rust/tests/compile-fail/stacked_borrows/illegal_read3.rs

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2018-11-07 10:33:41 -06:00
#![feature(untagged_unions)]
// A callee may not read the destination of our `&mut` without
// us noticing.
// Thise code got carefully checked to not introduce any reborrows
// that are not explicit in the source. Let's hope the compiler does not break this later!
use std::mem;
fn main() {
let mut x: i32 = 15;
let xref1 = &mut x;
let xref1_sneaky: usize = unsafe { mem::transmute_copy(&xref1) };
let xref2 = &mut *xref1; // derived from xref1, so using raw is still okay...
callee(xref1_sneaky);
let _val = *xref2; // ...but any use of it will invalidate our ref.
//~^ ERROR: does not exist on the borrow stack
2018-11-07 10:33:41 -06:00
}
fn callee(xref1: usize) {
// Transmuting through a union to avoid retagging
union UsizeToRef {
from: usize,
to: &'static mut i32,
}
let xref1 = UsizeToRef { from: xref1 };
// Doing the deref and the transmute (through the union) in the same place expression
// should avoid retagging.
let _val = unsafe { *xref1.to };
}