1 error[E0277]: `Rc<()>` cannot be sent between threads safely
2 --> $DIR/issue-21763.rs:9:5
4 LL | fn foo<T: Send>() {}
5 | ---- required by this bound in `foo`
7 LL | foo::<HashMap<Rc<()>, Rc<()>>>();
8 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `Rc<()>` cannot be sent between threads safely
10 = help: within `(Rc<()>, Rc<()>)`, the trait `Send` is not implemented for `Rc<()>`
11 = note: required because it appears within the type `(Rc<()>, Rc<()>)`
12 = note: required because of the requirements on the impl of `Send` for `hashbrown::raw::RawTable<(Rc<()>, Rc<()>)>`
13 = note: required because it appears within the type `hashbrown::map::HashMap<Rc<()>, Rc<()>, RandomState>`
14 = note: required because it appears within the type `HashMap<Rc<()>, Rc<()>>`
16 error: aborting due to previous error
18 For more information about this error, try `rustc --explain E0277`.