use async fn for async trait

src/lib.rs

@@ -37,16 +37,25 @@ pub trait SmartLedsWrite {
 }
 
 pub mod asynch {
-    use core::future::Future;
-
     /// An async trait that Smart Led Drivers implement
     ///
     /// The amount of time each iteration of `iterator` might take is undefined.
     /// Drivers, where this might lead to issues, aren't expected to work in all cases.
     pub trait SmartLedsWriteAsync {
         type Error;
         type Color;
-        fn write<T, I>(&mut self, iterator: T) -> impl Future<Output = Result<(), Self::Error>>
+        // The async_fn_in_trait warning doesn't really matter for embedded cases because
+        // no_std async executors don't require futures to be Send. Also, embedded-hal-async
+        // does not have Send bounds in its traits, so the HAL functions called in
+        // implementations of this trait wouldn't return Send futures anyway. It's
+        // questionable if it would be desirable for embedded HALs to return a Send future
+        // for the write function for a peripheral because you probably don't want to
+        // write data to the same peripheral from multiple threads simultaneously and have
+        // the data get interleaved, nor have the embedded HAL implement a synchronization
+        // mechanism with a run time cost to avoid that.
+        // https://github.com/rust-embedded/embedded-hal/pull/515#issuecomment-1763525962
+        #[allow(async_fn_in_trait)]
+        async fn write<T, I>(&mut self, iterator: T) -> Result<(), Self::Error>
         where
             T: IntoIterator<Item = I>,
             I: Into<Self::Color>;