{"ast_node_type":"other","tokens":[{"end":98,"kind":"keyword","start":0,"text":"expr_collector.lower_type_ref_opt(ret_type.ty(),"}]}
        expr_collector.lower_type_ref_opt(ret_type.ty(), &mut ExprCollector::impl_trait_allocator)
    let return_type = fn_.value.ret_type().map(|ret_type| {
    });