Fixed #14664 -- Logged a warning if MiddlewareNotUsed is raised in DEBUG mode.

django/core/handlers/base.py

@@ -49,7 +49,12 @@ class BaseHandler(object):
             mw_class = import_string(middleware_path)
             try:
                 mw_instance = mw_class()
-            except MiddlewareNotUsed:
+            except MiddlewareNotUsed as exc:
+                if settings.DEBUG:
+                    if six.text_type(exc):
+                        logger.debug('MiddlewareNotUsed(%r): %s', middleware_path, exc)
+                    else:
+                        logger.debug('MiddlewareNotUsed: %r', middleware_path)
                 continue
 
             if hasattr(mw_instance, 'process_request'):

docs/releases/1.8.txt

@@ -337,6 +337,10 @@ Middleware
   <django.middleware.common.CommonMiddleware.response_redirect_class>`
   attribute allows you to customize the redirects issued by the middleware.
 
+* A debug message will be logged to the ``django.request`` logger when a
+  middleware raises a :exc:`~django.core.exceptions.MiddlewareNotUsed` exception
+  in :setting:`DEBUG` mode.
+
 Migrations
 ^^^^^^^^^^
 

docs/topics/http/middleware.txt

@@ -269,7 +269,14 @@ Marking middleware as unused
 It's sometimes useful to determine at run-time whether a piece of middleware
 should be used. In these cases, your middleware's ``__init__`` method may
 raise :exc:`django.core.exceptions.MiddlewareNotUsed`. Django will then remove
-that piece of middleware from the middleware process.
+that piece of middleware from the middleware process and a debug message will
+be logged to the ``django.request`` logger when :setting:`DEBUG` is set to
+``True``.
+
+.. versionchanged:: 1.8
+
+    Previously, :exc:`~django.core.exceptions.MiddlewareNotUsed` exceptions
+    weren't logged.
 
 Guidelines
 ----------

tests/middleware_exceptions/tests.py

 import sys
 
 from django.conf import settings
+from django.core.exceptions import MiddlewareNotUsed
 from django.core.signals import got_request_exception
 from django.http import HttpResponse
 from django.template.response import TemplateResponse
 from django.template import Template
-from django.test import TestCase, override_settings
+from django.test import RequestFactory, TestCase, override_settings
+from django.test.utils import patch_logger
 
 
 class TestException(Exception):
@@ -832,3 +834,65 @@ class RootUrlconfTests(TestCase):
         # the previously defined settings.
         del settings.ROOT_URLCONF
         self.assertRaises(AttributeError, self.client.get, "/middleware_exceptions/view/")
+
+
+class MyMiddleware(object):
+
+    def __init__(self):
+        raise MiddlewareNotUsed
+
+    def process_request(self, request):
+        pass
+
+
+class MyMiddlewareWithExceptionMessage(object):
+
+    def __init__(self):
+        raise MiddlewareNotUsed('spam eggs')
+
+    def process_request(self, request):
+        pass
+
+
+@override_settings(
+    DEBUG=True,
+    ROOT_URLCONF='middleware_exceptions.urls',
+)
+class MiddlewareNotUsedTests(TestCase):
+
+    rf = RequestFactory()
+
+    def test_raise_exception(self):
+        request = self.rf.get('middleware_exceptions/view/')
+        with self.assertRaises(MiddlewareNotUsed):
+            MyMiddleware().process_request(request)
+
+    @override_settings(MIDDLEWARE_CLASSES=(
+        'middleware_exceptions.tests.MyMiddleware',
+    ))
+    def test_log(self):
+        with patch_logger('django.request', 'debug') as calls:
+            self.client.get('/middleware_exceptions/view/')
+        self.assertEqual(len(calls), 1)
+        self.assertEqual(
+            calls[0],
+            "MiddlewareNotUsed: 'middleware_exceptions.tests.MyMiddleware'"
+        )
+
+    @override_settings(MIDDLEWARE_CLASSES=(
+        'middleware_exceptions.tests.MyMiddlewareWithExceptionMessage',
+    ))
+    def test_log_custom_message(self):
+        with patch_logger('django.request', 'debug') as calls:
+            self.client.get('/middleware_exceptions/view/')
+        self.assertEqual(len(calls), 1)
+        self.assertEqual(
+            calls[0],
+            "MiddlewareNotUsed('middleware_exceptions.tests.MyMiddlewareWithExceptionMessage'): spam eggs"
+        )
+
+    @override_settings(DEBUG=False)
+    def test_do_not_log_when_debug_is_false(self):
+        with patch_logger('django.request', 'debug') as calls:
+            self.client.get('/middleware_exceptions/view/')
+        self.assertEqual(len(calls), 0)