alt Hacker NewsI think they're saying that since they denote specific compiler versions as "officially supported", they can get away with saying the "UB" is not an issue in those versions only because they've already tested its behavior there, and anything else you compile with is untested and unsupported 'here be dragons' land.
You may wish they target every possible compiler brand and version, but they are free to disagree with you and only "support" specific ones.
Unfortunately this also has the same effect as the Linux kernel now in that it is no longer technically compliant with any C++ (or C) standard.
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?
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."