_Noreturn: pacify gcc -std=gnu99 -Wpedantic

Problem reported by Helmut Eller <https://bugs.gnu.org/78903>.
* lib/_Noreturn.h (_Noreturn):
* m4/gnulib-common.m4 (gl_COMMON_BODY): Prefer __attribute__
((__noreturn__)) to _Noreturn if __STDC_VERSION__ < 201112, to
pacify gcc -std=gnu99 -Wpedantic.  Simplify.  Do not bother
suggesting -D_GL_WORK_AROUND_LLVM_BUG_59792; suggest the
equivalent -D_Noreturn= instead, and remove the test on
_GL_WORK_AROUND_LLVM_BUG_59792.

diff --git a/ChangeLog b/ChangeLog
index 3acaa92d0a073a41c7a8fa02e1cfc79d22c8a45b..317862e1ec626526f934feffd9c6f05540794b77 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,15 @@
+2025-06-27  Paul Eggert  <eggert@cs.ucla.edu>
+
+       _Noreturn: pacify gcc -std=gnu99 -Wpedantic
+       Problem reported by Helmut Eller <https://bugs.gnu.org/78903>.
+       * lib/_Noreturn.h (_Noreturn):
+       * m4/gnulib-common.m4 (gl_COMMON_BODY): Prefer __attribute__
+       ((__noreturn__)) to _Noreturn if __STDC_VERSION__ < 201112, to
+       pacify gcc -std=gnu99 -Wpedantic.  Simplify.  Do not bother
+       suggesting -D_GL_WORK_AROUND_LLVM_BUG_59792; suggest the
+       equivalent -D_Noreturn= instead, and remove the test on
+       _GL_WORK_AROUND_LLVM_BUG_59792.
+
 2025-06-27  Bruno Haible  <bruno@clisp.org>
 
        options: Fix typo in comment.

diff --git a/lib/_Noreturn.h b/lib/_Noreturn.h
index 0d452649fb23541446f4896987a994506f8506da..8e63387914cfe1fa272fae42cfd54b8661047713 100644 (file)
--- a/lib/_Noreturn.h
+++ b/lib/_Noreturn.h
@@ -14,33 +14,25 @@
    You should have received a copy of the GNU Lesser General Public License
    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
 
+/* The _Noreturn keyword of C11.
+   Do not use [[noreturn]], because with it the syntax
+     extern _Noreturn void func (...);
+   would not be valid; such a declaration would be valid only with 'extern'
+   and '_Noreturn' swapped, or without the 'extern' keyword.  However, some
+   AIX system header files and several gnulib header files use precisely
+   this syntax with 'extern'.  So even though C23 deprecates _Noreturn,
+   it is currently more portable to prefer it to [[noreturn]].
+
+   Also, do not try to work around LLVM bug 59792 (clang 15 or earlier).
+   This rare bug can be worked around by compiling with 'clang -D_Noreturn=',
+   though the workaround may generate many false-alarm warnings.  */
 #ifndef _Noreturn
-# if (defined __cplusplus \
-      && ((201103 <= __cplusplus && !(__GNUC__ == 4 && __GNUC_MINOR__ == 7)) \
-          || (defined _MSC_VER && 1900 <= _MSC_VER)) \
-      && 0)
-    /* [[noreturn]] is not practically usable, because with it the syntax
-         extern _Noreturn void func (...);
-       would not be valid; such a declaration would only be valid with 'extern'
-       and '_Noreturn' swapped, or without the 'extern' keyword.  However, some
-       AIX system header files and several gnulib header files use precisely
-       this syntax with 'extern'.  */
-#  define _Noreturn [[noreturn]]
-# elif (defined __clang__ && __clang_major__ < 16 \
-        && defined _GL_WORK_AROUND_LLVM_BUG_59792)
-   /* Compile with -D_GL_WORK_AROUND_LLVM_BUG_59792 to work around
-      that rare LLVM bug, though you may get many false-alarm warnings.  */
-#  define _Noreturn
-# elif ((!defined __cplusplus || defined __clang__) \
-        && (201112 <= (defined __STDC_VERSION__ ? __STDC_VERSION__ : 0) \
-            || (!defined __STRICT_ANSI__ \
-                && (4 < __GNUC__ + (7 <= __GNUC_MINOR__) && !defined __clang__ \
-                    || (defined __apple_build_version__ \
-                        ? 6000000 <= __apple_build_version__ \
-                        : 3 < __clang_major__ + (5 <= __clang_minor__))))))
+# if 201112 <= (defined __STDC_VERSION__ ? __STDC_VERSION__ : 0)
    /* _Noreturn works as-is.  */
 # elif (2 < __GNUC__ + (8 <= __GNUC_MINOR__) || defined __clang__ \
         || 0x5110 <= __SUNPRO_C)
+   /* Prefer __attribute__ ((__noreturn__)) to plain _Noreturn even if the
+      latter works, as 'gcc -std=gnu99 -Wpedantic' warns about _Noreturn.  */
 #  define _Noreturn __attribute__ ((__noreturn__))
 # elif 1200 <= (defined _MSC_VER ? _MSC_VER : 0)
 #  define _Noreturn __declspec (noreturn)

diff --git a/m4/gnulib-common.m4 b/m4/gnulib-common.m4
index 5d1944a4f583d9da8c18d79ead9044e604542776..d525d8b1faab8b82e6271d38acd194a49c64e994 100644 (file)
--- a/m4/gnulib-common.m4
+++ b/m4/gnulib-common.m4
@@ -1,5 +1,5 @@
 # gnulib-common.m4
-# serial 111
+# serial 112
 dnl Copyright (C) 2007-2025 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -57,33 +57,24 @@ AC_DEFUN([gl_COMMON_BODY], [
 #endif
 ])
   AH_VERBATIM([_Noreturn],
-[/* The _Noreturn keyword of C11.  */
+[/* The _Noreturn keyword of C11.
+   Do not use [[noreturn]], because with it the syntax
+     extern _Noreturn void func (...);
+   would not be valid; such a declaration would be valid only with 'extern'
+   and '_Noreturn' swapped, or without the 'extern' keyword.  However, some
+   AIX system header files and several gnulib header files use precisely
+   this syntax with 'extern'.  So even though C23 deprecates _Noreturn,
+   it is currently more portable to prefer it to [[noreturn]].
+
+   Also, do not try to work around LLVM bug 59792 (clang 15 or earlier).
+   This rare bug can be worked around by compiling with 'clang -D_Noreturn=',
+   though the workaround may generate many false-alarm warnings.  */
 #ifndef _Noreturn
-# if (defined __cplusplus \
-      && ((201103 <= __cplusplus && !(__GNUC__ == 4 && __GNUC_MINOR__ == 7)) \
-          || (defined _MSC_VER && 1900 <= _MSC_VER)) \
-      && 0)
-    /* [[noreturn]] is not practically usable, because with it the syntax
-         extern _Noreturn void func (...);
-       would not be valid; such a declaration would only be valid with 'extern'
-       and '_Noreturn' swapped, or without the 'extern' keyword.  However, some
-       AIX system header files and several gnulib header files use precisely
-       this syntax with 'extern'.  */
-#  define _Noreturn [[noreturn]]
-# elif (defined __clang__ && __clang_major__ < 16 \
-        && defined _GL_WORK_AROUND_LLVM_BUG_59792)
-   /* Compile with -D_GL_WORK_AROUND_LLVM_BUG_59792 to work around
-      that rare LLVM bug, though you may get many false-alarm warnings.  */
-#  define _Noreturn
-# elif ((!defined __cplusplus || defined __clang__) \
-        && (201112 <= (defined __STDC_VERSION__ ? __STDC_VERSION__ : 0) \
-            || (!defined __STRICT_ANSI__ \
-                && (_GL_GNUC_PREREQ (4, 7) \
-                    || (defined __apple_build_version__ \
-                        ? 6000000 <= __apple_build_version__ \
-                        : 3 < __clang_major__ + (5 <= __clang_minor__))))))
+# if 201112 <= (defined __STDC_VERSION__ ? __STDC_VERSION__ : 0)
    /* _Noreturn works as-is.  */
 # elif _GL_GNUC_PREREQ (2, 8) || defined __clang__ || 0x5110 <= __SUNPRO_C
+   /* Prefer __attribute__ ((__noreturn__)) to plain _Noreturn even if the
+      latter works, as 'gcc -std=gnu99 -Wpedantic' warns about _Noreturn.  */
 #  define _Noreturn __attribute__ ((__noreturn__))
 # elif 1200 <= (defined _MSC_VER ? _MSC_VER : 0)
 #  define _Noreturn __declspec (noreturn)