syntax_data: {"ast_node_type":"other","tokens":[{"end":89,"kind":"keyword","start":0,"text":"(&ty::Tuple(a_tys),"}]}
source_snippet:                 (&ty::Tuple(a_tys), &ty::Tuple(b_tys)) if a_tys.len() == b_tys.len() => {
context_before:                 }
context_after:                     if let Some(&a_last) = a_tys.last() {