Vendor dependencies for 0.3.0 release

vendor/bevy_tasks/src/wasm_task.rs

@@ -0,0 +1,93 @@
+use alloc::boxed::Box;
+use core::{
+    any::Any,
+    future::{Future, IntoFuture},
+    panic::{AssertUnwindSafe, UnwindSafe},
+    pin::Pin,
+    task::{Context, Poll},
+};
+
+use futures_channel::oneshot;
+
+/// Wraps an asynchronous task, a spawned future.
+///
+/// Tasks are also futures themselves and yield the output of the spawned future.
+#[derive(Debug)]
+pub struct Task<T>(oneshot::Receiver<Result<T, Panic>>);
+
+impl<T: 'static> Task<T> {
+    pub(crate) fn wrap_future(future: impl Future<Output = T> + 'static) -> Self {
+        let (sender, receiver) = oneshot::channel();
+        wasm_bindgen_futures::spawn_local(async move {
+            // Catch any panics that occur when polling the future so they can
+            // be propagated back to the task handle.
+            let value = CatchUnwind(AssertUnwindSafe(future)).await;
+            let _ = sender.send(value);
+        });
+        Self(receiver.into_future())
+    }
+
+    /// When building for Wasm, this method has no effect.
+    /// This is only included for feature parity with other platforms.
+    pub fn detach(self) {}
+
+    /// Requests a task to be cancelled and returns a future that suspends until it completes.
+    /// Returns the output of the future if it has already completed.
+    ///
+    /// # Implementation
+    ///
+    /// When building for Wasm, it is not possible to cancel tasks, which means this is the same
+    /// as just awaiting the task. This method is only included for feature parity with other platforms.
+    pub async fn cancel(self) -> Option<T> {
+        match self.0.await {
+            Ok(Ok(value)) => Some(value),
+            Err(_) => None,
+            Ok(Err(panic)) => {
+                // drop this to prevent the panic payload from resuming the panic on drop.
+                // this also leaks the box but I'm not sure how to avoid that
+                core::mem::forget(panic);
+                None
+            }
+        }
+    }
+}
+
+impl<T> Future for Task<T> {
+    type Output = T;
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        match Pin::new(&mut self.0).poll(cx) {
+            Poll::Ready(Ok(Ok(value))) => Poll::Ready(value),
+            // NOTE: Propagating the panic here sorta has parity with the async_executor behavior.
+            // For those tasks, polling them after a panic returns a `None` which gets `unwrap`ed, so
+            // using `resume_unwind` here is essentially keeping the same behavior while adding more information.
+            #[cfg(feature = "std")]
+            Poll::Ready(Ok(Err(panic))) => std::panic::resume_unwind(panic),
+            #[cfg(not(feature = "std"))]
+            Poll::Ready(Ok(Err(_panic))) => {
+                unreachable!("catching a panic is only possible with std")
+            }
+            Poll::Ready(Err(_)) => panic!("Polled a task after it was cancelled"),
+            Poll::Pending => Poll::Pending,
+        }
+    }
+}
+
+type Panic = Box<dyn Any + Send + 'static>;
+
+#[pin_project::pin_project]
+struct CatchUnwind<F: UnwindSafe>(#[pin] F);
+
+impl<F: Future + UnwindSafe> Future for CatchUnwind<F> {
+    type Output = Result<F::Output, Panic>;
+    fn poll(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Self::Output> {
+        let f = AssertUnwindSafe(|| self.project().0.poll(cx));
+
+        #[cfg(feature = "std")]
+        let result = std::panic::catch_unwind(f)?;
+
+        #[cfg(not(feature = "std"))]
+        let result = f();
+
+        result.map(Ok)
+    }
+}