Fixed #34634 -- Adjusted system check for clashing fields to warn about links to common parent for MTI models.

django/db/models/base.py

@@ -1775,6 +1775,21 @@ class Model(AltersData, metaclass=ModelBase):
                 if f not in used_fields:
                     used_fields[f.name] = f
 
+        # Check that parent links in diamond-shaped MTI models don't clash.
+        for parent_link in cls._meta.parents.values():
+            if not parent_link:
+                continue
+            clash = used_fields.get(parent_link.name) or None
+            if clash:
+                errors.append(
+                    checks.Error(
+                        f"The field '{parent_link.name}' clashes with the field "
+                        f"'{clash.name}' from model '{clash.model._meta}'.",
+                        obj=cls,
+                        id="models.E006",
+                    )
+                )
+
         for f in cls._meta.local_fields:
             clash = used_fields.get(f.name) or used_fields.get(f.attname) or None
             # Note that we may detect clash between user-defined non-unique

tests/invalid_models_tests/test_models.py

@@ -1070,6 +1070,31 @@ class ShadowingFieldsTests(SimpleTestCase):
             ],
         )
 
+    def test_diamond_mti_common_parent(self):
+        class GrandParent(models.Model):
+            pass
+
+        class Parent(GrandParent):
+            pass
+
+        class Child(Parent):
+            pass
+
+        class MTICommonParentModel(Child, GrandParent):
+            pass
+
+        self.assertEqual(
+            MTICommonParentModel.check(),
+            [
+                Error(
+                    "The field 'grandparent_ptr' clashes with the field "
+                    "'grandparent_ptr' from model 'invalid_models_tests.parent'.",
+                    obj=MTICommonParentModel,
+                    id="models.E006",
+                )
+            ],
+        )
+
     def test_id_clash(self):
         class Target(models.Model):
             pass