error[E0596]: cannot borrow `*x` as mutable, as it is behind a `&` reference
  --> $DIR/borrowck-call-method-from-mut-aliasable.rs:17:5
   |
LL |     x.h();
   |     ^ `x` is a `&` reference, so the data it refers to cannot be borrowed as mutable
   |
help: consider changing this to be a mutable reference
   |
LL | fn b(x: &mut Foo) {
   |          +++

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0596`.