use rustc_errors::struct_span_err;
use rustc_hir as hir;
use rustc_infer::infer::InferCtxt;
-use rustc_middle::ty::{self, TraitRef, Ty, TyCtxt, WithConstness};
+use rustc_middle::ty::{self, TraitRef, Ty, TyCtxt};
use rustc_middle::ty::{ToPredicate, TypeFoldable};
use rustc_session::{DiagnosticMessageId, Limit};
use rustc_span::def_id::LOCAL_CRATE;