auto_enums_derive 0.5.4

This library provides an attribute macro like a wrapper of `#[derive]`, implementing the supported traits and passing unsupported traits to `#[derive]`.
Documentation 
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use crate::utils::*;

pub(crate) const NAME: &[&str] = &["FnOnce"];

pub(crate) fn derive(data: &Data, stack: &mut Stack<ItemImpl>) -> Result<()> {
    let trait_path = quote!(::core::ops::FnOnce);
    let trait_ = quote!(#trait_path(__T) -> __U);
    let fst = data.fields().iter().next();

    let mut impls = data.impl_with_capacity(2)?;

    *impls.trait_() = Some(Trait::new(
        syn::parse2(trait_path.clone())?,
        parse_quote!(#trait_path<(__T,)>)?,
    ));
    impls.push_generic_param(param_ident("__T"));
    impls.push_generic_param(param_ident("__U"));

    impls.push_where_predicate(parse_quote!(#fst: #trait_)?);
    data.fields()
        .iter()
        .skip(1)
        .try_for_each(|f| parse_quote!(#f: #trait_).map(|f| impls.push_where_predicate(f)))?;

    impls.append_items_from_trait(parse_quote! {
        trait FnOnce {
            type Output;
            #[inline]
            extern "rust-call" fn call_once(self, args: (__T,)) -> Self::Output;
        }
    }?)?;

    stack.push(impls.build_item());
    Ok(())
}