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#![recursion_limit = "128"]
extern crate proc_macro;
use quote::quote;
use syn::spanned::Spanned;
use syn::visit_mut::visit_type_mut;
use syn::{
parse_macro_input, parse_quote, FnArg, Ident, ItemTrait, Lifetime, ReturnType, TraitItem,
TraitItemMethod, Type,
};
type Error = syn::parse::Error;
#[proc_macro_attribute]
pub fn shadow(
_args: proc_macro::TokenStream,
item_tokens: proc_macro::TokenStream,
) -> proc_macro::TokenStream {
let item_tokens_clone = item_tokens.clone();
let item_tokens = proc_macro2::TokenStream::from(item_tokens);
let shadow = parse_macro_input!(item_tokens_clone as ItemTrait);
let shadow_tokens = match generate_shadow(shadow) {
Err(err) => err.to_compile_error().into(),
Ok(tokens) => tokens,
};
let output = quote! {
#item_tokens
#shadow_tokens
};
output.into()
}
fn generate_shadow(mut shadow_trait: ItemTrait) -> Result<proc_macro2::TokenStream, Error> {
let target_ident = shadow_trait.ident.clone();
let shadow_ident = Ident::new(&format!("{}Shadow", target_ident), target_ident.span());
let details_ident = Ident::new(&format!("{}ShadowInfo", target_ident), target_ident.span());
let bind_box_ident = Ident::new(&format!("bind_{}_box", target_ident), target_ident.span());
let visibility = shadow_trait.vis.clone();
shadow_trait.ident = shadow_ident.clone();
shadow_trait.unsafety = Some(syn::token::Unsafe {
span: shadow_trait.ident.span(),
});
if !shadow_trait.supertraits.is_empty() {
return Err(Error::new(
shadow_trait.supertraits.span(),
"supertraits are not supported yet!",
));
}
let mut funcs = Vec::new();
for item in &mut shadow_trait.items {
if let TraitItem::Method(ref mut method) = item {
let (lifetime, mutability) = self_lifetime(method)?.clone();
let first_mut = method.sig.decl.inputs.iter_mut().next().unwrap();
*first_mut = parse_quote! { data: &#lifetime #mutability Self::Data };
let mut arg_types = Vec::new();
for arg in &method.sig.decl.inputs {
if let FnArg::Captured(arg) = arg {
let mut ty = arg.ty.clone();
visit_type_mut(&mut EraseLifetimes {}, &mut ty);
arg_types.push(ty);
} else {
return Err(Error::new(arg.span(), "argument not supported"));
}
}
let mut ret_type: Type = match method.sig.decl.output {
ReturnType::Default => parse_quote! { () },
ReturnType::Type(_, ref ty) => ty.as_ref().clone(),
};
visit_type_mut(&mut EraseLifetimes {}, &mut ret_type);
let func_ident = &method.sig.ident;
funcs.push(quote! {
traitor::details::ShadowLayout {
ret_slots: ret_slots::<#ret_type>(),
arg_slots: #(slots::<#arg_types>())+*,
func_ptr: <S as #shadow_ident>::#func_ident as *const u8,
}
});
method
.sig
.decl
.inputs
.push(parse_quote! { meta: &#lifetime Self });
}
}
shadow_trait.items.push(parse_quote! {
type Data: Sized;
});
let details_struct = quote! {
#visibility struct #details_ident<'meta, S>
where
S: #shadow_ident + 'meta,
{
inner: S,
_phantom: std::marker::PhantomData<&'meta S>,
}
};
let details_impl = quote! {
impl<'meta, S> #details_ident<'meta, S>
where
S: #shadow_ident + 'meta,
{
pub fn new(meta: S) -> Self {
Self {
inner: meta,
_phantom: Default::default(),
}
}
}
};
let details_binding = quote! {
impl<'meta, S> traitor::details::InternalBindingInfo for #details_ident<'meta, S>
where
S: #shadow_ident + 'meta,
{
type Data = <S as #shadow_ident>::Data;
type Shadow = S;
type Target = #target_ident;
fn layout() -> traitor::details::LayoutInfo {
const US: usize = std::mem::size_of::<usize>();
fn slots<T>() -> usize {
match (std::mem::size_of::<T>() + US - 1) / US {
v if v <= 2 => v,
_ => 1,
}
}
fn ret_slots<T>() -> usize {
match (std::mem::size_of::<T>() + US - 1) / US {
v if v > 2 => 1,
_ => 0,
}
}
traitor::details::LayoutInfo {
shadow: vec![
#(#funcs),*
],
other: vec![
],
}
}
fn into_shadow(self) -> S {
self.inner
}
}
};
let bind_box = quote! {
pub fn #bind_box_ident<'b, D>(
data: Box<D>,
binder: &'b traitor::Binder<D, #target_ident>
) -> Box<#target_ident + 'b> {
unsafe {
let raw = Box::into_raw(data);
let bound = binder.bind_mut(std::mem::transmute::<*mut D, &mut D>(raw));
Box::from_raw(bound)
}
}
};
let result = quote! {
#shadow_trait
#details_struct
#details_impl
#details_binding
#bind_box
};
Ok(result)
}
fn self_lifetime(method: &TraitItemMethod) -> Result<(Lifetime, Option<syn::token::Mut>), Error> {
match method.sig.decl.inputs.first().as_ref().map(|v| v.value()) {
Some(FnArg::SelfRef(self_ref)) => {
let lifetime = self_ref.lifetime.as_ref().ok_or_else(|| {
Error::new(
self_ref.self_token.span,
"&self argument must have an explicit lifetime!",
)
})?;
Ok((lifetime.clone(), self_ref.mutability.clone()))
}
_ => {
return Err(Error::new(
method.sig.ident.span(),
"function must be object-safe and have `&self` as a first argument!",
));
}
}
}
struct EraseLifetimes {}
impl syn::visit_mut::VisitMut for EraseLifetimes {
fn visit_type_reference_mut(&mut self, tr: &mut syn::TypeReference) {
tr.lifetime = None;
syn::visit_mut::visit_type_reference_mut(self, tr)
}
fn visit_angle_bracketed_generic_arguments_mut(
&mut self,
list: &mut syn::AngleBracketedGenericArguments,
) {
let old = std::mem::replace(&mut list.args, Default::default());
for item in old {
if let syn::GenericArgument::Lifetime(_) = item {
} else {
list.args.push(item);
}
}
syn::visit_mut::visit_angle_bracketed_generic_arguments_mut(self, list)
}
}