[Tom Lane <tgl@sss.pgh.pa.us>]

Last night I updated the machine that hosts sifaka and indri
to spankin' new macOS Sequoia 15.4, and that promptly broke
the build on both animals:

snprintf.c:350:1: error: static declaration of 'strchrnul' follows non-static declaration
  350 | strchrnul(const char *s, int c)
      | ^
/Library/Developer/CommandLineTools/SDKs/MacOSX15.4.sdk/usr/include/_string.h:198:9: note: previous declaration is here
  198 |         strchrnul(const char *__s, int __c);
      |         ^
snprintf.c:414:27: error: 'strchrnul' is only available on macOS 15.4 or newer [-Werror,-Wunguarded-availability-new]
  414 |                         const char *next_pct = strchrnul(format + 1, '%');
      |                                                ^~~~~~~~~
/Library/Developer/CommandLineTools/SDKs/MacOSX15.4.sdk/usr/include/_string.h:198:9: note: 'strchrnul' has been marked as being introduced in macOS 15.4 here, but the deployment target is macOS 15.0.0
  198 |         strchrnul(const char *__s, int __c);
      |         ^
snprintf.c:414:27: note: enclose 'strchrnul' in a __builtin_available check to silence this warning


That is, the function exists now in macOS' libc, and so configure's
does-it-link test for HAVE_STRCHRNUL finds it, but <string.h>
will not let you use it unless you monkey around with

export MACOSX_DEPLOYMENT_TARGET=15.4

or similar.  I don't think we want to require people to do that,
so we need to fix things so that the code works with or without
a deployment target that satisfies <string.h>.  This is pretty
reminiscent of a problem that we faced a couple years ago with
preadv and pwritev, and solved in commit f014b1b9b by depending
on AC_CHECK_DECLS instead of AC_CHECK_FUNCS.  I made a patch
(attached) to solve this similarly.  Interestingly, this actually
makes the one usage in snprintf.c simpler, since we no longer
need to special-case the situation where GNU <string.h> doesn't
agree with the does-it-link test.

However ... testing this here shows that it fixes the autoconf
build as desired, with or without MACOSX_DEPLOYMENT_TARGET.
But the meson version *does not work*: it will set
HAVE_DECL_STRCHRNUL to 1 with or without MACOSX_DEPLOYMENT_TARGET,
and in the "without" case the build then blows up.

I speculate that the meson test for preadv/pwritev has never worked
for macOS either, and we haven't noticed because nobody has tried to
build with meson on a machine with low enough default deployment
target to not have preadv/pwritev.

I do not know nearly enough about meson to fix that test;
can anyone help?

			regards, tom lane

Attachments:

wip-fix-configure-strchrnul-check.patch (text/x-diff, 4.8K) download
diff --git a/configure b/configure
index 30d949c3c46..3d0e701c745 100755
--- a/configure
+++ b/configure
@@ -15401,7 +15401,7 @@ fi
 LIBS_including_readline="$LIBS"
 LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
 
-for ac_func in backtrace_symbols copyfile copy_file_range elf_aux_info getauxval getifaddrs getpeerucred inet_pton kqueue localeconv_l mbstowcs_l memset_s posix_fallocate ppoll pthread_is_threaded_np setproctitle setproctitle_fast strchrnul strsignal syncfs sync_file_range uselocale wcstombs_l
+for ac_func in backtrace_symbols copyfile copy_file_range elf_aux_info getauxval getifaddrs getpeerucred inet_pton kqueue localeconv_l mbstowcs_l memset_s posix_fallocate ppoll pthread_is_threaded_np setproctitle setproctitle_fast strsignal syncfs sync_file_range uselocale wcstombs_l
 do :
   as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
 ac_fn_c_check_func "$LINENO" "$ac_func" "$as_ac_var"
@@ -15955,6 +15955,18 @@ cat >>confdefs.h <<_ACEOF
 #define HAVE_DECL_PWRITEV $ac_have_decl
 _ACEOF
 
+ac_fn_c_check_decl "$LINENO" "strchrnul" "ac_cv_have_decl_strchrnul" "#include <string.h>
+"
+if test "x$ac_cv_have_decl_strchrnul" = xyes; then :
+  ac_have_decl=1
+else
+  ac_have_decl=0
+fi
+
+cat >>confdefs.h <<_ACEOF
+#define HAVE_DECL_STRCHRNUL $ac_have_decl
+_ACEOF
+
 
 # This is probably only present on macOS, but may as well check always
 ac_fn_c_check_decl "$LINENO" "F_FULLFSYNC" "ac_cv_have_decl_F_FULLFSYNC" "#include <fcntl.h>
diff --git a/configure.ac b/configure.ac
index 25cdfcf65af..47a287926bc 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1772,7 +1772,6 @@ AC_CHECK_FUNCS(m4_normalize([
 	pthread_is_threaded_np
 	setproctitle
 	setproctitle_fast
-	strchrnul
 	strsignal
 	syncfs
 	sync_file_range
@@ -1812,6 +1811,7 @@ AC_CHECK_DECLS([strlcat, strlcpy, strnlen, strsep])
 # won't handle deployment target restrictions on macOS
 AC_CHECK_DECLS([preadv], [], [], [#include <sys/uio.h>])
 AC_CHECK_DECLS([pwritev], [], [], [#include <sys/uio.h>])
+AC_CHECK_DECLS([strchrnul], [], [], [#include <string.h>])
 
 # This is probably only present on macOS, but may as well check always
 AC_CHECK_DECLS(F_FULLFSYNC, [], [], [#include <fcntl.h>])
diff --git a/meson.build b/meson.build
index b8da4966297..6932a0f00f7 100644
--- a/meson.build
+++ b/meson.build
@@ -2577,6 +2577,7 @@ decl_checks = [
 decl_checks += [
   ['preadv', 'sys/uio.h'],
   ['pwritev', 'sys/uio.h'],
+  ['strchrnul', 'string.h'],
 ]
 
 # Check presence of some optional LLVM functions.
@@ -2802,7 +2803,6 @@ func_checks = [
   ['shm_unlink', {'dependencies': [rt_dep], 'define': false}],
   ['shmget', {'dependencies': [cygipc_dep], 'define': false}],
   ['socket', {'dependencies': [socket_dep], 'define': false}],
-  ['strchrnul'],
   ['strerror_r', {'dependencies': [thread_dep]}],
   ['strlcat'],
   ['strlcpy'],
diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
index 92f0616c400..2ac61575883 100644
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -103,6 +103,10 @@
    don't. */
 #undef HAVE_DECL_PWRITEV
 
+/* Define to 1 if you have the declaration of `strchrnul', and to 0 if you
+   don't. */
+#undef HAVE_DECL_STRCHRNUL
+
 /* Define to 1 if you have the declaration of `strlcat', and to 0 if you
    don't. */
 #undef HAVE_DECL_STRLCAT
@@ -373,9 +377,6 @@
 /* Define to 1 if you have the <stdlib.h> header file. */
 #undef HAVE_STDLIB_H
 
-/* Define to 1 if you have the `strchrnul' function. */
-#undef HAVE_STRCHRNUL
-
 /* Define to 1 if you have the `strerror_r' function. */
 #undef HAVE_STRERROR_R
 
diff --git a/src/port/snprintf.c b/src/port/snprintf.c
index f8f2018ea0c..d0e99fdb072 100644
--- a/src/port/snprintf.c
+++ b/src/port/snprintf.c
@@ -343,8 +343,15 @@ static void trailing_pad(int padlen, PrintfTarget *target);
  *
  * Note: glibc declares this as returning "char *", but that would require
  * casting away const internally, so we don't follow that detail.
+ *
+ * Note: macOS has this too as of Sequoia 15.4, but it's hidden behind
+ * a deployment-target check that causes compile errors if the deployment
+ * target isn't high enough.  To work around that, use a macro to redefine
+ * what "strchrnul" means.
  */
-#ifndef HAVE_STRCHRNUL
+#if !HAVE_DECL_STRCHRNUL
+
+#define strchrnul pg_strchrnul
 
 static inline const char *
 strchrnul(const char *s, int c)
@@ -354,19 +361,7 @@ strchrnul(const char *s, int c)
 	return s;
 }
 
-#else
-
-/*
- * glibc's <string.h> declares strchrnul only if _GNU_SOURCE is defined.
- * While we typically use that on glibc platforms, configure will set
- * HAVE_STRCHRNUL whether it's used or not.  Fill in the missing declaration
- * so that this file will compile cleanly with or without _GNU_SOURCE.
- */
-#ifndef _GNU_SOURCE
-extern char *strchrnul(const char *s, int c);
-#endif
-
-#endif							/* HAVE_STRCHRNUL */
+#endif							/* !HAVE_DECL_STRCHRNUL */
 
 
 /*