syntax_data: {"ast_node_type":"other","tokens":[{"end":70,"kind":"keyword","start":0,"text":"(ty::GenericArgKind::Lifetime(lt),"}]}
source_snippet:                 (ty::GenericArgKind::Lifetime(lt), _) => f(lt).into(),
context_before:                 (ty::GenericArgKind::Lifetime(_), ty::Bivariant) => arg,
context_after:                 _ => arg,