{"ast_node_type":"variable","tokens":[{"end":77,"kind":"keyword","start":0,"text":"let"}]}
                        let tag_val = ImmTy::from_uint(tag_bits, tag_layout);
                        // variant_index_relative = tag_val - niche_start_val
                        let niche_start_val = ImmTy::from_uint(niche_start, tag_layout);