error: `?` may only modify trait bounds, not lifetime bounds
  --> $DIR/issue-68890-2.rs:3:15
   |
LL | type X<'a> = (?'a) +;
   |               ^

error[E0224]: at least one trait is required for an object type
  --> $DIR/issue-68890-2.rs:3:14
   |
LL | type X<'a> = (?'a) +;
   |              ^^^^^^^

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0224`.