From 21f5f108e00a7fa9c5419b1ae8b92ba91845c35d Mon Sep 17 00:00:00 2001
From: Jiahao XU <Jiahao_XU@outlook.com>
Date: Fri, 21 Jul 2023 18:05:58 +1000
Subject: [PATCH] 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 or if feature
`parking_lot` is enabled.

Signed-off-by: Jiahao XU <Jiahao_XU@outlook.com>
---
 tokio/src/sync/batch_semaphore.rs |  5 ++++-
 tokio/src/sync/mutex.rs           | 10 ++++++++--
 tokio/src/sync/notify.rs          | 10 ++++++++--
 tokio/src/sync/once_cell.rs       | 10 ++++++++--
 tokio/src/sync/rwlock.rs          | 10 ++++++++--
 tokio/src/sync/semaphore.rs       |  9 +++++++--
 6 files changed, 43 insertions(+), 11 deletions(-)

diff --git a/tokio/src/sync/batch_semaphore.rs b/tokio/src/sync/batch_semaphore.rs
index a762f799d56..030095a4ce0 100644
--- a/tokio/src/sync/batch_semaphore.rs
+++ b/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
diff --git a/tokio/src/sync/mutex.rs b/tokio/src/sync/mutex.rs
index 549c77b321e..561850763a3 100644
--- a/tokio/src/sync/mutex.rs
+++ b/tokio/src/sync/mutex.rs
@@ -378,8 +378,14 @@ 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 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"))))]
     pub const fn const_new(t: T) -> Self
     where
         T: Sized,
diff --git a/tokio/src/sync/notify.rs b/tokio/src/sync/notify.rs
index 0f104b71aa2..8cf1659cece 100644
--- a/tokio/src/sync/notify.rs
+++ b/tokio/src/sync/notify.rs
@@ -443,8 +443,14 @@ 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 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"))))]
     pub const fn const_new() -> Notify {
         Notify {
             state: AtomicUsize::new(0),
diff --git a/tokio/src/sync/once_cell.rs b/tokio/src/sync/once_cell.rs
index 90ea5cd6862..d215cb956d8 100644
--- a/tokio/src/sync/once_cell.rs
+++ b/tokio/src/sync/once_cell.rs
@@ -171,8 +171,14 @@ 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 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"))))]
     pub const fn const_new() -> Self {
         OnceCell {
             value_set: AtomicBool::new(false),
diff --git a/tokio/src/sync/rwlock.rs b/tokio/src/sync/rwlock.rs
index dd4928546fc..6b5878c6a20 100644
--- a/tokio/src/sync/rwlock.rs
+++ b/tokio/src/sync/rwlock.rs
@@ -334,8 +334,14 @@ 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 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"))))]
     pub const fn const_new(value: T) -> RwLock<T>
     where
         T: Sized,
diff --git a/tokio/src/sync/semaphore.rs b/tokio/src/sync/semaphore.rs
index e679d0e6b04..77ca157bd4e 100644
--- a/tokio/src/sync/semaphore.rs
+++ b/tokio/src/sync/semaphore.rs
@@ -173,8 +173,13 @@ 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 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"))))]
     pub const fn const_new(permits: usize) -> Self {
         #[cfg(all(tokio_unstable, feature = "tracing"))]
         return Self {