Vendor dependencies for 0.3.0 release

vendor/bevy_tasks/src/futures.rs

@@ -0,0 +1,56 @@
+#![expect(unsafe_code, reason = "Futures require unsafe code.")]
+
+//! Utilities for working with [`Future`]s.
+use core::{
+    future::Future,
+    pin::Pin,
+    task::{Context, Poll, RawWaker, RawWakerVTable, Waker},
+};
+
+/// Consumes a future, polls it once, and immediately returns the output
+/// or returns `None` if it wasn't ready yet.
+///
+/// This will cancel the future if it's not ready.
+pub fn now_or_never<F: Future>(mut future: F) -> Option<F::Output> {
+    let noop_waker = noop_waker();
+    let mut cx = Context::from_waker(&noop_waker);
+
+    // SAFETY: `future` is not moved and the original value is shadowed
+    let future = unsafe { Pin::new_unchecked(&mut future) };
+
+    match future.poll(&mut cx) {
+        Poll::Ready(x) => Some(x),
+        _ => None,
+    }
+}
+
+/// Polls a future once, and returns the output if ready
+/// or returns `None` if it wasn't ready yet.
+pub fn check_ready<F: Future + Unpin>(future: &mut F) -> Option<F::Output> {
+    let noop_waker = noop_waker();
+    let mut cx = Context::from_waker(&noop_waker);
+
+    let future = Pin::new(future);
+
+    match future.poll(&mut cx) {
+        Poll::Ready(x) => Some(x),
+        _ => None,
+    }
+}
+
+fn noop_clone(_data: *const ()) -> RawWaker {
+    noop_raw_waker()
+}
+fn noop(_data: *const ()) {}
+
+const NOOP_WAKER_VTABLE: RawWakerVTable = RawWakerVTable::new(noop_clone, noop, noop, noop);
+
+fn noop_raw_waker() -> RawWaker {
+    RawWaker::new(core::ptr::null(), &NOOP_WAKER_VTABLE)
+}
+
+fn noop_waker() -> Waker {
+    // SAFETY: the `RawWakerVTable` is just a big noop and doesn't violate any of the rules in `RawWakerVTable`s documentation
+    // (which talks about retaining and releasing any "resources", of which there are none in this case)
+    unsafe { Waker::from_raw(noop_raw_waker()) }
+}