29 lines
987 B
Rust
29 lines
987 B
Rust
// A callee may not read the destination of our `&mut` without us noticing.
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// Thise code got carefully checked to not introduce any reborrows
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// that are not explicit in the source. Let's hope the compiler does not break this later!
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use std::mem;
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union HiddenRef {
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// We avoid retagging at this type, and we only read, so shared vs mutable does not matter.
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r: &'static i32,
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}
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fn main() {
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let mut x: i32 = 15;
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let xref1 = &mut x;
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let xref1_sneaky: HiddenRef = unsafe { mem::transmute_copy(&xref1) };
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// Derived from `xref1`, so using raw value is still ok, ...
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let xref2 = &mut *xref1;
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callee(xref1_sneaky);
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// ... though any use of it will invalidate our ref.
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let _val = *xref2;
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//~^ ERROR: /read access .* tag does not exist in the borrow stack/
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}
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fn callee(xref1: HiddenRef) {
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// Doing the deref and the transmute (through the union) in the same place expression
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// should avoid retagging.
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let _val = unsafe { *xref1.r };
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}
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