1 error[E0596]: cannot borrow `v` as mutable, as it is not declared as mutable
2 --> $DIR/issue-33819.rs:4:34
4 LL | Some(ref v) => { let a = &mut v; },
7 | cannot borrow as mutable
8 | help: try removing `&mut` here
10 error: aborting due to previous error
12 For more information about this error, try `rustc --explain E0596`.