Refs #27829 -- Added warning for settings.DEFAULT_CONTENT_TYPE usage outside of Django.

django/conf/__init__.py

@@ -9,9 +9,11 @@ for a list of all possible variables.
 import importlib
 import os
 import time
+import traceback
 import warnings
 from pathlib import Path
 
+import django
 from django.conf import global_settings
 from django.core.exceptions import ImproperlyConfigured
 from django.utils.deprecation import RemovedInDjango30Warning
@@ -19,6 +21,8 @@ from django.utils.functional import LazyObject, empty
 
 ENVIRONMENT_VARIABLE = "DJANGO_SETTINGS_MODULE"
 
+DEFAULT_CONTENT_TYPE_DEPRECATED_MSG = 'The DEFAULT_CONTENT_TYPE setting is deprecated.'
+
 
 class LazySettings(LazyObject):
     """
@@ -93,6 +97,20 @@ class LazySettings(LazyObject):
         """Return True if the settings have already been configured."""
         return self._wrapped is not empty
 
+    @property
+    def DEFAULT_CONTENT_TYPE(self):
+        stack = traceback.extract_stack()
+        # Show a warning if the setting is used outside of Django.
+        # Stack index: -1 this line, -2 the caller.
+        filename, _line_number, _function_name, _text = stack[-2]
+        if not filename.startswith(os.path.dirname(django.__file__)):
+            warnings.warn(
+                DEFAULT_CONTENT_TYPE_DEPRECATED_MSG,
+                RemovedInDjango30Warning,
+                stacklevel=2,
+            )
+        return self.__getattr__('DEFAULT_CONTENT_TYPE')
+
 
 class Settings:
     def __init__(self, settings_module):
@@ -126,7 +144,7 @@ class Settings:
             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)
+            warnings.warn(DEFAULT_CONTENT_TYPE_DEPRECATED_MSG, RemovedInDjango30Warning)
 
         if hasattr(time, 'tzset') and self.TIME_ZONE:
             # When we can, attempt to validate the timezone. If we can't find
@@ -172,7 +190,7 @@ 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)
+            warnings.warn(DEFAULT_CONTENT_TYPE_DEPRECATED_MSG, RemovedInDjango30Warning)
         super().__setattr__(name, value)
 
     def __delattr__(self, name):

tests/view_tests/tests/test_default_content_type.py

 import sys
 from types import ModuleType
 
-from django.conf import Settings
+from django.conf import DEFAULT_CONTENT_TYPE_DEPRECATED_MSG, Settings, 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.'
+    msg = DEFAULT_CONTENT_TYPE_DEPRECATED_MSG
 
     @ignore_warnings(category=RemovedInDjango30Warning)
     def test_default_content_type_is_text_html(self):
@@ -42,3 +42,17 @@ class DefaultContentTypeTests(SimpleTestCase):
                 Settings('fake_settings_module')
         finally:
             del sys.modules['fake_settings_module']
+
+    def test_access_warning(self):
+        with self.assertRaisesMessage(RemovedInDjango30Warning, self.msg):
+            settings.DEFAULT_CONTENT_TYPE
+        # Works a second time.
+        with self.assertRaisesMessage(RemovedInDjango30Warning, self.msg):
+            settings.DEFAULT_CONTENT_TYPE
+
+    @ignore_warnings(category=RemovedInDjango30Warning)
+    def test_access(self):
+        with self.settings(DEFAULT_CONTENT_TYPE='text/xml'):
+            self.assertEqual(settings.DEFAULT_CONTENT_TYPE, 'text/xml')
+            # Works a second time.
+            self.assertEqual(settings.DEFAULT_CONTENT_TYPE, 'text/xml')