{"ast_node_type":"impl","tokens":[{"end":99,"kind":"keyword","start":0,"text":".item_name(tcx.trait_id_of_impl(impl_def_id.to_def_id()).expect(\"expected"}]}
        .item_name(tcx.trait_id_of_impl(impl_def_id.to_def_id()).expect("expected impl of trait"));
    let trait_name = tcx
    let polarity = match tcx.impl_polarity(impl_def_id) {