attempt to re-add ty::Unevaluated visitor and friends

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -619,11 +619,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     }
                 }
 
-                ty::PredicateKind::ConstEvaluatable(def_id, substs) => {
+                ty::PredicateKind::ConstEvaluatable(uv) => {
                     match const_evaluatable::is_const_evaluatable(
                         self.infcx,
-                        def_id,
-                        substs,
+                        uv,
                         obligation.param_env,
                         obligation.cause.span,
                     ) {
@@ -645,7 +644,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                         if let (ty::ConstKind::Unevaluated(a), ty::ConstKind::Unevaluated(b)) =
                             (c1.val, c2.val)
                         {
-                            if self.infcx.try_unify_abstract_consts(a, b) {
+                            if self.infcx.try_unify_abstract_consts(a.shrink(), b.shrink()) {
                                 return Ok(EvaluatedToOk);
                             }
                         }