terrible.rs

// Problem:
macro_rules! generate_impl {
    ($x:ident) => {
        unsafe impl cxx::ExternType for $x {
            // Won't work, `type_id!()` wants a literal, not a macro call
            type Id = cxx::type_id!(stringify!($x));
            type Kind = cxx::kind::Trivial;
        }
    };
}

// Solution:
macro_rules! generate_impl {
    ($x:ident) => {
        ::paste::paste! {
            // `paste!()` concatenates strings with idents in doc comments
            generate_impl!(@ $x #[doc = "" $x]);
        }
    };
    (@ $x:ident #[doc = $i:literal]) => {
        unsafe impl cxx::ExternType for $x {
            type Id = cxx::type_id!($i);
            type Kind = cxx::kind::Trivial;
        }
    }
}