Fixed #10919 -- Added delete_confirmation_max_display to ModelAdmin.

The new ModelAdmin.delete_confirmation_max_display attribute allows
limiting the number of related objects shown on the delete confirmation
page. When the limit is reached, a "…and N more objects." message is shown.

The feature relies on a new truncated_unordered_list template filter
added to django.contrib.admin.templatetags.admin_filters.

Thanks Jacob Tyler Walls for the review and guidance, Tobias McNulty for the report,
and terminator14 for the solution suggested.

1 files changed, 13 insertions, 0 deletions

diff --git a/tests/admin_views/test_actions.py b/tests/admin_views/test_actions.py
index c2c18e0b74..de5f5462a3 100644
--- a/tests/admin_views/test_actions.py
+++ b/tests/admin_views/test_actions.py
@@ -220,6 +220,19 @@ class AdminActionsTest(TestCase):
         # BookAdmin.get_deleted_objects() returns custom text.
         self.assertContains(response, "a deletable object")
 
+    def test_delete_selected_uses_delete_confirmation_max_display(self):
+        book = Book.objects.create(name="Test Book")
+        data = {
+            ACTION_CHECKBOX_NAME: [book.pk],
+            "action": "delete_selected",
+            "index": 0,
+        }
+        response = self.client.post(reverse("admin2:admin_views_book_changelist"), data)
+        self.assertContains(response, "a deletable object")
+        self.assertContains(response, "…and 2 more objects.")
+        self.assertNotContains(response, "another object")
+        self.assertNotContains(response, "last object")
+
     def test_custom_function_mail_action(self):
         """A custom action may be defined in a function."""
         action_data = {