModuleType('fake_settings_module')
+        settings_module.DEFAULT_CONTENT_TYPE = 'text/xml'
+        settings_module.SECRET_KEY = 'abc'
+        sys.modules['fake_settings_module'] = settings_module
+        try:
+            with self.assertRaisesMessage(RemovedInDjango30Warning, self.msg):
+                Settings('fake_settings_module')
+        finally:
+            del sys.modules['fake_settings_module']

tests/view_tests/tests/test_defaults.py

@@ -104,23 +104,6 @@ class DefaultsTests(TestCase):
         self.assertTrue(getattr(article.get_absolute_url, 'purge', False),
                         'The attributes of the original get_absolute_url must be added.')
 
-    @override_settings(DEFAULT_CONTENT_TYPE="text/xml")
-    def test_default_content_type_is_text_html(self):
-        """
-        Content-Type of the default error responses is text/html. Refs #20822.
-        """
-        response = self.client.get('/raises400/')
-        self.assertEqual(response['Content-Type'], 'text/html')
-
-        response = self.client.get('/raises403/')
-        self.assertEqual(response['Content-Type'], 'text/html')
-
-        response = self.client.get('/nonexistent_url/')
-        self.assertEqual(response['Content-Type'], 'text/html')
-
-        response = self.client.get('/server_error/')
-        self.assertEqual(response['Content-Type'], 'text/html')
-
     def test_custom_templates_wrong(self):
         """
         Default error views should raise TemplateDoesNotExist when passed a