error: unconstrained opaque type
  --> $DIR/normalize-tait-in-const.rs:14:26
   |
LL |     pub type Alias<'a> = impl T<Item = &'a ()>;
   |                          ^^^^^^^^^^^^^^^^^^^^^
   |
   = note: `Alias` must be used in combination with a concrete type within the same crate

error[E0308]: mismatched types
  --> $DIR/normalize-tait-in-const.rs:22:9
   |
LL |     pub type Alias<'a> = impl T<Item = &'a ()>;
   |                          --------------------- the expected opaque type
...
LL |     pub const fn filter_positive<'a>() -> &'a Alias<'a> {
   |                                           ------------- expected `&'a foo::Alias<'a>` because of return type
LL |         &&S
   |         ^^^ expected `&Alias<'_>`, found `&&S`
   |
   = note: expected reference `&'a foo::Alias<'a>`
              found reference `&&S`
note: this item must have a `#[define_opaque(foo::Alias)]` attribute to be able to define hidden types
  --> $DIR/normalize-tait-in-const.rs:21:18
   |
LL |     pub const fn filter_positive<'a>() -> &'a Alias<'a> {
   |                  ^^^^^^^^^^^^^^^

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0308`.