syntax_data: {"ast_node_type":"function","tokens":[{"end":64,"kind":"keyword","start":0,"text":"fn"}]}
source_snippet:     fn visit_opaque_ty(&mut self, alias_ty: ty::AliasTy<'tcx>) {
context_before:     #[instrument(level = "debug", skip(self))]
context_after:         if !self.seen.insert(alias_ty.def_id.expect_local()) {