{"ast_node_type":"variable","tokens":[{"end":65,"kind":"keyword","start":0,"text":"let"}]}
            let impl_args = ecx.fresh_args_for_item(impl_def_id);
        ecx.probe_trait_candidate(CandidateSource::Impl(impl_def_id)).enter(|ecx| {
            let impl_trait_ref = impl_trait_ref.instantiate(cx, impl_args);