Macro define_proc_macros 

macro_rules! define_proc_macros {
    (
        $(
            $( #[$attr:meta] )*
            pub fn $proc_macro_name: ident ($input: ident : &str) -> String
            $body: block
        )+
    ) => { ... };
}

This macro wraps &str -> String functions in custom derive implementations with #[proc_macro_derive].

See crate documentation for details.