alt Hacker NewsHow does a library writer testing that their library works with a specific version of a compiler that was already released have anything to do with a compiler implementation providing special treatment for that library?
Your interpretation contradicts the statement that "during development for a new release, MSVC were to land some changes that broke GSL, Microsoft's testing would catch that and ensure that the changes were reverted or fixed to support the latter, prior to shipping."
> How does a library writer testing that their library works with a specific version of a compiler that was already released have anything to do with a compiler implementation providing special treatment for that library?
Not special treatment for the library, but the library being able to assume that specific UB handling in certain existing compiler versions exists, can be relied on, and is compatible with the library's assumptions of such behavior, as long as those are the only versions they officially "support."