On 1/8/21 8:31 PM, Joe Nelson wrote:
Hi, my project uses lib/_Noreturn.h, but gets a warning when compiled
with "-std=c99 -pedantic":

        warning: _Noreturn functions are a C11-specific feature

-pedantic can be such a pain sometimes, as can Clang. Thanks for reporting the problem, I guess. I installed the attached patch; please give it a try.
>From 077ffc1e416a6be980dd45979547201e572962f6 Mon Sep 17 00:00:00 2001
From: Paul Eggert <egg...@cs.ucla.edu>
Date: Sat, 9 Jan 2021 14:17:32 -0800
Subject: [PATCH] snippet/_Noreturn: port to pedantic clang

Problem reported by Joe Nelson in:
https://lists.gnu.org/r/bug-gnulib/2021-01/msg00152.html
* doc/noreturn.texi: Improve.
* lib/_Noreturn.h (_Noreturn):
* m4/gnulib-common.m4 (gl_COMMON_BODY):
Do not assume _Noreturn works as-is when __STRICT_ANSI__ is
defined, unless __STDC_VERSION__ indicates C11 or later.
* lib/_Noreturn.h (_Noreturn): Fall back on __attribute__
((__noreturn__)) if Clang; this merges the
2020-08-10T23:53:13zbr...@clisp.org patch to m4/gnulib-common.m4.
---
 ChangeLog           | 14 ++++++++++++++
 doc/noreturn.texi   | 20 ++++++++++++--------
 lib/_Noreturn.h     | 16 +++++++++-------
 m4/gnulib-common.m4 | 11 ++++++-----
 4 files changed, 41 insertions(+), 20 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index b713bedb4..4329b81d9 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,17 @@
+2021-01-09  Paul Eggert  <egg...@cs.ucla.edu>
+
+	snippet/_Noreturn: port to pedantic clang
+	Problem reported by Joe Nelson in:
+	https://lists.gnu.org/r/bug-gnulib/2021-01/msg00152.html
+	* doc/noreturn.texi: Improve.
+	* lib/_Noreturn.h (_Noreturn):
+	* m4/gnulib-common.m4 (gl_COMMON_BODY):
+	Do not assume _Noreturn works as-is when __STRICT_ANSI__ is
+	defined, unless __STDC_VERSION__ indicates C11 or later.
+	* lib/_Noreturn.h (_Noreturn): Fall back on __attribute__
+	((__noreturn__)) if Clang; this merges the
+	2020-08-10T23:53:13zbr...@clisp.org patch to m4/gnulib-common.m4.
+
 2021-01-09  Darshit Shah  <dar...@gnu.org>
 
 	Allow setting CVS username for gnu-web-doc-update.
diff --git a/doc/noreturn.texi b/doc/noreturn.texi
index e119ff88a..86bcc351e 100644
--- a/doc/noreturn.texi
+++ b/doc/noreturn.texi
@@ -23,17 +23,14 @@ declared with a @code{void} return type.
 It helps the compiler's ability to emit sensible warnings, following
 data-flow analysis, to declare which functions are non-returning.
 
+To decorate function declarations and function definitions, you can
+use the @code{_Noreturn} keyword.  No modules are needed, as Gnulib
+arranges for @code{<config.h>} to define @code{_Noreturn} to an
+appropriate replacement on platforms lacking it.
+
 Gnulib has two modules that support such a declaration:
 
 @itemize @bullet
-@item
-The @samp{stdnoreturn} module.  It provides a way to put this
-declaration at function declarations and function definitions, but not
-in function pointer types.  The identifier to use is @code{_Noreturn}
-or @code{noreturn}; @code{_Noreturn} is to be preferred because
-@code{noreturn} is a no-op on some platforms.  The include file is
-@code{<stdnoreturn.h>}.
-
 @item
 The @samp{noreturn} module.  It provides a way to put this declaration
 at function declarations, at function definitions, and in function
@@ -47,6 +44,13 @@ definitions.
 @end itemize
 @noindent
 The include file is @code{<noreturn.h>}.
+
+@item
+The @samp{stdnoreturn} module.  This can improve readability by
+letting you use @code{noreturn} instead of @code{_Noreturn};
+unfortunately, @code{noreturn} is a no-op on some platforms even
+though @code{_Noreturn} works on them.  The include file is
+@code{<stdnoreturn.h>}.
 @end itemize
 
 Which of the two modules to use?  If the non-returning functions you
diff --git a/lib/_Noreturn.h b/lib/_Noreturn.h
index f5003b9be..cb72f2620 100644
--- a/lib/_Noreturn.h
+++ b/lib/_Noreturn.h
@@ -26,14 +26,16 @@
        AIX system header files and several gnulib header files use precisely
        this syntax with 'extern'.  */
 #  define _Noreturn [[noreturn]]
-# elif ((!defined __cplusplus || defined __clang__)                     \
-        && (201112 <= (defined __STDC_VERSION__ ? __STDC_VERSION__ : 0)  \
-            || 4 < __GNUC__ + (7 <= __GNUC_MINOR__) \
-            || (defined __apple_build_version__ \
-                ? 6000000 <= __apple_build_version__ \
-                : 3 < __clang_major__ + (5 <= __clang_minor__))))
+# elif ((!defined __cplusplus || defined __clang__) \
+        && (201112 <= (defined __STDC_VERSION__ ? __STDC_VERSION__ : 0) \
+            || (!defined __STRICT_ANSI__ \
+                && (__4 < __GNUC__ + (7 <= __GNUC_MINOR__) \
+                    || (defined __apple_build_version__ \
+                        ? 6000000 <= __apple_build_version__ \
+                        : 3 < __clang_major__ + (5 <= __clang_minor__))))))
    /* _Noreturn works as-is.  */
-# elif 2 < __GNUC__ + (8 <= __GNUC_MINOR__) || 0x5110 <= __SUNPRO_C
+# elif (2 < __GNUC__ + (8 <= __GNUC_MINOR__) || defined __clang__ \
+        || 0x5110 <= __SUNPRO_C)
 #  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 535359b2c..3d87fd840 100644
--- a/m4/gnulib-common.m4
+++ b/m4/gnulib-common.m4
@@ -39,11 +39,12 @@ AC_DEFUN([gl_COMMON_BODY], [
        this syntax with 'extern'.  */
 #  define _Noreturn [[noreturn]]
 # elif ((!defined __cplusplus || defined __clang__) \
-        && (201112 <= (defined __STDC_VERSION__ ? __STDC_VERSION__ : 0)  \
-            || _GL_GNUC_PREREQ (4, 7) \
-            || (defined __apple_build_version__ \
-                ? 6000000 <= __apple_build_version__ \
-                : 3 < __clang_major__ + (5 <= __clang_minor__))))
+        && (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__))))))
    /* _Noreturn works as-is.  */
 # elif _GL_GNUC_PREREQ (2, 8) || defined __clang__ || 0x5110 <= __SUNPRO_C
 #  define _Noreturn __attribute__ ((__noreturn__))
-- 
2.27.0

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