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::Slice(a_t), ty::Slice(b_t)) => {
context_after:             Ok(Ty::new_slice(cx, t))