{"ast_node_type":"other","tokens":[{"end":56,"kind":"keyword","start":0,"text":")"}]}
    ) -> Option<(ErrorGuaranteed, Ty<'tcx>, Ty<'tcx>)> {
        base_ty: Ty<'tcx>,
        let index_trait_def_id = self.tcx.lang_items().index_trait()?;