compiler/rustc_macros/src/lift.rs

   1 use quote::quote;
   2 use syn::{self, parse_quote};
   3
   4 pub fn lift_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::TokenStream {
   5     s.add_bounds(synstructure::AddBounds::Generics);
   6     s.bind_with(|_| synstructure::BindStyle::Move);
   7
   8     let tcx: syn::Lifetime = parse_quote!('tcx);
   9     let newtcx: syn::GenericParam = parse_quote!('__lifted);
  10
  11     let lifted = {
  12         let ast = s.ast();
  13         let ident = &ast.ident;
  14
  15         // Replace `'tcx` lifetime by the `'__lifted` lifetime
  16         let (_, generics, _) = ast.generics.split_for_impl();
  17         let mut generics: syn::AngleBracketedGenericArguments = syn::parse_quote! { #generics };
  18         for arg in generics.args.iter_mut() {
  19             match arg {
  20                 syn::GenericArgument::Lifetime(l) if *l == tcx => {
  21                     *arg = parse_quote!('__lifted);
  22                 }
  23                 syn::GenericArgument::Type(t) => {
  24                     *arg = syn::parse_quote! { #t::Lifted };
  25                 }
  26                 _ => {}
  27             }
  28         }
  29
  30         quote! { #ident #generics }
  31     };
  32
  33     let body = s.each_variant(|vi| {
  34         let bindings = &vi.bindings();
  35         vi.construct(|_, index| {
  36             let bi = &bindings[index];
  37             quote! { __tcx.lift(#bi)?  }
  38         })
  39     });
  40
  41     s.add_impl_generic(newtcx);
  42     s.bound_impl(
  43         quote!(::rustc_middle::ty::Lift<'__lifted>),
  44         quote! {
  45             type Lifted = #lifted;
  46
  47             fn lift_to_tcx(self, __tcx: ::rustc_middle::ty::TyCtxt<'__lifted>) -> Option<#lifted> {
  48                 Some(match self { #body })
  49             }
  50         },
  51     )
  52 }