1 A cross-crate opt-out trait was implemented on something which wasn't a struct
4 Erroneous code example:
7 #![feature(auto_traits)]
13 unsafe impl Send for &'static Foo {}
14 // error: cross-crate traits with a default impl, like `core::marker::Send`,
15 // can only be implemented for a struct/enum type, not
19 Only structs and enums are permitted to impl Send, Sync, and other opt-out
20 trait, and the struct or enum must be local to the current crate. So, for
21 example, `unsafe impl Send for Rc<Foo>` is not allowed.