error[E0121]: the type placeholder `_` is not allowed within types on item signatures for return types
  --> $DIR/issue-80779.rs:10:28
   |
LL | pub fn g(_: T<'static>) -> _ {}
   |                            ^
   |                            |
   |                            not allowed in type signatures
   |                            help: replace with the correct return type: `()`

error[E0121]: the type placeholder `_` is not allowed within types on item signatures for return types
  --> $DIR/issue-80779.rs:5:29
   |
LL | pub fn f<'a>(val: T<'a>) -> _ {
   |                             ^
   |                             |
   |                             not allowed in type signatures
   |                             help: replace with the correct return type: `()`

error: aborting due to 2 previous errors

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