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.

5 files changed, 93 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)
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 = {
diff --git a/tests/admin_views/tests.py b/tests/admin_views/tests.py
index 399c485fea..1fdb90822c 100644
--- a/tests/admin_views/tests.py
+++ b/tests/admin_views/tests.py
@@ -4198,6 +4198,26 @@ class AdminViewDeletedObjectsTest(TestCase):
         # BookAdmin.get_deleted_objects() returns custom text.
         self.assertContains(response, "a deletable object")
 
+    def test_delete_view_uses_delete_confirmation_max_display(self):
+        book = Book.objects.create(name="Test Book")
+        response = self.client.get(
+            reverse("admin2:admin_views_book_delete", args=(book.pk,))
+        )
+        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_delete_view_hides_objects_when_delete_confirmation_max_display_is_zero(
+        self,
+    ):
+        book = Book.objects.create(name="Test Book")
+        response = self.client.get(
+            reverse("admin_zero_display:admin_views_book_delete", args=(book.pk,))
+        )
+        self.assertNotContains(response, "<h2>Objects</h2>")
+        self.assertNotContains(response, 'id="deleted-objects"')
+
 
 @override_settings(ROOT_URLCONF="admin_views.urls")
 class TestGenericRelations(TestCase):
diff --git a/tests/admin_views/urls.py b/tests/admin_views/urls.py
index 3c43b8721d..0ebe688cfc 100644
--- a/tests/admin_views/urls.py
+++ b/tests/admin_views/urls.py
@@ -35,6 +35,7 @@ urlpatterns = [
     path("test_admin/admin11/", admin.site11.urls),
     path("test_admin/admin12/", admin.site12.urls),
     path("test_admin/admin13/", admin.site13.urls),
+    path("test_admin/admin_zero_display/", customadmin.zero_display_site.urls),
     path("test_admin/has_permission_admin/", custom_has_permission_admin.site.urls),
     path("test_admin/autocomplete_admin/", autocomplete_site.urls),
     # Shares the admin URL prefix.
diff --git a/tests/modeladmin/test_checks.py b/tests/modeladmin/test_checks.py
index c493148eb9..496e46e8b0 100644
--- a/tests/modeladmin/test_checks.py
+++ b/tests/modeladmin/test_checks.py
@@ -1020,6 +1020,50 @@ class ListMaxShowAllCheckTests(CheckTestCase):
         self.assertIsValid(TestModelAdmin, ValidationTestModel)
 
 
+class DeleteConfirmationMaxObjectsCheckTests(CheckTestCase):
+    def test_not_integer(self):
+        class TestModelAdmin(ModelAdmin):
+            delete_confirmation_max_display = "hello"
+
+        self.assertIsInvalid(
+            TestModelAdmin,
+            ValidationTestModel,
+            (
+                "The value of "
+                "'delete_confirmation_max_display'"
+                " must be a non-negative integer or None."
+            ),
+            "admin.E131",
+        )
+
+    def test_negative_integer(self):
+        class TestModelAdmin(ModelAdmin):
+            delete_confirmation_max_display = -1
+
+        self.assertIsInvalid(
+            TestModelAdmin,
+            ValidationTestModel,
+            (
+                "The value of "
+                "'delete_confirmation_max_display'"
+                " must be a non-negative integer or None."
+            ),
+            "admin.E131",
+        )
+
+    def test_valid_case(self):
+        class TestModelAdmin(ModelAdmin):
+            delete_confirmation_max_display = 100
+
+        self.assertIsValid(TestModelAdmin, ValidationTestModel)
+
+    def test_valid_none(self):
+        class TestModelAdmin(ModelAdmin):
+            delete_confirmation_max_display = None
+
+        self.assertIsValid(TestModelAdmin, ValidationTestModel)
+
+
 class SearchFieldsCheckTests(CheckTestCase):
     def test_not_iterable(self):
         class TestModelAdmin(ModelAdmin):