syntax_data: {"ast_node_type":"variable","tokens":[{"end":57,"kind":"keyword","start":0,"text":"if"}]}
source_snippet:                     if let Some(&a_last) = a_tys.last() {
context_before:                 (&ty::Tuple(a_tys), &ty::Tuple(b_tys)) if a_tys.len() == b_tys.len() => {
context_after:                         a = a_last;