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-rw-r--r--m4/c-bool.m451
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diff --git a/m4/c-bool.m4 b/m4/c-bool.m4
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+# Check for bool that conforms to C2023.
+
+dnl Copyright 2022-2023 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_C_BOOL],
+[
+ AC_CACHE_CHECK([for bool, true, false], [gl_cv_c_bool],
+ [AC_COMPILE_IFELSE(
+ [AC_LANG_SOURCE([[
+ #if true == false
+ #error "true == false"
+ #endif
+ extern bool b;
+ bool b = true == false;]])],
+ [gl_cv_c_bool=yes],
+ [gl_cv_c_bool=no])])
+ if test "$gl_cv_c_bool" = yes; then
+ AC_DEFINE([HAVE_C_BOOL], [1],
+ [Define to 1 if bool, true and false work as per C2023.])
+ fi
+
+ AC_CHECK_HEADERS_ONCE([stdbool.h])
+
+ dnl The "zz" puts this toward config.h's end, to avoid potential
+ dnl collisions with other definitions.
+ dnl If 'bool', 'true' and 'false' do not work, arrange for them to work.
+ dnl In C, this means including <stdbool.h> if it is not already included.
+ dnl However, if the preprocessor mistakenly treats 'true' as 0,
+ dnl define it to a bool expression equal to 1; this is needed in
+ dnl Sun C++ 5.11 (Oracle Solaris Studio 12.2, 2010) and older.
+ AH_VERBATIM([zzbool],
+[#ifndef HAVE_C_BOOL
+# if !defined __cplusplus && !defined __bool_true_false_are_defined
+# if HAVE_STDBOOL_H
+# include <stdbool.h>
+# else
+# if defined __SUNPRO_C
+# error "<stdbool.h> is not usable with this configuration. To make it usable, add -D_STDC_C99= to $CC."
+# else
+# error "<stdbool.h> does not exist on this platform. Use gnulib module 'stdbool-c99' instead of gnulib module 'stdbool'."
+# endif
+# endif
+# endif
+# if !true
+# define true (!false)
+# endif
+#endif])
+])