Macro feature_gated_function 

macro_rules! feature_gated_function {
    (
        mod $mod_name:ident,
        $feature_name:literal,
        async fn $func_name:ident ( $( $param_name:ident : $param_type:ty ),* $(,)? ) -> $ret_type:ty
    ) => { ... };
}

Define a feature-gated function from a module.

This macro conditionally includes a module and re-exports a function from it. When the feature is disabled, it generates a stub function that returns an error.