{"ast_node_type":"variable","tokens":[{"end":88,"kind":"keyword","start":0,"text":"let"}]}
                        let opt_label = this.lower_label(*opt_label, e.id, expr_hir_id);
                            this.mark_span_with_reason(DesugaringKind::WhileLoop, e.span, None);
                        this.lower_expr_while_in_loop_scope(span, cond, body, opt_label)