{"ast_node_type":"other","tokens":[{"end":36,"kind":"keyword","start":0,"text":"expr:"}]}
        expr: &'tcx hir::Expr<'tcx>,
        obligation: &traits::ImplDerivedCause<'tcx>,
    ) -> Result<&'tcx hir::Expr<'tcx>, &'tcx hir::Expr<'tcx>> {