[PATCH] stdnoreturn: deprecate

[Paul Eggert]

C23 says <stdnoreturn.h> is obsolescent, so deprecate the
stdnoreturn module.  I don't think it was being used anyway
as it had too many problems.
* modules/stdnoreturn: Mark as obsolete.
---
 ChangeLog                          |  8 +++++++
 NEWS                               |  3 +++
 doc/noreturn.texi                  | 35 ++++++++++++++----------------
 doc/posix-headers/stdnoreturn.texi |  2 ++
 lib/stdnoreturn.in.h               |  4 +++-
 modules/stdnoreturn                |  6 +++++
 6 files changed, 38 insertions(+), 20 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 3b6c6cf98e..91370af964 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2022-12-24  Paul Eggert  <eggert@cs.ucla.edu>
+
+       stdnoreturn: deprecate
+       C23 says <stdnoreturn.h> is obsolescent, so deprecate the
+       stdnoreturn module.  I don't think it was being used anyway
+       as it had too many problems.
+       * modules/stdnoreturn: Mark as obsolete.
+
 2022-12-23  Paul Eggert  <eggert@cs.ucla.edu>
 
        file-has-acl: improve recent NFSv4 support
diff --git a/NEWS b/NEWS
index bc620ce86a..dd2374c4fd 100644
--- a/NEWS
+++ b/NEWS
@@ -74,6 +74,9 @@ User visible incompatible changes
 
 Date        Modules         Changes
 
+2022-12-24  stdnoreturn     This module is deprecated.  Use _Noreturn
+                            or the noreturn module instead.
+
 2022-12-21  ctime           This module is deprecated.  Use localtime_r
                             and strftime (or even sprintf) instead.
 
diff --git a/doc/noreturn.texi b/doc/noreturn.texi
index a3a394409c..ad0a286f4a 100644
--- a/doc/noreturn.texi
+++ b/doc/noreturn.texi
@@ -15,22 +15,26 @@
 @cindex @code{noreturn}
 @cindex @code{stdnoreturn}
 A "non-returning" function is a function which cannot return normally.
-It can transfer control only through @code{longjmp()}, @code{throw}
-(in C++), or similar mechanisms.  The most prominent function of this
-class is the @code{abort} function.  Non-returning functions are
+Instead of returning, it can loop forever, or it can transfer control via
+@code{abort}, @code{execvp}, @code{exit}, @code{longjmp}, @code{throw}
+(in C++), or similar mechanisms.  Non-returning functions are
 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.
+It can also help generate more-efficient code, as there is no need
+to save a return address when calling a non-returning function.
 
-To decorate function declarations and function definitions, you can
-use the @code{_Noreturn} keyword.  No modules are needed, as Gnulib
+Gnulib has multiple ways to support such a declaration''
+
+@itemize @bullet
+@item
+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.
+Unfortunately, although this approach works for all current C versions,
+the @code{_Noreturn} keyword is obsolescent in C23.
 
-Gnulib has two modules that support such a declaration:
-
-@itemize @bullet
 @item
 The @samp{noreturn} module.  It provides a way to put this declaration
 at function declarations, at function definitions, and in function
@@ -44,20 +48,13 @@ 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
+Which of the approaches to use?  If the non-returning functions you
 have to declare are unlikely to be accessed through function pointers,
-you should use module @code{stdnoreturn}; otherwise the module
+you should use @code{_Noreturn}; otherwise the module
 @code{noreturn} provides for better data-flow analysis and thus for
 better warnings.
 
-For a detailed description of the @code{stdnoreturn} module, see
-@ref{stdnoreturn.h}.
+There is also an obsolete @code{stdnoreturn} module, but its use is no
+longer recommended.
diff --git a/doc/posix-headers/stdnoreturn.texi 
b/doc/posix-headers/stdnoreturn.texi
index 3e1c5882db..ebe31ffc9f 100644
--- a/doc/posix-headers/stdnoreturn.texi
+++ b/doc/posix-headers/stdnoreturn.texi
@@ -22,6 +22,8 @@ MSVC/clang.
 Portability problems not fixed by Gnulib:
 @itemize
 @item
+@code{<stdnoreturn.h>} and the @code{noreturn} macro are obsolescent in C23.
+@item
 @code{<stdnoreturn.h>} cannot be #included in C++ mode on some platforms:
 FreeBSD 13.1.
 @item
diff --git a/lib/stdnoreturn.in.h b/lib/stdnoreturn.in.h
index d9e746699d..446e11b0b2 100644
--- a/lib/stdnoreturn.in.h
+++ b/lib/stdnoreturn.in.h
@@ -24,7 +24,9 @@
    References:
    ISO C11 (latest free draft
    <http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf>)
-   section 7.23 */
+   section 7.23
+
+   <stdnoreturn.h> is obsolescent in C23, so new code should avoid it.  */
 
 /* The definition of _Noreturn is copied here.  */
 
diff --git a/modules/stdnoreturn b/modules/stdnoreturn
index 1ef894d51f..ce6b04a35e 100644
--- a/modules/stdnoreturn
+++ b/modules/stdnoreturn
@@ -1,6 +1,12 @@
 Description:
 A <stdnoreturn.h> that nearly conforms to ISO C11.
 
+Status:
+obsolete
+
+Notice:
+This module is obsolete.
+
 Files:
 lib/stdnoreturn.in.h
 m4/stdnoreturn.m4
-- 
2.25.1