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