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#![cfg_attr(docs_rs_workaround, feature(proc_macro))]
#![recursion_limit = "128"]
#[macro_use]
extern crate quote;
#[macro_use]
extern crate syn;
extern crate proc_macro;
extern crate proc_macro2;
use proc_macro::TokenStream;
use proc_macro2::TokenStream as TokenStream2;
use syn::parse::{Parse, ParseStream, Result};
use syn::{Attribute, Generics, Ident, Token, Type, Visibility};
struct Nothing;
impl Parse for Nothing {
fn parse(_input: ParseStream) -> Result<Self> {
Ok(Nothing)
}
}
struct FnArg {
ident: Ident,
ty: Type,
}
impl Parse for FnArg {
fn parse(input: ParseStream) -> Result<Self> {
let ident = input.parse()?;
input.parse::<Token![:]>()?;
let ty = input.parse()?;
Ok(FnArg { ident, ty })
}
}
struct HackFn {
impl_attrs: Vec<Attribute>,
generics: Generics,
self_ty: Type,
fn_attrs: Vec<Attribute>,
vis: Visibility,
method: Ident,
args: Vec<FnArg>,
ret_ty: Option<Type>,
body: TokenStream2,
}
impl Parse for HackFn {
fn parse(input: ParseStream) -> Result<Self> {
let impl_attrs = input.call(Attribute::parse_outer)?;
input.parse::<Token![impl ]>()?;
let mut generics: Generics = input.parse()?;
let self_ty: Type = input.parse()?;
generics.where_clause = input.parse()?;
let impl_block;
braced!(impl_block in input);
let fn_attrs = impl_block.call(Attribute::parse_outer)?;
let vis: Visibility = impl_block.parse()?;
impl_block.parse::<Token![fn]>()?;
let method: Ident = impl_block.parse()?;
let argument_list;
parenthesized!(argument_list in impl_block);
argument_list.parse::<Token![&]>()?;
argument_list.parse::<Token![self]>()?;
let mut args = Vec::new();
while !argument_list.is_empty() {
argument_list.parse::<Token![,]>()?;
if argument_list.is_empty() {
break;
}
args.push(argument_list.parse::<FnArg>()?);
}
let ret_ty = if impl_block.parse::<Option<Token![->]>>()?.is_some() {
Some(impl_block.parse::<Type>()?)
} else {
None
};
let body;
braced!(body in impl_block);
let body: TokenStream2 = body.parse()?;
Ok(HackFn {
impl_attrs,
generics,
self_ty,
fn_attrs,
vis,
method,
args,
ret_ty,
body,
})
}
}
#[proc_macro_attribute]
pub fn hackfn(args: TokenStream, input: TokenStream) -> TokenStream {
parse_macro_input!(args as Nothing);
let HackFn {
impl_attrs,
generics,
self_ty,
fn_attrs,
vis,
method,
args,
ret_ty,
body,
} = parse_macro_input!(input as HackFn);
let impl_attrs = &impl_attrs;
let ret_ty = &ret_ty;
let where_clause = &generics.where_clause;
let arg_names = args.iter().map(|fn_arg| &fn_arg.ident);
let arg_types = args.iter().map(|fn_arg| &fn_arg.ty);
let arg_names2 = arg_names.clone();
let arg_names3 = arg_names.clone();
let arg_types2 = arg_types.clone();
let arg_types3 = arg_types.clone();
let target = quote! {
::std::ops::Fn(#(#arg_types2),*) #(-> #ret_ty)*
};
let expanded = quote! {
#(#impl_attrs)*
impl #generics #self_ty #where_clause {
#(#fn_attrs)*
#vis fn #method(&self #(, #arg_names: #arg_types)*) #(-> #ret_ty)* {
#body
}
}
#(#impl_attrs)*
impl #generics ::std::ops::Deref for #self_ty #where_clause {
type Target = #target;
fn deref(&self) -> &Self::Target {
let __this: Self = unsafe { ::std::mem::uninitialized() };
let __closure = move |#(#arg_names2 : #arg_types3),*| #(-> #ret_ty)* {
Self::#method(&__this #(, #arg_names3)*)
};
let __size_of_closure = ::std::mem::size_of_val(&__closure);
fn __second<'__a, __T>(__first: &__T, __second: &'__a __T) -> &'__a __T {
__second
}
let __ret = __second(&__closure, unsafe { ::std::mem::transmute(self) });
::std::mem::forget(__closure);
assert_eq!(__size_of_closure, ::std::mem::size_of::<Self>());
unsafe { ::std::mem::transmute(__ret as &#target) }
}
}
};
TokenStream::from(expanded)
}