error[E0038]: the trait `issue_3907::Foo` cannot be made into an object --> $DIR/issue-3907-2.rs:20:1 | LL | fn bar(_x: Foo) {} | ^^^^^^^^^^^^^^^ the trait `issue_3907::Foo` cannot be made into an object | = note: method `bar` has no receiver error: aborting due to previous error If you want more information on this error, try using "rustc --explain E0038"