Make {Mutex, Notify, OnceCell, RwLock, Semaphore}::const_new available on rust-version >= 1.63

From rust version 1.63, `Mutex::new` is usable in const context, however
`tokio` would still require feature `parking_lot` to be enabled for
these functions to be available.

This patch makes these function available on rust-version >= 1.63 given
that `--cfg tokio_no_const_mutex_new` is not specified or if feature
`parking_lot` is enabled.

Signed-off-by: Jiahao XU <[email protected]>

Author: NobodyXu

tokio/src/sync/batch_semaphore.rs

@@ -181,7 +181,10 @@ impl Semaphore {
     ///
     /// If the specified number of permits exceeds the maximum permit amount
     /// Then the value will get clamped to the maximum number of permits.
-    #[cfg(all(feature = "parking_lot", not(all(loom, test))))]
+    #[cfg(all(
+        any(feature = "parking_lot", not(tokio_no_const_mutex_new)),
+        not(all(loom, test))
+    ))]
     pub(crate) const fn const_new(mut permits: usize) -> Self {
         // NOTE: assertions and by extension panics are still being worked on: https://github.com/rust-lang/rust/issues/74925
         // currently we just clamp the permit count when it exceeds the max

tokio/src/sync/mutex.rs

@@ -378,8 +378,18 @@ impl<T: ?Sized> Mutex<T> {
     ///
     /// static LOCK: Mutex<i32> = Mutex::const_new(5);
     /// ```
-    #[cfg(all(feature = "parking_lot", not(all(loom, test)),))]
-    #[cfg_attr(docsrs, doc(cfg(feature = "parking_lot")))]
+    ///
+    /// NOTE that this function is available if your rust compiler
+    /// is newer than 1.63 and does not specify `--cfg tokio_no_const_mutex_new`
+    /// or if you enabled feature `parking_lot`.
+    #[cfg(all(
+        any(feature = "parking_lot", not(tokio_no_const_mutex_new)),
+        not(all(loom, test))
+    ))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(any(feature = "parking_lot", not(tokio_no_const_mutex_new))))
+    )]
     pub const fn const_new(t: T) -> Self
     where
         T: Sized,

tokio/src/sync/notify.rs

@@ -443,8 +443,18 @@ impl Notify {
     ///
     /// static NOTIFY: Notify = Notify::const_new();
     /// ```
-    #[cfg(all(feature = "parking_lot", not(all(loom, test))))]
-    #[cfg_attr(docsrs, doc(cfg(feature = "parking_lot")))]
+    ///
+    /// NOTE that this function is available if your rust compiler
+    /// is newer than 1.63 and does not specify `--cfg tokio_no_const_mutex_new`
+    /// or if you enabled feature `parking_lot`.
+    #[cfg(all(
+        any(feature = "parking_lot", not(tokio_no_const_mutex_new)),
+        not(all(loom, test))
+    ))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(any(feature = "parking_lot", not(tokio_no_const_mutex_new))))
+    )]
     pub const fn const_new() -> Notify {
         Notify {
             state: AtomicUsize::new(0),

tokio/src/sync/once_cell.rs

@@ -171,8 +171,18 @@ impl<T> OnceCell<T> {
     ///     assert_eq!(*result, 2);
     /// }
     /// ```
-    #[cfg(all(feature = "parking_lot", not(all(loom, test))))]
-    #[cfg_attr(docsrs, doc(cfg(feature = "parking_lot")))]
+    ///
+    /// NOTE that this function is available if your rust compiler
+    /// is newer than 1.63 and does not specify `--cfg tokio_no_const_mutex_new`
+    /// or if you enabled feature `parking_lot`.
+    #[cfg(all(
+        any(feature = "parking_lot", not(tokio_no_const_mutex_new)),
+        not(all(loom, test))
+    ))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(any(feature = "parking_lot", not(tokio_no_const_mutex_new))))
+    )]
     pub const fn const_new() -> Self {
         OnceCell {
             value_set: AtomicBool::new(false),

tokio/src/sync/rwlock.rs

@@ -334,8 +334,18 @@ impl<T: ?Sized> RwLock<T> {
     ///
     /// static LOCK: RwLock<i32> = RwLock::const_new(5);
     /// ```
-    #[cfg(all(feature = "parking_lot", not(all(loom, test))))]
-    #[cfg_attr(docsrs, doc(cfg(feature = "parking_lot")))]
+    ///
+    /// NOTE that this function is available if your rust compiler
+    /// is newer than 1.63 and does not specify `--cfg tokio_no_const_mutex_new`
+    /// or if you enabled feature `parking_lot`.
+    #[cfg(all(
+        any(feature = "parking_lot", not(tokio_no_const_mutex_new)),
+        not(all(loom, test))
+    ))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(any(feature = "parking_lot", not(tokio_no_const_mutex_new))))
+    )]
     pub const fn const_new(value: T) -> RwLock<T>
     where
         T: Sized,

tokio/src/sync/semaphore.rs

@@ -173,8 +173,17 @@ impl Semaphore {
     /// static SEM: Semaphore = Semaphore::const_new(10);
     /// ```
     ///
-    #[cfg(all(feature = "parking_lot", not(all(loom, test))))]
-    #[cfg_attr(docsrs, doc(cfg(feature = "parking_lot")))]
+    /// NOTE that this function is available if your rust compiler
+    /// is newer than 1.63 and does not specify `--cfg tokio_no_const_mutex_new`
+    /// or if you enabled feature `parking_lot`.
+    #[cfg(all(
+        any(feature = "parking_lot", not(tokio_no_const_mutex_new)),
+        not(all(loom, test))
+    ))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(any(feature = "parking_lot", not(tokio_no_const_mutex_new))))
+    )]
     pub const fn const_new(permits: usize) -> Self {
         #[cfg(all(tokio_unstable, feature = "tracing"))]
         return Self {