{"ast_node_type":"function","tokens":[{"end":97,"kind":"keyword","start":0,"text":"fn"}]}
    fn relate_bound(&mut self, v: Ty<'tcx>, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, ()> {
    // type variable obligations. See caller for details.
        let at = self.infcx.at(&self.trace.cause, self.param_env);