Wrong code example for the "`ref` on an entire `let` pattern is discouraged" lint

[stanislav-tkach]

Clippy gives confusing help-message for the following code:

let mut v = vec![1i8, 2, 3];
for ref mut val in &mut v {
    ...
}

warning: `ref` on an entire `let` pattern is discouraged, take a reference with `&` instead
 --> src/main.rs:3:9
  |
3 |     for ref mut _val in &mut v {
  |         ^^^^^^^^^^^^
  |
  = note: #[warn(toplevel_ref_arg)] on by default
  = help: for further information visit https://github.com/Manishearth/rust-clippy/wiki#toplevel_ref_arg
help: try
  |     let _val = &mut for ref mut _val in &mut v {
  |     };

ref mut can simply be removed, let isn't needed here.

[oli-obk]

This occurs due to the lack of expansion info we get from rustc. This should get fixed along with those fixes.

[camsteffen]

No longer reproducible