dnl 'extern inline' a la ISO C99.

dnl Copyright 2012-2023 Free Software Foundation, Inc.
dnl This file is free software; the Free Software Foundation
dnl gives unlimited permission to copy and/or distribute it,
dnl with or without modifications, as long as this notice is preserved.

AC_DEFUN([gl_EXTERN_INLINE],
[
  AC_CACHE_CHECK([whether ctype.h defines __header_inline],
    [gl_cv_have___header_inline],
    [AC_PREPROC_IFELSE(
       [AC_LANG_SOURCE([[#include <ctype.h>
                         #ifndef __header_inline
                          #error "<ctype.h> does not define __header_inline"
                         #endif
                        ]])],
       [gl_cv_have___header_inline=yes],
       [gl_cv_have___header_inline=no])])
  if test "$gl_cv_have___header_inline" = yes; then
    AC_DEFINE([HAVE___HEADER_INLINE], [1],
      [Define to 1 if ctype.h defines __header_inline.])
  fi

  AH_VERBATIM([HAVE___HEADER_INLINE_1],
[/* Please see the Gnulib manual for how to use these macros.

   Suppress extern inline with HP-UX cc, as it appears to be broken; see
   <https://lists.gnu.org/r/bug-texinfo/2013-02/msg00030.html>.

   Suppress extern inline with Sun C in standards-conformance mode, as it
   mishandles inline functions that call each other.  E.g., for 'inline void f
   (void) { } inline void g (void) { f (); }', c99 incorrectly complains
   'reference to static identifier "f" in extern inline function'.
   This bug was observed with Oracle Developer Studio 12.6
   (Sun C 5.15 SunOS_sparc 2017/05/30).

   Suppress extern inline (with or without __attribute__ ((__gnu_inline__)))
   on configurations that mistakenly use 'static inline' to implement
   functions or macros in standard C headers like <ctype.h>.  For example,
   if isdigit is mistakenly implemented via a static inline function,
   a program containing an extern inline function that calls isdigit
   may not work since the C standard prohibits extern inline functions
   from calling static functions (ISO C 99 section 6.7.4.(3).
   This bug is known to occur on:

     OS X 10.8 and earlier; see:
     https://lists.gnu.org/r/bug-gnulib/2012-12/msg00023.html

     DragonFly; see
     http://muscles.dragonflybsd.org/bulk/clang-master-potential/20141111_102002/logs/ah-tty-0.3.12.log

     FreeBSD; see:
     https://lists.gnu.org/r/bug-gnulib/2014-07/msg00104.html

   OS X 10.9 has a macro __header_inline indicating the bug is fixed for C and
   for clang but remains for g++; see <https://trac.macports.org/ticket/41033>.
   Assume DragonFly and FreeBSD will be similar.

   GCC 4.3 and above with -std=c99 or -std=gnu99 implements ISO C99
   inline semantics, unless -fgnu89-inline is used.  It defines a macro
   __GNUC_STDC_INLINE__ to indicate this situation or a macro
   __GNUC_GNU_INLINE__ to indicate the opposite situation.
   GCC 4.2 with -std=c99 or -std=gnu99 implements the GNU C inline
   semantics but warns, unless -fgnu89-inline is used:
     warning: C99 inline functions are not supported; using GNU89
     warning: to disable this warning use -fgnu89-inline or the gnu_inline function attribute
   It defines a macro __GNUC_GNU_INLINE__ to indicate this situation.
 */
#if (((defined __APPLE__ && defined __MACH__) \
      || defined __DragonFly__ || defined __FreeBSD__) \
     && (defined HAVE___HEADER_INLINE \
         ? (defined __cplusplus && defined __GNUC_STDC_INLINE__ \
            && ! defined __clang__) \
         : ((! defined _DONT_USE_CTYPE_INLINE_ \
             && (defined __GNUC__ || defined __cplusplus)) \
            || (defined _FORTIFY_SOURCE && 0 < _FORTIFY_SOURCE \
                && defined __GNUC__ && ! defined __cplusplus))))
# define _GL_EXTERN_INLINE_STDHEADER_BUG
#endif
#if ((__GNUC__ \
      ? (defined __GNUC_STDC_INLINE__ && __GNUC_STDC_INLINE__ \
         && !defined __PCC__) \
      : (199901L <= __STDC_VERSION__ \
         && !defined __HP_cc \
         && !defined __PGI \
         && !(defined __SUNPRO_C && __STDC__))) \
     && !defined _GL_EXTERN_INLINE_STDHEADER_BUG)
# define _GL_INLINE inline
# define _GL_EXTERN_INLINE extern inline
# define _GL_EXTERN_INLINE_IN_USE
#elif (2 < __GNUC__ + (7 <= __GNUC_MINOR__) && !defined __STRICT_ANSI__ \
       && !defined __PCC__ \
       && !defined _GL_EXTERN_INLINE_STDHEADER_BUG)
# if defined __GNUC_GNU_INLINE__ && __GNUC_GNU_INLINE__
   /* __gnu_inline__ suppresses a GCC 4.2 diagnostic.  */
#  define _GL_INLINE extern inline __attribute__ ((__gnu_inline__))
# else
#  define _GL_INLINE extern inline
# endif
# define _GL_EXTERN_INLINE extern
# define _GL_EXTERN_INLINE_IN_USE
#else
# define _GL_INLINE _GL_UNUSED static
# define _GL_EXTERN_INLINE _GL_UNUSED static
#endif

/* In GCC 4.6 (inclusive) to 5.1 (exclusive),
   suppress bogus "no previous prototype for 'FOO'"
   and "no previous declaration for 'FOO'" diagnostics,
   when FOO is an inline function in the header; see
   <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=54113> and
   <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63877>.  */
#if __GNUC__ == 4 && 6 <= __GNUC_MINOR__
# if defined __GNUC_STDC_INLINE__ && __GNUC_STDC_INLINE__
#  define _GL_INLINE_HEADER_CONST_PRAGMA
# else
#  define _GL_INLINE_HEADER_CONST_PRAGMA \
     _Pragma ("GCC diagnostic ignored \"-Wsuggest-attribute=const\"")
# endif
# define _GL_INLINE_HEADER_BEGIN \
    _Pragma ("GCC diagnostic push") \
    _Pragma ("GCC diagnostic ignored \"-Wmissing-prototypes\"") \
    _Pragma ("GCC diagnostic ignored \"-Wmissing-declarations\"") \
    _GL_INLINE_HEADER_CONST_PRAGMA
# define _GL_INLINE_HEADER_END \
    _Pragma ("GCC diagnostic pop")
#else
# define _GL_INLINE_HEADER_BEGIN
# define _GL_INLINE_HEADER_END
#endif])
])