{"ast_node_type":"variable","tokens":[{"end":58,"kind":"keyword","start":0,"text":"let"}]}
        let BlameConstraint { category, cause, .. } = self
    ) -> (ConstraintCategory<'tcx>, ObligationCause<'tcx>) {
            .best_blame_constraint(fr1, fr1_origin, |r| self.provides_universal_region(r, fr1, fr2))