error[E0478]: lifetime bound not satisfied
  --> $DIR/issue-28848.rs:10:5
   |
LL |     Foo::<'a, 'b>::xmute(u)
   |     ^^^^^^^^^^^^^^^^^^^^
   |
note: lifetime parameter instantiated with the lifetime 'b as defined on the function body at 9:16
  --> $DIR/issue-28848.rs:9:16
   |
LL | pub fn foo<'a, 'b>(u: &'b ()) -> &'a () {
   |                ^^
note: but lifetime parameter must outlive the lifetime 'a as defined on the function body at 9:12
  --> $DIR/issue-28848.rs:9:12
   |
LL | pub fn foo<'a, 'b>(u: &'b ()) -> &'a () {
   |            ^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0478`.