warning: impl trait in impl method signature does not match trait method signature
  --> $DIR/unconstrained-lt.rs:8:18
   |
LL |     fn test() -> impl Sized;
   |                  ---------- return type from trait method defined here
...
LL |     fn test() -> &'a () {
   |                  ^^^^^^
   |
   = note: add `#[allow(refining_impl_trait)]` if it is intended for this to be part of the public API of this crate
   = note: we are soliciting feedback, see issue #121718 <https://github.com/rust-lang/rust/issues/121718> for more information
   = note: `#[warn(refining_impl_trait_internal)]` (part of `#[warn(refining_impl_trait)]`) on by default
help: replace the return type so that it matches the trait
   |
LL -     fn test() -> &'a () {
LL +     fn test() -> impl Sized {
   |

error[E0207]: the lifetime parameter `'a` is not constrained by the impl trait, self type, or predicates
  --> $DIR/unconstrained-lt.rs:5:6
   |
LL | impl<'a, T> Foo for T {
   |      ^^ unconstrained lifetime parameter

error: aborting due to 1 previous error; 1 warning emitted

For more information about this error, try `rustc --explain E0207`.