5f42c9ab6d
# Objective - Resolve several warnings encountered when compiling for `no_std` around `dead_code` - Fix compatibility with `wasm32-unknown-unknown` when using `no_std` (identified by Sachymetsu on [Discord](https://discord.com/channels/691052431525675048/692572690833473578/1323365426901549097)) ## Solution - Removed some unused imports - Added `allow(dead_code)` for certain private items when compiling on `no_std` - Fixed `bevy_app` and `bevy_tasks` compatibility with WASM when compiling without `std` by appropriately importing `Box` and feature gating panic unwinding ## Testing - CI
94 lines
3.4 KiB
Rust
94 lines
3.4 KiB
Rust
use alloc::boxed::Box;
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use core::{
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any::Any,
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future::{Future, IntoFuture},
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panic::{AssertUnwindSafe, UnwindSafe},
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pin::Pin,
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task::{Context, Poll},
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};
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use futures_channel::oneshot;
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/// Wraps an asynchronous task, a spawned future.
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///
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/// Tasks are also futures themselves and yield the output of the spawned future.
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#[derive(Debug)]
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pub struct Task<T>(oneshot::Receiver<Result<T, Panic>>);
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impl<T: 'static> Task<T> {
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pub(crate) fn wrap_future(future: impl Future<Output = T> + 'static) -> Self {
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let (sender, receiver) = oneshot::channel();
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wasm_bindgen_futures::spawn_local(async move {
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// Catch any panics that occur when polling the future so they can
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// be propagated back to the task handle.
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let value = CatchUnwind(AssertUnwindSafe(future)).await;
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let _ = sender.send(value);
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});
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Self(receiver.into_future())
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}
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/// When building for Wasm, this method has no effect.
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/// This is only included for feature parity with other platforms.
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pub fn detach(self) {}
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/// Requests a task to be cancelled and returns a future that suspends until it completes.
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/// Returns the output of the future if it has already completed.
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///
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/// # Implementation
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///
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/// When building for Wasm, it is not possible to cancel tasks, which means this is the same
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/// as just awaiting the task. This method is only included for feature parity with other platforms.
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pub async fn cancel(self) -> Option<T> {
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match self.0.await {
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Ok(Ok(value)) => Some(value),
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Err(_) => None,
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Ok(Err(panic)) => {
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// drop this to prevent the panic payload from resuming the panic on drop.
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// this also leaks the box but I'm not sure how to avoid that
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core::mem::forget(panic);
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None
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}
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}
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}
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}
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impl<T> Future for Task<T> {
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type Output = T;
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fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
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match Pin::new(&mut self.0).poll(cx) {
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Poll::Ready(Ok(Ok(value))) => Poll::Ready(value),
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// NOTE: Propagating the panic here sorta has parity with the async_executor behavior.
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// For those tasks, polling them after a panic returns a `None` which gets `unwrap`ed, so
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// using `resume_unwind` here is essentially keeping the same behavior while adding more information.
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#[cfg(feature = "std")]
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Poll::Ready(Ok(Err(panic))) => std::panic::resume_unwind(panic),
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#[cfg(not(feature = "std"))]
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Poll::Ready(Ok(Err(_panic))) => {
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unreachable!("catching a panic is only possible with std")
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}
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Poll::Ready(Err(_)) => panic!("Polled a task after it was cancelled"),
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Poll::Pending => Poll::Pending,
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}
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}
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}
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type Panic = Box<dyn Any + Send + 'static>;
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#[pin_project::pin_project]
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struct CatchUnwind<F: UnwindSafe>(#[pin] F);
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impl<F: Future + UnwindSafe> Future for CatchUnwind<F> {
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type Output = Result<F::Output, Panic>;
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fn poll(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Self::Output> {
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let f = AssertUnwindSafe(|| self.project().0.poll(cx));
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#[cfg(feature = "std")]
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let result = std::panic::catch_unwind(f)?;
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#[cfg(not(feature = "std"))]
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let result = f();
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result.map(Ok)
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}
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}
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