c: Add <stdcountof.h> [PR117025]

	PR c/117025

gcc/ChangeLog:

	* Makefile.in (USER_H): Add <stdcountof.h>.
	* ginclude/stdcountof.h: New file.

gcc/testsuite/ChangeLog:

	* gcc.dg/countof-stdcountof.c: New test.

Signed-off-by: Alejandro Colomar <alx@kernel.org>

3 files changed, 56 insertions, 0 deletions

diff --git a/gcc/Makefile.in b/gcc/Makefile.in
index a452386..49869531 100644
--- a/gcc/Makefile.in
+++ b/gcc/Makefile.in
@@ -480,6 +480,7 @@ USER_H = $(srcdir)/ginclude/float.h \
 	 $(srcdir)/ginclude/stdalign.h \
 	 $(srcdir)/ginclude/stdatomic.h \
 	 $(srcdir)/ginclude/stdckdint.h \
+	 $(srcdir)/ginclude/stdcountof.h \
 	 $(EXTRA_HEADERS)
 
 USER_H_INC_NEXT_PRE = @user_headers_inc_next_pre@
diff --git a/gcc/ginclude/stdcountof.h b/gcc/ginclude/stdcountof.h
new file mode 100644
index 0000000..1d914f4
--- /dev/null
+++ b/gcc/ginclude/stdcountof.h
@@ -0,0 +1,31 @@
+/* Copyright (C) 2025 Free Software Foundation, Inc.
+
+This file is part of GCC.
+
+GCC is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 3, or (at your option)
+any later version.
+
+GCC is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+Under Section 7 of GPL version 3, you are granted additional
+permissions described in the GCC Runtime Library Exception, version
+3.1, as published by the Free Software Foundation.
+
+You should have received a copy of the GNU General Public License and
+a copy of the GCC Runtime Library Exception along with this program;
+see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
+<http://www.gnu.org/licenses/>.  */
+
+/* ISO C2Y: 7.21 Array count <stdcountof.h>.  */
+
+#ifndef _STDCOUNTOF_H
+#define _STDCOUNTOF_H
+
+#define countof  _Countof
+
+#endif	/* stdcountof.h */
diff --git a/gcc/testsuite/gcc.dg/countof-stdcountof.c b/gcc/testsuite/gcc.dg/countof-stdcountof.c
new file mode 100644
index 0000000..2fb0c63
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/countof-stdcountof.c
@@ -0,0 +1,24 @@
+/* { dg-do run } */
+/* { dg-options "-std=c2y -pedantic-errors" } */
+
+#include <stdcountof.h>
+
+#define assert(e)  ((e) ? (void) 0 : __builtin_abort ())
+
+extern int strcmp (const char *, const char *);
+
+#ifndef countof
+#error "countof not defined"
+#endif
+
+int a[3];
+int b[countof a];
+
+#define str(x) #x
+#define xstr(x) str(x)
+
+int
+main (void)
+{
+  assert (strcmp (xstr(countof), "_Countof") == 0);
+}