tor-browser

The Tor Browser
git clone https://git.dasho.dev/tor-browser.git
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to_shmem.rs (2672B)

      1 /* This Source Code Form is subject to the terms of the Mozilla Public
      2 * License, v. 2.0. If a copy of the MPL was not distributed with this
      3 * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
      4 
      5 use crate::util::{add_predicate, fmap2_match, parse_field_attrs, parse_input_attrs};
      6 use darling::{FromDeriveInput, FromField};
      7 use proc_macro2::TokenStream;
      8 use quote::quote;
      9 use syn::{self, parse_quote};
     10 use synstructure::{BindStyle, Structure};
     11 
     12 pub fn derive(mut input: syn::DeriveInput) -> TokenStream {
     13    let mut where_clause = input.generics.where_clause.take();
     14    let attrs = parse_input_attrs::<ShmemInputAttrs>(&input);
     15    if !attrs.no_bounds {
     16        for param in input.generics.type_params() {
     17            add_predicate(&mut where_clause, parse_quote!(#param: ::to_shmem::ToShmem));
     18        }
     19    }
     20    for variant in Structure::new(&input).variants() {
     21        for binding in variant.bindings() {
     22            let attrs = parse_field_attrs::<ShmemFieldAttrs>(&binding.ast());
     23            if attrs.field_bound {
     24                let ty = &binding.ast().ty;
     25                add_predicate(&mut where_clause, parse_quote!(#ty: ::to_shmem::ToShmem))
     26            }
     27        }
     28    }
     29 
     30    input.generics.where_clause = where_clause;
     31 
     32    // Do all of the `to_shmem()?` calls before the `ManuallyDrop::into_inner()`
     33    // calls, so that we don't drop a value in the shared memory buffer if one
     34    // of the `to_shmem`s fails.
     35    let match_body = fmap2_match(
     36        &input,
     37        BindStyle::Ref,
     38        |binding| {
     39            quote! {
     40                ::to_shmem::ToShmem::to_shmem(#binding, builder)?
     41            }
     42        },
     43        |binding| {
     44            Some(quote! {
     45                ::std::mem::ManuallyDrop::into_inner(#binding)
     46            })
     47        },
     48    );
     49 
     50    let name = &input.ident;
     51    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
     52 
     53    quote! {
     54        impl #impl_generics ::to_shmem::ToShmem for #name #ty_generics #where_clause {
     55            #[allow(unused_variables, unreachable_code)]
     56            fn to_shmem(
     57                &self,
     58                builder: &mut ::to_shmem::SharedMemoryBuilder,
     59            ) -> ::to_shmem::Result<Self> {
     60                Ok(::std::mem::ManuallyDrop::new(
     61                    match *self {
     62                        #match_body
     63                    }
     64                ))
     65            }
     66        }
     67    }
     68 }
     69 
     70 #[derive(Default, FromDeriveInput)]
     71 #[darling(attributes(shmem), default)]
     72 pub struct ShmemInputAttrs {
     73    pub no_bounds: bool,
     74 }
     75 
     76 #[derive(Default, FromField)]
     77 #[darling(attributes(shmem), default)]
     78 pub struct ShmemFieldAttrs {
     79    pub field_bound: bool,
     80 }