error[E0667]: `impl Trait` is not allowed in path parameters --> $DIR/issue-57979-impl-trait-in-path.rs:8:48 | LL | pub fn demo(_: impl Quux<(), Assoc=<() as Quux>::Assoc>) { } | ^^^^^^^^ error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0667`.