{"ast_node_type":"variable","tokens":[{"end":88,"kind":"keyword","start":0,"text":"let"}]}
    let trait_m_sig = tcx.liberate_late_bound_regions(impl_m.def_id, bound_trait_m_sig);
    let bound_trait_m_sig = tcx.fn_sig(trait_m.def_id).instantiate(tcx, trait_m_to_impl_m_args);
    // replace the self type of the trait ref with `Self` so that diagnostics render better.