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

6 files changed, 52 insertions, 34 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index d2ea294d2d0..bd344dad35a 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,10 @@
+2011-08-08  Chong Yidong  <cyd@stupidchicken.com>
+
+        * 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 (Bug#7337).
+
 2011-08-08  Daiki Ueno  <ueno@unixuser.org>
 
         * epg.el (epg--status-KEYEXPIRED, epg--status-KEYREVOKED): Fix typo.
diff --git a/lisp/time-stamp.el b/lisp/time-stamp.el
index 59340583997..fda8cd1438d 100644
--- a/lisp/time-stamp.el
+++ b/lisp/time-stamp.el
@@ -424,10 +424,10 @@ format the string."
           (let ((ts-real-time-zone (getenv "TZ")))
             (unwind-protect
                 (progn
-                  (set-time-zone-rule time-stamp-time-zone)
+                  (setenv "TZ" time-stamp-time-zone)
                   (format-time-string
                    (time-stamp-string-preprocess ts-format)))
-              (set-time-zone-rule ts-real-time-zone)))
+              (setenv "TZ" ts-real-time-zone)))
         (format-time-string
          (time-stamp-string-preprocess ts-format)))
     ;; handle version 1 compatibility
diff --git a/lisp/time.el b/lisp/time.el
index b158ef64691..f8fea0c64a2 100644
--- a/lisp/time.el
+++ b/lisp/time.el
@@ -156,21 +156,24 @@ LABEL is a string to display as the label of that TIMEZONE's time."
 (defcustom display-time-world-list
   ;; Determine if zoneinfo style timezones are supported by testing that
   ;; America/New York and Europe/London return different timezones.
-  (let (gmt nyt)
-    (set-time-zone-rule "America/New_York")
-    (setq nyt (format-time-string "%z"))
-    (set-time-zone-rule "Europe/London")
-    (setq gmt (format-time-string "%z"))
-    (set-time-zone-rule nil)
+  (let ((old-tz (getenv "TZ"))
+        gmt nyt)
+    (unwind-protect
+        (progn
+          (setenv "TZ" "America/New_York")
+          (setq nyt (format-time-string "%z"))
+          (setenv "TZ" "Europe/London")
+          (setq gmt (format-time-string "%z")))
+      (setenv "TZ" old-tz))
     (if (string-equal nyt gmt)
         legacy-style-world-list
       zoneinfo-style-world-list))
   "Alist of time zones and places for `display-time-world' to display.
 Each element has the form (TIMEZONE LABEL).
-TIMEZONE should be in the format supported by `set-time-zone-rule' on
-your system.  See the documentation of `zoneinfo-style-world-list' and
-\`legacy-style-world-list' for two widely used formats.
-LABEL is a string to display as the label of that TIMEZONE's time."
+TIMEZONE should be in a format supported by your system.  See the
+documentation of `zoneinfo-style-world-list' and
+\`legacy-style-world-list' for two widely used formats.  LABEL is
+a string to display as the label of that TIMEZONE's time."
   :group 'display-time
   :type '(repeat (list string string))
   :version "23.1")
@@ -521,26 +524,26 @@ See `display-time-world'."
 (defun display-time-world-display (alist)
   "Replace current buffer text with times in various zones, based on ALIST."
   (let ((inhibit-read-only t)
-        (buffer-undo-list t))
+        (buffer-undo-list t)
+        (old-tz (getenv "TZ"))
+        (max-width 0)
+        result fmt)
     (erase-buffer)
-    (let ((max-width 0)
-          (result ())
-          fmt)
-      (unwind-protect
-          (dolist (zone alist)
-            (let* ((label (cadr zone))
-                   (width (string-width label)))
-              (set-time-zone-rule (car zone))
-              (push (cons label
-                          (format-time-string display-time-world-time-format))
-                    result)
-              (when (> width max-width)
-                (setq max-width width))))
-        (set-time-zone-rule nil))
-      (setq fmt (concat "%-" (int-to-string max-width) "s %s\n"))
-      (dolist (timedata (nreverse result))
-        (insert (format fmt (car timedata) (cdr timedata)))))
-    (delete-char -1)))
+    (unwind-protect
+        (dolist (zone alist)
+          (let* ((label (cadr zone))
+                 (width (string-width label)))
+            (setenv "TZ" (car zone))
+            (push (cons label
+                        (format-time-string display-time-world-time-format))
+                  result)
+            (when (> width max-width)
+              (setq max-width width))))
+      (setenv "TZ" old-tz))
+    (setq fmt (concat "%-" (int-to-string max-width) "s %s\n"))
+    (dolist (timedata (nreverse result))
+      (insert (format fmt (car timedata) (cdr timedata)))))
+  (delete-char -1))
 
 ;;;###autoload
 (defun display-time-world ()
diff --git a/lisp/vc/add-log.el b/lisp/vc/add-log.el
index e5aead2309f..9170d7b9424 100644
--- a/lisp/vc/add-log.el
+++ b/lisp/vc/add-log.el
@@ -853,9 +853,9 @@ non-nil, otherwise in local time."
                             (let ((tz (getenv "TZ")))
                               (unwind-protect
                                   (progn
-                                    (set-time-zone-rule add-log-time-zone-rule)
+                                    (setenv "TZ" add-log-time-zone-rule)
                                     (funcall add-log-time-format))
-                                (set-time-zone-rule tz)))
+                                (setenv "TZ" tz)))
                           (funcall add-log-time-format))
                         "  " full-name
                         "  <" addr ">"))
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;