syntax_data: {"ast_node_type":"other","tokens":[{"end":73,"kind":"keyword","start":0,"text":"(ty::Infer(ty::TyVar(a_id)),"}]}
source_snippet:             (ty::Infer(ty::TyVar(a_id)), ty::Infer(ty::TyVar(b_id))) => {
context_before:         match (a.kind(), b.kind()) {
context_after:                 match self.ambient_variance {