[4.0.x] Refs #33263 -- Added warning to BaseDeleteView when delete() method is overridden.

Follow up to 3a45fea0832c5910acee6e0d29f230f347a50462.
Backport of 6bc437c0d82675ebe6aa92c8e249892205c316ef from main

2 files changed, 42 insertions, 1 deletions

diff --git a/django/views/generic/edit.py b/django/views/generic/edit.py
index d0de788c46..8cbdeb8d13 100644
--- a/django/views/generic/edit.py
+++ b/django/views/generic/edit.py
@@ -1,3 +1,5 @@
+import warnings
+
 from django.core.exceptions import ImproperlyConfigured
 from django.forms import Form, models as model_forms
 from django.http import HttpResponseRedirect
@@ -225,6 +227,11 @@ class DeletionMixin:
                 "No URL to redirect to. Provide a success_url.")
 
 
+# RemovedInDjango50Warning.
+class DeleteViewCustomDeleteWarning(Warning):
+    pass
+
+
 class BaseDeleteView(DeletionMixin, FormMixin, BaseDetailView):
     """
     Base view for deleting an object.
@@ -233,6 +240,19 @@ class BaseDeleteView(DeletionMixin, FormMixin, BaseDetailView):
     """
     form_class = Form
 
+    def __init__(self, *args, **kwargs):
+        # RemovedInDjango50Warning.
+        if self.__class__.delete is not DeletionMixin.delete:
+            warnings.warn(
+                f'DeleteView uses FormMixin to handle POST requests. As a '
+                f'consequence, any custom deletion logic in '
+                f'{self.__class__.__name__}.delete() handler should be moved '
+                f'to form_valid().',
+                DeleteViewCustomDeleteWarning,
+                stacklevel=2,
+            )
+        super().__init__(*args, **kwargs)
+
     def post(self, request, *args, **kwargs):
         # Set self.object before the usual form processing flow.
         # Inlined because having DeletionMixin as the first base, for
diff --git a/tests/generic_views/test_edit.py b/tests/generic_views/test_edit.py
index d69ae6463e..4292600911 100644
--- a/tests/generic_views/test_edit.py
+++ b/tests/generic_views/test_edit.py
@@ -4,7 +4,10 @@ from django.test import SimpleTestCase, TestCase, override_settings
 from django.test.client import RequestFactory
 from django.urls import reverse
 from django.views.generic.base import View
-from django.views.generic.edit import CreateView, FormMixin, ModelFormMixin
+from django.views.generic.edit import (
+    CreateView, DeleteView, DeleteViewCustomDeleteWarning, FormMixin,
+    ModelFormMixin,
+)
 
 from . import views
 from .forms import AuthorForm
@@ -426,3 +429,21 @@ class DeleteViewTests(TestCase):
             res.context_data['form'].errors['confirm'],
             ['This field is required.'],
         )
+
+    # RemovedInDjango50Warning.
+    def test_delete_with_custom_delete(self):
+        class AuthorDeleteView(DeleteView):
+            model = Author
+
+            def delete(self, request, *args, **kwargs):
+                # Custom logic.
+                pass
+
+        msg = (
+            'DeleteView uses FormMixin to handle POST requests. As a '
+            'consequence, any custom deletion logic in '
+            'AuthorDeleteView.delete() handler should be moved to '
+            'form_valid().'
+        )
+        with self.assertWarnsMessage(DeleteViewCustomDeleteWarning, msg):
+            AuthorDeleteView()