src/librustc_macros/src/type_foldable.rs

   1 use synstructure;
   2 use syn;
   3 use quote::quote;
   4
   5 pub fn type_foldable_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::TokenStream {
   6     if let syn::Data::Union(_) = s.ast().data {
   7         panic!("cannot derive on union")
   8     }
   9
  10     s.add_bounds(synstructure::AddBounds::Generics);
  11     let body_fold = s.each_variant(|vi| {
  12         let bindings = vi.bindings();
  13         vi.construct(|_, index| {
  14             let bind = &bindings[index];
  15             quote!{
  16                 ::rustc::ty::fold::TypeFoldable::fold_with(#bind, __folder)
  17             }
  18         })
  19     });
  20     let body_visit = s.fold(false, |acc, bind| {
  21         quote!{ #acc || ::rustc::ty::fold::TypeFoldable::visit_with(#bind, __folder) }
  22     });
  23
  24     s.bound_impl(quote!(::rustc::ty::fold::TypeFoldable<'tcx>), quote!{
  25         fn super_fold_with<__F: ::rustc::ty::fold::TypeFolder<'tcx>>(
  26             &self,
  27             __folder: &mut __F
  28         ) -> Self {
  29             match *self { #body_fold }
  30         }
  31
  32         fn super_visit_with<__F: ::rustc::ty::fold::TypeVisitor<'tcx>>(
  33             &self,
  34             __folder: &mut __F
  35         ) -> bool {
  36             match *self { #body_visit }
  37         }
  38     })
  39 }