Macro define_signal_enum 

macro_rules! define_signal_enum {
    (
        $(#[$outer:meta])*
        pub enum Signal {
            $(
                $(#[cfg($($inner_cfg:tt)*)])?
                $(#[doc $($inner_doc:tt)*])*
                $name:ident = $value:ident,
            )*
        }
    ) => { ... };
}