Add impl polarity to fields

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

@@ -947,6 +947,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                         substs: self.tcx().mk_substs_trait(ty, &[]),
                     },
                     constness: ty::BoundConstness::ConstIfConst,
+                    polarity: ty::ImplPolarity::Positive,
                 }));
 
             let const_drop_stack = self.push_stack(obligation_stack.list(), &const_drop_obligation);