{"ast_node_type":"variable","tokens":[{"end":61,"kind":"keyword","start":0,"text":"let"}]}
                let callee_ty = self.monomorphize(callee_ty);
                self.used_mentioned_items.insert(MentionedItem::Fn(callee_ty));
                visit_fn_use(self.tcx, callee_ty, true, source, &mut self.used_items)