Add simple async drop glue generation

Explainer: https://zetanumbers.github.io/book/async-drop-design.html

rust-lang/rust#121801

Author: zetanumbers

tests/pass/async-drop.rs

@@ -0,0 +1,191 @@
+//@revisions: stack tree
+//@compile-flags: -Zmiri-strict-provenance
+//@[tree]compile-flags: -Zmiri-tree-borrows
+#![feature(async_drop, impl_trait_in_assoc_type, noop_waker, async_closure)]
+#![allow(incomplete_features, dead_code)]
+
+// FIXME(zetanumbers): consider AsyncDestruct::async_drop cleanup tests
+use core::future::{async_drop_in_place, AsyncDrop, Future};
+use core::hint::black_box;
+use core::mem::{self, ManuallyDrop};
+use core::pin::{pin, Pin};
+use core::task::{Context, Poll, Waker};
+
+async fn test_async_drop<T>(x: T) {
+    let mut x = mem::MaybeUninit::new(x);
+    let dtor = pin!(unsafe { async_drop_in_place(x.as_mut_ptr()) });
+    test_idempotency(dtor).await;
+}
+
+fn test_idempotency<T>(mut x: Pin<&mut T>) -> impl Future<Output = ()> + '_
+where
+    T: Future<Output = ()>,
+{
+    core::future::poll_fn(move |cx| {
+        assert_eq!(x.as_mut().poll(cx), Poll::Ready(()));
+        assert_eq!(x.as_mut().poll(cx), Poll::Ready(()));
+        Poll::Ready(())
+    })
+}
+
+fn main() {
+    let waker = Waker::noop();
+    let mut cx = Context::from_waker(&waker);
+
+    let i = 13;
+    let fut = pin!(async {
+        test_async_drop(Int(0)).await;
+        test_async_drop(AsyncInt(0)).await;
+        test_async_drop([AsyncInt(1), AsyncInt(2)]).await;
+        test_async_drop((AsyncInt(3), AsyncInt(4))).await;
+        test_async_drop(5).await;
+        let j = 42;
+        test_async_drop(&i).await;
+        test_async_drop(&j).await;
+        test_async_drop(AsyncStruct { b: AsyncInt(8), a: AsyncInt(7), i: 6 }).await;
+        test_async_drop(ManuallyDrop::new(AsyncInt(9))).await;
+
+        let foo = AsyncInt(10);
+        test_async_drop(AsyncReference { foo: &foo }).await;
+
+        let foo = AsyncInt(11);
+        test_async_drop(|| {
+            black_box(foo);
+            let foo = AsyncInt(10);
+            foo
+        })
+        .await;
+
+        test_async_drop(AsyncEnum::A(AsyncInt(12))).await;
+        test_async_drop(AsyncEnum::B(SyncInt(13))).await;
+
+        test_async_drop(SyncInt(14)).await;
+        test_async_drop(SyncThenAsync { i: 15, a: AsyncInt(16), b: SyncInt(17), c: AsyncInt(18) })
+            .await;
+
+        let async_drop_fut = pin!(core::future::async_drop(AsyncInt(19)));
+        test_idempotency(async_drop_fut).await;
+
+        let foo = AsyncInt(20);
+        test_async_drop(async || {
+            black_box(foo);
+            let foo = AsyncInt(19);
+            // Await point there, but this is async closure so it's fine
+            black_box(core::future::ready(())).await;
+            foo
+        })
+        .await;
+
+        test_async_drop(AsyncUnion { signed: 21 }).await;
+    });
+    let res = fut.poll(&mut cx);
+    assert_eq!(res, Poll::Ready(()));
+}
+
+struct AsyncInt(i32);
+
+impl AsyncDrop for AsyncInt {
+    type Dropper<'a> = impl Future<Output = ()>;
+
+    fn async_drop(self: Pin<&mut Self>) -> Self::Dropper<'_> {
+        async move {
+            println!("AsyncInt::Dropper::poll: {}", self.0);
+        }
+    }
+}
+
+struct SyncInt(i32);
+
+impl Drop for SyncInt {
+    fn drop(&mut self) {
+        println!("SyncInt::drop: {}", self.0);
+    }
+}
+
+struct SyncThenAsync {
+    i: i32,
+    a: AsyncInt,
+    b: SyncInt,
+    c: AsyncInt,
+}
+
+impl Drop for SyncThenAsync {
+    fn drop(&mut self) {
+        println!("SyncThenAsync::drop: {}", self.i);
+    }
+}
+
+struct AsyncReference<'a> {
+    foo: &'a AsyncInt,
+}
+
+impl AsyncDrop for AsyncReference<'_> {
+    type Dropper<'a> = impl Future<Output = ()> where Self: 'a;
+
+    fn async_drop(self: Pin<&mut Self>) -> Self::Dropper<'_> {
+        async move {
+            println!("AsyncReference::Dropper::poll: {}", self.foo.0);
+        }
+    }
+}
+
+struct Int(i32);
+
+struct AsyncStruct {
+    i: i32,
+    a: AsyncInt,
+    b: AsyncInt,
+}
+
+impl AsyncDrop for AsyncStruct {
+    type Dropper<'a> = impl Future<Output = ()>;
+
+    fn async_drop(self: Pin<&mut Self>) -> Self::Dropper<'_> {
+        async move {
+            println!("AsyncStruct::Dropper::poll: {}", self.i);
+        }
+    }
+}
+
+enum AsyncEnum {
+    A(AsyncInt),
+    B(SyncInt),
+}
+
+impl AsyncDrop for AsyncEnum {
+    type Dropper<'a> = impl Future<Output = ()>;
+
+    fn async_drop(mut self: Pin<&mut Self>) -> Self::Dropper<'_> {
+        async move {
+            let new_self = match &*self {
+                AsyncEnum::A(foo) => {
+                    println!("AsyncEnum(A)::Dropper::poll: {}", foo.0);
+                    AsyncEnum::B(SyncInt(foo.0))
+                }
+                AsyncEnum::B(foo) => {
+                    println!("AsyncEnum(B)::Dropper::poll: {}", foo.0);
+                    AsyncEnum::A(AsyncInt(foo.0))
+                }
+            };
+            mem::forget(mem::replace(&mut *self, new_self));
+        }
+    }
+}
+
+// FIXME(zetanumbers): Disallow types with `AsyncDrop` in unions
+union AsyncUnion {
+    signed: i32,
+    unsigned: u32,
+}
+
+impl AsyncDrop for AsyncUnion {
+    type Dropper<'a> = impl Future<Output = ()>;
+
+    fn async_drop(self: Pin<&mut Self>) -> Self::Dropper<'_> {
+        async move {
+            println!("AsyncUnion::Dropper::poll: {}, {}", unsafe { self.signed }, unsafe {
+                self.unsigned
+            });
+        }
+    }
+}

tests/pass/async-drop.stack.stdout

@@ -0,0 +1,22 @@
+AsyncInt::Dropper::poll: 0
+AsyncInt::Dropper::poll: 1
+AsyncInt::Dropper::poll: 2
+AsyncInt::Dropper::poll: 3
+AsyncInt::Dropper::poll: 4
+AsyncStruct::Dropper::poll: 6
+AsyncInt::Dropper::poll: 7
+AsyncInt::Dropper::poll: 8
+AsyncReference::Dropper::poll: 10
+AsyncInt::Dropper::poll: 11
+AsyncEnum(A)::Dropper::poll: 12
+SyncInt::drop: 12
+AsyncEnum(B)::Dropper::poll: 13
+AsyncInt::Dropper::poll: 13
+SyncInt::drop: 14
+SyncThenAsync::drop: 15
+AsyncInt::Dropper::poll: 16
+SyncInt::drop: 17
+AsyncInt::Dropper::poll: 18
+AsyncInt::Dropper::poll: 19
+AsyncInt::Dropper::poll: 20
+AsyncUnion::Dropper::poll: 21, 21

tests/pass/async-drop.tree.stdout

@@ -0,0 +1,22 @@
+AsyncInt::Dropper::poll: 0
+AsyncInt::Dropper::poll: 1
+AsyncInt::Dropper::poll: 2
+AsyncInt::Dropper::poll: 3
+AsyncInt::Dropper::poll: 4
+AsyncStruct::Dropper::poll: 6
+AsyncInt::Dropper::poll: 7
+AsyncInt::Dropper::poll: 8
+AsyncReference::Dropper::poll: 10
+AsyncInt::Dropper::poll: 11
+AsyncEnum(A)::Dropper::poll: 12
+SyncInt::drop: 12
+AsyncEnum(B)::Dropper::poll: 13
+AsyncInt::Dropper::poll: 13
+SyncInt::drop: 14
+SyncThenAsync::drop: 15
+AsyncInt::Dropper::poll: 16
+SyncInt::drop: 17
+AsyncInt::Dropper::poll: 18
+AsyncInt::Dropper::poll: 19
+AsyncInt::Dropper::poll: 20
+AsyncUnion::Dropper::poll: 21, 21