syntax_data: {"ast_node_type":"variable","tokens":[{"end":76,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:                 let v = iter::zip(a, b).map(|(a, b)| relation.relate(a, b));
context_before:                 }
context_after:                 let patterns = tcx.mk_patterns_from_iter(v)?;