syntax_data: {"ast_node_type":"other","tokens":[{"end":49,"kind":"keyword","start":0,"text":"(ty::Infer(ty::TyVar(a_vid)),"}]}
source_snippet:             (ty::Infer(ty::TyVar(a_vid)), _) => {
context_after:                 infcx.instantiate_ty_var_raw(self, true, a_vid, self.ambient_variance, b)?;