error[E0499]: cannot borrow `xs` as mutable more than once at a time
  --> $DIR/vec-mut-iter-borrow.rs:15:9
   |
LL |     for x in &mut xs {
   |              -------
   |              |
   |              first mutable borrow occurs here
   |              borrow used here, in later iteration of loop
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`.