Better double checked locking in load_schema

activerecord/lib/active_record/model_schema.rb

@@ -478,6 +478,9 @@ def load_schema
             load_schema!
 
             @schema_loaded = true
+          rescue
+            reload_schema_from_cache # If the schema loading failed half way through, we must reset the state.
+            raise
           end
         end
 

activerecord/test/cases/base_test.rb

@@ -77,6 +77,22 @@ def test_generated_relation_methods_module_name
     assert_equal "Post::GeneratedRelationMethods", mod.inspect
   end
 
+  def test_incomplete_schema_loading
+    topic = Topic.first
+    payload = { foo: 42 }
+    topic.update!(content: payload)
+
+    Topic.reset_column_information
+
+    Topic.connection.stub(:lookup_cast_type_from_column, ->(_) { raise "Some Error" }) do
+      assert_raises RuntimeError do
+        Topic.columns_hash
+      end
+    end
+
+    assert_equal payload, Topic.first.content
+  end
+
   def test_column_names_are_escaped
     conn      = ActiveRecord::Base.connection
     classname = conn.class.name[/[^:]*$/]