Re: max_align_t fails with clang 6.1 on OS X 10.10

[Bruno Haible]

Paul Eggert wrote:
> Bruno Haible wrote:
> > +} _gl_max_align_t;
> > +#define max_align_t _gl_max_align_t
> >   #endif
> >   
> >   #  endif /* address@hidden@_STDDEF_H */
> > 
> > 
> > This one is not brittle and is not a big change. If Paul agrees, I would 
> > commit
> > this, and you (Werner) would not need to reorganize your package's 
> > configuration.
> 
> Sure, that works for me.

OK, here's what I'm committing: the same idiom as we use for wint_t.


2017-09-08  Bruno Haible  <address@hidden>

        stddef: Avoid conflict with system-defined max_align_t.
        The configure-determined HAVE_MAX_ALIGN_T may not always be accurate.
        Reported by Werner Lemberg <address@hidden> in
        <https://lists.gnu.org/archive/html/bug-gnulib/2017-08/msg00185.html>.
        * lib/stddef.in.h (rpl_max_align_t): Renamed from max_align_t.
        (max_align_t): Define as a macro.
        (GNULIB_defined_max_align_t): New macro. Guards against multiple
        definitions of rpl_max_align_t in different copies of gnulib-generated
        <stddef.h>.

diff --git a/lib/stddef.in.h b/lib/stddef.in.h
index 2a11d2b..a79f536 100644
--- a/lib/stddef.in.h
+++ b/lib/stddef.in.h
@@ -85,24 +85,28 @@
    a hack in case the configure-time test was done with g++ even though
    we are currently compiling with gcc.  */
 #if ! (@HAVE_MAX_ALIGN_T@ || defined _GCC_MAX_ALIGN_T)
+# if !GNULIB_defined_max_align_t
 /* On the x86, the maximum storage alignment of double, long, etc. is 4,
    but GCC's C11 ABI for x86 says that max_align_t has an alignment of 8,
    and the C11 standard allows this.  Work around this problem by
    using __alignof__ (which returns 8 for double) rather than _Alignof
    (which returns 4), and align each union member accordingly.  */
-# ifdef __GNUC__
-#  define _GL_STDDEF_ALIGNAS(type) \
-     __attribute__ ((__aligned__ (__alignof__ (type))))
-# else
-#  define _GL_STDDEF_ALIGNAS(type) /* */
-# endif
+#  ifdef __GNUC__
+#   define _GL_STDDEF_ALIGNAS(type) \
+      __attribute__ ((__aligned__ (__alignof__ (type))))
+#  else
+#   define _GL_STDDEF_ALIGNAS(type) /* */
+#  endif
 typedef union
 {
   char *__p _GL_STDDEF_ALIGNAS (char *);
   double __d _GL_STDDEF_ALIGNAS (double);
   long double __ld _GL_STDDEF_ALIGNAS (long double);
   long int __i _GL_STDDEF_ALIGNAS (long int);
-} max_align_t;
+} rpl_max_align_t;
+#  define max_align_t rpl_max_align_t
+#  define GNULIB_defined_max_align_t 1
+# endif
 #endif
 
 #  endif /* address@hidden@_STDDEF_H */