error: lifetime may not live long enough
  --> $DIR/wf-check-hidden-type.rs:14:5
   |
LL | fn boom<'a, 'b>() -> impl Extend<'a, 'b> {
   |         --  -- lifetime `'b` defined here
   |         |
   |         lifetime `'a` defined here
LL |     None::<&'_ &'_ ()>
   |     ^^^^^^^^^^^^^^^^^^ function was supposed to return data with lifetime `'b` but it is returning data with lifetime `'a`
   |
   = help: consider adding the following bound: `'a: 'b`

error: aborting due to 1 previous error