use proc_macro2::TokenStream;
use quote::ToTokens;
#[proc_macro_attribute]
pub fn my_attr(
 attr: proc_macro::TokenStream,
 item: proc_macro::TokenStream,
) -> proc_macro::TokenStream {
 match main(attr.into(), item.into()) {
 Ok(retval) => retval.into(),
 Err(err) => err.into_compile_error().into(),
 }
}
fn main(_attr: TokenStream, item: TokenStream) -> syn::Result<TokenStream> {
 let mut item: syn::ItemFn = syn::parse2(item)?;
 item.sig = syn::parse_quote! {
 fn my_test_fn(arg: u8)
 };
 if cfg!(feature = "reset_hygiene") {
 Ok(syn::parse_str(&item.to_token_stream().to_string())?)
 } else {
 Ok(item.to_token_stream())
 }
}

macro_rules! m {
 (
 $(#[$meta:meta])*
 $vis:vis fn $($rest:tt)*
 ) => {
 $(#[$meta])*
 $vis fn $($rest)*
 };
}
m! {
 #[my_macros::my_attr]
 pub fn my_test_fn() {
 dbg!(arg);
 }
}

error[E0425]: cannot find value `arg` in this scope
 --> src/lib.rs:15:14
 |
15 | dbg!(arg);
 | ^^^ not found in this scope