Unsure whats going on but this didn't make the enum exhaustive. I wonder if the compiler recognized that this variant cannot be constructed so therefore it doesn't need to be matched?

Uff, maybe this comes from some of the newer uninhabited type matching ...

Since private::Never is private, we can make the type inhabited but not constructible. Would changing this be a breaking change?

Currently, people can exhaustively match on Number. Making it actually non-exhaustive would then be a breaking change.

We’ll definitely need a compile-fail test then to ensure there are no more slip ups - I’m sorry that the first fix didn’t catch this.