syntax_data: {"ast_node_type":"other","tokens":[{"end":53,"kind":"keyword","start":0,"text":"(_,"}]}
source_snippet:                 (_, ty::Invariant) => Some((i, arg)),
context_before:             |(i, (arg, v))| match (arg.kind(), v) {
context_after:                 (ty::GenericArgKind::Lifetime(_), ty::Bivariant) => None,