Change has_atomic_cas to no_atomic_cas to implement the first workaround

futures-channel/build.rs

@@ -16,8 +16,12 @@ fn main() {
         }
     };
 
-    if cfg.probe_expression("core::sync::atomic::AtomicPtr::<()>::compare_exchange") {
-        println!("cargo:rustc-cfg=has_atomic_cas");
+    // Note that this is `no_atomic_cas`, not `has_atomic_cas`. This allows to
+    // treat `cfg(target_has_atomic = "ptr")` as true when the build script
+    // doesn't run. This is needed for compatibility with non-cargo build
+    // systems that don't run build scripts.
+    if !cfg.probe_expression("core::sync::atomic::AtomicPtr::<()>::compare_exchange") {
+        println!("cargo:rustc-cfg=no_atomic_cas");
     }
     println!("cargo:rerun-if-changed=build.rs");
 }

futures-channel/src/lib.rs

@@ -22,7 +22,7 @@
 
 macro_rules! cfg_target_has_atomic {
     ($($item:item)*) => {$(
-        #[cfg(has_atomic_cas)]
+        #[cfg(not(no_atomic_cas))]
         $item
     )*};
 }

futures-core/build.rs

@@ -16,8 +16,12 @@ fn main() {
         }
     };
 
-    if cfg.probe_expression("core::sync::atomic::AtomicPtr::<()>::compare_exchange") {
-        println!("cargo:rustc-cfg=has_atomic_cas");
+    // Note that this is `no_atomic_cas`, not `has_atomic_cas`. This allows to
+    // treat `cfg(target_has_atomic = "ptr")` as true when the build script
+    // doesn't run. This is needed for compatibility with non-cargo build
+    // systems that don't run build scripts.
+    if !cfg.probe_expression("core::sync::atomic::AtomicPtr::<()>::compare_exchange") {
+        println!("cargo:rustc-cfg=no_atomic_cas");
     }
     println!("cargo:rerun-if-changed=build.rs");
 }

futures-core/src/task/__internal/mod.rs

@@ -1,4 +1,4 @@
-#[cfg(has_atomic_cas)]
+#[cfg(not(no_atomic_cas))]
 mod atomic_waker;
-#[cfg(has_atomic_cas)]
+#[cfg(not(no_atomic_cas))]
 pub use self::atomic_waker::AtomicWaker;

futures-task/build.rs

@@ -16,8 +16,12 @@ fn main() {
         }
     };
 
-    if cfg.probe_expression("core::sync::atomic::AtomicPtr::<()>::compare_exchange") {
-        println!("cargo:rustc-cfg=has_atomic_cas");
+    // Note that this is `no_atomic_cas`, not `has_atomic_cas`. This allows to
+    // treat `cfg(target_has_atomic = "ptr")` as true when the build script
+    // doesn't run. This is needed for compatibility with non-cargo build
+    // systems that don't run build scripts.
+    if !cfg.probe_expression("core::sync::atomic::AtomicPtr::<()>::compare_exchange") {
+        println!("cargo:rustc-cfg=no_atomic_cas");
     }
     println!("cargo:rerun-if-changed=build.rs");
 }

futures-task/src/lib.rs

@@ -19,7 +19,7 @@ extern crate alloc;
 
 macro_rules! cfg_target_has_atomic {
     ($($item:item)*) => {$(
-        #[cfg(has_atomic_cas)]
+        #[cfg(not(no_atomic_cas))]
         $item
     )*};
 }

futures-util/build.rs

@@ -16,8 +16,12 @@ fn main() {
         }
     };
 
-    if cfg.probe_expression("core::sync::atomic::AtomicPtr::<()>::compare_exchange") {
-        println!("cargo:rustc-cfg=has_atomic_cas");
+    // Note that this is `no_atomic_cas`, not `has_atomic_cas`. This allows to
+    // treat `cfg(target_has_atomic = "ptr")` as true when the build script
+    // doesn't run. This is needed for compatibility with non-cargo build
+    // systems that don't run build scripts.
+    if !cfg.probe_expression("core::sync::atomic::AtomicPtr::<()>::compare_exchange") {
+        println!("cargo:rustc-cfg=no_atomic_cas");
     }
     println!("cargo:rerun-if-changed=build.rs");
 }

futures-util/src/lib.rs

@@ -57,7 +57,7 @@ pub mod __private {
 
 macro_rules! cfg_target_has_atomic {
     ($($item:item)*) => {$(
-        #[cfg(has_atomic_cas)]
+        #[cfg(not(no_atomic_cas))]
         $item
     )*};
 }

futures-util/src/stream/mod.rs

@@ -31,11 +31,11 @@ pub use self::stream::ReadyChunks;
 #[cfg_attr(docsrs, doc(cfg(feature = "sink")))]
 pub use self::stream::Forward;
 
-#[cfg(has_atomic_cas)]
+#[cfg(not(no_atomic_cas))]
 #[cfg(feature = "alloc")]
 pub use self::stream::{BufferUnordered, Buffered, ForEachConcurrent};
 
-#[cfg(has_atomic_cas)]
+#[cfg(not(no_atomic_cas))]
 #[cfg(feature = "sink")]
 #[cfg_attr(docsrs, doc(cfg(feature = "sink")))]
 #[cfg(feature = "alloc")]
@@ -53,7 +53,7 @@ pub use self::try_stream::{
 #[cfg(feature = "std")]
 pub use self::try_stream::IntoAsyncRead;
 
-#[cfg(has_atomic_cas)]
+#[cfg(not(no_atomic_cas))]
 #[cfg(feature = "alloc")]
 pub use self::try_stream::{TryBufferUnordered, TryBuffered, TryForEachConcurrent};
 

futures-util/src/stream/stream/mod.rs

@@ -917,7 +917,7 @@ pub trait StreamExt: Stream {
     /// fut.await;
     /// # })
     /// ```
-    #[cfg(has_atomic_cas)]
+    #[cfg(not(no_atomic_cas))]
     #[cfg(feature = "alloc")]
     fn for_each_concurrent<Fut, F>(
         self,
@@ -1140,7 +1140,7 @@ pub trait StreamExt: Stream {
     ///
     /// This method is only available when the `std` or `alloc` feature of this
     /// library is activated, and it is activated by default.
-    #[cfg(has_atomic_cas)]
+    #[cfg(not(no_atomic_cas))]
     #[cfg(feature = "alloc")]
     fn buffered(self, n: usize) -> Buffered<Self>
     where
@@ -1185,7 +1185,7 @@ pub trait StreamExt: Stream {
     /// assert_eq!(buffered.next().await, None);
     /// # Ok::<(), i32>(()) }).unwrap();
     /// ```
-    #[cfg(has_atomic_cas)]
+    #[cfg(not(no_atomic_cas))]
     #[cfg(feature = "alloc")]
     fn buffer_unordered(self, n: usize) -> BufferUnordered<Self>
     where
@@ -1349,7 +1349,7 @@ pub trait StreamExt: Stream {
     /// library is activated, and it is activated by default.
     #[cfg(feature = "sink")]
     #[cfg_attr(docsrs, doc(cfg(feature = "sink")))]
-    #[cfg(has_atomic_cas)]
+    #[cfg(not(no_atomic_cas))]
     #[cfg(feature = "alloc")]
     fn split<Item>(self) -> (SplitSink<Self, Item>, SplitStream<Self>)
     where

futures-util/src/stream/try_stream/mod.rs

@@ -515,7 +515,7 @@ pub trait TryStreamExt: TryStream {
     /// assert_eq!(Err(oneshot::Canceled), fut.await);
     /// # })
     /// ```
-    #[cfg(has_atomic_cas)]
+    #[cfg(not(no_atomic_cas))]
     #[cfg(feature = "alloc")]
     fn try_for_each_concurrent<Fut, F>(
         self,
@@ -836,7 +836,7 @@ pub trait TryStreamExt: TryStream {
     /// assert_eq!(buffered.next().await, Some(Err("error in the stream")));
     /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
     /// ```
-    #[cfg(has_atomic_cas)]
+    #[cfg(not(no_atomic_cas))]
     #[cfg(feature = "alloc")]
     fn try_buffer_unordered(self, n: usize) -> TryBufferUnordered<Self>
     where
@@ -912,7 +912,7 @@ pub trait TryStreamExt: TryStream {
     /// assert_eq!(buffered.next().await, Some(Err("error in the stream")));
     /// # Ok::<(), Box<dyn std::error::Error>>(()) }).unwrap();
     /// ```
-    #[cfg(has_atomic_cas)]
+    #[cfg(not(no_atomic_cas))]
     #[cfg(feature = "alloc")]
     fn try_buffered(self, n: usize) -> TryBuffered<Self>
     where

futures/build.rs

@@ -16,8 +16,12 @@ fn main() {
         }
     };
 
-    if cfg.probe_expression("core::sync::atomic::AtomicPtr::<()>::compare_exchange") {
-        println!("cargo:rustc-cfg=has_atomic_cas");
+    // Note that this is `no_atomic_cas`, not `has_atomic_cas`. This allows to
+    // treat `cfg(target_has_atomic = "ptr")` as true when the build script
+    // doesn't run. This is needed for compatibility with non-cargo build
+    // systems that don't run build scripts.
+    if !cfg.probe_expression("core::sync::atomic::AtomicPtr::<()>::compare_exchange") {
+        println!("cargo:rustc-cfg=no_atomic_cas");
     }
     println!("cargo:rerun-if-changed=build.rs");
 }

futures/src/lib.rs

@@ -125,7 +125,7 @@ pub use futures_util::{pending, poll, join, try_join, select_biased}; // Async-a
 #[cfg(feature = "async-await")]
 pub use futures_util::select;
 
-#[cfg(has_atomic_cas)]
+#[cfg(not(no_atomic_cas))]
 #[cfg(feature = "alloc")]
 pub mod channel {
     //! Cross-task communication.
@@ -286,7 +286,7 @@ pub mod future {
         select_ok, SelectOk,
     };
 
-    #[cfg(has_atomic_cas)]
+    #[cfg(not(no_atomic_cas))]
     #[cfg(feature = "alloc")]
     pub use futures_util::future::{
         abortable, Abortable, AbortHandle, AbortRegistration, Aborted,
@@ -347,7 +347,7 @@ pub mod io {
     pub use futures_util::io::WriteAllVectored;
 }
 
-#[cfg(has_atomic_cas)]
+#[cfg(not(no_atomic_cas))]
 #[cfg(feature = "alloc")]
 pub mod lock {
     //! Futures-powered synchronization primitives.
@@ -473,7 +473,7 @@ pub mod stream {
         Chunks, ReadyChunks,
     };
 
-    #[cfg(has_atomic_cas)]
+    #[cfg(not(no_atomic_cas))]
     #[cfg(feature = "alloc")]
     pub use futures_util::stream::{
         FuturesOrdered,
@@ -492,7 +492,7 @@ pub mod stream {
         CatchUnwind,
     };
 
-    #[cfg(has_atomic_cas)]
+    #[cfg(not(no_atomic_cas))]
     #[cfg(feature = "alloc")]
     pub use futures_util::stream::{
         // For TryStreamExt:
@@ -531,11 +531,11 @@ pub mod task {
     #[cfg(feature = "alloc")]
     pub use futures_util::task::{SpawnExt, LocalSpawnExt};
 
-    #[cfg(has_atomic_cas)]
+    #[cfg(not(no_atomic_cas))]
     #[cfg(feature = "alloc")]
     pub use futures_util::task::{waker, waker_ref, WakerRef, ArcWake};
 
-    #[cfg(has_atomic_cas)]
+    #[cfg(not(no_atomic_cas))]
     pub use futures_util::task::AtomicWaker;
 }