Merge pull request #325 from taiki-e/const_fn_trait_bound

README.md

@@ -91,9 +91,6 @@ lock.
 
 There are a few restrictions when using this library on stable Rust:
 
-- You will have to use the `const_*` functions (e.g. `const_mutex(val)`) to
-  statically initialize the locking primitives. Using e.g. `Mutex::new(val)`
-  does not work on stable Rust yet.
 - The `wasm32-unknown-unknown` target is only fully supported on nightly with
   `-C target-feature=+atomics` in `RUSTFLAGS` and `-Z build-std` passed to cargo.
   parking_lot will work mostly fine on stable, the only difference is it will

lock_api/Cargo.toml

@@ -18,6 +18,9 @@ owning_ref = { version = "0.4.1", optional = true }
 # support, just pass "--features serde" when building this crate.
 serde = { version = "1.0.126", default-features = false, optional = true }
 
+[build-dependencies]
+autocfg = "1.1.0"
+
 [features]
 nightly = []
 arc_lock = []

lock_api/build.rs

@@ -0,0 +1,7 @@
+fn main() {
+    let cfg = autocfg::new();
+
+    if cfg.probe_rustc_version(1, 61) {
+        println!("cargo:rustc-cfg=has_const_fn_trait_bound");
+    }
+}

lock_api/src/lib.rs

@@ -84,13 +84,10 @@
 //! - `owning_ref`: Allows your lock types to be used with the `owning_ref` crate.
 //! - `arc_lock`: Enables locking from an `Arc`. This enables types such as `ArcMutexGuard`. Note that this
 //!   requires the `alloc` crate to be present.
-//! - `nightly`: Enables nightly-only features. At the moment the only such
-//!   feature is `const fn` constructors for lock types.
 
 #![no_std]
 #![warn(missing_docs)]
 #![warn(rust_2018_idioms)]
-#![cfg_attr(feature = "nightly", feature(const_fn_trait_bound))]
 
 #[macro_use]
 extern crate scopeguard;

lock_api/src/mutex.rs

@@ -149,7 +149,7 @@ unsafe impl<R: RawMutex + Sync, T: ?Sized + Send> Sync for Mutex<R, T> {}
 
 impl<R: RawMutex, T> Mutex<R, T> {
     /// Creates a new mutex in an unlocked state ready for use.
-    #[cfg(feature = "nightly")]
+    #[cfg(has_const_fn_trait_bound)]
     #[inline]
     pub const fn new(val: T) -> Mutex<R, T> {
         Mutex {
@@ -159,7 +159,7 @@ impl<R: RawMutex, T> Mutex<R, T> {
     }
 
     /// Creates a new mutex in an unlocked state ready for use.
-    #[cfg(not(feature = "nightly"))]
+    #[cfg(not(has_const_fn_trait_bound))]
     #[inline]
     pub fn new(val: T) -> Mutex<R, T> {
         Mutex {

lock_api/src/remutex.rs

@@ -230,7 +230,7 @@ unsafe impl<R: RawMutex + Sync, G: GetThreadId + Sync, T: ?Sized + Send> Sync
 
 impl<R: RawMutex, G: GetThreadId, T> ReentrantMutex<R, G, T> {
     /// Creates a new reentrant mutex in an unlocked state ready for use.
-    #[cfg(feature = "nightly")]
+    #[cfg(has_const_fn_trait_bound)]
     #[inline]
     pub const fn new(val: T) -> ReentrantMutex<R, G, T> {
         ReentrantMutex {
@@ -245,7 +245,7 @@ impl<R: RawMutex, G: GetThreadId, T> ReentrantMutex<R, G, T> {
     }
 
     /// Creates a new reentrant mutex in an unlocked state ready for use.
-    #[cfg(not(feature = "nightly"))]
+    #[cfg(not(has_const_fn_trait_bound))]
     #[inline]
     pub fn new(val: T) -> ReentrantMutex<R, G, T> {
         ReentrantMutex {

lock_api/src/rwlock.rs

@@ -366,7 +366,7 @@ unsafe impl<R: RawRwLock + Sync, T: ?Sized + Send + Sync> Sync for RwLock<R, T>
 
 impl<R: RawRwLock, T> RwLock<R, T> {
     /// Creates a new instance of an `RwLock<T>` which is unlocked.
-    #[cfg(feature = "nightly")]
+    #[cfg(has_const_fn_trait_bound)]
     #[inline]
     pub const fn new(val: T) -> RwLock<R, T> {
         RwLock {
@@ -376,7 +376,7 @@ impl<R: RawRwLock, T> RwLock<R, T> {
     }
 
     /// Creates a new instance of an `RwLock<T>` which is unlocked.
-    #[cfg(not(feature = "nightly"))]
+    #[cfg(not(has_const_fn_trait_bound))]
     #[inline]
     pub fn new(val: T) -> RwLock<R, T> {
         RwLock {
@@ -892,7 +892,7 @@ impl<R: RawRwLockRecursive, T: ?Sized> RwLock<R, T> {
     /// Attempts to lock this `RwLock` with shared read access, through an `Arc`.
     ///
     /// This method is similar to the `try_read_recursive` method; however, it requires the `RwLock` to be inside
-    /// of an `Arc` and the resulting read guard has no lifetime requirements.   
+    /// of an `Arc` and the resulting read guard has no lifetime requirements.
     #[cfg(feature = "arc_lock")]
     #[inline]
     pub fn try_read_recursive_arc(self: &Arc<Self>) -> Option<ArcRwLockReadGuard<R, T>> {

src/condvar.rs

@@ -53,7 +53,7 @@ impl WaitTimeoutResult {
 ///   woken up.
 /// - Only requires 1 word of space, whereas the standard library boxes the
 ///   `Condvar` due to platform limitations.
-/// - Can be statically constructed (requires the `const_fn` nightly feature).
+/// - Can be statically constructed.
 /// - Does not require any drop glue when dropped.
 /// - Inline fast path for the uncontended case.
 ///

src/fair_mutex.rs

@@ -35,7 +35,7 @@ use lock_api;
 /// - No poisoning, the lock is released normally on panic.
 /// - Only requires 1 byte of space, whereas the standard library boxes the
 ///   `FairMutex` due to platform limitations.
-/// - Can be statically constructed (requires the `const_fn` nightly feature).
+/// - Can be statically constructed.
 /// - Does not require any drop glue when dropped.
 /// - Inline fast path for the uncontended case.
 /// - Efficient handling of micro-contention using adaptive spinning.

src/mutex.rs

@@ -42,7 +42,7 @@ use lock_api;
 /// - No poisoning, the lock is released normally on panic.
 /// - Only requires 1 byte of space, whereas the standard library boxes the
 ///   `Mutex` due to platform limitations.
-/// - Can be statically constructed (requires the `const_fn` nightly feature).
+/// - Can be statically constructed.
 /// - Does not require any drop glue when dropped.
 /// - Inline fast path for the uncontended case.
 /// - Efficient handling of micro-contention using adaptive spinning.

src/rwlock.rs

@@ -55,7 +55,7 @@ use lock_api;
 /// - No poisoning, the lock is released normally on panic.
 /// - Only requires 1 word of space, whereas the standard library boxes the
 ///   `RwLock` due to platform limitations.
-/// - Can be statically constructed (requires the `const_fn` nightly feature).
+/// - Can be statically constructed.
 /// - Does not require any drop glue when dropped.
 /// - Inline fast path for the uncontended case.
 /// - Efficient handling of micro-contention using adaptive spinning.