error[E0658]: associated const equality is incomplete
  --> $DIR/unconstrained_impl_param.rs:15:45
   |
LL | impl<U> Trait for () where (U,): AssocConst<A = { 0 }> {}
   |                                             ^^^^^^^^^
   |
   = note: see issue #92827 <https://github.com/rust-lang/rust/issues/92827> for more information
   = help: add `#![feature(associated_const_equality)]` to the crate attributes to enable
   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date

error[E0207]: the type parameter `U` is not constrained by the impl trait, self type, or predicates
  --> $DIR/unconstrained_impl_param.rs:15:6
   |
LL | impl<U> Trait for () where (U,): AssocConst<A = { 0 }> {}
   |      ^ unconstrained type parameter

error[E0271]: type mismatch resolving `<(_,) as AssocConst>::A == 0`
  --> $DIR/unconstrained_impl_param.rs:21:5
   |
LL |     (): Trait,
   |     ^^^^^^^^^ expected `0`, found `<(_,) as AssocConst>::A`
   |
   = note: expected constant `0`
              found constant `<(_,) as AssocConst>::A`
note: required for `()` to implement `Trait`
  --> $DIR/unconstrained_impl_param.rs:15:9
   |
LL | impl<U> Trait for () where (U,): AssocConst<A = { 0 }> {}
   |         ^^^^^     ^^                        --------- unsatisfied trait bound introduced here
   = help: see issue #48214
help: add `#![feature(trivial_bounds)]` to the crate attributes to enable
   |
LL + #![feature(trivial_bounds)]
   |

error: aborting due to 3 previous errors

Some errors have detailed explanations: E0207, E0271, E0658.
For more information about an error, try `rustc --explain E0207`.