alignasof: new module

This splits off support for the C23 keywords alignas and alignof,
from the now-deprecated stdalign module.  The latter now merely
provides C11 support.
* MODULES.html.sh, NEWS, doc/gnulib.texi:
* doc/posix-headers/stdalign.texi: Document the change.
* lib/stdalign.in.h: Remove most of the definitions (which are now
supplied by the alignasof module), leaving only
__alignas_is_defined and __alignof_is_defined.
* modules/alignasof, modules/alignasof-tests: New files.
* m4/stdalign.m4 (gl_ALIGNASOF): New macro, with
most of the contents of the old gl_STDALIGN_H.
Do not define __alignas_is_defined or __alignof_is_defined.
(gl_STDALIGN_H): Rely on gl_ALIGNASOF for most of the work.
* modules/alignalloc, modules/alignof, modules/argp:
* modules/crypto/md4-buffer, modules/crypto/md5-buffer:
* modules/crypto/sha1-buffer, modules/crypto/sha256-buffer:
* modules/crypto/sha512-buffer, modules/crypto/sm3-buffer:
* modules/fts, modules/rawmemchr, modules/relocatable-prog-wrapper:
* modules/stddef-tests, modules/sys_socket:
Depend on alignasof, not stdalign.
* modules/stdalign: Deprecate.  Depend on alignasof.
* modules/stdalign-tests: Move most contents to the new module
alignasof-tests, and depend on that.

2 files changed, 23 insertions, 15 deletions

diff --git a/doc/gnulib.texi b/doc/gnulib.texi
index 0f645206bf..7388fb0b45 100644
--- a/doc/gnulib.texi
+++ b/doc/gnulib.texi
@@ -873,10 +873,10 @@ substituted by Gnulib.
 @node alignof
 @section @code{alignof} and @code{alignas}
 
-Gnulib module: stdalign
+Gnulib module: alignasof
 
-The @code{stdalign} module arranges for @code{alignas}, @code{alignof}, and
-@code{<stdalign.h>} to be more like standard C@.  @xref{stdalign.h}.
+The @code{alignasof} module arranges for @code{alignas} and @code{alignof}
+to be more like standard C@.
 
 Portability problems fixed by Gnulib:
 @itemize
@@ -886,6 +886,7 @@ Pre-C11 platforms lack @code{alignas} and @code{alignof}.
 @item
 On pre-C23 platforms, @code{<stdalign.h>} must be included before
 using @code{alignas} or @code{alignof}.
+@xref{stdalign.h}.
 @end itemize
 
 Portability problems not fixed by Gnulib:
diff --git a/doc/posix-headers/stdalign.texi b/doc/posix-headers/stdalign.texi
index be3cec80d1..7f75a15540 100644
--- a/doc/posix-headers/stdalign.texi
+++ b/doc/posix-headers/stdalign.texi
@@ -1,15 +1,17 @@
 @node stdalign.h
 @section @file{stdalign.h}
 
-POSIX specification:@* Not in POSIX yet, but we expect it will be.
-ISO C11 (latest free draft
-@url{http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf})
+POSIX specification:@* Not in POSIX yet, but we expect it will be,
+at least temporarily until it becomes obsolete due to its phasing
+out starting in C23.
+ISO C23 (latest free draft
+@url{http://www.open-std.org/jtc1/sc22/wg14/www/docs/n3047.pdf})
 sections 6.5.3.4, 6.7.5, 7.15.
 C++11 (latest free draft
 @url{http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3242.pdf})
 section 18.10.
 
-Gnulib module: stdalign
+Gnulib module: alignasof
 
 Portability problems fixed by Gnulib:
 @itemize
@@ -17,6 +19,10 @@ Portability problems fixed by Gnulib:
 On older C platforms @code{<stdalign.h>} must be included before using
 @code{alignas} or @code{alignof}.  For example, GCC versions before 13 do not
 support these keywords, which were standardized by C23.
+On C23 and later platforms, @code{<stdalign.h>} has no effect and need
+not be included.  (Gnulib-using code should not include
+@code{<stdalign.h>} without also employing Gnulib's now-deprecated
+@code{stdalign} module.)
 @item
 This header file is missing on many platforms:
 FreeBSD 6.4, NetBSD 7.1, OpenBSD 6.7, Minix 3.3.0, AIX 7.1, HP-UX 11.31, IRIX 6.5, Solaris 11.3, mingw, MSVC 14, Android 9.0.
@@ -30,6 +36,15 @@ Older C platforms might not support the obsolescent
 @code{_Alignas} and @code{_Alignof} keywords or macros.
 This portability problem should not matter with code using this module,
 as such code should use @code{alignas} and @code{alignof} instead.
+@item
+In C11 and C17, @code{<stdalign.h>} defines the macros
+@code{__alignas_is_defined} and
+@code{__alignof_is_defined} to 1.
+In C23, these macros are not defined.
+This portability problem should not matter with code using Gnulib's
+@code{alignasof} module, as such code should use @code{alignas} and
+@code{alignof} without checking these two macros.  (Gnulib's
+now-deprecated @code{stdalign} module defines these two macros.)
 @end itemize
 
 Portability problems not fixed by Gnulib:
@@ -66,14 +81,6 @@ external variables that are declared close together with
 @code{alignas}.  The bug is fixed in Sun C 5.15, also known as Oracle
 Developer Studio 12.6 (2017).
 @item
-@code{<stdalign.h>} must be #included before @code{_Alignas} and
-@code{_Alignof} can be used.
-@item
-In C11 and C17, @code{<stdalign.h>} defines the macros
-@code{__alignas_is_defined} and
-@code{__alignof_is_defined} to 1.
-In C23, these macros are not defined.
-@item
 You cannot assume that @code{alignas} and @code{alignof} are reserved words;
 they might be macros.
 @end itemize