{"ast_node_type":"variable","tokens":[{"end":65,"kind":"keyword","start":0,"text":"let"}]}
                            let fn_ty = self.monomorphize(fn_ty);
                            self.used_mentioned_items.insert(MentionedItem::Fn(fn_ty));
                            visit_fn_use(self.tcx, fn_ty, false, source, self.used_items);