Fix failing tests in non-daylight saving time zones

* lisp/org.el (org-time-string-to-time): Remove optional POS and
  BUFFER arguments.  Accept new optional ZONE argument.
(org-time-string-to-seconds): Accept optional ZONE argument.
(org-check-before-date):
(org-check-after-date):
(org-check-dates-range):
(org-goto-calendar):
* lisp/ob-gnuplot.el (org-time-string-to-time):
* lisp/org-agenda.el (org-agenda-get-blocks):
* lisp/org-clock.el (org-clock-timestamps-change):
* lisp/org-list.el (org-time-string-to-seconds): Use UTC for time
  difference and time comparison.

* testing/lisp/test-org-clock.el (org-test-clock-create-clock): Use
  UTC for time differences.

etc/ORG-NEWS

@@ -23,7 +23,7 @@ Consider setting ~org-duration-units~ instead.
 
 *** ~org-at-timestamp-p~ optional argument accepts different values
 
-See docustrings for the allowed values.  For backward compatibility,
+See docstrings for the allowed values.  For backward compatibility,
 ~(org-at-timestamp-p t)~ is still supported, but should be updated
 accordingly.
 
@@ -85,6 +85,8 @@ list as their first argument.
 The optional argument is now a string to extract the repeater from.
 See docstring for details.
 
+*** Change signature for ~org-time-string-to-time~
+See docstring for changes.
 ** New features
 *** New Org duration library
 This new library implements tools to read and print time durations in
@@ -392,6 +394,7 @@ suitable as a default value.
 *** New entities : ~\dollar~ and ~\USD~
 *** ~org-parse-time-string~ accepts a new optional argument
 =ZONE= specifies the current time zone.
+*** ~org-time-string-to-seconds~ now accepts an optional =ZONE= argument
 *** Support for date style URLs in =org-protocol://open-source=
     URLs like =https://cool-blog.com/2017/05/20/cool-post/= are
     covered by rewrite rules.

lisp/ob-gnuplot.el

@@ -40,7 +40,7 @@
 ;;; Code:
 (require 'ob)
 
-(declare-function org-time-string-to-time "org" (s &optional buffer pos))
+(declare-function org-time-string-to-time "org" (s &optional zone))
 (declare-function org-combine-plists "org" (&rest plists))
 (declare-function orgtbl-to-generic "org-table" (table params))
 (declare-function gnuplot-mode "ext:gnuplot-mode" ())

lisp/org-agenda.el

@@ -6264,8 +6264,26 @@ scheduled items with an hour specification like [h]h:mm."
 	      (end-time (match-string 2)))
 	  (setq s1 (match-string 1)
 		s2 (match-string 2)
-		d1 (time-to-days (org-time-string-to-time s1 (current-buffer) pos))
-		d2 (time-to-days (org-time-string-to-time s2 (current-buffer) pos)))
+		d1 (time-to-days
+		    (condition-case err
+			(org-time-string-to-time s1)
+		      (error
+		       (error
+			"Bad timestamp %S at %d in buffer %S\nError was: %s"
+			s1
+			pos
+			(current-buffer)
+			(error-message-string err)))))
+		d2 (time-to-days
+		    (condition-case err
+			(org-time-string-to-time s2)
+		      (error
+		       (error
+			"Bad timestamp %S at %d in buffer %S\nError was: %s"
+			s2
+			pos
+			(current-buffer)
+			(error-message-string err))))))
 	  (if (and (> (- d0 d1) -1) (> (- d2 d0) -1))
 	      ;; Only allow days between the limits, because the normal
 	      ;; date stamps will catch the limits.

lisp/org-clock.el

@@ -1701,8 +1701,8 @@ Optional argument N tells to change by that many units."
 	      (begts (if updatets1 begts1 begts2)))
 	  (setq tdiff
 		(time-subtract
-		 (org-time-string-to-time org-last-changed-timestamp)
-		 (org-time-string-to-time ts)))
+		 (org-time-string-to-time org-last-changed-timestamp t)
+		 (org-time-string-to-time ts t)))
 	  (save-excursion
 	    (goto-char begts)
 	    (org-timestamp-change

lisp/org-list.el

@@ -149,7 +149,7 @@
 (declare-function org-remove-indentation "org" (code &optional n))
 (declare-function org-show-subtree "org" ())
 (declare-function org-sort-remove-invisible "org" (S))
-(declare-function org-time-string-to-seconds "org" (s))
+(declare-function org-time-string-to-seconds "org" (s &optional zone))
 (declare-function org-timer-hms-to-secs "org-timer" (hms))
 (declare-function org-timer-item "org-timer" (&optional arg))
 (declare-function org-trim "org" (s &optional keep-lead))

lisp/org.el

@@ -17439,8 +17439,8 @@ both scheduled and deadline timestamps."
 			   'timestamp)
 		     (org-at-planning-p))
 		   (time-less-p
-		    (org-time-string-to-time match)
-		    (org-time-string-to-time d)))))))
+		    (org-time-string-to-time match t)
+		    (org-time-string-to-time d t)))))))
     (message "%d entries before %s"
 	     (org-occur regexp nil callback)
 	     d)))
@@ -17461,8 +17461,8 @@ both scheduled and deadline timestamps."
 			   'timestamp)
 		     (org-at-planning-p))
 		   (not (time-less-p
-			 (org-time-string-to-time match)
-			 (org-time-string-to-time d))))))))
+			 (org-time-string-to-time match t)
+			 (org-time-string-to-time d t))))))))
     (message "%d entries after %s"
 	     (org-occur regexp nil callback)
 	     d)))
@@ -17485,11 +17485,11 @@ both scheduled and deadline timestamps."
 			'timestamp)
 		  (org-at-planning-p))
 		(not (time-less-p
-		      (org-time-string-to-time match)
-		      (org-time-string-to-time start-date)))
+		      (org-time-string-to-time match t)
+		      (org-time-string-to-time start-date t)))
 		(time-less-p
-		 (org-time-string-to-time match)
-		 (org-time-string-to-time end-date))))))))
+		 (org-time-string-to-time match t)
+		 (org-time-string-to-time end-date t))))))))
     (message "%d entries between %s and %s"
 	     (org-occur regexp nil callback) start-date end-date)))
 
@@ -17574,19 +17574,19 @@ days in order to avoid rounding problems."
       (push m l))
     (apply 'format fmt (nreverse l))))
 
-(defun org-time-string-to-time (s &optional buffer pos)
-  "Convert a timestamp string into internal time."
-  (condition-case errdata
-      (apply 'encode-time (org-parse-time-string s))
-    (error (error "Bad timestamp `%s'%s\nError was: %s"
-		  s (if (not (and buffer pos))
-			""
-		      (format-message " at %d in buffer `%s'" pos buffer))
-		  (cdr errdata)))))
+(defun org-time-string-to-time (s &optional zone)
+  "Convert timestamp string S into internal time.
+The optional ZONE is omitted or nil for Emacs local time, t for
+Universal Time, ‘wall’ for system wall clock time, or a string as
+in the TZ environment variable."
+  (apply #'encode-time (org-parse-time-string s nil zone)))
 
-(defun org-time-string-to-seconds (s)
-  "Convert a timestamp string to a number of seconds."
-  (float-time (org-time-string-to-time s)))
+(defun org-time-string-to-seconds (s &optional zone)
+  "Convert a timestamp string S into a number of seconds.
+The optional ZONE is omitted or nil for Emacs local time, t for
+Universal Time, ‘wall’ for system wall clock time, or a string as
+in the TZ environment variable."
+  (float-time (org-time-string-to-time s zone)))
 
 (org-define-error 'org-diary-sexp-no-match "Unable to match diary sexp")
 
@@ -18159,8 +18159,7 @@ A prefix ARG can be used to force the current date."
     (when (or (org-at-timestamp-p 'lax)
 	      (org-match-line (concat ".*" org-ts-regexp)))
       (let ((d1 (time-to-days (current-time)))
-	    (d2 (time-to-days
-		 (org-time-string-to-time (match-string 1)))))
+	    (d2 (time-to-days (org-time-string-to-time (match-string 1)))))
 	(setq diff (- d2 d1))))
     (calendar)
     (calendar-goto-today)

testing/lisp/test-org-clock.el

@@ -48,8 +48,9 @@ range.  INPUT2 can be omitted if clock hasn't finished yet.
 Return the clock line as a string."
   (let* ((beg (org-test-clock-create-timestamp input1 t t))
          (end (and input2 (org-test-clock-create-timestamp input2 t t)))
-         (sec-diff (and input2 (floor (- (org-time-string-to-seconds end)
-                                         (org-time-string-to-seconds beg))))))
+         (sec-diff (and input2
+			(floor (- (org-time-string-to-seconds end t)
+				  (org-time-string-to-seconds beg t))))))
     (concat org-clock-string " " beg
             (when end
               (concat "--" end " => "