There is absolutely no special treatment afforded to the GSL by any of the target platforms. While we can't inspect MSVC's source code, both clang and GCC do not have any support or affordance for the GSL whatsoever and it would be very unusual to expect MSVC's source code to have some kind of affordance for this library.
The 'special treatment' isn't technical, it's procedural -- insofar as if, 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. Since they're built as part of the same operating system, they can make sure not to step on one another's toes -- which is not a guarantee that they can make to third-party applications.
I have no idea where you possibly got this idea from since the Github Issues tracker for GSL has numerous instances of new releases of MSVC breaking GSL compilation.
I 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."
> 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."
Here is the original statement about special treatment:
"It was originally created by Microsoft and as Herb mentions "all our target platforms", so most likely it gets special treatment."
My claim is that Microsoft is not giving any special treatment to the GSL... the GSL is written using functionality that is officially available to any third party library, and hence not special.
Are you disputing this? If so then what is the special treatment you're claiming that Microsoft is giving to GSL or what special treatment is GSL making use of?
I am not claiming there is any special treatment at all. I think the situation is much simpler:
They (Microsoft) test GSL with specific compiler versions to observe how their usage of the UB is treated, and if satisfactory, that compiler version is now "supported" in their eyes. They do not claim to "support" any other version because they have not tested them to know how the UB functions there.
What is the relationship between your claim, and the claim I replied to about GSL having special treatment? In other words, why did you reply to me with an interpretation about a post that claimed GSL is afforded special treatment by MSVC if your claim is that GSL does not get any special treatment from MSVC?
I'm not sure exactly where the disagreement really is. Perhaps when OP said "ensure that the changes were reverted or fixed to support" you were thinking they meant MSVC reverting changes, while I was thinking of GSL doing it instead, in order to "support" specific compiler versions they have on hand at the time to test.
Either way I think we are on the same page in thinking that compilers don't know/care that GSL exists and aren't doing anything special for it, and that's good enough for me.
