tzfree now preserves errno

* Makefile, NEWS, newtzset.3: Mention this.
* localtime.c (FREE_PRESERVES_ERRNO):
Default to 1 if 'free' is known to preserve errno, 0 otherwise.
(tzfree): Preserve errno if 'free' does not.

Author: eggert

Makefile

@@ -239,6 +239,8 @@ LDLIBS=
 #  -DEPOCH_OFFSET=N if the 'time' function returns a value N greater
 #	than what POSIX specifies, assuming local time is UT.
 #	For example, N is 252460800 on AmigaOS.
+#  -DFREE_PRESERVES_ERRNO=[01] if the 'free' function munges or preserves errno
+#	(default is guessed)
 #  -DHAVE_DECL_ASCTIME_R=0 if <time.h> does not declare asctime_r
 #	on POSIX platforms predating POSIX.1-2024
 #  -DHAVE_DECL_ENVIRON if <unistd.h> declares 'environ'

NEWS

@@ -93,6 +93,8 @@ Unreleased, experimental changes
     option is incompatible with POSIX.1-2024 and earlier.  It also
     costs CPU time and memory.
 
+    tzfree now preserves errno, consistently with POSIX.1-2024 'free'.
+
     tzcode now uses mempcpy if available, guessing its availability.
     Compile with -DHAVE_MEMPCPY=1 or 0 to override the guess.
 

localtime.c

@@ -2061,10 +2061,25 @@ tzalloc(char const *name)
   return sp;
 }
 
+#ifndef FREE_PRESERVES_ERRNO
+# if ((defined _POSIX_VERSION && 202405 <= _POSIX_VERSION) \
+      || (defined __GLIBC__ && 2 < __GLIBC__ + (33 <= __GLIBC_MINOR__)) \
+      || defined __OpenBSD__ || defined __sun)
+#  define FREE_PRESERVES_ERRNO 1
+# else
+#  define FREE_PRESERVES_ERRNO 0
+# endif
+#endif
+
 void
 tzfree(timezone_t sp)
 {
+  int err;
+  if (!FREE_PRESERVES_ERRNO)
+    err = errno;
   free(sp);
+  if (!FREE_PRESERVES_ERRNO)
+    errno = err;
 }
 
 /*

newtzset.3

@@ -379,6 +379,10 @@ If successful, the
 function returns a nonnull pointer to the newly allocated object.
 Otherwise, it returns a null pointer and sets
 .IR errno .
+The
+.B tzfree
+function does not modify
+.IR errno .
 .SH ERRORS
 .TP
 .B EOVERFLOW