syntax_data: {"ast_node_type":"other","tokens":[{"end":90,"kind":"keyword","start":0,"text":"(ty::Invariant,"}]}
source_snippet:                     (ty::Invariant, VarianceDiagInfo::Invariant { ty: a, param_index: 0 })
context_before:                 Mutability::Mut => {
context_after:                 }