1 files changed, 60 insertions, 9 deletions

diff --git a/gl/m4/stddef_h.m4 b/gl/m4/stddef_h.m4
index a2322ebb..127ec05b 100644
--- a/gl/m4/stddef_h.m4
+++ b/gl/m4/stddef_h.m4
@@ -1,15 +1,16 @@
-# stddef_h.m4 serial 13
-dnl Copyright (C) 2009-2023 Free Software Foundation, Inc.
+# stddef_h.m4
+# serial 23
+dnl Copyright (C) 2009-2025 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.
+dnl This file is offered as-is, without any warranty.
 
 dnl A placeholder for <stddef.h>, for platforms that have issues.
 
 AC_DEFUN_ONCE([gl_STDDEF_H],
 [
   AC_REQUIRE([gl_STDDEF_H_DEFAULTS])
-  AC_REQUIRE([gt_TYPE_WCHAR_T])
 
   dnl Persuade OpenBSD <stddef.h> to declare max_align_t.
   AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])
@@ -51,11 +52,6 @@ AC_DEFUN_ONCE([gl_STDDEF_H],
     GL_GENERATE_STDDEF_H=true
   fi
 
-  if test $gt_cv_c_wchar_t = no; then
-    HAVE_WCHAR_T=0
-    GL_GENERATE_STDDEF_H=true
-  fi
-
   AC_CACHE_CHECK([whether NULL can be used in arbitrary expressions],
     [gl_cv_decl_null_works],
     [AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <stddef.h>
@@ -68,6 +64,60 @@ AC_DEFUN_ONCE([gl_STDDEF_H],
     GL_GENERATE_STDDEF_H=true
   fi
 
+  AC_CACHE_CHECK([for unreachable in C],
+    [gl_cv_c_func_unreachable],
+    [AC_LINK_IFELSE(
+       [AC_LANG_PROGRAM(
+          [[#include <stddef.h>
+          ]],
+          [[unreachable ();
+          ]])],
+       [gl_cv_c_func_unreachable=yes],
+       [gl_cv_c_func_unreachable=no])
+    ])
+  if test $gl_cv_c_func_unreachable = no; then
+    GL_GENERATE_STDDEF_H=true
+    HAVE_C_UNREACHABLE=0
+  else
+    HAVE_C_UNREACHABLE=1
+  fi
+  AC_SUBST([HAVE_C_UNREACHABLE])
+  dnl Provide gl_unreachable() unconditionally.
+  GL_GENERATE_STDDEF_H=true
+
+  dnl https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114869
+  AC_CACHE_CHECK([whether nullptr_t needs <stddef.h>],
+    [gl_cv_nullptr_t_needs_stddef],
+    [AC_COMPILE_IFELSE([AC_LANG_DEFINES_PROVIDED[nullptr_t x;]],
+       [gl_cv_nullptr_t_needs_stddef=no],
+       [gl_cv_nullptr_t_needs_stddef=yes])])
+  if test "$gl_cv_nullptr_t_needs_stddef" = no; then
+    NULLPTR_T_NEEDS_STDDEF=0
+    GL_GENERATE_STDDEF_H=true
+  fi
+
+  dnl https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114870
+  dnl affects GCC 13.3 and 14.2.
+  AC_CACHE_CHECK([whether <stddef.h> is idempotent],
+    [gl_cv_stddef_idempotent],
+    [AC_COMPILE_IFELSE([AC_LANG_SOURCE(
+       [[
+       #if \
+           ((__GNUC__ == 13 && __GNUC_MINOR__ <= 3) \
+            || (__GNUC__ == 14 && __GNUC_MINOR__ <= 2))
+        #error "bug 114870 is present"
+       #endif
+       ]])],
+       [gl_cv_stddef_idempotent="guessing yes"],
+       [gl_cv_stddef_idempotent="guessing no"])
+    ])
+  case "$gl_cv_stddef_idempotent" in
+    *yes) ;;
+    *) STDDEF_NOT_IDEMPOTENT=1
+       GL_GENERATE_STDDEF_H=true
+       ;;
+  esac
+
   if $GL_GENERATE_STDDEF_H; then
     gl_NEXT_HEADERS([stddef.h])
   fi
@@ -98,7 +148,8 @@ AC_DEFUN([gl_STDDEF_H_REQUIRE_DEFAULTS],
 AC_DEFUN([gl_STDDEF_H_DEFAULTS],
 [
   dnl Assume proper GNU behavior unless another module says otherwise.
+  NULLPTR_T_NEEDS_STDDEF=1;      AC_SUBST([NULLPTR_T_NEEDS_STDDEF])
+  STDDEF_NOT_IDEMPOTENT=0;       AC_SUBST([STDDEF_NOT_IDEMPOTENT])
   REPLACE_NULL=0;                AC_SUBST([REPLACE_NULL])
   HAVE_MAX_ALIGN_T=1;            AC_SUBST([HAVE_MAX_ALIGN_T])
-  HAVE_WCHAR_T=1;                AC_SUBST([HAVE_WCHAR_T])
 ])