error: lifetime may not live long enough
  --> $DIR/implied_bounds.rs:17:9
   |
LL | impl<'a> Convert<'a> for () {
   |      -- lifetime `'a` defined here
...
LL |     fn convert<'b, T: ?Sized>(_proof: &'b WithLifetime<'a>, x: &'a T) -> &'b T {
   |                -- lifetime `'b` defined here
...
LL |         x
   |         ^ associated 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 previous error