Fix timezone-related functions on MS-Windows

* src/editfns.c (set_time_zone_rule) [WINDOWSNT]: Always call
'xputenv', even if no reallocation of tzvalbuf was necessary.
This fixes a bug in timezone-related functions on MS-Windows.
Reported by Fabrice Popineau <fabrice.popineau@gmail.com>.

1 files changed, 12 insertions, 1 deletions

diff --git a/src/editfns.c b/src/editfns.c
index c387dc78c7d..bfa67e20e3e 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -2318,7 +2318,18 @@ set_time_zone_rule (const char *tzstring)
       tzval[tzeqlen] = 0;
     }
 
-  if (new_tzvalbuf)
+  if (new_tzvalbuf
+#ifdef WINDOWSNT
+      /* MS-Windows implementation of 'putenv' copies the argument
+         string into a block it allocates, so modifying tzval string
+         does not change the environment.  OTOH, the other threads run
+         by Emacs on MS-Windows never call 'xputenv' or 'putenv' or
+         'unsetenv', so the original cause for the dicey in-place
+         modification technique doesn't exist there in the first
+         place.  */
+      || 1
+#endif
+      )
     {
       /* Although this is not thread-safe, in practice this runs only
          on startup when there is only one thread.  */