Affected versions of this crate called some methods using auto-ref. The affected code looked like this.
let mut arr = $crate::__core::mem::MaybeUninit::uninit();
let mut vec = $crate::__ArrayVec::<T>::new(arr.as_mut_ptr() as *mut T);
In this case, the problem is that as_mut_ptr is a method of &mut MaybeUninit, not MaybeUninit. This made it possible for traits to hijack the method calls in order to cause unsoundness.
trait AsMutPtr<T> {
fn as_mut_ptr(&self) -> *mut T;
}
impl<T> AsMutPtr<T> for std::mem::MaybeUninit<T> {
fn as_mut_ptr(&self) -> *mut T {
std::ptr::null_mut()
}
}
array![0; 1];
The flaw was corrected by explicitly referencing variables in macro body in order to avoid auto-ref.