Fixed #32260 -- Made View.as_view() do not use update_wrapper().

View.as_view() should not use update_wrapper() for copying attributes
it's unintended and have side-effects such as adding `self` to the
signature.

This also fixes system check for arguments of custom error handler
views with class-based views.

Co-authored-by: Nick Pope <nick.pope@flightdataservices.com>

django/views/generic/base.py

@@ -1,5 +1,4 @@
 import logging
-from functools import update_wrapper
 
 from django.core.exceptions import ImproperlyConfigured
 from django.http import (
@@ -71,12 +70,16 @@ class View:
         view.view_class = cls
         view.view_initkwargs = initkwargs
 
-        # take name and docstring from class
-        update_wrapper(view, cls, updated=())
+        # __name__ and __qualname__ are intentionally left unchanged as
+        # view_class should be used to robustly determine the name of the view
+        # instead.
+        view.__doc__ = cls.__doc__
+        view.__module__ = cls.__module__
+        view.__annotations__ = cls.dispatch.__annotations__
+        # Copy possible attributes set by decorators, e.g. @csrf_exempt, from
+        # the dispatch method.
+        view.__dict__.update(cls.dispatch.__dict__)
 
-        # and possible attributes set by decorators
-        # like csrf_exempt from dispatch
-        update_wrapper(view, cls.dispatch, assigned=())
         return view
 
     def setup(self, request, *args, **kwargs):

tests/check_framework/test_urls.py

@@ -167,20 +167,41 @@ class UpdatedToPathTests(SimpleTestCase):
 
 class CheckCustomErrorHandlersTests(SimpleTestCase):
 
-    @override_settings(ROOT_URLCONF='check_framework.urls.bad_error_handlers')
-    def test_bad_handlers(self):
+    @override_settings(
+        ROOT_URLCONF='check_framework.urls.bad_function_based_error_handlers',
+    )
+    def test_bad_function_based_handlers(self):
         result = check_url_config(None)
         self.assertEqual(len(result), 4)
         for code, num_params, error in zip([400, 403, 404, 500], [2, 2, 2, 1], result):
             with self.subTest('handler{}'.format(code)):
                 self.assertEqual(error, Error(
-                    "The custom handler{} view "
-                    "'check_framework.urls.bad_error_handlers.bad_handler' "
+                    "The custom handler{} view 'check_framework.urls."
+                    "bad_function_based_error_handlers.bad_handler' "
                     "does not take the correct number of arguments (request{})."
                     .format(code, ', exception' if num_params == 2 else ''),
                     id='urls.E007',
                 ))
 
+    @override_settings(
+        ROOT_URLCONF='check_framework.urls.bad_class_based_error_handlers',
+    )
+    def test_bad_class_based_handlers(self):
+        result = check_url_config(None)
+        self.assertEqual(len(result), 4)
+        for code, num_params, error in zip([400, 403, 404, 500], [2, 2, 2, 1], result):
+            with self.subTest('handler%s' % code):
+                self.assertEqual(error, Error(
+                    "The custom handler%s view 'check_framework.urls."
+                    "bad_class_based_error_handlers.HandlerView.as_view."
+                    "<locals>.view' does not take the correct number of "
+                    "arguments (request%s)." % (
+                        code,
+                        ', exception' if num_params == 2 else '',
+                    ),
+                    id='urls.E007',
+                ))
+
     @override_settings(ROOT_URLCONF='check_framework.urls.bad_error_handlers_invalid_path')
     def test_bad_handlers_invalid_path(self):
         result = check_url_config(None)
@@ -204,8 +225,17 @@ class CheckCustomErrorHandlersTests(SimpleTestCase):
                     id='urls.E008',
                 ))
 
-    @override_settings(ROOT_URLCONF='check_framework.urls.good_error_handlers')
-    def test_good_handlers(self):
+    @override_settings(
+        ROOT_URLCONF='check_framework.urls.good_function_based_error_handlers',
+    )
+    def test_good_function_based_handlers(self):
+        result = check_url_config(None)
+        self.assertEqual(result, [])
+
+    @override_settings(
+        ROOT_URLCONF='check_framework.urls.good_class_based_error_handlers',
+    )
+    def test_good_class_based_handlers(self):
         result = check_url_config(None)
         self.assertEqual(result, [])
 

tests/check_framework/urls/bad_class_based_error_handlers.py

@@ -0,0 +1,16 @@
+urlpatterns = []
+
+
+class HandlerView:
+    @classmethod
+    def as_view(cls):
+        def view():
+            pass
+
+        return view
+
+
+handler400 = HandlerView.as_view()
+handler403 = HandlerView.as_view()
+handler404 = HandlerView.as_view()
+handler500 = HandlerView.as_view()

tests/check_framework/urls/good_class_based_error_handlers.py

@@ -0,0 +1,9 @@
+from django.views.generic import View
+
+urlpatterns = []
+
+
+handler400 = View.as_view()
+handler403 = View.as_view()
+handler404 = View.as_view()
+handler500 = View.as_view()

tests/generic_views/test_base.py

@@ -172,12 +172,16 @@ class ViewTest(SimpleTestCase):
 
     def test_class_attributes(self):
         """
-        The callable returned from as_view() has proper
-        docstring, name and module.
+        The callable returned from as_view() has proper special attributes.
         """
-        self.assertEqual(SimpleView.__doc__, SimpleView.as_view().__doc__)
-        self.assertEqual(SimpleView.__name__, SimpleView.as_view().__name__)
-        self.assertEqual(SimpleView.__module__, SimpleView.as_view().__module__)
+        cls = SimpleView
+        view = cls.as_view()
+        self.assertEqual(view.__doc__, cls.__doc__)
+        self.assertEqual(view.__name__, 'view')
+        self.assertEqual(view.__module__, cls.__module__)
+        self.assertEqual(view.__qualname__, f'{cls.as_view.__qualname__}.<locals>.view')
+        self.assertEqual(view.__annotations__, cls.dispatch.__annotations__)
+        self.assertFalse(hasattr(view, '__wrapped__'))
 
     def test_dispatch_decoration(self):
         """