mirror of https://github.com/rust-lang/rust
47 lines
1.7 KiB
Rust
47 lines
1.7 KiB
Rust
#![feature(const_refs_to_cell)]
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use std::cell::*;
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// not ok, because this creates a dangling pointer, just like `let x = Cell::new(42).as_ptr()` would
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static FOO: Wrap<*mut u32> = Wrap(Cell::new(42).as_ptr());
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//~^ ERROR encountered dangling pointer
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const FOO_CONST: Wrap<*mut u32> = Wrap(Cell::new(42).as_ptr());
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//~^ ERROR encountered dangling pointer
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// Ok, these are just base values and it is the `Wrap` author's job to uphold `Send` and `Sync`
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// invariants, since they used `unsafe impl`.
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static FOO3: Wrap<Cell<u32>> = Wrap(Cell::new(42));
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const FOO3_CONST: Wrap<Cell<u32>> = Wrap(Cell::new(42));
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// ok, we are referring to the memory of another static item.
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static FOO4: Wrap<*mut u32> = Wrap(FOO3.0.as_ptr());
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// not ok, the use of a constant here is equivalent to an inline declaration of the value, so
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// its memory will get freed before the constant is finished evaluating, thus creating a dangling
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// pointer. This would happen exactly the same at runtime.
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const FOO4_CONST: Wrap<*mut u32> = Wrap(FOO3_CONST.0.as_ptr());
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//~^ ERROR encountered dangling pointer
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// not ok, because the `as_ptr` call takes a reference to a temporary that will get freed
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// before the constant is finished evaluating.
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const FOO2: *mut u32 = Cell::new(42).as_ptr();
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//~^ ERROR encountered dangling pointer
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struct IMSafeTrustMe(UnsafeCell<u32>);
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unsafe impl Send for IMSafeTrustMe {}
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unsafe impl Sync for IMSafeTrustMe {}
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static BAR: IMSafeTrustMe = IMSafeTrustMe(UnsafeCell::new(5));
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struct Wrap<T>(T);
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unsafe impl<T> Send for Wrap<T> {}
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unsafe impl<T> Sync for Wrap<T> {}
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static BAR_PTR: Wrap<*mut u32> = Wrap(BAR.0.get());
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const fn fst_ref<T, U>(x: &(T, U)) -> &T { &x.0 }
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fn main() {}
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