error[E0210]: type parameter `Foo` must be used as the type parameter for some local type (e.g., `MyStruct`) --> $DIR/issue-28981.rs:5:6 | LL | impl Deref for Foo { } | ^^^ type parameter `Foo` must be used as the type parameter for some local type | = note: implementing a foreign trait is only possible if at least one of the types for which it is implemented is local = note: only traits defined in the current crate can be implemented for a type parameter error: aborting due to previous error For more information about this error, try `rustc --explain E0210`.