compiler/rustc_macros/src/type_foldable.rs

   1 use quote::quote;
   2 use syn::parse_quote;
   3
   4 pub fn type_foldable_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::TokenStream {
   5     if let syn::Data::Union(_) = s.ast().data {
   6         panic!("cannot derive on union")
   7     }
   8
   9     if !s.ast().generics.lifetimes().any(|lt| lt.lifetime.ident == "tcx") {
  10         s.add_impl_generic(parse_quote! { 'tcx });
  11     }
  12
  13     s.add_bounds(synstructure::AddBounds::Generics);
  14     s.bind_with(|_| synstructure::BindStyle::Move);
  15     let body_fold = s.each_variant(|vi| {
  16         let bindings = vi.bindings();
  17         vi.construct(|_, index| {
  18             let bind = &bindings[index];
  19             quote! {
  20                 ::rustc_middle::ty::fold::TypeFoldable::try_fold_with(#bind, __folder)?
  21             }
  22         })
  23     });
  24
  25     s.bound_impl(
  26         quote!(::rustc_middle::ty::fold::TypeFoldable<'tcx>),
  27         quote! {
  28             fn try_fold_with<__F: ::rustc_middle::ty::fold::FallibleTypeFolder<'tcx>>(
  29                 self,
  30                 __folder: &mut __F
  31             ) -> Result<Self, __F::Error> {
  32                 Ok(match self { #body_fold })
  33             }
  34         },
  35     )
  36 }