zephyr: sync: Conditionalize PinWeak on alloc

This only makes sense when alloc is enabled.  Move the type into a
module, and use it, all conditional on having alloc defined.

Signed-off-by: David Brown <david.brown@linaro.org>

Author: d3zd3z

zephyr/src/sync.rs

@@ -25,41 +25,47 @@ pub mod atomic {
     pub use portable_atomic::*;
 }
 
-use core::pin::Pin;
-
 #[cfg(CONFIG_RUST_ALLOC)]
 pub use portable_atomic_util::Arc;
 #[cfg(CONFIG_RUST_ALLOC)]
 pub use portable_atomic_util::Weak;
 
-/// Safe Pinned Weak references.
-///
-/// Pin<Arc<T>> can't be converted to/from Weak safely, because there is know way to know if a given
-/// weak reference came from a pinned Arc.  This wraps the weak reference in a new type so we know
-/// that it came from a pinned Arc.
-///
-/// There is a pin-weak crate that provides this for `std::sync::Arc`, but not for the one in the
-/// portable-atomic-utils crate.
-pub struct PinWeak<T>(Weak<T>);
+#[cfg(CONFIG_RUST_ALLOC)]
+mod pinweak {
+    use core::pin::Pin;
 
-impl<T> PinWeak<T> {
-    /// Downgrade an `Pin<Arc<T>>` into a `PinWeak`.
+    /// Safe Pinned Weak references.
     ///
-    /// This would be easier to use if it could be added to Arc.
-    pub fn downgrade(this: Pin<Arc<T>>) -> Self {
-        // SAFETY: we will never return anything other than a Pin<Arc<T>>.
-        Self(Arc::downgrade(&unsafe { Pin::into_inner_unchecked(this) }))
-    }
+    /// Pin<Arc<T>> can't be converted to/from Weak safely, because there is know way to know if a given
+    /// weak reference came from a pinned Arc.  This wraps the weak reference in a new type so we know
+    /// that it came from a pinned Arc.
+    ///
+    /// There is a pin-weak crate that provides this for `std::sync::Arc`, but not for the one in the
+    /// portable-atomic-utils crate.
+    pub struct PinWeak<T>(Weak<T>);
 
-    /// Upgrade back to a `Pin<Arc<T>>`.
-    pub fn upgrade(&self) -> Option<Pin<Arc<T>>> {
-        // SAFETY: The weak was only constructed from a `Pin<Arc<T>>`.
-        self.0
-            .upgrade()
-            .map(|arc| unsafe { Pin::new_unchecked(arc) })
+    impl<T> PinWeak<T> {
+        /// Downgrade an `Pin<Arc<T>>` into a `PinWeak`.
+        ///
+        /// This would be easier to use if it could be added to Arc.
+        pub fn downgrade(this: Pin<Arc<T>>) -> Self {
+            // SAFETY: we will never return anything other than a Pin<Arc<T>>.
+            Self(Arc::downgrade(&unsafe { Pin::into_inner_unchecked(this) }))
+        }
+
+        /// Upgrade back to a `Pin<Arc<T>>`.
+        pub fn upgrade(&self) -> Option<Pin<Arc<T>>> {
+            // SAFETY: The weak was only constructed from a `Pin<Arc<T>>`.
+            self.0
+                .upgrade()
+                .map(|arc| unsafe { Pin::new_unchecked(arc) })
+        }
     }
 }
 
+#[cfg(CONFIG_RUST_ALLOC)]
+pub use pinweak::*;
+
 mod mutex;
 
 pub use mutex::{Condvar, LockResult, Mutex, MutexGuard, TryLockError, TryLockResult};