Test of whether attribute macros can emit attributes

lib.rs

extern crate proc_macro;
use proc_macro::TokenStream;

#[proc_macro_attribute]
pub fn widget(attr: TokenStream, item: TokenStream) -> TokenStream {
    r#"
    #[track_caller]
    fn answer() -> u32 {
        println!("{:?}", std::panic::Location::caller());
        42
    }"#.parse().unwrap()
}

main.rs

extern crate attrib_derive;
use attrib_derive::widget;

#[widget]
fn answer() {
    // Body isn't actually parsed.
}

fn main() {
    println!("{}", answer());
}