> In fact, C is even safer, because it actually does have a specification that lists all the invariants that the programmer has to uphold themselves because the compiler doesn't check them.

The difference is that the C spec intentionally frees the compiler from upholding those invariants. In this case the Rust compiler is failing to catch something it is required to catch.

A more accurate analogy would be a C compiler incorrectly failing to reject an assignment through a pointer to const without a cast. The spec requires that such a thing be rejected, so it's a compiler bug.