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, 15 insertions, 1 deletions

diff --git a/tests/admin_views/customadmin.py b/tests/admin_views/customadmin.py
index a63d24a9ee..9621cb4d52 100644
--- a/tests/admin_views/customadmin.py
+++ b/tests/admin_views/customadmin.py
@@ -60,8 +60,19 @@ class CustomPwdTemplateUserAdmin(UserAdmin):
 
 
 class BookAdmin(admin.ModelAdmin):
+    delete_confirmation_max_display = 1
+
     def get_deleted_objects(self, objs, request):
-        return ["a deletable object"], {"books": 1}, set(), []
+        return (
+            ["a deletable object", "another object", "last object"],
+            {"books": 1},
+            set(),
+            [],
+        )
+
+
+class BookAdminZeroDisplay(BookAdmin):
+    delete_confirmation_max_display = 0
 
 
 site = Admin2(name="admin2")
@@ -80,3 +91,6 @@ site.register(models.Simple, base_admin.AttributeErrorRaisingAdmin)
 
 simple_site = Admin2(name="admin4")
 simple_site.register(User, CustomPwdTemplateUserAdmin)
+
+zero_display_site = Admin2(name="admin_zero_display")
+zero_display_site.register(models.Book, BookAdminZeroDisplay)