I can't bring myself not to think of it as a "false positive". compile_assert is asking the question "Is it known at compile time that this condition is true?"

There are cases where the answer is yes, but the compiler can't prove it, so it explodes and gives you a false positive diagnostic.

One could say that this feature has no false positives and false negatives when phrasing what compile_assert does in terms of compiler mechanics, but that doesn't seem helpful. When the compiler gives you an error when it theoretically shouldn't, and it only does so due to insufficient cleverness, that's a false positive to me. We treat compiler warnings as a false positive when that happens.