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, 44 insertions, 0 deletions

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):