Fixed #16869 -- BaseGenericInlineFormSet.save_new should use form's save() method

Thanks mattaustin for the report and Pablo Recio (pyriku) for the patch.

django/contrib/contenttypes/generic.py

@@ -415,13 +415,12 @@ class BaseGenericInlineFormSet(BaseModelFormSet):
         ))
 
     def save_new(self, form, commit=True):
-        kwargs = {
-            self.ct_field.get_attname(): ContentType.objects.get_for_model(
-                self.instance, for_concrete_model=self.for_concrete_model).pk,
-            self.ct_fk_field.get_attname(): self.instance.pk,
-        }
-        new_obj = self.model(**kwargs)
-        return save_instance(form, new_obj, commit=commit)
+        setattr(form.instance, self.ct_field.get_attname(),
+            ContentType.objects.get_for_model(self.instance).pk)
+        setattr(form.instance, self.ct_fk_field.get_attname(),
+            self.instance.pk)
+        return form.save(commit=commit)
+
 
 def generic_inlineformset_factory(model, form=ModelForm,
                                   formset=BaseGenericInlineFormSet,

tests/generic_relations/tests.py

@@ -306,6 +306,32 @@ class GenericInlineFormsetTest(TestCase):
         form = Formset().forms[0]
         self.assertIsInstance(form['tag'].field.widget, CustomWidget)
 
+    def test_save_new_uses_form_save(self):
+        """
+        Regression for #16260: save_new should call form.save()
+        """
+        class SaveTestForm(forms.ModelForm):
+            def save(self, *args, **kwargs):
+                self.instance.saved_by = "custom method"
+                return super(SaveTestForm, self).save(*args, **kwargs)
+
+        Formset = generic_inlineformset_factory(
+            ForProxyModelModel, fields='__all__', form=SaveTestForm)
+
+        instance = ProxyRelatedModel.objects.create()
+
+        data = {
+            'form-TOTAL_FORMS': '1',
+            'form-INITIAL_FORMS': '0',
+            'form-MAX_NUM_FORMS': '',
+            'form-0-title': 'foo',
+        }
+
+        formset = Formset(data, instance=instance, prefix='form')
+        self.assertTrue(formset.is_valid())
+        new_obj = formset.save()[0]
+        self.assertEqual(new_obj.saved_by, "custom method")
+
     def test_save_new_for_proxy(self):
         Formset = generic_inlineformset_factory(ForProxyModelModel,
             fields='__all__', for_concrete_model=False)