WS-2022-0463

Date: August 19, 2025

cell-project used incorrect variance when projecting through &Cell<T>. The issue lies in the implementation of the cell_project macro which used field as *const _ instead of field as *mut _. The problem being that *const T is covariant in T while *mut T is invariant in T. Keep in mind that &Cell<T> is invariant in T, so casting to *const T relaxed the variance, and lead to unsoundness, as shown in the example below. fixed in 0.1.4.

Language: RUST