Use Arc::as_ptr

This fixes stacked borrows violations with -Zmiri-tag-raw-pointers.

Author: taiki-e

.github/workflows/ci.yml

@@ -244,9 +244,9 @@ jobs:
       - name: Install Rust
         run: rustup toolchain install nightly --component miri && rustup default nightly
       # futures-executor uses boxed futures so many tests trigger https://github.com/rust-lang/miri/issues/1038
-      - run: cargo miri test --workspace --exclude futures-executor --all-features
+      - run: cargo miri test --workspace --exclude futures-executor --all-features --no-fail-fast
         env:
-          MIRIFLAGS: -Zmiri-disable-isolation # TODO: use -Zmiri-tag-raw-pointers
+          MIRIFLAGS: -Zmiri-disable-isolation -Zmiri-tag-raw-pointers
 
   san:
     name: cargo test -Z sanitizer=${{ matrix.sanitizer }}

futures-task/src/waker_ref.rs

@@ -55,7 +55,7 @@ where
 {
     // simply copy the pointer instead of using Arc::into_raw,
     // as we don't actually keep a refcount by using ManuallyDrop.<
-    let ptr = (&**wake as *const W) as *const ();
+    let ptr = Arc::as_ptr(wake).cast::<()>();
 
     let waker =
         ManuallyDrop::new(unsafe { Waker::from_raw(RawWaker::new(ptr, waker_vtable::<W>())) });

futures-util/src/stream/futures_unordered/mod.rs

@@ -150,7 +150,7 @@ impl<Fut> FuturesUnordered<Fut> {
             queued: AtomicBool::new(true),
             ready_to_run_queue: Weak::new(),
         });
-        let stub_ptr = &*stub as *const Task<Fut>;
+        let stub_ptr = Arc::as_ptr(&stub);
         let ready_to_run_queue = Arc::new(ReadyToRunQueue {
             waker: AtomicWaker::new(),
             head: AtomicPtr::new(stub_ptr as *mut _),
@@ -403,7 +403,7 @@ impl<Fut> FuturesUnordered<Fut> {
         // The `ReadyToRunQueue` stub is never inserted into the `head_all`
         // list, and its pointer value will remain valid for the lifetime of
         // this `FuturesUnordered`, so we can make use of its value here.
-        &*self.ready_to_run_queue.stub as *const _ as *mut _
+        Arc::as_ptr(&self.ready_to_run_queue.stub) as *mut _
     }
 }
 

futures-util/src/stream/futures_unordered/ready_to_run_queue.rs

@@ -83,7 +83,7 @@ impl<Fut> ReadyToRunQueue<Fut> {
     }
 
     pub(super) fn stub(&self) -> *const Task<Fut> {
-        &*self.stub
+        Arc::as_ptr(&self.stub)
     }
 
     // Clear the queue of tasks.

futures-util/src/stream/futures_unordered/task.rs

@@ -62,7 +62,7 @@ impl<Fut> ArcWake for Task<Fut> {
         // still.
         let prev = arc_self.queued.swap(true, SeqCst);
         if !prev {
-            inner.enqueue(&**arc_self);
+            inner.enqueue(Arc::as_ptr(arc_self));
             inner.waker.wake();
         }
     }