error[E0261]: use of undeclared lifetime name `'a`
  --> $DIR/missing-lifetimes-in-signature.rs:36:11
   |
LL | fn baz<G: 'a, T>(g: G, dest: &mut T) -> impl FnOnce() + '_
   |        -  ^^ undeclared lifetime
   |        |
   |        help: consider introducing lifetime `'a` here: `'a,`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0261`.