macro_withstate/
lib.rs

1extern crate proc_macro;
2extern crate quote;
3extern crate syn;
4
5use proc_macro::TokenStream;
6use quote::quote;
7use syn::{ItemStruct, TypePath, parse_macro_input};
8
9/// Use attribute while `derive(WithState<State>)` is unavailable.
10#[proc_macro_attribute]
11pub fn with_state(attr: TokenStream, item: TokenStream) -> TokenStream {
12    let attr_input = parse_macro_input!(attr as TypePath);
13    let item_input = parse_macro_input!(item as ItemStruct);
14    let state = attr_input;
15    let node = item_input.ident.clone();
16
17    let expand = quote! {
18        #item_input
19        impl WithState<#state> for #node {}
20    };
21    TokenStream::from(expand)
22}