error[E0621]: explicit lifetime required in the type of `y`
  --> $DIR/issue-40288-2.rs:17:9
   |
LL | fn lifetime_transmute_slice<'a, T: ?Sized>(x: &'a T, y: &T) -> &'a T {
   |                                                         -- help: add explicit lifetime `'a` to the type of `y`: `&'a T`
...
LL |         slice[0] = y;
   |         ^^^^^^^^^^^^ lifetime `'a` required

error[E0621]: explicit lifetime required in the type of `y`
  --> $DIR/issue-40288-2.rs:32:9
   |
LL | fn lifetime_transmute_struct<'a, T: ?Sized>(x: &'a T, y: &T) -> &'a T {
   |                                                          -- help: add explicit lifetime `'a` to the type of `y`: `&'a T`
...
LL |         dst.head = y;
   |         ^^^^^^^^^^^^ lifetime `'a` required

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0621`.