use syn::spanned::Spanned;
pub fn derive_ord_no_bound(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
let input: syn::DeriveInput = match syn::parse(input) {
Ok(input) => input,
Err(e) => return e.to_compile_error().into(),
};
let name = &input.ident;
let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
let impl_ = match input.data {
syn::Data::Struct(struct_) => match struct_.fields {
syn::Fields::Named(named) => {
let fields = named
.named
.iter()
.map(|i| &i.ident)
.map(|i| quote::quote_spanned!(i.span() => self.#i.cmp(&other.#i) ));
quote::quote!( core::cmp::Ordering::Equal #( .then_with(|| #fields) )* )
},
syn::Fields::Unnamed(unnamed) => {
let fields = unnamed
.unnamed
.iter()
.enumerate()
.map(|(i, _)| syn::Index::from(i))
.map(|i| quote::quote_spanned!(i.span() => self.#i.cmp(&other.#i) ));
quote::quote!( core::cmp::Ordering::Equal #( .then_with(|| #fields) )* )
},
syn::Fields::Unit => {
quote::quote!(core::cmp::Ordering::Equal)
},
},
syn::Data::Enum(_) => {
let msg = "Enum type not supported by `derive(OrdNoBound)`";
return syn::Error::new(input.span(), msg).to_compile_error().into()
},
syn::Data::Union(_) => {
let msg = "Union type not supported by `derive(OrdNoBound)`";
return syn::Error::new(input.span(), msg).to_compile_error().into()
},
};
quote::quote!(
const _: () = {
impl #impl_generics core::cmp::Ord for #name #ty_generics #where_clause {
fn cmp(&self, other: &Self) -> core::cmp::Ordering {
#impl_
}
}
};
)
.into()
}