{"ast_node_type":"other","tokens":[{"end":50,"kind":"keyword","start":0,"text":"if"}]}
                    if param.kind.is_synthetic() {
                    let param = self.tcx.generics_of(self.body_id).type_param(param, self.tcx);
                        // if it's `impl Fn() -> ..` then just fall down to the def-id based logic