[1.8.x] Refs #24354 -- Prevented repointing of relations on superclasses when migrating a subclass's name change

Forwardport of test and release note from stable/1.7.x

Backport of ae87ad005f from master

docs/releases/1.7.7.txt

@@ -9,4 +9,6 @@ Django 1.7.7 fixes several bugs in 1.7.6.
 Bugfixes
 ========
 
-* ...
+* Fixed renaming of classes in migrations where renaming a subclass would
+  cause incorrect state to be recorded for objects that referenced the
+  superclass (:ticket:`24354`).

tests/migrations/test_operations.py

@@ -538,6 +538,41 @@ class OperationTests(OperationTestBase):
             self.assertFKExists("test_rmwsrf_rider", ["friend_id"], ("test_rmwsrf_rider", "id"))
             self.assertFKNotExists("test_rmwsrf_rider", ["friend_id"], ("test_rmwsrf_horserider", "id"))
 
+    def test_rename_model_with_superclass_fk(self):
+        """
+        Tests the RenameModel operation on a model which has a superclass that
+        has a foreign key.
+        """
+        project_state = self.set_up_test_model("test_rmwsc", related_model=True, mti_model=True)
+        # Test the state alteration
+        operation = migrations.RenameModel("ShetlandPony", "LittleHorse")
+        self.assertEqual(operation.describe(), "Rename model ShetlandPony to LittleHorse")
+        new_state = project_state.clone()
+        operation.state_forwards("test_rmwsc", new_state)
+        self.assertNotIn(("test_rmwsc", "shetlandpony"), new_state.models)
+        self.assertIn(("test_rmwsc", "littlehorse"), new_state.models)
+        # RenameModel shouldn't repoint the superclass's relations, only local ones
+        self.assertEqual(
+            project_state.models["test_rmwsc", "rider"].fields[1][1].rel.to,
+            new_state.models["test_rmwsc", "rider"].fields[1][1].rel.to
+        )
+        # Before running the migration we have a table for Shetland Pony, not Little Horse
+        self.assertTableExists("test_rmwsc_shetlandpony")
+        self.assertTableNotExists("test_rmwsc_littlehorse")
+        if connection.features.supports_foreign_keys:
+            # and the foreign key on rider points to pony, not shetland pony
+            self.assertFKExists("test_rmwsc_rider", ["pony_id"], ("test_rmwsc_pony", "id"))
+            self.assertFKNotExists("test_rmwsc_rider", ["pony_id"], ("test_rmwsc_shetlandpony", "id"))
+        with connection.schema_editor() as editor:
+            operation.database_forwards("test_rmwsc", editor, project_state, new_state)
+        # Now we have a little horse table, not shetland pony
+        self.assertTableNotExists("test_rmwsc_shetlandpony")
+        self.assertTableExists("test_rmwsc_littlehorse")
+        if connection.features.supports_foreign_keys:
+            # but the Foreign keys still point at pony, not little horse
+            self.assertFKExists("test_rmwsc_rider", ["pony_id"], ("test_rmwsc_pony", "id"))
+            self.assertFKNotExists("test_rmwsc_rider", ["pony_id"], ("test_rmwsc_littlehorse", "id"))
+
     def test_rename_model_with_self_referential_m2m(self):
         app_label = "test_rename_model_with_self_referential_m2m"