error: lifetime may not live long enough
  --> $DIR/regions-creating-enums3.rs:7:5
   |
LL | fn mk_add_bad1<'a,'b>(x: &'a Ast<'a>, y: &'b Ast<'b>) -> Ast<'a> {
   |                -- -- lifetime `'b` defined here
   |                |
   |                lifetime `'a` defined here
LL |     Ast::Add(x, y)
   |     ^^^^^^^^^^^^^^ function was supposed to return data with lifetime `'a` but it is returning data with lifetime `'b`
   |
   = help: consider adding the following bound: `'b: 'a`

error: aborting due to 1 previous error