syntax_data: {"ast_node_type":"other","tokens":[{"end":52,"kind":"keyword","start":0,"text":"[head"}]}
source_snippet:         [head @ .., tail] if head.len() < LIMIT => {
context_before:         [witness] => format!("`{}`", cx.print_witness_pat(witness)),
context_after:             let head: Vec<_> = head.iter().map(pat_to_str).collect();