Fixed #27915 -- Allowed Meta.indexes to be defined in abstract models.

Thanks Markus Holtermann for review.

tests/migrations/test_state.py

@@ -1043,6 +1043,33 @@ class ModelStateTests(SimpleTestCase):
         state = ModelState.from_model(PrivateFieldModel)
         self.assertNotIn('order_with_respect_to', state.options)
 
+    @isolate_apps('migrations')
+    def test_abstract_model_children_inherit_indexes(self):
+        class Abstract(models.Model):
+            name = models.CharField(max_length=50)
+
+            class Meta:
+                app_label = 'migrations'
+                abstract = True
+                indexes = [models.indexes.Index(fields=['name'])]
+
+        class Child1(Abstract):
+            pass
+
+        class Child2(Abstract):
+            pass
+
+        child1_state = ModelState.from_model(Child1)
+        child2_state = ModelState.from_model(Child2)
+        index_names = [index.name for index in child1_state.options['indexes']]
+        self.assertEqual(index_names, ['migrations__name_b0afd7_idx'])
+        index_names = [index.name for index in child2_state.options['indexes']]
+        self.assertEqual(index_names, ['migrations__name_016466_idx'])
+
+        # Modifying the state doesn't modify the index on the model.
+        child1_state.options['indexes'][0].name = 'bar'
+        self.assertEqual(Child1._meta.indexes[0].name, 'migrations__name_b0afd7_idx')
+
 
 class RelatedModelsTests(SimpleTestCase):