error: cannot borrow immutable borrowed content `*x` as mutable
  --> $DIR/borrowck-fn-in-const-b.rs:17:9
   |
16 |     fn broken(x: &Vec<String>) {
   |                  ------------ use `&mut Vec<String>` here to make mutable
17 |         x.push(format!("this is broken"));
   |         ^

error: aborting due to previous error