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#![recursion_limit = "128"]
extern crate proc_macro;
use proc_macro::{TokenStream, TokenTree};
use quote::quote;
use quote::ToTokens;
use std::iter::FromIterator;
use syn::export::TokenStream2;
use syn::*;
#[proc_macro_attribute]
pub fn boxed(_attr: TokenStream, item: TokenStream) -> TokenStream {
match parse::<ItemFn>(item.clone()) {
Ok(fn_) => boxed_fn(fn_),
Err(_) => {
let item = TokenStream::from_iter(item.into_iter().filter(|x| match x {
TokenTree::Ident(x) if x.to_string() == "async" => false,
_ => true,
}));
let method: TraitItemMethod = parse(item).unwrap();
boxed_trait_method(method)
}
}
}
fn boxed_fn(fn_: ItemFn) -> TokenStream {
let attrs = &fn_.attrs;
let vis = &fn_.vis;
let sig = boxed_fn_sig(&fn_.sig);
let block = &fn_.block;
let tokens = quote! {
#(#attrs)*
#vis #sig {
use futures::future::FutureExt;
let task = async move #block;
task.boxed()
}
};
tokens.into()
}
fn boxed_trait_method(method: TraitItemMethod) -> TokenStream {
let attrs = &method.attrs;
let sig = boxed_fn_sig(&method.sig);
let tokens = quote! {
#(#attrs)*
#sig;
};
tokens.into()
}
fn boxed_fn_sig(sig: &Signature) -> TokenStream2 {
let constness = &sig.constness;
let ident = &sig.ident;
let generics = &sig.generics;
let inputs = &sig.inputs;
let return_ty = match &sig.output {
ReturnType::Default => quote!(()),
ReturnType::Type(_, ty) => ty.into_token_stream(),
};
quote! {
#constness fn #ident #generics(#inputs) -> futures::future::BoxFuture<'_, #return_ty>
}
}
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