Prohibit cycles behind references while static initialization #149973
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ShoyuVanilla
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Dec 14, 2025
| if !tcx.is_foreign_item(static_def_id) { | ||
| // Fire the query to detect cycles. We cannot restrict this to only when | ||
| // evaluating statics, since static reference cycles can also be formed | ||
| // through consts, especially promoted ones. |
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Not skiping firing the query when machine.static_root_ids.is_none() here further prohibits some currently compiled codes such as
static FOO: i32 = {
let x = &BAR;
42
};
const BAR: i32 = {
let x = &FOO;
42
};but I guess we might have to refute const cases as well because the following codes slightly modified from the original issue still make problems with it:
enum Never {}
// &&X creates a promoted const
static X: &Never = weird(&&X);
const fn weird(a: &&&Never) -> &'static Never {
// SAFETY: our argument type has an unsatisfiable
// library invariant; therefore, this code is unreachable.
unsafe { std::hint::unreachable_unchecked() };
}// for privacy
mod mrow {
pub struct InBoundsIndex<const N: usize>(());
impl<const N: usize> InBoundsIndex<N> {
pub const fn new() -> Option<InBoundsIndex<N>> {
if N < 32 {
Some(Self(()))
} else {
None
}
}
}
}
use mrow::InBoundsIndex;
static IDX: InBoundsIndex<64> = {
FOO;
// THIS SHOULD PANIC!!! but we do UB first on the line above
InBoundsIndex::<64>::new().unwrap()
};
const FOO: () = {
let _x = index([0; 32], &IDX);
};
const fn index<const N: usize>(arr: [u8; 32], _: &InBoundsIndex<N>) -> u8 {
// SAFETY: InBoundsIndex can only be created by its new, which ensures N is < 32
unsafe { arr.as_ptr().add(N).read() }
}
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Oh, this already breaks things as hell like in: static POSTFIX: [(Input, Action); 10] = [
(Keyword("as"), SetState(&[(ExpectType, SetState(&POSTFIX))])),
... |
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Dec 14, 2025
Prohibit cycles behind references while static initialization
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Fixes #143047