backoff-macro 0.2.0

Mark an async function with #[backoff] to get the default ExponentialBackoff behavior. (tokio compatible)
Documentation 
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#![warn(dead_code)]
#![warn(unused_imports)]
extern crate proc_macro;

use proc_macro::TokenStream;
use quote::quote;
use syn::{parse_macro_input, ItemFn, ReturnType};

#[proc_macro_attribute]
pub fn backoff(_attr: TokenStream, item: TokenStream) -> TokenStream {

    let input    = parse_macro_input!(item as ItemFn);
    let fn_attrs = &input.attrs;
    let fn_vis   = &input.vis;
    let fn_sig   = &input.sig;
    let fn_block = &input.block;
    
    let output_type = match &input.sig.output {
        ReturnType::Type(_, ty) => ty,
        ReturnType::Default => {
            return syn::Error::new_spanned(&input.sig.output, "expected a return type")
                .to_compile_error()
                .into();
        }
    };

    let expanded = quote! {
        #(#fn_attrs)*
        #fn_vis #fn_sig {

            let result: #output_type = backoff::future::retry(backoff::ExponentialBackoff::default(), || async {
                Ok(#fn_block?)
            }).await;

            result
        }
    };

    TokenStream::from(expanded)
}