syntax_data: {"ast_node_type":"other","tokens":[{"end":57,"kind":"keyword","start":0,"text":"(Self::Seq(mut"}]}
source_snippet:             (Self::Seq(mut lhs), Self::Seq(mut rhs)) => {
context_before:             (Self::Seq(elts), other) | (other, Self::Seq(elts)) if elts.len() == 0 => other,
context_after:                 lhs.append(&mut rhs);