Rollup merge of #61757 - sfackler:deprecate-once-init, r=alexcrichton

Deprecate ONCE_INIT in future 1.38 release

Once::new() has been a stable const fn for a while now.

Closes #61746

src/librustc_metadata/dynamic_lib.rs

@@ -161,8 +161,8 @@ unsafe fn open_internal() -> *mut u8 {
     pub fn check_for_errors_in<T, F>(f: F) -> Result<T, String> where
         F: FnOnce() -> T,
     {
-        use std::sync::{Mutex, Once, ONCE_INIT};
-        static INIT: Once = ONCE_INIT;
+        use std::sync::{Mutex, Once};
+        static INIT: Once = Once::new();
         static mut LOCK: *mut Mutex<()> = 0 as *mut _;
         unsafe {
             INIT.call_once(|| {

src/libstd/sync/mod.rs

@@ -163,6 +163,7 @@
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::mutex::{Mutex, MutexGuard};
 #[stable(feature = "rust1", since = "1.0.0")]
+#[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};

src/libstd/sync/once.rs

@@ -115,6 +115,11 @@ pub struct OnceState {
 /// static START: Once = ONCE_INIT;
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_deprecated(
+    since = "1.38.0",
+    reason = "the `new` function is now preferred",
+    suggestion = "Once::new()",
+)]
 pub const ONCE_INIT: Once = Once::new();
 
 // Four states that a Once can be in, encoded into the lower bits of `state` in

src/test/run-pass/issues/issue-39367.rs

@@ -11,13 +11,13 @@ fn __static_ref_initialize() -> ArenaSet<Vec<u8>> {
         ArenaSet(vec![], &Z)
     }
     unsafe {
-        use std::sync::{Once, ONCE_INIT};
+        use std::sync::Once;
         fn require_sync<T: Sync>(_: &T) { }
         unsafe fn __stability() -> &'static ArenaSet<Vec<u8>> {
             use std::mem::transmute;
             static mut DATA: *const ArenaSet<Vec<u8>> = 0 as *const ArenaSet<Vec<u8>>;
 
-            static mut ONCE: Once = ONCE_INIT;
+            static mut ONCE: Once = Once::new();
             ONCE.call_once(|| {
                 DATA = transmute
                     ::<Box<ArenaSet<Vec<u8>>>, *const ArenaSet<Vec<u8>>>