error[E0277]: `RefCell<std::string::String>` cannot be shared between threads safely
  --> tests/subclass_compiletest/05-no-auto-send-sync-with-non-send-sync-parent.rs:66:11
   |
66 |     check(&obj);
   |     ----- ^^^^ `RefCell<std::string::String>` cannot be shared between threads safely
   |     |
   |     required by a bound introduced by this call
   |
   = help: within `imp_parent::TestParent`, the trait `Sync` is not implemented for `RefCell<std::string::String>`
   = note: if you want to do aliasing and mutation between multiple threads, use `std::sync::RwLock` instead
note: required because it appears within the type `TestParent`
  --> tests/subclass_compiletest/05-no-auto-send-sync-with-non-send-sync-parent.rs:6:16
   |
6  |     pub struct TestParent {
   |                ^^^^^^^^^^
   = note: required for `TypedObjectRef<imp_parent::TestParent, ()>` to implement `Send`
note: required because it appears within the type `TestParent`
  --> tests/subclass_compiletest/05-no-auto-send-sync-with-non-send-sync-parent.rs:20:16
   |
20 |     pub struct TestParent(ObjectSubclass<imp_parent::TestParent>);
   |                ^^^^^^^^^^
   = note: required for `TypedObjectRef<imp_object::TestObject, TestParent>` to implement `Send`
note: required because it appears within the type `TestObject`
  --> tests/subclass_compiletest/05-no-auto-send-sync-with-non-send-sync-parent.rs:53:16
   |
53 |     pub struct TestObject(ObjectSubclass<imp_object::TestObject>) @extends TestParent;
   |                ^^^^^^^^^^
note: required by a bound in `main::check`
  --> tests/subclass_compiletest/05-no-auto-send-sync-with-non-send-sync-parent.rs:63:17
   |
63 |     fn check<T: Send + Sync>(_obj: &T) {}
   |                 ^^^^ required by this bound in `check`
