error[E0631]: type mismatch in function arguments
  --> $DIR/suggest-option-asderef-inference-var.rs:7:56
   |
LL | fn deref_int(a: &i32) -> i32 {
   | ---------------------------- found signature defined here
...
LL |     let _has_inference_vars: Option<i32> = Some(0).map(deref_int);
   |                                                    --- ^^^^^^^^^ expected due to this
   |                                                    |
   |                                                    required by a bound introduced by this call
   |
   = note: expected function signature `fn({integer}) -> _`
              found function signature `for<'a> fn(&'a i32) -> _`
note: required by a bound in `Option::<T>::map`
  --> $SRC_DIR/core/src/option.rs:LL:COL
help: consider adjusting the signature so it does not borrow its argument
   |
LL - fn deref_int(a: &i32) -> i32 {
LL + fn deref_int(a: i32) -> i32 {
   |

error: aborting due to previous error

For more information about this error, try `rustc --explain E0631`.