Lisp code shouldn't use set-time-zone-rule except through setenv.

* time.el (display-time-world-list, display-time-world-display):
* time-stamp.el (time-stamp-string):
* vc/add-log.el (add-change-log-entry): Use setenv instead of
set-time-zone-rule.

* src/editfns.c (Fset_time_zone_rule): Document relationship with the
setenv function.

Fixes: debbugs:7337

2 files changed, 9 insertions, 1 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 4df4455e862..cbe2d8659b2 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,5 +1,8 @@
 2011-08-08  Chong Yidong  <cyd@stupidchicken.com>
 
+        * editfns.c (Fset_time_zone_rule): Document relationship with the
+        setenv function.
+
         * ftfont.c (ftfont_pattern_entity): Copy the extras argument to
         the font entity extracted from the cache (Bug#8109).
 
diff --git a/src/editfns.c b/src/editfns.c
index 5eed386afb7..297f7b6d7e4 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -2053,7 +2053,12 @@ static char *initial_tz;
 DEFUN ("set-time-zone-rule", Fset_time_zone_rule, Sset_time_zone_rule, 1, 1, 0,
        doc: /* Set the local time zone using TZ, a string specifying a time zone rule.
 If TZ is nil, use implementation-defined default time zone information.
-If TZ is t, use Universal Time.  */)
+If TZ is t, use Universal Time.
+
+Instead of calling this function, you typically want (setenv "TZ" TZ).
+That changes both the environment of the Emacs process and the
+variable `process-environment', whereas `set-time-zone-rule' affects
+only the former.  */)
   (Lisp_Object tz)
 {
   const char *tzstring;