assert-h, verify: Fix compilation error in C++ mode with MSVC 14

[Bruno Haible]

In a testdir for the 'assert-h' module, I'm seeing this compilation error:

/home/bruno/msvc/compile cl -nologo -DHAVE_CONFIG_H -I. -I../../gltests -I..  
-DGNULIB_STRICT_CHECKING=1 -DIN_GNULIB_TESTS=1 -I. -I../../gltests -I.. 
-I../../gltests/.. -I../gllib -I../../gltests/../gllib 
-D_WIN32_WINNT=_WIN32_WINNT_WIN7 -I/usr/local/msvc64/include  -MD -c -o 
test-assert-h-c++.obj `cygpath -w '../../gltests/test-assert-h-c++.cc'`
test-assert-h-c++.cc
C:\Program Files (x86)\Microsoft Visual Studio 
14.0\VC\include\xkeycheck.h(224): warning C4005: 'static_assert': macro 
redefinition
../gllib\assert.h(295): note: see previous definition of 'static_assert'
C:\Program Files (x86)\Microsoft Visual Studio 
14.0\VC\include\xkeycheck.h(250): fatal error C1189: #error:  The C++ Standard 
Library forbids macroizing keywords. Enable warning C4005 to find the forbidden 
macro.
make[4]: *** [Makefile:746: test-assert-h-c++.obj] Error 2

If we don't define static_assert as a macro, it supports only the 2-arguments
case, not the use with a single argument.

And if we do define it as a macro, xkeycheck.h complains about it. Fortunately,
there's a way to skip this check.


2023-02-05  Bruno Haible  <br...@clisp.org>

        assert-h, verify: Fix compilation error in C++ mode with MSVC 14.
        * lib/verify.h (static_assert): Define _ALLOW_KEYWORD_MACROS.
        * tests/test-assert-h-c++.cc: Strengthen test.
        * tests/test-assert-h-c++2.cc: Likewise.

diff --git a/lib/verify.h b/lib/verify.h
index 8f786af7f5..f0b3fc5851 100644
--- a/lib/verify.h
+++ b/lib/verify.h
@@ -265,6 +265,8 @@ template <int w>
 #   define _GL_SA3 static_assert
 #   define _GL_SA_PICK(x1,x2,x3,x4,...) x4
 #   define static_assert(...) 
_GL_EXPAND(_GL_SA_PICK(__VA_ARGS__,_GL_SA3,_GL_SA2,_GL_SA1)) (__VA_ARGS__)
+/* Avoid "fatal error C1189: #error:  The C++ Standard Library forbids 
macroizing keywords."  */
+#   define _ALLOW_KEYWORD_MACROS 1
 #  else
 #   define static_assert _Static_assert /* C11 requires this #define. */
 #  endif
diff --git a/tests/test-assert-h-c++.cc b/tests/test-assert-h-c++.cc
index 6b76565633..7da8b377fd 100644
--- a/tests/test-assert-h-c++.cc
+++ b/tests/test-assert-h-c++.cc
@@ -26,6 +26,9 @@
 #include <iostream>
 
 
+static_assert (2 + 2 == 4, "arithmetic does not work");
+static_assert (2 + 2 == 4);
+
 int
 main ()
 {
diff --git a/tests/test-assert-h-c++2.cc b/tests/test-assert-h-c++2.cc
index ffd7c8cf92..8808886202 100644
--- a/tests/test-assert-h-c++2.cc
+++ b/tests/test-assert-h-c++2.cc
@@ -22,3 +22,7 @@
 /* Check against conflicts between <cassert> and other C++ header files.  */
 #include <stddef.h>
 #include <iostream>
+
+
+static_assert (2 + 2 == 4, "arithmetic does not work");
+static_assert (2 + 2 == 4);