Compilation warnings on MinGW due to Gnulib's wcwidth

[Eli Zaretskii]

Building the current Texinfo trunk tip with MinGW produces a barrage
of compiler warnings like these:

  gcc -std=gnu99 -DHAVE_CONFIG_H -I. -I../..    -Id:/usr/include  -gdwarf-4 -g3 
-O2 -MT mbscasecmp.o -MD -MP -MF $depbase.Tpo -c -o mbscasecmp.o mbscasecmp.c 
&&\
  mv -f $depbase.Tpo $depbase.Po
  In file included from mbuiter.h:106:0,
                   from mbscasecmp.c:27:
  mbchar.h: In function 'mb_width_aux':
  mbchar.h:249:3: warning: implicit declaration of function 'wcwidth' 
[-Wimplicit-function-declaration]
     int w = wcwidth (wc);
     ^
  gcc -std=gnu99 -DHAVE_CONFIG_H -I. -I../..    -Id:/usr/include  -gdwarf-4 -g3 
-O
  2 -MT mbsncasecmp.o -MD -MP -MF $depbase.Tpo -c -o mbsncasecmp.o 
mbsncasecmp.c &
  &\
  mv -f $depbase.Tpo $depbase.Po
  In file included from mbuiter.h:106:0,
                   from mbsncasecmp.c:27:
  mbchar.h: In function 'mb_width_aux':
  mbchar.h:249:3: warning: implicit declaration of function 'wcwidth' 
[-Wimplicit-
  function-declaration]
     int w = wcwidth (wc);
     ^
  gcc -std=gnu99 -DHAVE_CONFIG_H -I. -I..  -I..                                
-I../gnulib/lib                     -I../gnulib/lib                   
-DLOCALEDIR=\"d:/usr/share/locale\"              
-DINFODIR=\"d:/usr/share/info\"          -DINFODIR2=\"d:/usr/share/info\"  
-Id:/usr/include  -gdwarf-4 -g3 -O2 -MT dir.o -MD -MP -MF .deps/dir.Tpo -c -o 
dir.o dir.c
  In file included from ../system.h:54:0,
                   from info.h:26,
                   from dir.c:22:
  ../gnulib/lib/mbchar.h: In function 'mb_width_aux':
  ../gnulib/lib/mbchar.h:249:3: warning: implicit declaration of function 
'wcwidth' [-Wimplicit-function-declaration]
     int w = wcwidth (wc);
     ^

As you see, the warnings are produced both while compiling Gnulib
files and while compiling the 'info' program.

I don't understand fully what's going on, since the prototype of
wcwidth is in Gnulib's wchar.h.  I think there's some snafu with this
tricky condition:

  #if defined __need_mbstate_t || defined __need_wint_t || (defined __hpux && 
((defined _INTTYPES_INCLUDED && !defined strtoimax) || defined 
_GL_JUST_INCLUDE_SYSTEM_WCHAR_H)) || defined _GL_ALREADY_INCLUDING_WCHAR_H
  /* Special invocation convention:
     - Inside glibc and uClibc header files.
     - On HP-UX 11.00 we have a sequence of nested includes
       <wchar.h> -> <stdlib.h> -> <stdint.h>, and the latter includes <wchar.h>,
       once indirectly <stdint.h> -> <sys/types.h> -> <inttypes.h> -> <wchar.h>
       and once directly.  In both situations 'wint_t' is not yet defined,
       therefore we cannot provide the function overrides; instead include only
       the system's <wchar.h>.
     - On IRIX 6.5, similarly, we have an include <wchar.h> -> <wctype.h>, and
       the latter includes <wchar.h>.  But here, we have no way to detect 
whether
       <wctype.h> is completely included or is still being included.  */

  #include_next <wchar.h>

  #else
  /* Normal invocation convention.  */

I think something (perhaps _GL_ALREADY_INCLUDING_WCHAR_H?) goes wrong
with this in several source files, and the result is that only MinGW's
own wchar.h is included, which lacks wcwidth declaration.

Let me know if I can provide more information.

Thanks.

P.S.  Please cc me on any replies, as I'm not subscribed to the list.