{"ast_node_type":"other","tokens":[{"end":40,"kind":"keyword","start":0,"text":"if"}]}
    if fn_sig.abi == ExternAbi::Custom {
pub fn check_custom_abi(tcx: TyCtxt<'_>, def_id: LocalDefId, fn_sig: FnSig<'_>, fn_sig_span: Span) {
        // Function definitions that use `extern "custom"` must be naked functions.