Rollup merge of #68348 - xfix:patch-14, r=nagisa
Make iter::Empty<T> Send and Sync for any T
Continuing from #57682
It's quite funny, when I initially submitted this pull request, I said "Likely nobody will be using that property of `iter::empty`", but then a year later I got a compilation error because it wasn't `Send` and `Sync`.
Unfortunately, `PhantomData<fn() -> T>` still errors out. Oh well. I proposed `
struct PhantomFnWorkaround<T>(fn() -> T);`, but dtolnay did not like it, so using explicit implementations.
diff --git a/src/libcore/iter/sources.rs b/src/libcore/iter/sources.rs
index a65d47c..25dfc57 100644
--- a/src/libcore/iter/sources.rs
+++ b/src/libcore/iter/sources.rs
@@ -208,6 +208,11 @@
#[stable(feature = "iter_empty", since = "1.2.0")]
pub struct Empty<T>(marker::PhantomData<T>);
+#[stable(feature = "iter_empty_send_sync", since = "1.42.0")]
+unsafe impl<T> Send for Empty<T> {}
+#[stable(feature = "iter_empty_send_sync", since = "1.42.0")]
+unsafe impl<T> Sync for Empty<T> {}
+
#[stable(feature = "core_impl_debug", since = "1.9.0")]
impl<T> fmt::Debug for Empty<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
diff --git a/src/test/ui/threads-sendsync/sync-send-iterators-in-libcore.rs b/src/test/ui/threads-sendsync/sync-send-iterators-in-libcore.rs
index 44beb9d..2f6d35f 100644
--- a/src/test/ui/threads-sendsync/sync-send-iterators-in-libcore.rs
+++ b/src/test/ui/threads-sendsync/sync-send-iterators-in-libcore.rs
@@ -88,6 +88,7 @@
is_sync_send!((1..));
is_sync_send!(repeat(1));
is_sync_send!(empty::<usize>());
+ is_sync_send!(empty::<*mut i32>());
is_sync_send!(once(1));
// for option.rs
