Imply always-const host effects the same as any other item bound

compiler/rustc_hir_analysis/src/collect/item_bounds.rs

@@ -124,6 +124,7 @@ fn remap_gat_vars_and_recurse_into_nested_projections<'tcx>(
         ty::ClauseKind::Trait(tr) => tr.self_ty(),
         ty::ClauseKind::Projection(proj) => proj.projection_term.self_ty(),
         ty::ClauseKind::TypeOutlives(outlives) => outlives.0,
+        ty::ClauseKind::HostEffect(host) => host.self_ty(),
         _ => return None,
     };
 

tests/ui/traits/const-traits/imply-always-const.rs

@@ -0,0 +1,19 @@
+//@ check-pass
+
+#![feature(const_trait_impl)]
+
+#[const_trait]
+trait A where Self::Assoc: const B {
+    type Assoc;
+}
+
+#[const_trait]
+trait B {}
+
+fn needs_b<T: const B>() {}
+
+fn test<T: A>() {
+    needs_b::<T::Assoc>();
+}
+
+fn main() {}