sig2str: Align with POSIX:2024

[Bruno Haible]

POSIX specifies that
  - SIG2STR_MAX "shall be suitable for use in #if preprocessing directives"
    <https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/signal.h.html>
  - sig2str and str2sig shall be declared in <signal.h>.
    <https://pubs.opengroup.org/onlinepubs/9799919799/functions/str2sig.html>

This patch implements this, by moving the declarations to <signal.h> and
by changing the way SIG2STR_MAX is defined (but without changing its value: 19).


2024-08-09  Bruno Haible  <bruno@clisp.org>

        sig2str: Align with POSIX:2024.
        * lib/signal.in.h (SIG2STR_MAX): New macro.
        (sig2str, str2sig): New declarations.
        * lib/sig2str.h: Don't include intprops.h.
        (SIG2STR_MAX): Remove macro.
        (sig2str, str2sig): Remove declarations.
        * lib/sig2str.c: Include <signal.h> as the specification header.
        * m4/signal_h.m4 (gl_SIGNAL_H): Test whether sig2str, str2sig are
        declared.
        (gl_SIGNAL_H_REQUIRE_DEFAULTS): Initialize GNULIB_SIG2STR.
        (gl_SIGNAL_H_DEFAULTS): Initialize HAVE_SIG2STR, HAVE_STR2SIG.
        * m4/sig2str.m4 (gl_FUNC_SIG2STR): Require gl_SIGNAL_H_DEFAULTS. Check
        also for str2sig. Set HAVE_SIG2STR, HAVE_STR2SIG.
        * modules/signal-h (Makefile.am): Substitute GNULIB_SIG2STR,
        HAVE_SIG2STR, HAVE_STR2SIG.
        * modules/sig2str (Depends-on): Add signal-h. Remove intprops.
        (configure.ac): Test HAVE_SIG2STR, HAVE_STR2SIG. Invoke
        gl_SIGNAL_MODULE_INDICATOR.
        (Include): Add <signal.h>.
        * doc/posix-functions/sig2str.texi: Mention as implemented through the
        sig2str module.
        * doc/posix-functions/str2sig.texi: Likewise.

diff --git a/doc/posix-functions/sig2str.texi b/doc/posix-functions/sig2str.texi
index 80a177a050..f874d9c875 100644
--- a/doc/posix-functions/sig2str.texi
+++ b/doc/posix-functions/sig2str.texi
@@ -4,18 +4,15 @@
 
 POSIX specification:@* 
@url{https://pubs.opengroup.org/onlinepubs/9799919799/functions/sig2str.html}
 
-Gnulib module: ---
+Gnulib module: sig2str
 
 Portability problems fixed by Gnulib:
 @itemize
-@end itemize
-
-Portability problems not fixed by Gnulib:
-@itemize
 @item
 This function is missing on many platforms:
 glibc 2.40, macOS 14, FreeBSD 14.0, NetBSD 10.0, OpenBSD 7.5, Minix 3.3.0, AIX 
7.3.1, HP-UX 11.31, Cygwin 3.2.x, mingw, MSVC 14, Android 9.0.
 @end itemize
 
-Note: Gnulib has a module @code{sig2str} that implements this function,
-but declares it in a different header file.
+Portability problems not fixed by Gnulib:
+@itemize
+@end itemize
diff --git a/doc/posix-functions/str2sig.texi b/doc/posix-functions/str2sig.texi
index 706d2cd0c7..f76b4e331d 100644
--- a/doc/posix-functions/str2sig.texi
+++ b/doc/posix-functions/str2sig.texi
@@ -4,18 +4,15 @@
 
 POSIX specification:@* 
@url{https://pubs.opengroup.org/onlinepubs/9799919799/functions/str2sig.html}
 
-Gnulib module: ---
+Gnulib module: sig2str
 
 Portability problems fixed by Gnulib:
 @itemize
-@end itemize
-
-Portability problems not fixed by Gnulib:
-@itemize
 @item
 This function is missing on many platforms:
 glibc 2.40, macOS 14, FreeBSD 14.0, NetBSD 10.0, OpenBSD 7.5, Minix 3.3.0, AIX 
7.3.1, HP-UX 11.31, Cygwin 3.2.x, mingw, MSVC 14, Android 9.0.
 @end itemize
 
-Note: Gnulib has a module @code{sig2str} that implements this function,
-but declares it in a different header file.
+Portability problems not fixed by Gnulib:
+@itemize
+@end itemize
diff --git a/lib/sig2str.c b/lib/sig2str.c
index c6b91e3849..2dad2cd5a3 100644
--- a/lib/sig2str.c
+++ b/lib/sig2str.c
@@ -19,8 +19,10 @@
 
 #include <config.h>
 
-#include <limits.h>
+/* Specification.  */
 #include <signal.h>
+
+#include <limits.h>
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
diff --git a/lib/sig2str.h b/lib/sig2str.h
index 391da4b1d1..1abdb140e5 100644
--- a/lib/sig2str.h
+++ b/lib/sig2str.h
@@ -19,27 +19,6 @@
 
 #include <signal.h>
 
-/* Don't override system declarations of SIG2STR_MAX, sig2str, str2sig.  */
-#ifndef SIG2STR_MAX
-
-# include "intprops.h"
-
-/* Size of a buffer needed to hold a signal name like "HUP".  */
-# define SIG2STR_MAX (sizeof "SIGRTMAX" + INT_STRLEN_BOUND (int) - 1)
-
-#ifdef __cplusplus
-extern "C" {
-#endif
-
-int sig2str (int, char *);
-int str2sig (char const *, int *);
-
-#ifdef __cplusplus
-}
-#endif
-
-#endif
-
 /* An upper bound on signal numbers allowed by the system.  */
 
 #if defined _sys_nsig
diff --git a/lib/signal.in.h b/lib/signal.in.h
index 7ea0242db3..a0effa21ba 100644
--- a/lib/signal.in.h
+++ b/lib/signal.in.h
@@ -139,6 +139,47 @@ typedef void (*sighandler_t) (int);
 #endif
 
 
+/* Maximum size of a signal name returned by sig2str(), including the
+   terminating NUL byte.  */
+#ifndef SIG2STR_MAX
+/* The longest one: "RTMAX", then "+" or "-", then up to 10 digits, then NUL.
+   Add + 2 as a reserve for the future.  */
+# define SIG2STR_MAX (5 + 1 + 10 + 1 + 2)
+#endif
+
+#if @GNULIB_SIG2STR@
+# if !@HAVE_SIG2STR@
+_GL_FUNCDECL_SYS (sig2str, int, (int signo, char *str));
+# endif
+_GL_CXXALIAS_SYS (sig2str, int, (int signo, char *str));
+# if __GLIBC__ >= 2
+_GL_CXXALIASWARN (sig2str);
+# endif
+#elif defined GNULIB_POSIXCHECK
+# undef sig2str
+# if HAVE_RAW_DECL_SIG2STR
+_GL_WARN_ON_USE (sig2str, "sig2str is not portable - "
+                 "use gnulib module sig2str for portability");
+# endif
+#endif
+
+#if @GNULIB_SIG2STR@
+# if !@HAVE_STR2SIG@
+_GL_FUNCDECL_SYS (str2sig, int, (char const *str, int *signo_p));
+# endif
+_GL_CXXALIAS_SYS (str2sig, int, (char const *str, int *signo_p));
+# if __GLIBC__ >= 2
+_GL_CXXALIASWARN (str2sig);
+# endif
+#elif defined GNULIB_POSIXCHECK
+# undef str2sig
+# if HAVE_RAW_DECL_STR2SIG
+_GL_WARN_ON_USE (str2sig, "str2sig is not portable - "
+                 "use gnulib module sig2str for portability");
+# endif
+#endif
+
+
 #if @GNULIB_PTHREAD_SIGMASK@
 # if @REPLACE_PTHREAD_SIGMASK@
 #  if !(defined __cplusplus && defined GNULIB_NAMESPACE)
diff --git a/m4/sig2str.m4 b/m4/sig2str.m4
index 096d0253fc..acef58a6a4 100644
--- a/m4/sig2str.m4
+++ b/m4/sig2str.m4
@@ -1,5 +1,5 @@
 # sig2str.m4
-# serial 7
+# serial 8
 dnl Copyright (C) 2002, 2005-2006, 2009-2024 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -7,7 +7,14 @@
 
 AC_DEFUN([gl_FUNC_SIG2STR],
 [
-  AC_CHECK_FUNCS([sig2str])
+  AC_REQUIRE([gl_SIGNAL_H_DEFAULTS])
+  AC_CHECK_FUNCS([sig2str str2sig])
+  if test $ac_cv_func_sig2str = no; then
+    HAVE_SIG2STR=0
+  fi
+  if test $ac_cv_func_str2sig = no; then
+    HAVE_STR2SIG=0
+  fi
 ])
 
 # Prerequisites of lib/sig2str.c.
diff --git a/m4/signal_h.m4 b/m4/signal_h.m4
index 65afa2a1de..7a7d2b3c52 100644
--- a/m4/signal_h.m4
+++ b/m4/signal_h.m4
@@ -1,5 +1,5 @@
 # signal_h.m4
-# serial 22
+# serial 23
 dnl Copyright (C) 2007-2024 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -32,7 +32,8 @@ AC_DEFUN_ONCE([gl_SIGNAL_H]
   dnl Check for declarations of anything we want to poison if the
   dnl corresponding gnulib module is not in use.
   gl_WARN_ON_USE_PREPARE([[#include <signal.h>
-    ]], [pthread_sigmask sigaction
+    ]], [sig2str str2sig
+    pthread_sigmask sigaction
     sigaddset sigdelset sigemptyset sigfillset sigismember
     sigpending sigprocmask])
 
@@ -74,6 +75,7 @@ AC_DEFUN([gl_SIGNAL_H_REQUIRE_DEFAULTS]
   m4_defun(GL_MODULE_INDICATOR_PREFIX[_SIGNAL_H_MODULE_INDICATOR_DEFAULTS], [
     gl_MODULE_INDICATOR_INIT_VARIABLE([GNULIB_PTHREAD_SIGMASK])
     gl_MODULE_INDICATOR_INIT_VARIABLE([GNULIB_RAISE])
+    gl_MODULE_INDICATOR_INIT_VARIABLE([GNULIB_SIG2STR])
     gl_MODULE_INDICATOR_INIT_VARIABLE([GNULIB_SIGNAL_H_SIGPIPE])
     gl_MODULE_INDICATOR_INIT_VARIABLE([GNULIB_SIGPROCMASK])
     gl_MODULE_INDICATOR_INIT_VARIABLE([GNULIB_SIGACTION])
@@ -88,9 +90,11 @@ AC_DEFUN([gl_SIGNAL_H_DEFAULTS]
   HAVE_POSIX_SIGNALBLOCKING=1; AC_SUBST([HAVE_POSIX_SIGNALBLOCKING])
   HAVE_PTHREAD_SIGMASK=1;      AC_SUBST([HAVE_PTHREAD_SIGMASK])
   HAVE_RAISE=1;                AC_SUBST([HAVE_RAISE])
+  HAVE_SIG2STR=1;              AC_SUBST([HAVE_SIG2STR])
   HAVE_SIGSET_T=1;             AC_SUBST([HAVE_SIGSET_T])
   HAVE_SIGINFO_T=1;            AC_SUBST([HAVE_SIGINFO_T])
   HAVE_SIGACTION=1;            AC_SUBST([HAVE_SIGACTION])
+  HAVE_STR2SIG=1;              AC_SUBST([HAVE_STR2SIG])
   HAVE_STRUCT_SIGACTION_SA_SIGACTION=1;
                                AC_SUBST([HAVE_STRUCT_SIGACTION_SA_SIGACTION])
   HAVE_TYPE_VOLATILE_SIG_ATOMIC_T=1;
diff --git a/modules/sig2str b/modules/sig2str
index cb26add2d0..8055a58ff1 100644
--- a/modules/sig2str
+++ b/modules/sig2str
@@ -7,14 +7,16 @@ lib/sig2str.c
 m4/sig2str.m4
 
 Depends-on:
-intprops
+signal-h
 
 configure.ac:
 gl_FUNC_SIG2STR
-gl_CONDITIONAL([GL_COND_OBJ_SIG2STR], [test $ac_cv_func_sig2str = no])
+gl_CONDITIONAL([GL_COND_OBJ_SIG2STR],
+               [test $HAVE_SIG2STR = 0 || test $HAVE_STR2SIG = 0])
 AM_COND_IF([GL_COND_OBJ_SIG2STR], [
   gl_PREREQ_SIG2STR
 ])
+gl_SIGNAL_MODULE_INDICATOR([sig2str])
 
 Makefile.am:
 if GL_COND_OBJ_SIG2STR
@@ -22,7 +24,8 @@ lib_SOURCES += sig2str.c
 endif
 
 Include:
-"sig2str.h"
+<signal.h>
+"sig2str.h" /* for SIGNUM_BOUND */
 
 License:
 GPL
diff --git a/modules/signal-h b/modules/signal-h
index be4cf1991b..15d8adee72 100644
--- a/modules/signal-h
+++ b/modules/signal-h
@@ -34,15 +34,18 @@ signal.h: signal.in.h $(top_builddir)/config.status 
$(CXXDEFS_H) $(ARG_NONNULL_H
              -e 's|@''NEXT_SIGNAL_H''@|$(NEXT_SIGNAL_H)|g' \
              -e 's/@''GNULIB_PTHREAD_SIGMASK''@/$(GNULIB_PTHREAD_SIGMASK)/g' \
              -e 's/@''GNULIB_RAISE''@/$(GNULIB_RAISE)/g' \
+             -e 's/@''GNULIB_SIG2STR''@/$(GNULIB_SIG2STR)/g' \
              -e 's/@''GNULIB_SIGNAL_H_SIGPIPE''@/$(GNULIB_SIGNAL_H_SIGPIPE)/g' 
\
              -e 's/@''GNULIB_SIGPROCMASK''@/$(GNULIB_SIGPROCMASK)/g' \
              -e 's/@''GNULIB_SIGACTION''@/$(GNULIB_SIGACTION)/g' \
              -e 
's|@''HAVE_POSIX_SIGNALBLOCKING''@|$(HAVE_POSIX_SIGNALBLOCKING)|g' \
              -e 's|@''HAVE_PTHREAD_SIGMASK''@|$(HAVE_PTHREAD_SIGMASK)|g' \
              -e 's|@''HAVE_RAISE''@|$(HAVE_RAISE)|g' \
+             -e 's|@''HAVE_SIG2STR''@|$(HAVE_SIG2STR)|g' \
              -e 's|@''HAVE_SIGSET_T''@|$(HAVE_SIGSET_T)|g' \
              -e 's|@''HAVE_SIGINFO_T''@|$(HAVE_SIGINFO_T)|g' \
              -e 's|@''HAVE_SIGACTION''@|$(HAVE_SIGACTION)|g' \
+             -e 's|@''HAVE_STR2SIG''@|$(HAVE_STR2SIG)|g' \
              -e 
's|@''HAVE_STRUCT_SIGACTION_SA_SIGACTION''@|$(HAVE_STRUCT_SIGACTION_SA_SIGACTION)|g'
 \
              -e 
's|@''HAVE_TYPE_VOLATILE_SIG_ATOMIC_T''@|$(HAVE_TYPE_VOLATILE_SIG_ATOMIC_T)|g' \
              -e 's|@''HAVE_SIGHANDLER_T''@|$(HAVE_SIGHANDLER_T)|g' \