error[E0623]: lifetime mismatch
  --> $DIR/underscore-lifetime-elison-mismatch.rs:1:49
   |
LL | fn foo(x: &mut Vec<&'_ u8>, y: &'_ u8) { x.push(y); }
   |                    ------      ------           ^ ...but data from `y` flows into `x` here
   |                                |
   |                                these two types are declared with different lifetimes...

error: aborting due to previous error

For more information about this error, try `rustc --explain E0623`.