ONCE_INIT is deprecated-in-future only for bootstrap

Author: RalfJung

src/libstd/io/util.rs

@@ -48,7 +48,7 @@ pub fn copy<R: ?Sized, W: ?Sized>(reader: &mut R, writer: &mut W) -> io::Result<
     // `MaybeUninit`. Revisit this once we decided whether that is valid or not.
     // This is still technically undefined behavior due to creating a reference
     // to uninitialized data, but within libstd we can rely on more guarantees
-    // than if this code were in an external lib
+    // than if this code were in an external lib.
     unsafe { reader.initializer().initialize(buf.get_mut()); }
 
     let mut written = 0;

src/libstd/sync/mod.rs

@@ -163,7 +163,8 @@ pub use self::condvar::{Condvar, WaitTimeoutResult};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::mutex::{Mutex, MutexGuard};
 #[stable(feature = "rust1", since = "1.0.0")]
-#[allow(deprecated_in_future)]
+#[cfg_attr(bootstrap, allow(deprecated_in_future))]
+#[allow(deprecated)]
 pub use self::once::{Once, OnceState, ONCE_INIT};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use crate::sys_common::poison::{PoisonError, TryLockError, TryLockResult, LockResult};