[libcxx] [test] In msvc_stdlib_force_include.hpp, use _HAS_CXX17 to set TEST_STD_VER.

[STL_MSFT]

Summary

[libcxx] [test] In msvc_stdlib_force_include.hpp, use _HAS_CXX17 to set TEST_STD_VER.

_HAS_CXX17 indicates whether MSVC's STL is in C++17 mode.

[EricWF]

LGTM after addressing inline comments.

test/support/msvc_stdlib_force_include.hpp

76

Is the stdlib.h include above not enough?

78

Should this be #if defined(_HAS_CXX17) && _HAS_CXX17 since Clang doesn't define it to the best of my knowledge? (Or maybe Clang/C2 does, IDK)

[EricWF]

Also you're free to commit to MSVC specific files without pre-commit review :-)

[STL_MSFT]

test/support/msvc_stdlib_force_include.hpp

76

It isn't enough. In MSVC there's a distinction between CRT headers like stdlib.h and STL headers like cstdlib. Only the STL headers drag in yvals.h, our internal STL-wide header that defines internal macros like _HAS_CXX17.

78

I guess I didn't explain the macro. _HAS_CXX17 is an MSVC STL library macro, unconditionally defined. We centralize everything on this, because we have to ask different questions to determine whether C1XX, EDG, or Clang is in 14 or 17 mode, and we additionally permit users to override the detection in one way (it's okay to ask for 17 from the compiler, but only 14 from the libs, at least for the moment; only noexcept in the type system will give us a headache).

As this header is for testing MSVC's STL, we can assume _HAS_CXX17 is defined.

test/support/msvc_stdlib_force_include.hpp

AssertionDialogAvoider() {
         _CrtSetReportFile(_CRT_ERROR, _CRTDBG_FILE_STDERR);
     }
 };
 
 const AssertionDialogAvoider assertion_dialog_avoider{};
 
 // MSVC frontend only configurations
 #if !defined(__clang__)
-    #define TEST_STD_VER 17
-
     // Simulate feature-test macros.
     #define __has_feature(X) _MSVC_HAS_FEATURE_ ## X
     #define _MSVC_HAS_FEATURE_cxx_exceptions    1
     #define _MSVC_HAS_FEATURE_cxx_rtti          1
     #define _MSVC_HAS_FEATURE_address_sanitizer 0
     #define _MSVC_HAS_FEATURE_memory_sanitizer  0
     #define _MSVC_HAS_FEATURE_thread_sanitizer  0
 

 // Enable features that /std:c++latest removes by default.
 #define _HAS_AUTO_PTR_ETC          1
 #define _HAS_FUNCTION_ASSIGN       1
 #define _HAS_OLD_IOSTREAMS_MEMBERS 1
 
 // Silence warnings about raw pointers and other unchecked iterators.
 #define _SCL_SECURE_NO_WARNINGS
 
+#include <ciso646>
+
+#if _HAS_CXX17
+    #define TEST_STD_VER 17
+#else // _HAS_CXX17
+    #define TEST_STD_VER 14
+#endif // _HAS_CXX17
+
 #endif // SUPPORT_MSVC_STDLIB_FORCE_INCLUDE_HPP