{"ast_node_type":"variable","tokens":[{"end":43,"kind":"keyword","start":0,"text":"let"}]}
    let target = trait_ref.args.type_at(1);
    assert_eq!(trait_ref.def_id, coerce_unsized_trait);
    debug!("visit_implementation_of_coerce_unsized: {:?} -> {:?} (bound)", source, target);