Fixed #21936 -- Allowed DeleteView to work with custom Forms and SuccessMessageMixin.

Thanks to Mariusz Felisiak for review.

Co-authored-by: Demetris Stavrou <demestav@gmail.com>
Co-authored-by: Caroline Simpson <github@hoojiboo.com>

django/views/generic/edit.py

@@ -1,5 +1,5 @@
 from django.core.exceptions import ImproperlyConfigured
-from django.forms import models as model_forms
+from django.forms import Form, models as model_forms
 from django.http import HttpResponseRedirect
 from django.views.generic.base import ContextMixin, TemplateResponseMixin, View
 from django.views.generic.detail import (
@@ -225,12 +225,30 @@ class DeletionMixin:
                 "No URL to redirect to. Provide a success_url.")
 
 
-class BaseDeleteView(DeletionMixin, BaseDetailView):
+class BaseDeleteView(DeletionMixin, FormMixin, BaseDetailView):
     """
     Base view for deleting an object.
 
     Using this base class requires subclassing to provide a response mixin.
     """
+    form_class = Form
+
+    def post(self, request, *args, **kwargs):
+        # Set self.object before the usual form processing flow.
+        # Inlined because having DeletionMixin as the first base, for
+        # get_success_url(), makes leveraging super() with ProcessFormView
+        # overly complex.
+        self.object = self.get_object()
+        form = self.get_form()
+        if form.is_valid():
+            return self.form_valid(form)
+        else:
+            return self.form_invalid(form)
+
+    def form_valid(self, form):
+        success_url = self.get_success_url()
+        self.object.delete()
+        return HttpResponseRedirect(success_url)
 
 
 class DeleteView(SingleObjectTemplateResponseMixin, BaseDeleteView):