syntax_data: {"ast_node_type":"variable","tokens":[{"end":24,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:     let mut best = None;
context_before:     let mut dist = dist.unwrap_or_else(|| cmp::max(lookup_len, 3) / 3);
context_after:     // store the candidates with the same distance, only for `use_substring_score` current.