error[E0596]: cannot borrow `x` as mutable, as it is not declared as mutable
  --> $DIR/patkind-ref-binding-issue-122415.rs:7:12
   |
LL | fn foo(&x: &i32) {
   |        -- help: consider changing this to be mutable: `&(mut x)`
LL |     mutate(&mut x);
   |            ^^^^^^ cannot borrow as mutable

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0596`.