34 lines
1.0 KiB
Rust
34 lines
1.0 KiB
Rust
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// Demonstrate that "rogue" `DerefMut` impls for `&T` are not allowed.
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//
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// https://github.com/rust-lang/rust/issues/66544
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use std::cell::Cell;
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use std::marker::PhantomPinned;
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use std::ops::DerefMut;
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use std::pin::Pin;
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struct MyType<'a>(Cell<Option<&'a mut MyType<'a>>>, PhantomPinned);
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impl<'a> DerefMut for &'a MyType<'a> { //~ ERROR conflicting implementations
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fn deref_mut(&mut self) -> &mut MyType<'a> {
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self.0.replace(None).unwrap()
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}
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}
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fn main() {
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let mut unpinned = MyType(Cell::new(None), PhantomPinned);
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let bad_addr = &unpinned as *const MyType<'_> as usize;
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let p = Box::pin(MyType(Cell::new(Some(&mut unpinned)), PhantomPinned));
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// p_ref is okay: it does not point to the bad_addr
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let mut p_ref: Pin<&MyType<'_>> = p.as_ref();
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assert_ne!(bad_addr, &*p_ref as *const _ as usize);
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// but p_mut does point to bad_addr! this is unsound
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let p_mut: Pin<&mut MyType<'_>> = p_ref.as_mut();
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assert_eq!(bad_addr, &*p_mut as *const _ as usize);
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println!("oh no!");
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}
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