error[E0277]: `RefCell<std::string::String>` cannot be shared between threads safely
  --> tests/compile-fail/non-sync.rs:10:17
   |
10 | impl Plugin for MyPlugin {
   |                 ^^^^^^^^ `RefCell<std::string::String>` cannot be shared between threads safely
   |
   = help: within `MyPlugin`, the trait `Sync` is not implemented for `RefCell<std::string::String>`, which is required by `MyPlugin: Sync`
   = 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 `MyPlugin`
  --> tests/compile-fail/non-sync.rs:6:12
   |
6  | pub struct MyPlugin {
   |            ^^^^^^^^
note: required by a bound in `Plugin`
  --> src/plugins.rs
   |
   | pub trait Plugin: Send + Sync + UnwindSafe + RefUnwindSafe {
   |                          ^^^^ required by this bound in `Plugin`

error[E0277]: the type `UnsafeCell<std::string::String>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
  --> tests/compile-fail/non-sync.rs:10:17
   |
10 | impl Plugin for MyPlugin {
   |                 ^^^^^^^^ `UnsafeCell<std::string::String>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
   |
   = help: within `MyPlugin`, the trait `RefUnwindSafe` is not implemented for `UnsafeCell<std::string::String>`, which is required by `MyPlugin: RefUnwindSafe`
note: required because it appears within the type `RefCell<std::string::String>`
  --> $RUST/core/src/cell.rs
   |
   | pub struct RefCell<T: ?Sized> {
   |            ^^^^^^^
note: required because it appears within the type `MyPlugin`
  --> tests/compile-fail/non-sync.rs:6:12
   |
6  | pub struct MyPlugin {
   |            ^^^^^^^^
note: required by a bound in `Plugin`
  --> src/plugins.rs
   |
   | pub trait Plugin: Send + Sync + UnwindSafe + RefUnwindSafe {
   |                                              ^^^^^^^^^^^^^ required by this bound in `Plugin`

error[E0277]: the type `UnsafeCell<isize>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
  --> tests/compile-fail/non-sync.rs:10:17
   |
10 | impl Plugin for MyPlugin {
   |                 ^^^^^^^^ `UnsafeCell<isize>` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
   |
   = help: within `MyPlugin`, the trait `RefUnwindSafe` is not implemented for `UnsafeCell<isize>`, which is required by `MyPlugin: RefUnwindSafe`
note: required because it appears within the type `Cell<isize>`
  --> $RUST/core/src/cell.rs
   |
   | pub struct Cell<T: ?Sized> {
   |            ^^^^
note: required because it appears within the type `RefCell<std::string::String>`
  --> $RUST/core/src/cell.rs
   |
   | pub struct RefCell<T: ?Sized> {
   |            ^^^^^^^
note: required because it appears within the type `MyPlugin`
  --> tests/compile-fail/non-sync.rs:6:12
   |
6  | pub struct MyPlugin {
   |            ^^^^^^^^
note: required by a bound in `Plugin`
  --> src/plugins.rs
   |
   | pub trait Plugin: Send + Sync + UnwindSafe + RefUnwindSafe {
   |                                              ^^^^^^^^^^^^^ required by this bound in `Plugin`