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[iddm]

I have made a procedural macro which implements a trait with some functions for a enums. This the whole code:

#[proc_macro_derive(StateMachine, attributes(state_transitions))]
pub fn fxsm(input: TokenStream) -> TokenStream {
    // Construct a string representation of the type definition
    let s = input.to_string();

    // Parse the string representation
    let ast = syn::parse_derive_input(&s).unwrap();

    // Build the impl
    let gen = impl_fsm(&ast);

    // Return the generated impl
    gen.parse().unwrap()
}

fn impl_fsm(ast: &syn::DeriveInput) -> Tokens {
    if let syn::Body::Enum(ref variants) = ast.body {
        if let Some(ref a) = ast.attrs.iter().find(|a| a.name() == "derive") {
            if let syn::MetaItem::List(_, ref nested) = a.value {
                if derives(nested, "Copy") {
                    return gen_for_copyable(&ast.ident,
                                            &variants,
                                            &ast.generics);
                } else if derives(nested, "Clone") {
                    return gen_for_clonable(&ast.ident,
                                            &variants,
                                            &ast.generics);
                } else {
                    panic!("Unable to produce State Machine code on a enum which does not drive Copy nor Clone traits.");
                }
            } else {
                panic!("Unable to produce State Machine code on a enum which does not drive Copy nor Clone traits.");
            }
        } else {
            panic!("How were you able to call me without derive!?!?");
        }
    } else {
        panic!("State Machine must be derived on a enum.");
    }
}

This code worked perfectly like 2 weeks ago but now I have tried to compile it and it can't find any attribute on this struct! As you can see, I try to see what derives does the enum have but now this list is empty! What happened?

[dtolnay]

This changed in rust-lang/rust#39572. Open a Rust issue explaining your use case and asking for rust-lang/rust#39572 (comment).

[iddm]

@dtolnay thanks for pointing me there.