error[E0121]: the placeholder `_` is not allowed within types on item signatures for return types
  --> $DIR/suggest-return-closure.rs:1:17
   |
LL | fn fn_once() -> _ {
   |                 ^
   |                 |
   |                 not allowed in type signatures
   |                 help: replace with an appropriate return type: `impl FnOnce()`
   |
   = note: for more information on `Fn` traits and closure types, see https://doc.rust-lang.org/book/ch13-01-closures.html

error[E0121]: the placeholder `_` is not allowed within types on item signatures for return types
  --> $DIR/suggest-return-closure.rs:13:16
   |
LL | fn fn_mut() -> _ {
   |                ^
   |                |
   |                not allowed in type signatures
   |                help: replace with an appropriate return type: `impl FnMut(char)`
   |
   = note: for more information on `Fn` traits and closure types, see https://doc.rust-lang.org/book/ch13-01-closures.html

error[E0121]: the placeholder `_` is not allowed within types on item signatures for return types
  --> $DIR/suggest-return-closure.rs:25:13
   |
LL | fn fun() -> _ {
   |             ^
   |             |
   |             not allowed in type signatures
   |             help: replace with an appropriate return type: `impl Fn() -> i32`
   |
   = note: for more information on `Fn` traits and closure types, see https://doc.rust-lang.org/book/ch13-01-closures.html

error: aborting due to 3 previous errors

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