1 error[E0277]: `Rc<()>` cannot be sent between threads safely
2 --> $DIR/issue-21763.rs:9:5
4 LL | foo::<HashMap<Rc<()>, Rc<()>>>();
5 | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `Rc<()>` cannot be sent between threads safely
7 = help: within `(Rc<()>, Rc<()>)`, the trait `Send` is not implemented for `Rc<()>`
8 = note: required because it appears within the type `(Rc<()>, Rc<()>)`
9 = note: required because of the requirements on the impl of `Send` for `hashbrown::raw::RawTable<(Rc<()>, Rc<()>)>`
10 = note: required because it appears within the type `hashbrown::map::HashMap<Rc<()>, Rc<()>, RandomState>`
11 = note: required because it appears within the type `HashMap<Rc<()>, Rc<()>>`
12 note: required by a bound in `foo`
13 --> $DIR/issue-21763.rs:6:11
15 LL | fn foo<T: Send>() {}
16 | ^^^^ required by this bound in `foo`
18 error: aborting due to previous error
20 For more information about this error, try `rustc --explain E0277`.