error[E0425]: cannot find function `f` in this scope
  --> $DIR/for_loop_unfixable.rs:37:12
   |
LL |         if f(&vec[i], &vec[i]) {
   |            ^ help: a local variable with a similar name exists: `i`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0425`.