syntax_data: {"ast_node_type":"other","tokens":[{"end":53,"kind":"keyword","start":0,"text":"(Self::Alt(mut"}]}
source_snippet:             (Self::Alt(mut lhs), Self::Alt(rhs)) => {
context_before:             (Self::Alt(alts), other) | (other, Self::Alt(alts)) if alts.len() == 0 => other,
context_after:                 lhs.extend(rhs);