use std::panic::{self, PanicInfo};
use std::sync::atomic::*;
use std::sync::Once;
static WORKS: AtomicUsize = AtomicUsize::new(0);
static INIT: Once = Once::new();
pub(crate) fn inside_proc_macro() -> bool {
match WORKS.load(Ordering::SeqCst) {
1 => return false,
2 => return true,
_ => {}
}
INIT.call_once(initialize);
inside_proc_macro()
}
pub(crate) fn force_fallback() {
WORKS.store(1, Ordering::SeqCst);
}
pub(crate) fn unforce_fallback() {
initialize();
}
fn initialize() {
type PanicHook = dyn Fn(&PanicInfo) + Sync + Send + 'static;
let null_hook: Box<PanicHook> = Box::new(|_panic_info| { });
let sanity_check = &*null_hook as *const PanicHook;
let original_hook = panic::take_hook();
panic::set_hook(null_hook);
let works = panic::catch_unwind(proc_macro::Span::call_site).is_ok();
WORKS.store(works as usize + 1, Ordering::SeqCst);
let hopefully_null_hook = panic::take_hook();
panic::set_hook(original_hook);
if sanity_check != &*hopefully_null_hook {
panic!("observed race condition in proc_macro2::inside_proc_macro");
}
}