Add RTN support to rustdoc

compiler/rustc_hir_analysis/src/lib.rs

@@ -252,7 +252,9 @@ pub fn lower_ty<'tcx>(tcx: TyCtxt<'tcx>, hir_ty: &hir::Ty<'tcx>) -> Ty<'tcx> {
     // def-ID that will be used to determine the traits/predicates in
     // scope. This is derived from the enclosing item-like thing.
     let env_def_id = tcx.hir_get_parent_item(hir_ty.hir_id);
-    collect::ItemCtxt::new(tcx, env_def_id.def_id).lower_ty(hir_ty)
+    collect::ItemCtxt::new(tcx, env_def_id.def_id)
+        .lowerer()
+        .lower_ty_maybe_return_type_notation(hir_ty)
 }
 
 /// This is for rustdoc.