// Copyright 2019 The Servo Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
//
http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
//
http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or
http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
use proc_macro2::{Span, TokenStream};
use quote::quote;
use syn::{Ident, Index, TraitBound};
use synstructure::{decl_derive, Structure, BindStyle, AddBounds};
/// Calculates size type for number of variants (used for enums)
fn get_discriminant_size_type(len: usize) -> TokenStream {
if len <= u8::MAX as usize {
quote! { u8 }
} else if len <= u16::MAX as usize {
quote! { u16 }
} else {
quote! { u32 }
}
}
fn is_struct(s: &Structure) -> bool {
// a single variant with no prefix is 'struct'
matches!(s.variants(), [v] if v.prefix.is_none())
}
fn derive_max_size(s: &Structure) -> TokenStream {
let max_size = s.variants().iter().fold(quote!(0), |acc, vi| {
let variant_size = vi.bindings().iter().fold(quote!(0), |acc, bi| {
// compute size of each variant by summing the sizes of its bindings
let ty = &bi.ast().ty;
quote!(#acc + <#ty>::max_size())
});
// find the maximum of each variant
quote! {
max(#acc, #variant_size)
}
});
let body = if is_struct(s) {
max_size
} else {
let discriminant_size_type = get_discriminant_size_type(s.variants().len());
quote! {
#discriminant_size_type ::max_size() + #max_size
}
};
quote! {
#[inline(always)]
fn max_size() -> usize {
use std::cmp::max;
#body
}
}
}
fn derive_peek_from_for_enum(s: &mut Structure) -> TokenStream {
assert!(!is_struct(s));
s.bind_with(|_| BindStyle::Move);
let num_variants = s.variants().len();
let discriminant_size_type = get_discriminant_size_type(num_variants);
let body = s
.variants()
.iter()
.enumerate()
.fold(quote!(), |acc, (i, vi)| {
let bindings = vi
.bindings()
.iter()
.map(|bi| quote!(#bi))
.collect::<Vec<_>>();
let variant_pat = Index::from(i);
let poke_exprs = bindings.iter().fold(quote!(), |acc, bi| {
quote! {
#acc
let (#bi, bytes) = peek_poke::peek_from_default(bytes);
}
});
let construct = vi.construct(|_, i| {
let bi = &bindings[i];
quote!(#bi)
});
quote! {
#acc
#variant_pat => {
#poke_exprs
*output = #construct;
bytes
}
}
});
let type_name = s.ast().ident.to_string();
let max_tag_value = num_variants - 1;
quote! {
#[inline(always)]
unsafe fn peek_from(bytes: *const u8, output: *mut Self) -> *const u8 {
let (variant, bytes) = peek_poke::peek_from_default::<#discriminant_size_type>(bytes);
match variant {
#body
out_of_range_tag => {
panic!("WRDL: memory corruption detected while parsing {} - enum tag should be <= {}, but was {}"
,
#type_name, #max_tag_value, out_of_range_tag);
}
}
}
}
}
fn derive_peek_from_for_struct(s: &mut Structure) -> TokenStream {
assert!(is_struct(s));
s.variants_mut()[0].bind_with(|_| BindStyle::RefMut);
let pat = s.variants()[0].pat();
let peek_exprs = s.variants()[0].bindings().iter().fold(quote!(), |acc, bi| {
let ty = &bi.ast().ty;
quote! {
#acc
let bytes = <#ty>::peek_from(bytes, #bi);
}
});
let body = quote! {
#pat => {
#peek_exprs
bytes
}
};
quote! {
#[inline(always)]
unsafe fn peek_from(bytes: *const u8, output: *mut Self) -> *const u8 {
match &mut (*output) {
#body
}
}
}
}
fn derive_poke_into(s: &Structure) -> TokenStream {
let is_struct = is_struct(s);
let discriminant_size_type = get_discriminant_size_type(s.variants().len());
let body = s
.variants()
.iter()
.enumerate()
.fold(quote!(), |acc, (i, vi)| {
let init = if !is_struct {
let index = Index::from(i);
quote! {
let bytes = #discriminant_size_type::poke_into(&#index, bytes);
}
} else {
quote!()
};
let variant_pat = vi.pat();
let poke_exprs = vi.bindings().iter().fold(init, |acc, bi| {
quote! {
#acc
let bytes = #bi.poke_into(bytes);
}
});
quote! {
#acc
#variant_pat => {
#poke_exprs
bytes
}
}
});
quote! {
#[inline(always)]
unsafe fn poke_into(&self, bytes: *mut u8) -> *mut u8 {
match &*self {
#body
}
}
}
}
fn peek_poke_derive(mut s: Structure) -> TokenStream {
s.binding_name(|_, i| Ident::new(&format!("__self_{}", i), Span::call_site()));
let max_size_fn = derive_max_size(&s);
let poke_into_fn = derive_poke_into(&s);
let peek_from_fn = if is_struct(&s) {
derive_peek_from_for_struct(&mut s)
} else {
derive_peek_from_for_enum(&mut s)
};
let poke_impl = s.gen_impl(quote! {
extern crate peek_poke;
gen unsafe impl peek_poke::Poke for @Self {
#max_size_fn
#poke_into_fn
}
});
// To implement `fn peek_from` we require that types implement `Default`
// trait to create temporary values. This code does the addition all
// manually until https://github.com/mystor/synstructure/issues/24 is fixed.
let default_trait = syn::parse_str::<TraitBound>("::std::default::Default").unwrap();
let peek_trait = syn::parse_str::<TraitBound>("peek_poke::Peek").unwrap();
let ast = s.ast();
let name = &ast.ident;
let (impl_generics, ty_generics, where_clause) = ast.generics.split_for_impl();
let mut where_clause = where_clause.cloned();
s.add_trait_bounds(&default_trait, &mut where_clause, AddBounds::Generics);
s.add_trait_bounds(&peek_trait, &mut where_clause, AddBounds::Generics);
let peek_impl = quote! {
#[allow(non_upper_case_globals)]
const _: () = {
extern crate peek_poke;
impl #impl_generics peek_poke::Peek for #name #ty_generics #where_clause {
#peek_from_fn
}
};
};
quote! {
#poke_impl
#peek_impl
}
}
decl_derive!([PeekPoke] => peek_poke_derive);
