mkdtemp: Provide declaration in <stdlib.h>

Building a testdir of the modules
  acl areadlinkat areadlinkat-with-size argmatch argp argp-version-etc array-map array-omap array-oset array-set backup-rename backupfile bitset bitsetv c-nstrftime c-xvasprintf canonicalize chdir-long chmodat chown chownat classpath clean-temp clean-temp-simple closein closeout copy-file csharpcomp csharpexec cygpath dfa dirname error exclude execute faccessat fchmodat fchownat fdopendir fdutimensat file-remote file-set filenamecat findprog fstatat fstrcmp fts futimens getaddrinfo getcwd getlogin getumask getusershell glob hamt hash-map hash-set hash-triple hashcode-file-inode human idcache issymlinkat javacomp javaexec javaversion jit/cache kwset lchmod lchown linebuffer linkat linkedhash-map linkedhash-set list-c++ map-c++ mem-hash-map mkancesdirs mkdir-p mkdirat mkfifoat modechange mountlist nonblocking-pipe-tests nonblocking-socket-tests nonblocking nstrftime obstack-printf-gnu obstack-printf-posix obstack-printf obstack-zprintf omap-c++ openat openat-die openat-safer openat openat2 opendirat oset-c++ pagealign_alloc parse-duration perror pipe-filter-gi pipe-filter-ii posix_spawn_file_actions_addchdir posix_spawn_file_actions_addfchdir propername quote quotearg quotearg-simple quotearg random readlinkat readtokens readutmp regex-quote relocatable-lib relocatable-prog renameat renameatu same save-cwd savedir savewd selinux-at set-c++ sh-quote sigpipe-die spawn-pipe stack stat-time statat strerror strerror_l string-desc-quotearg supersede symlinkat system-quote term-style-control trim unicodeio uniname/uniname uninorm/nfc uninorm/nfd uninorm/nfkc uninorm/nfkd unistdio/u16-vsnprintf unistdio/u16-vsprintf unistdio/u32-vsnprintf unistdio/u32-vsprintf unistdio/u8-vsnprintf unistdio/u8-vsprintf unistdio/ulc-vsnprintf unistdio/ulc-vsprintf unlinkat userspec utime utimecmp utimens utimensat vc-mtime verror wait-process windows-cygpath xalignalloc xalloc xalloc-die xbinary-io xconcat-filename xfreopen xgetcwd xgetcwd-lgpl xgetdomainname xgetgroups xgethostname xhash xlist xmalloca xmap xmemcoll xmemdup0 xomap xoset xprintf xprintf-gnu xprintf-posix xreadlink xreadlinkat xset xsetenv xstdopen xstrerror xstriconv xstriconveh xstring-buffer xstring-buffer-reversed xstring-desc xstrndup xstrtol-error xstrtol xsublist xvasprintf xvasprintf-gnu xvasprintf-posix xvasprintf yesno
with option --with-c++-tests on macOS 26, I see this compilation error:

depbase=`echo test-assert-h-c++.o | sed 's|[^/]*$|.deps/&|;s|\.o$||'`;\
        c++ -DHAVE_CONFIG_H -DEXEEXT=\"\" -DEXEEXT=\"\" -I. -I../../gltests -I..  -DGNULIB_STRICT_CHECKING=1 -DIN_GNULIB_TESTS=1 -I. -I../../gltests -I.. -I../../gltests/.. -I../gllib -I../../gltests/../gllib -I/Users/haible/include -Wall -Wno-error -Wno-error -g -O2 -MT test-assert-h-c++.o -MD -MP -MF $depbase.Tpo -c -o test-assert-h-c++.o ../../gltests/test-assert-h-c++.cc &&\
        mv -f $depbase.Tpo $depbase.Po
In file included from ../../gltests/test-assert-h-c++.cc:27:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/iostream:45:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/ios:228:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/__locale:17:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/__locale_dir/locale_base_api.h:115:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/__locale_dir/support/apple.h:21:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/__locale_dir/support/bsd_like.h:19:
../gllib/stdlib.h:1435:19: error: no member named 'mkdtemp' in the global namespace
 1435 | _GL_CXXALIAS_SYS (mkdtemp, char *, (char * /*template*/));
      |                   ^~~~~~~
../gllib/stdlib.h:1436:19: error: use of undeclared identifier 'mkdtemp'
 1436 | _GL_CXXALIASWARN (mkdtemp);
      |                   ^~~~~~~
In file included from ../../gltests/test-assert-h-c++.cc:27:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/iostream:45:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/ios:228:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/__locale:28:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/string:654:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/string_view:951:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/algorithm:2057:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/atomic:607:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/__atomic/atomic_flag.h:19:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/__thread/support.h:112:
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/v1/__thread/support/pthread.h:198:10: warning: The symbol ::nanosleep refers to the system function. Use gnulib::nanosleep instead. [-Wuser-defined-warnings]
  198 |   while (nanosleep(&__ts, &__ts) == -1 && errno == EINTR)
      |          ^
../gllib/time.h:788:1: note: from 'diagnose_if' attribute on 'nanosleep':
  788 | _GL_CXXALIASWARN (nanosleep);
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
../gllib/locale.h:381:4: note: expanded from macro '_GL_CXXALIASWARN'
  381 |    _GL_CXXALIASWARN_1 (func, GNULIB_NAMESPACE)
      |    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../gllib/locale.h:383:4: note: expanded from macro '_GL_CXXALIASWARN_1'
  383 |    _GL_CXXALIASWARN_2 (func, namespace)
      |    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../gllib/locale.h:388:5: note: expanded from macro '_GL_CXXALIASWARN_2'
  388 |     _GL_WARN_ON_USE (func, \
      |     ^~~~~~~~~~~~~~~~~~~~~~~~
  389 |                      "The symbol ::" #func " refers to the system function. " \
      |                      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  390 |                      "Use " #namespace "::" #func " instead.")
      |                      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../gllib/locale.h:556:19: note: expanded from macro '_GL_WARN_ON_USE'
  556 |   __attribute__ ((__diagnose_if__ (1, message, "warning")))
      |                   ^                ~
../../gltests/test-assert-h-c++.cc:32:26: warning: 'static_assert' with no message is a C++17 extension [-Wc++17-extensions]
   32 | static_assert (2 + 2 == 4);
      |                          ^
      |                          , ""
2 warnings and 2 errors generated.
make[3]: *** [test-assert-h-c++.o] Error 1


This patch fixes it.


2026-06-26  Bruno Haible  <[email protected]>

	mkdtemp: Provide declaration in <stdlib.h>.
	* lib/stdlib.in.h: Include <unistd.h> when needed for mkdtemp.
	* doc/posix-functions/mkdtemp.texi: Document macOS bug.

diff --git a/doc/posix-functions/mkdtemp.texi b/doc/posix-functions/mkdtemp.texi
index 75780faaa2..aa50da2046 100644
--- a/doc/posix-functions/mkdtemp.texi
+++ b/doc/posix-functions/mkdtemp.texi
@@ -12,6 +12,10 @@
 @item
 This function is missing on some platforms:
 AIX 5.1, HP-UX 11, Solaris 10, mingw, MSVC 14.
+@item
+This function is declared in @code{<unistd.h>} instead of @code{<stdlib.h>}
+on some platforms:
+macOS 26.
 @end itemize
 
 Portability problems not fixed by Gnulib:
diff --git a/lib/stdlib.in.h b/lib/stdlib.in.h
index 3c2004611f..6f63c87969 100644
--- a/lib/stdlib.in.h
+++ b/lib/stdlib.in.h
@@ -103,7 +103,8 @@ struct random_data
 # endif
 #endif
 
-#if (@GNULIB_MKSTEMP@ || @GNULIB_MKSTEMPS@ || @GNULIB_MKOSTEMP@ || @GNULIB_MKOSTEMPS@ || @GNULIB_GETSUBOPT@ || defined GNULIB_POSIXCHECK) && ! defined __GLIBC__ && !(defined _WIN32 && ! defined __CYGWIN__)
+#if (@GNULIB_MKDTEMP@ || @GNULIB_MKSTEMP@ || @GNULIB_MKSTEMPS@ || @GNULIB_MKOSTEMP@ || @GNULIB_MKOSTEMPS@ || @GNULIB_GETSUBOPT@ || defined GNULIB_POSIXCHECK) && ! defined __GLIBC__ && !(defined _WIN32 && ! defined __CYGWIN__)
+/* On macOS 26, only <unistd.h> declares mkdtemp.  */
 /* On Mac OS X 10.3, only <unistd.h> declares mkstemp.  */
 /* On Mac OS X 10.5, only <unistd.h> declares mkstemps.  */
 /* On Mac OS X 10.13, only <unistd.h> declares mkostemp and mkostemps.  */