Expose BiLock as unstable API

.travis.yml

@@ -75,7 +75,7 @@ matrix:
       rust: nightly
       script:
         - cargo bench --all
-        - cargo bench --manifest-path futures-util/Cargo.toml --features=bench,unstable
+        - cargo bench --manifest-path futures-util/Cargo.toml --features=bilock,unstable
 
     - name: cargo +stable build --no-default-features
       rust: stable
@@ -146,11 +146,18 @@ matrix:
         - cargo check --manifest-path futures-util/Cargo.toml --features io-compat
         - cargo check --manifest-path futures-util/Cargo.toml --features sink,compat
         - cargo check --manifest-path futures-util/Cargo.toml --features sink,channel
+        - cargo check --manifest-path futures-util/Cargo.toml --features bilock,unstable
+        - cargo check --manifest-path futures-util/Cargo.toml --features sink,bilock,unstable
+        - cargo check --manifest-path futures-util/Cargo.toml --features io,bilock,unstable
+        - cargo check --manifest-path futures-util/Cargo.toml --features sink,io
 
         - cargo check --manifest-path futures-util/Cargo.toml --no-default-features
         - cargo check --manifest-path futures-util/Cargo.toml --no-default-features --features sink
         - cargo check --manifest-path futures-util/Cargo.toml --no-default-features --features alloc,sink
         - cargo check --manifest-path futures-util/Cargo.toml --no-default-features --features async-await
+        - cargo check --manifest-path futures-util/Cargo.toml --no-default-features --features bilock,unstable
+        - cargo check --manifest-path futures-util/Cargo.toml --no-default-features --features sink,bilock,unstable
+        - cargo check --manifest-path futures-util/Cargo.toml --no-default-features --features io,bilock,unstable
 
     - name: cargo doc
       rust: nightly

futures-util/Cargo.toml

@@ -32,7 +32,7 @@ select-macro = ["async-await", "futures-select-macro-preview", "proc-macro-hack"
 # `unstable` feature as an explicit opt-in to unstable API.
 unstable = ["futures-core-preview/unstable"]
 cfg-target-has-atomic = ["futures-core-preview/cfg-target-has-atomic"]
-bench = []
+bilock = []
 
 [dependencies]
 futures-core-preview = { path = "../futures-core", version = "=0.3.0-alpha.18", default-features = false }

futures-util/benches_disabled/bilock.rs

@@ -1,6 +1,6 @@
 #![feature(test)]
 
-#[cfg(feature = "bench")]
+#[cfg(feature = "bilock")]
 mod bench {
 use futures::task::{Context, Waker};
 use futures::executor::LocalPool;

futures-util/src/lib.rs

@@ -16,8 +16,8 @@
 #[cfg(all(feature = "cfg-target-has-atomic", not(feature = "unstable")))]
 compile_error!("The `cfg-target-has-atomic` feature requires the `unstable` feature as an explicit opt-in to unstable features");
 
-#[cfg(all(feature = "bench", not(feature = "unstable")))]
-compile_error!("The `bench` feature requires the `unstable` feature as an explicit opt-in to unstable features");
+#[cfg(all(feature = "bilock", not(feature = "unstable")))]
+compile_error!("The `bilock` feature requires the `unstable` feature as an explicit opt-in to unstable features");
 
 #[cfg(feature = "alloc")]
 extern crate alloc;

futures-util/src/lock/bilock.rs

@@ -1,11 +1,10 @@
 //! Futures-powered synchronization primitives.
-#![allow(unused)]
 
+#[cfg(feature = "bilock")]
 use futures_core::future::Future;
 use futures_core::task::{Context, Poll, Waker};
 use core::cell::UnsafeCell;
 use core::fmt;
-use core::mem;
 use core::ops::{Deref, DerefMut};
 use core::pin::Pin;
 use core::sync::atomic::AtomicUsize;
@@ -35,6 +34,9 @@ use std::error::Error;
 /// example a TCP stream could be both a reader and a writer or a framing layer
 /// could be both a stream and a sink for messages. A `BiLock` enables splitting
 /// these two and then using each independently in a futures-powered fashion.
+///
+/// This type is only available when the `bilock` feature of this
+/// library is activated.
 #[derive(Debug)]
 pub struct BiLock<T> {
     arc: Arc<Inner<T>>,
@@ -140,6 +142,7 @@ impl<T> BiLock<T> {
     /// `BiLockGuard<T>`.
     ///
     /// Note that the returned future will never resolve to an error.
+    #[cfg(feature = "bilock")]
     pub fn lock(&self) -> BiLockAcquire<'_, T> {
         BiLockAcquire {
             bilock: self,
@@ -149,6 +152,7 @@ impl<T> BiLock<T> {
     /// Attempts to put the two "halves" of a `BiLock<T>` back together and
     /// recover the original value. Succeeds only if the two `BiLock<T>`s
     /// originated from the same call to `BiLock::new`.
+    #[cfg(any(feature = "bilock", feature = "sink"))]
     pub fn reunite(self, other: Self) -> Result<T, ReuniteError<T>>
     where
         T: Unpin,
@@ -182,6 +186,7 @@ impl<T> BiLock<T> {
     }
 }
 
+#[cfg(any(feature = "bilock", feature = "sink"))]
 impl<T: Unpin> Inner<T> {
     unsafe fn into_value(mut self) -> T {
         self.value.take().unwrap().into_inner()
@@ -255,15 +260,18 @@ impl<T> Drop for BiLockGuard<'_, T> {
 
 /// Future returned by `BiLock::lock` which will resolve when the lock is
 /// acquired.
+#[cfg(feature = "bilock")]
 #[must_use = "futures do nothing unless you `.await` or poll them"]
 #[derive(Debug)]
 pub struct BiLockAcquire<'a, T> {
     bilock: &'a BiLock<T>,
 }
 
 // Pinning is never projected to fields
+#[cfg(feature = "bilock")]
 impl<T> Unpin for BiLockAcquire<'_, T> {}
 
+#[cfg(feature = "bilock")]
 impl<'a, T> Future for BiLockAcquire<'a, T> {
     type Output = BiLockGuard<'a, T>;
 

futures-util/src/lock/mod.rs

@@ -1,16 +1,18 @@
 //! Futures-powered synchronization primitives.
+//!
+//! This module is only available when the `std` or `alloc` feature of this
+//! library is activated, and it is activated by default.
 
 #[cfg(feature = "std")]
 mod mutex;
 #[cfg(feature = "std")]
 pub use self::mutex::{Mutex, MutexLockFuture, MutexGuard};
 
-#[cfg(any(feature = "sink", feature = "io"))]
-#[allow(unreachable_pub)]
+#[cfg(any(feature = "bilock", feature = "sink", feature = "io"))]
+#[cfg_attr(not(feature = "bilock"), allow(unreachable_pub))]
 mod bilock;
-#[cfg(any(feature = "sink", feature = "io"))]
-#[cfg(any(test, feature = "bench"))]
+#[cfg(feature = "bilock")]
 pub use self::bilock::{BiLock, BiLockAcquire, BiLockGuard, ReuniteError};
 #[cfg(any(feature = "sink", feature = "io"))]
-#[cfg(not(any(test, feature = "bench")))]
+#[cfg(not(feature = "bilock"))]
 pub(crate) use self::bilock::BiLock;

futures/Cargo.toml

@@ -48,6 +48,7 @@ io-compat = ["compat", "futures-util-preview/io-compat"]
 # `unstable` feature as an explicit opt-in to unstable API.
 unstable = ["futures-core-preview/unstable", "futures-channel-preview/unstable", "futures-util-preview/unstable"]
 cfg-target-has-atomic = ["futures-core-preview/cfg-target-has-atomic", "futures-channel-preview/cfg-target-has-atomic", "futures-util-preview/cfg-target-has-atomic"]
+bilock = ["futures-util-preview/bilock"]
 
 [package.metadata.docs.rs]
 all-features = true

futures/src/lib.rs

@@ -37,6 +37,9 @@
 #[cfg(all(feature = "cfg-target-has-atomic", not(feature = "unstable")))]
 compile_error!("The `cfg-target-has-atomic` feature requires the `unstable` feature as an explicit opt-in to unstable features");
 
+#[cfg(all(feature = "bilock", not(feature = "unstable")))]
+compile_error!("The `bilock` feature requires the `unstable` feature as an explicit opt-in to unstable features");
+
 #[doc(hidden)] pub use futures_core::core_reexport;
 
 #[doc(hidden)] pub use futures_core::future::Future;
@@ -307,13 +310,21 @@ pub mod io {
     };
 }
 
-#[cfg(feature = "std")]
+#[cfg_attr(
+    feature = "cfg-target-has-atomic",
+    cfg(all(target_has_atomic = "cas", target_has_atomic = "ptr"))
+)]
+#[cfg(feature = "alloc")]
 pub mod lock {
     //! Futures-powered synchronization primitives.
     //!
-    //! This module is only available when the `std` feature of this
+    //! This module is only available when the `std` or `alloc` feature of this
     //! library is activated, and it is activated by default.
 
+    #[cfg(feature = "bilock")]
+    pub use futures_util::lock::{BiLock, BiLockAcquire, BiLockGuard, ReuniteError};
+
+    #[cfg(feature = "std")]
     pub use futures_util::lock::{Mutex, MutexLockFuture, MutexGuard};
 }