syntax_data: {"ast_node_type":"other","tokens":[{"end":86,"kind":"keyword","start":0,"text":"ty::FnDef(def_id,"}]}
source_snippet:             ty::FnDef(def_id, args) => ty::FnDef(def_id, args.try_fold_with(folder)?),
context_before:             ty::Tuple(ts) => ty::Tuple(ts.try_fold_with(folder)?),
context_after:             ty::FnPtr(sig_tys, hdr) => ty::FnPtr(sig_tys.try_fold_with(folder)?, hdr),