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https://github.com/rust-lang/rust
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45 lines
1 KiB
Rust
45 lines
1 KiB
Rust
// Check that constants with interior mutability inside unions are rejected
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// during validation.
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//
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// Note that this test case relies on undefined behaviour to construct a
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// constant with interior mutability that is "invisible" to the static checks.
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// If for some reason this approach no longer works, it is should be fine to
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// remove the test case.
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//
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// build-fail
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// stderr-per-bitwidth
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#![feature(const_mut_refs)]
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use std::cell::Cell;
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use std::mem::ManuallyDrop;
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#[repr(C)]
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struct S {
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x: u32,
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y: E,
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}
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#[repr(u32)]
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enum E {
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A,
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B(U)
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}
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union U {
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cell: ManuallyDrop<Cell<u32>>,
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}
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const C: S = {
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let s = S { x: 0, y: E::A };
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// Go through an &u32 reference which is definitely not allowed to mutate anything.
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let p = &s.x as *const u32 as *mut u32;
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// Change enum tag to E::B.
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unsafe { *p.add(1) = 1 };
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s
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};
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fn main() { //~ ERROR it is undefined behavior to use this value
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// FIXME the span here is wrong, sould be pointing at the line below, not above.
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let _: &'static _ = &C;
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}
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