error[E0277]: `Rc<i32>` cannot be shared between threads safely
 --> tests/ui/non-sync.rs:6:21
  |
6 | inventory::collect!(Thing);
  |                     ^^^^^ `Rc<i32>` cannot be shared between threads safely
  |
  = help: within `Thing`, the trait `Sync` is not implemented for `Rc<i32>`
note: required because it appears within the type `Thing`
 --> tests/ui/non-sync.rs:4:8
  |
4 | struct Thing(Rc<i32>);
  |        ^^^^^
note: required by a bound in `Collect`
 --> src/lib.rs
  |
  | pub trait Collect: Sync + Sized + 'static {
  |                    ^^^^ required by this bound in `Collect`