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     let body_visit = s.each(|bind| {
  15         quote! {
  16             ::rustc_middle::ty::fold::TypeFoldable::visit_with(#bind, __folder)?;
  17         }
  18     });
  19     s.bind_with(|_| synstructure::BindStyle::Move);
  20     let body_fold = s.each_variant(|vi| {
  21         let bindings = vi.bindings();
  22         vi.construct(|_, index| {
  23             let bind = &bindings[index];
  24             quote! {
  25                 ::rustc_middle::ty::fold::TypeFoldable::try_fold_with(#bind, __folder)?
  26             }
  27         })
  28     });
  29
  30     s.bound_impl(
  31         quote!(::rustc_middle::ty::fold::TypeFoldable<'tcx>),
  32         quote! {
  33             fn try_fold_with<__F: ::rustc_middle::ty::fold::FallibleTypeFolder<'tcx>>(
  34                 self,
  35                 __folder: &mut __F
  36             ) -> Result<Self, __F::Error> {
  37                 Ok(match self { #body_fold })
  38             }
  39
  40             fn visit_with<__F: ::rustc_middle::ty::fold::TypeVisitor<'tcx>>(
  41                 &self,
  42                 __folder: &mut __F
  43             ) -> ::std::ops::ControlFlow<__F::BreakTy> {
  44                 match *self { #body_visit }
  45                 ::std::ops::ControlFlow::CONTINUE
  46             }
  47         },
  48     )
  49 }