src/test/run-pass-fulldeps/auxiliary/macro-crate-test.rs

// force-host
// no-prefer-dynamic

#![crate_type = "proc-macro"]
#![feature(rustc_private)]

extern crate syntax;
extern crate rustc;
extern crate rustc_plugin;
extern crate syntax_pos;
extern crate proc_macro;

use proc_macro::{TokenTree, TokenStream};

#[proc_macro_attribute]
pub fn rustc_duplicate(attr: TokenStream, item: TokenStream) -> TokenStream {
    let mut new_name = Some(attr.into_iter().nth(0).unwrap());
    let mut encountered_idents = 0;
    let input = item.to_string();
    let ret = item.into_iter().map(move |token| match token {
        TokenTree::Ident(_) if encountered_idents == 1 => {
            encountered_idents += 1;
            new_name.take().unwrap()
        }
        TokenTree::Ident(_) => {
            encountered_idents += 1;
            token
        }
        _ => token
    }).collect::<TokenStream>();
    let mut input_again = input.parse::<TokenStream>().unwrap();
    input_again.extend(ret);
    input_again
}