src/librustc_macros/src/lift.rs

   1 use proc_macro2;
   2 use quote::quote;
   3 use syn::{self, parse_quote};
   4 use synstructure;
   5
   6 pub fn lift_derive(mut s: synstructure::Structure<'_>) -> proc_macro2::TokenStream {
   7     s.add_bounds(synstructure::AddBounds::Generics);
   8
   9     let tcx: syn::Lifetime = parse_quote!('tcx);
  10     let newtcx: syn::GenericParam = parse_quote!('__lifted);
  11
  12     let lifted = {
  13         let ast = s.ast();
  14         let ident = &ast.ident;
  15
  16         // Replace `'tcx` lifetime by the `'__lifted` lifetime
  17         let (_, generics, _) = ast.generics.split_for_impl();
  18         let mut generics: syn::AngleBracketedGenericArguments = syn::parse_quote! { #generics };
  19         for arg in generics.args.iter_mut() {
  20             match arg {
  21                 syn::GenericArgument::Lifetime(l) if *l == tcx => {
  22                     *arg = parse_quote!('__lifted);
  23                 }
  24                 syn::GenericArgument::Type(t) => {
  25                     *arg = syn::parse_quote! { #t::Lifted };
  26                 }
  27                 _ => {}
  28             }
  29         }
  30
  31         quote! { #ident #generics }
  32     };
  33
  34     let body = s.each_variant(|vi| {
  35         let bindings = &vi.bindings();
  36         vi.construct(|_, index| {
  37             let bi = &bindings[index];
  38             quote! { __tcx.lift(#bi)?  }
  39         })
  40     });
  41
  42     s.add_impl_generic(newtcx);
  43     s.bound_impl(
  44         quote!(::rustc::ty::Lift<'__lifted>),
  45         quote! {
  46             type Lifted = #lifted;
  47
  48             fn lift_to_tcx(&self, __tcx: ::rustc::ty::TyCtxt<'__lifted>) -> Option<#lifted> {
  49                 Some(match *self { #body })
  50             }
  51         },
  52     )
  53 }