use rustc_hir::lang_items::LangItem;
use rustc_hir::{GenericArg, GenericArgs, OpaqueTyOrigin};
use rustc_middle::middle::stability::AllowUnstable;
-use rustc_middle::ty::subst::{self, GenericArgKind, InternalSubsts, Subst, SubstsRef};
+use rustc_middle::ty::subst::{self, GenericArgKind, InternalSubsts, SubstsRef};
use rustc_middle::ty::DynKind;
use rustc_middle::ty::GenericParamDefKind;
use rustc_middle::ty::{