syntax_data: {"ast_node_type":"other","tokens":[{"end":75,"kind":"keyword","start":0,"text":"Mutability::Not"}]}
source_snippet:                 Mutability::Not => (ty::Covariant, VarianceDiagInfo::None),
context_before:             let (variance, info) = match a_mutbl {
context_after:                 Mutability::Mut => {