error[E0499]: cannot borrow `xs` as mutable more than once at a time
  --> $DIR/vec-mut-iter-borrow.rs:5:9
   |
LL |     for x in &mut xs {
   |                   --
   |                   ||
   |                   |first borrow ends here
   |                   first mutable borrow occurs here
LL |         xs.push(1) //~ ERROR cannot borrow `xs`
   |         ^^ second mutable borrow occurs here

error: aborting due to previous error

For more information about this error, try `rustc --explain E0499`.