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use quote::quote;
use syn::{parse_quote, Attribute, Meta, NestedMeta};
pub fn type_visitable_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::TokenStream {
if let syn::Data::Union(_) = s.ast().data {
panic!("cannot derive on union")
}
// ignore fields with #[type_visitable(ignore)]
s.filter(|bi| {
!bi.ast()
.attrs
.iter()
.map(Attribute::parse_meta)
.filter_map(Result::ok)
.flat_map(|attr| match attr {
Meta::List(list) if list.path.is_ident("type_visitable") => list.nested,
_ => Default::default(),
})
.any(|nested| match nested {
NestedMeta::Meta(Meta::Path(path)) => path.is_ident("ignore"),
_ => false,
})
});
if !s.ast().generics.lifetimes().any(|lt| lt.lifetime.ident == "tcx") {
s.add_impl_generic(parse_quote! { 'tcx });
}
s.add_bounds(synstructure::AddBounds::Generics);
let body_visit = s.each(|bind| {
quote! {
::rustc_middle::ty::visit::TypeVisitable::visit_with(#bind, __visitor)?;
}
});
s.bind_with(|_| synstructure::BindStyle::Move);
s.bound_impl(
quote!(::rustc_middle::ty::visit::TypeVisitable<::rustc_middle::ty::TyCtxt<'tcx>>),
quote! {
fn visit_with<__V: ::rustc_middle::ty::visit::TypeVisitor<::rustc_middle::ty::TyCtxt<'tcx>>>(
&self,
__visitor: &mut __V
) -> ::std::ops::ControlFlow<__V::BreakTy> {
match *self { #body_visit }
::std::ops::ControlFlow::Continue(())
}
},
)
}
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