syntax_data: {"ast_node_type":"variable","tokens":[{"end":53,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:             let pat = relation.relate(a_pat, b_pat)?;
context_before:             let ty = relation.relate(a_ty, b_ty)?;
context_after:             Ok(Ty::new_pat(cx, ty, pat))