macro_rules! expand {
    (
        #[foo]
        $(#[$attr:meta])*
        pub fn foo() {}
    ) => (
        expand! {
            $(#[$attr])*
            pub fn foo() {}
        }
    );

    (
        #[bar($a:meta)]
        pub fn foo() {}
    ) => (
        expand! {
            pub fn foo() {}
        }
    );

    (
        pub fn foo() {}
    ) => (
        pub fn foo() {}
    )
}

expand! {
    #[foo]
    #[bar(a)]
    pub fn foo() {}
}