src/test/compile-fail-fulldeps/proc-macro/feature-gate-proc_macro.rs

// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

// aux-build:attr_proc_macro.rs
#![feature(use_extern_macros)]

extern crate attr_proc_macro;
use attr_proc_macro::attr_proc_macro;

#[attr_proc_macro]
//~^ ERROR: attribute procedural macros are experimental
struct Foo;

fn main() {
    let _ = Foo;
}