error[E0121]: the placeholder `_` is not allowed within types on item signatures for functions
  --> $DIR/bad-infer-in-trait-impl.rs:6:15
   |
LL |     fn bar(s: _) {}
   |               ^ not allowed in type signatures
   |
help: use type parameters instead
   |
LL |     fn bar<T>(s: T) {}
   |           +++    ~

error: aborting due to previous error

For more information about this error, try `rustc --explain E0121`.