{"ast_node_type":"variable","tokens":[{"end":100,"kind":"keyword","start":0,"text":"let"}]}
    let mut collector = ImplTraitInTraitCollector::new(&ocx, return_span, param_env, impl_m_def_id);
    // We will use these inference variables to collect the hidden types of RPITITs.
    let unnormalized_trait_sig = tcx