{"ast_node_type":"variable","tokens":[{"end":82,"kind":"keyword","start":0,"text":"let"}]}
    let impl_adt_ty = Ty::new_adt(tcx, tcx.adt_def(adt_def_id), adt_to_impl_args);
    // this we "rename" the ADT's params to be the impl's params which should not affect behaviour.
    let adt_env =