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// check-pass
// known-bug: #85099
// Should fail. Can coerce `Pin<T>` into `Pin<U>` where
// `T: Deref<Target: Unpin>` and `U: Deref<Target: !Unpin>`, using the
// `CoerceUnsized` impl on `Pin` and an unorthodox `DerefMut` impl for
// `Pin<&_>`.
// This should not be allowed, since one can unpin `T::Target` (since it is
// `Unpin`) to gain unpinned access to the previously pinned `U::Target` (which
// is `!Unpin`) and then move it.
use std::{
cell::{RefCell, RefMut},
future::Future,
ops::DerefMut,
pin::Pin,
};
struct SomeLocalStruct<'a, Fut>(&'a RefCell<Fut>);
trait SomeTrait<'a, Fut> {
#[allow(clippy::mut_from_ref)]
fn deref_helper(&self) -> &mut (dyn SomeTrait<'a, Fut> + 'a) {
unimplemented!()
}
fn downcast(self: Pin<&mut Self>) -> Pin<&mut Fut> {
unimplemented!()
}
}
impl<'a, Fut: Future<Output = ()>> SomeTrait<'a, Fut> for SomeLocalStruct<'a, Fut> {
fn deref_helper(&self) -> &mut (dyn SomeTrait<'a, Fut> + 'a) {
let x = Box::new(self.0.borrow_mut());
let x: &'a mut RefMut<'a, Fut> = Box::leak(x);
&mut **x
}
}
impl<'a, Fut: Future<Output = ()>> SomeTrait<'a, Fut> for Fut {
fn downcast(self: Pin<&mut Self>) -> Pin<&mut Fut> {
self
}
}
impl<'b, 'a, Fut> DerefMut for Pin<&'b dyn SomeTrait<'a, Fut>> {
fn deref_mut<'c>(
self: &'c mut Pin<&'b dyn SomeTrait<'a, Fut>>,
) -> &'c mut (dyn SomeTrait<'a, Fut> + 'b) {
self.deref_helper()
}
}
// obviously a "working" function with this signature is problematic
pub fn unsound_pin<Fut: Future<Output = ()>>(
fut: Fut,
callback: impl FnOnce(Pin<&mut Fut>),
) -> Fut {
let cell = RefCell::new(fut);
let s: &SomeLocalStruct<'_, Fut> = &SomeLocalStruct(&cell);
let p: Pin<Pin<&SomeLocalStruct<'_, Fut>>> = Pin::new(Pin::new(s));
let mut p: Pin<Pin<&dyn SomeTrait<'_, Fut>>> = p;
let r: Pin<&mut dyn SomeTrait<'_, Fut>> = p.as_mut();
let f: Pin<&mut Fut> = r.downcast();
callback(f);
cell.into_inner()
}
fn main() {}
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