error[E0308]: mismatched types
  --> $DIR/issue-50716.rs:8:27
   |
LL | fn foo<'a, T: 'static>(s: Box<<&'a T as A>::X>)
   |                           ^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
   |
   = note: expected trait `<<&'a T as A>::X as MetaSized>`
              found trait `<<&'static T as A>::X as MetaSized>`
note: the lifetime `'a` as defined here...
  --> $DIR/issue-50716.rs:8:8
   |
LL | fn foo<'a, T: 'static>(s: Box<<&'a T as A>::X>)
   |        ^^
   = note: ...does not necessarily outlive the static lifetime

error: lifetime may not live long enough
  --> $DIR/issue-50716.rs:13:14
   |
LL | fn foo<'a, T: 'static>(s: Box<<&'a T as A>::X>)
   |        -- lifetime `'a` defined here
...
LL |     let _x = *s;
   |              ^^ proving this value is `Sized` requires that `'a` must outlive `'static`

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0308`.