{"ast_node_type":"variable","tokens":[{"end":63,"kind":"keyword","start":0,"text":"let"}]}
    let unsized_predicate = WhereClause::Implemented(TraitRef {
    let self_ty = placeholder_subst.as_slice(Interner)[trait_self_idx].assert_ty_ref(Interner);
        trait_id: to_chalk_trait_id(unsize_did),