Re: [boost] Clang 600 and BOOST_SYSTEM_CONSTEXPR causes error_code.hpp compile failure.

Subject: Re: [boost] Clang 600 and BOOST_SYSTEM_CONSTEXPR causes error_code.hpp compile failure.
From: Peter Dimov (lists_at_[hidden])
Date: 2018-07-08 16:53:21

John Maddock wrote:
> I preprocessed the source and it's picking up the latest headers for me: 
> m:\\compilers\\vc2017\\vc\\tools\\msvc\\14.13.26128\\include\\system_error
>
> and I still see:
>
> class error_category
>      {    // categorize an error
> public:
>      /* constexpr */ error_category() _NOEXCEPT    // TRANSITION

I have 14.14.26428 and I see the same. :-/

Well this sure simplifies version checking for this particular issue if 
nothing else.

> Defines wise we have:
...
>     _CPPLIB_VER                             =650

After looking at the config_info output from the test matrix, the values 
are, for reference:

_CPPLIB_VER=405: msvc-8.0
_CPPLIB_VER=505: msvc-9.0
_CPPLIB_VER=520: msvc-10.0
_CPPLIB_VER=540: msvc-11.0
_CPPLIB_VER=610: msvc-12.0
_CPPLIB_VER=650: msvc-14.0 and above

The new macros are:

"The STL now identifies itself with two macros, defined by including any STL 
header (e.g. <ciso646>). _MSVC_STL_VERSION is defined as 141 and will remain 
that way for the VS 2017 v141 toolset series. _MSVC_STL_UPDATE is defined as 
201709 in VS 2017 15.5, and will be increased as features are added in 
future updates. (The year-month typically won’t correspond to an update’s 
release date. Our process for updating this macro is “we’re checking in 
std::meow() and it’s now October, so we need to change the value”, and 
depending on branch/merge timing, it might take a month or more to ship.) 
The value for VS 2017 15.6 is not yet set in stone, but it will be 201711 or 
greater."

https://blogs.msdn.microsoft.com/vcblog/2017/12/19/c17-progress-in-vs-2017-15-5-and-15-6/

and I was going to suggest we add them, but someone already did:

https://github.com/boostorg/config/commit/d5986d697ca534e18d192bd28b8c1177fe220157

Incidentally... while looking into this, I encountered

https://github.com/boostorg/config/commit/15a0c119a13938bd00b99273e6fb876ff019c688

which uses the compiler version to decide on a library feature. It will 
define BOOST_NO_CXX17_STD_APPLY under Clang.

It might be a good idea to codify the above knowledge somehow into a 
BOOST_MSSTL_VERSION macro and then check that instead of _MSC_VER or 
BOOST_MSVC which generally doesn't work with Clang.