Re: [PROPOSED 2/2] assert-h: prefer to ‘verify’

[Bruno Haible]

Paul Eggert wrote:
> Where it’s easy, prefer ‘static_assert’ to ‘verify’,

Compiling a current GNU gettext with MSVC 14, I get this compilation error:

libtool: compile:  /home/bruno/msvc/compile cl -nologo -DIN_LIBASPRINTF 
-DHAVE_CONFIG_H -D__USE_MINGW_ANSI_STDIO=0 -I. 
-I../../../gettext-runtime/libasprintf -Ignulib-lib 
-I../../../gettext-runtime/libasprintf/gnulib-lib 
-D_WIN32_WINNT=_WIN32_WINNT_WIN7 -I/usr/local/msvc64/include -MD -c 
../../../gettext-runtime/libasprintf/autosprintf.cc -o autosprintf.obj
autosprintf.cc
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include\xstddef(376): 
error C2720: 'std::hash<_Kty>::_gl_static_assert_function3': 'extern' 
storage-class specifier illegal on members
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include\xstddef(378): 
note: see reference to class template instantiation 'std::hash<_Kty>' being 
compiled
C:\Program Files (x86)\Microsoft Visual Studio 
14.0\VC\include\type_traits(744): error C2720: 
'std::_Change_sign<_Ty>::_gl_static_assert_function4': 'extern' storage-class 
specifier illegal on members
C:\Program Files (x86)\Microsoft Visual Studio 
14.0\VC\include\type_traits(777): note: see reference to class template 
instantiation 'std::_Change_sign<_Ty>' being compiled
C:\Program Files (x86)\Microsoft Visual Studio 
14.0\VC\include\type_traits(1193): error C2720: 
'std::integer_sequence<_Ty,_Vals...>::_gl_static_assert_function5': 'extern' 
storage-class specifier illegal on members
C:\Program Files (x86)\Microsoft Visual Studio 
14.0\VC\include\type_traits(1203): note: see reference to class template 
instantiation 'std::integer_sequence<_Ty,_Vals...>' being compiled
C:\Program Files (x86)\Microsoft Visual Studio 
14.0\VC\include\type_traits(1502): error C2720: 
'std::result_of<_Fty>::_gl_static_assert_function7': 'extern' storage-class 
specifier illegal on members
C:\Program Files (x86)\Microsoft Visual Studio 
14.0\VC\include\type_traits(1505): note: see reference to class template 
instantiation 'std::result_of<_Fty>' being compiled
C:\Program Files (x86)\Microsoft Visual Studio 
14.0\VC\include\type_traits(1580): error C2720: 
'std::reference_wrapper<_Ty>::_gl_static_assert_function8': 'extern' 
storage-class specifier illegal on members
C:\Program Files (x86)\Microsoft Visual Studio 
14.0\VC\include\type_traits(1612): note: see reference to class template 
instantiation 'std::reference_wrapper<_Ty>' being compiled
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include\utility(423): 
error C2720: 
'std::tuple_element<_Idx,std::array<_Ty,_Size>>::_gl_static_assert_function9': 
'extern' storage-class specifier illegal on members
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include\utility(426): 
note: see reference to class template instantiation 
'std::tuple_element<_Idx,std::array<_Ty,_Size>>' being compiled
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include\utility(445): 
error C2059: syntax error: ')'
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include\utility(447): 
note: see reference to class template instantiation 
'std::tuple_element<_Index,std::tuple<>>' being compiled
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include\utility(445): 
error C2947: expecting '>' to terminate template-argument-list, found '>'
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include\utility(445): 
error C2976: 'std::integral_constant': too few template arguments
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include\xtr1common(23): 
note: see declaration of 'std::integral_constant'
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include\utility(447): 
error C2143: syntax error: missing ';' before '}'
C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\include\utility(447): 
fatal error C1004: unexpected end-of-file found
make[4]: *** [Makefile:1412: autosprintf.lo] Error 1

The situation with this compiler (in C++ mode) is:
  - It supports 'static_assert' with 2 arguments.
  - It does not support 'static_assert' with 1 argument.
  - Its header files make use of the 'static_assert' with 2 arguments,
    for example:

        template<size_t _Index>
        struct tuple_element<_Index, tuple<> >
        {       // enforce bounds checking
        static_assert(_Always_false<integral_constant<size_t, _Index> >::value,
                "tuple index out of bounds");
        };

Thus, our existing definition of static_assert via _Static_assert an _GL_VERIFY
does not work, because 'extern' is not allowed inside a struct/class definition.

This attempted patch

diff --git a/lib/verify.h b/lib/verify.h
index a0d597f3d4..608c9bda20 100644
--- a/lib/verify.h
+++ b/lib/verify.h
@@ -229,7 +229,13 @@ template <int w>
 # if (!defined static_assert \
       && __STDC_VERSION__ < 202311 \
       && __cpp_static_assert < 201411 && __GNUG__ < 6)
-#  define static_assert _Static_assert /* C11 requires this #define.  */
+#  if defined __cplusplus && _MSC_VER >= 1900
+/* MSVC 14 in C++ mode supports the 2-arguments static_assert but not the
+   one-argument static_assert, and it does not support _Static_assert.  */
+#   define static_assert(R, ...) static_assert((R), "static assertion failed")
+#  else
+#   define static_assert _Static_assert /* C11 requires this #define.  */
+#  endif
 # endif
 #endif
 
does not work either, because when we define static_assert as a macro, it
parses

static_assert(_Always_false<integral_constant<size_t, _Index> >::value,
                "tuple index out of bounds");

as a macro call with 3 arguments:
  argument 1:   _Always_false<integral_constant<size_t
  argument 2:   _Index> >::value
  argument 3:   "tuple index out of bounds"

Any ideas how to get this working?

Bruno