3 files changed, 35 insertions, 28 deletions

diff --git a/doc/emacs/files.texi b/doc/emacs/files.texi
index bfa55d38701..3d5562dcc47 100644
--- a/doc/emacs/files.texi
+++ b/doc/emacs/files.texi
@@ -881,9 +881,10 @@ Time-stamp: " "
 @code{before-save-hook} (@pxref{Hooks}).  When you save the file, this
 function then automatically updates the time stamp with the current
 date and time.  You can also use the command @kbd{M-x time-stamp} to
-update the time stamp manually.  For other customizations, see the
-Custom group @code{time-stamp}.  Note that the time stamp is formatted
-according to your locale setting (@pxref{Environment}).
+update the time stamp manually.  By default the time stamp is
+formatted according to your locale setting (@pxref{Environment}) and
+time zone (@pxref{Time of Day,,, elisp, The Emacs Lisp Reference
+Manual}).  For customizations, see the Custom group @code{time-stamp}.
 
 @node Reverting
 @section Reverting a Buffer
diff --git a/doc/misc/autotype.texi b/doc/misc/autotype.texi
index 839782a3b51..6bdbd344c7a 100644
--- a/doc/misc/autotype.texi
+++ b/doc/misc/autotype.texi
@@ -531,15 +531,17 @@ then @code{time-stamp} is conveniently listed as an option in the
 customization buffer.
 
 @vindex time-stamp-active
+@findex time-stamp-toggle-active
 @vindex time-stamp-format
-@vindex time-stamp-start
+@vindex time-stamp-time-zone
 The time stamp is updated only if the customizable variable
 @code{time-stamp-active} is on, which it is by default; the command
 @code{time-stamp-toggle-active} can be used to toggle it.  The format of
-the time stamp is set by the customizable variable
-@code{time-stamp-format}.
+the time stamp is set by the customizable variables
+@code{time-stamp-format} and @code{time-stamp-time-zone}.
 
 @vindex time-stamp-line-limit
+@vindex time-stamp-start
 @vindex time-stamp-end
 @vindex time-stamp-count
 @vindex time-stamp-inserts-lines
diff --git a/lisp/time-stamp.el b/lisp/time-stamp.el
index 46c993e1f5f..dffd59010db 100644
--- a/lisp/time-stamp.el
+++ b/lisp/time-stamp.el
@@ -121,9 +121,12 @@ If nil, no notification is given."
   :group 'time-stamp)
 
 (defcustom time-stamp-time-zone nil
-  "If non-nil, a string naming the timezone to be used by \\[time-stamp].
-Format is the same as that used by the environment variable TZ on your system."
-  :type '(choice (const nil) string)
+  "The time zone to be used by \\[time-stamp].
+Its format is that of the ZONE argument of the `format-time-string' function,"
+  :type '(choice (const :tag "Emacs local time" nil)
+                 (const :tag "Universal Time" t)
+                 (const :tag "system wall clock time" wall)
+                 (string :tag "TZ environment variable value"))
   :group 'time-stamp
   :version "20.1")
 ;;;###autoload(put 'time-stamp-time-zone 'safe-local-variable 'string-or-null-p)
@@ -412,6 +415,8 @@ With ARG, turn time stamping on if and only if arg is positive."
           (> (prefix-numeric-value arg) 0)))
   (message "time-stamp is now %s." (if time-stamp-active "active" "off")))
 
+(defun time-stamp--format (format time)
+  (format-time-string format time time-stamp-time-zone))
 
 (defun time-stamp-string (&optional ts-format)
   "Generate the new string to be inserted by \\[time-stamp].
@@ -420,8 +425,7 @@ format the string."
   (or ts-format
       (setq ts-format time-stamp-format))
   (if (stringp ts-format)
-      (format-time-string (time-stamp-string-preprocess ts-format)
-                          nil time-stamp-time-zone)
+      (time-stamp--format (time-stamp-string-preprocess ts-format) nil)
     ;; handle version 1 compatibility
     (cond ((or (eq time-stamp-old-format-warn 'error)
                (and (eq time-stamp-old-format-warn 'ask)
@@ -515,32 +519,32 @@ and all `time-stamp-format' compatibility."
           "%%")
          ((eq cur-char ?a)              ;day of week
           (if change-case
-              (format-time-string "%#a" time)
+              (time-stamp--format "%#a" time)
             (or alt-form (not (string-equal field-width ""))
                 (time-stamp-conv-warn "%a" "%:a"))
             (if (and alt-form (not (string-equal field-width "")))
                 ""                      ;discourage "%:3a"
-              (format-time-string "%A" time))))
+              (time-stamp--format "%A" time))))
          ((eq cur-char ?A)
           (if alt-form
-              (format-time-string "%A" time)
+              (time-stamp--format "%A" time)
             (or change-case (not (string-equal field-width ""))
                 (time-stamp-conv-warn "%A" "%#A"))
-            (format-time-string "%#A" time)))
+            (time-stamp--format "%#A" time)))
          ((eq cur-char ?b)              ;month name
           (if change-case
-              (format-time-string "%#b" time)
+              (time-stamp--format "%#b" time)
             (or alt-form (not (string-equal field-width ""))
                 (time-stamp-conv-warn "%b" "%:b"))
             (if (and alt-form (not (string-equal field-width "")))
                 ""                      ;discourage "%:3b"
-            (format-time-string "%B" time))))
+            (time-stamp--format "%B" time))))
          ((eq cur-char ?B)
           (if alt-form
-              (format-time-string "%B" time)
+              (time-stamp--format "%B" time)
             (or change-case (not (string-equal field-width ""))
                 (time-stamp-conv-warn "%B" "%#B"))
-            (format-time-string "%#B" time)))
+            (time-stamp--format "%#B" time)))
          ((eq cur-char ?d)              ;day of month, 1-31
           (time-stamp-do-number cur-char alt-form field-width time))
          ((eq cur-char ?H)              ;hour, 0-23
@@ -554,27 +558,27 @@ and all `time-stamp-format' compatibility."
          ((eq cur-char ?p)              ;am or pm
           (or change-case
               (time-stamp-conv-warn "%p" "%#p"))
-          (format-time-string "%#p" time))
+          (time-stamp--format "%#p" time))
          ((eq cur-char ?P)              ;AM or PM
-          (format-time-string "%p" time))
+          (time-stamp--format "%p" time))
          ((eq cur-char ?S)              ;seconds, 00-60
           (time-stamp-do-number cur-char alt-form field-width time))
          ((eq cur-char ?w)              ;weekday number, Sunday is 0
-          (format-time-string "%w" time))
+          (time-stamp--format "%w" time))
          ((eq cur-char ?y)              ;year
           (or alt-form (not (string-equal field-width ""))
               (time-stamp-conv-warn "%y" "%:y"))
-          (string-to-number (format-time-string "%Y" time)))
+          (string-to-number (time-stamp--format "%Y" time)))
          ((eq cur-char ?Y)              ;4-digit year, new style
-          (string-to-number (format-time-string "%Y" time)))
+          (string-to-number (time-stamp--format "%Y" time)))
          ((eq cur-char ?z)              ;time zone lower case
           (if change-case
               ""                        ;discourage %z variations
-            (format-time-string "%#Z" time)))
+            (time-stamp--format "%#Z" time)))
          ((eq cur-char ?Z)
           (if change-case
-              (format-time-string "%#Z" time)
-            (format-time-string "%Z" time)))
+              (time-stamp--format "%#Z" time)
+            (time-stamp--format "%Z" time)))
          ((eq cur-char ?f)              ;buffer-file-name, base name only
           (if buffer-file-name
               (file-name-nondirectory buffer-file-name)
@@ -634,7 +638,7 @@ width specification or \"\".  TIME is the time to convert."
                                (format "%%:%c" format-char)))
     (if (and alt-form (not (string-equal field-width "")))
         ""                              ;discourage "%:2d" and the like
-      (string-to-number (format-time-string format-string time)))))
+      (string-to-number (time-stamp--format format-string time)))))
 
 (defvar time-stamp-conversion-warn t
   "Warn about soon-to-be-unsupported forms in `time-stamp-format'.