syntax_data: {"ast_node_type":"variable","tokens":[{"end":47,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:             let t = relation.relate(a_t, b_t)?;
context_before:         (ty::Array(a_t, sz_a), ty::Array(b_t, sz_b)) => {
context_after:             match relation.relate(sz_a, sz_b) {