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

[Bruno Haible]

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

On MSVC 14, in C mode, I get compilation errors:

...\gnulib-tests\test-assert.c(27): warning C4116: unnamed type definition in 
parentheses
...\gnulib-tests\test-assert.c(27): error C2057: expected constant expression
...\gnulib-tests\test-assert.c(27): error C2149: 
'_gl_static_assert_error_if_negative': named bit field cannot have zero width
...\gnulib-tests\test-assert.c(43): warning C4116: unnamed type definition in 
parentheses
...\gnulib-tests\test-assert.c(43): error C2057: expected constant expression
...\gnulib-tests\test-assert.c(43): error C2149: 
'_gl_static_assert_error_if_negative': named bit field cannot have zero width
...\gnulib-tests\test-assert.c(55): warning C4116: unnamed type definition in 
parentheses
...\gnulib-tests\test-assert.c(55): error C2057: expected constant expression
...\gnulib-tests\test-assert.c(55): error C2149: 
'_gl_static_assert_error_if_negative': named bit field cannot have zero width
...\gnulib-tests\test-assert.c(67): warning C4116: unnamed type definition in 
parentheses
...\gnulib-tests\test-assert.c(67): error C2057: expected constant expression
...\gnulib-tests\test-assert.c(67): error C2149: 
'_gl_static_assert_error_if_negative': named bit field cannot have zero width
make[3]: *** [Makefile:7324: test-assert.obj] Error 2

How come? These lines from the test program

  static_assert (2 + 2 == 4, "arithmetic does not work");
  static_assert (2 + 2 == 4);
  static_assert (sizeof (char) == 1, "sizeof does not work");
  static_assert (sizeof (char) == 1);

macroexpand to

  extern int (*_gl_static_assert_function2 (void)) [(!!sizeof (struct { 
unsigned int _gl_static_assert_error_if_negative: (2 + 2 == 4, "arithmetic does 
not work") ? 1 : -1; }))];
  extern int (*_gl_static_assert_function3 (void)) [(!!sizeof (struct { 
unsigned int _gl_static_assert_error_if_negative: (2 + 2 == 4) ? 1 : -1; }))];
  extern int (*_gl_static_assert_function4 (void)) [(!!sizeof (struct { 
unsigned int _gl_static_assert_error_if_negative: (sizeof (char) == 1, "sizeof 
does not work") ? 1 : -1; }))];
  extern int (*_gl_static_assert_function5 (void)) [(!!sizeof (struct { 
unsigned int _gl_static_assert_error_if_negative: (sizeof (char) == 1) ? 1 : 
-1; }))];

which obviously is nonsense, as the value of a comma expression is the last
part, not the first part.

This patch fixes it.


2022-09-14  Bruno Haible  <bruno@clisp.org>

        verify: Avoid syntax error due to static_assert with MSVC 14.
        * lib/verify.h (_Static_assert): Pass only the first argument to
        _GL_VERIFY.

diff --git a/lib/verify.h b/lib/verify.h
index 154a5b76bf..a0d597f3d4 100644
--- a/lib/verify.h
+++ b/lib/verify.h
@@ -223,8 +223,8 @@ template <int w>
 /* _GL_STATIC_ASSERT_H is defined if this code is copied into assert.h.  */
 #ifdef _GL_STATIC_ASSERT_H
 # if !defined _GL_HAVE__STATIC_ASSERT1 && !defined _Static_assert
-#  define _Static_assert(...) \
-     _GL_VERIFY (__VA_ARGS__, "static assertion failed", -)
+#  define _Static_assert(R, ...) \
+     _GL_VERIFY ((R), "static assertion failed", -)
 # endif
 # if (!defined static_assert \
       && __STDC_VERSION__ < 202311 \