syntax_data: {"ast_node_type":"other","tokens":[{"end":81,"kind":"keyword","start":0,"text":"ty::FnDef(def_id,"}]}
source_snippet:             ty::FnDef(def_id, args) => ty::FnDef(def_id, args.fold_with(folder)),
context_before:             ty::Tuple(ts) => ty::Tuple(ts.fold_with(folder)),
context_after:             ty::FnPtr(sig_tys, hdr) => ty::FnPtr(sig_tys.fold_with(folder), hdr),