Add FIXMEs for subsecond support

This adds FIXMEs to areas where Lisp code should support
subsecond information in broken-down timestamps.
It also fixes some unnecessary truncation of timestamps, and
ports the code to a hypothetical future Emacs version where
(decode-time) returns subsecond timestamps by default.
* lisp/calc/calc-forms.el (calc-time, math-iso-dt-to-date)
(calcFunc-now):
* lisp/calendar/icalendar.el (icalendar--add-decoded-times):
* lisp/calendar/iso8601.el (iso8601-parse-interval):
Truncate seconds to an integer, and add a FIXME about
subseconds support.
* lisp/calendar/icalendar.el (icalendar--decode-isodatetime)
(icalendar--decode-isoduration):
Add a FIXME about subseconds support.
* lisp/gnus/gnus-delay.el (gnus-delay-article):
Don’t truncate seconds to an integer, as there’s no need
to do that here.
* lisp/gnus/gnus-util.el (gnus-seconds-today)
(gnus-seconds-month, gnus-seconds-year):
* lisp/gnus/message.el (message-make-expires-date):
* lisp/org/org-timer.el (org-timer-show-remaining-time):
* lisp/vc/ediff-mult.el (ediff-format-date):
Truncate seconds to an integer, as that’s what’s wanted here.
* lisp/midnight.el (midnight-next):
Ceiling seconds to an integer, as that’s what wanted here.

9 files changed, 28 insertions, 18 deletions

diff --git a/lisp/calc/calc-forms.el b/lisp/calc/calc-forms.el
index c410ffe449c..7e8a8dcc9d0 100644
--- a/lisp/calc/calc-forms.el
+++ b/lisp/calc/calc-forms.el
@@ -37,7 +37,7 @@
 (defun calc-time ()
   (interactive)
   (calc-wrapper
-   (let ((time (decode-time)))
+   (let ((time (decode-time nil nil 'integer))) ;; FIXME: Support subseconds.
      (calc-enter-result 0 "time"
 			(list 'mod
 			      (list 'hms
@@ -499,7 +499,8 @@ in the Gregorian calendar and the remaining part determines the time."
 	(math-add (math-float date)
 		  (math-div (math-add (+ (* (nth 3 dt) 3600)
 					 (* (nth 4 dt) 60))
-				      (nth 5 dt))
+				      ;; FIXME: Support subseconds.
+				      (time-convert (nth 5 dt) 'integer))
 			    '(float 864 2)))
       date)))
 
@@ -1327,7 +1328,8 @@ as measured in the integer number of days before December 31, 1 BC (Gregorian)."
           (math-parse-iso-date-validate isoyear isoweek isoweekday hour minute second)))))
 
 (defun calcFunc-now (&optional zone)
-  (let ((date (let ((now (decode-time)))
+  ;; FIXME: Support subseconds.
+  (let ((date (let ((now (decode-time nil nil 'integer)))
 		(list 'date (math-dt-to-date
 			     (list (decoded-time-year now)
                                    (decoded-time-month now)
diff --git a/lisp/calendar/icalendar.el b/lisp/calendar/icalendar.el
index c2688705e30..3c46982c7b0 100644
--- a/lisp/calendar/icalendar.el
+++ b/lisp/calendar/icalendar.el
@@ -628,6 +628,7 @@ FIXME: multiple comma-separated values should be allowed!"
         (when (> (length isodatetimestring) 14)
           ;; seconds present
           (setq second (read (substring isodatetimestring 13 15))))
+	;; FIXME: Support subseconds.
         (when (and (> (length isodatetimestring) 15)
                    ;; UTC specifier present
                    (char-equal ?Z (aref isodatetimestring 15)))
@@ -703,6 +704,7 @@ FIXME: multiple comma-separated values should be allowed!"
                 (setq minutes (read (substring isodurationstring
                                                (match-beginning 10)
                                                (match-end 10)))))
+	    ;; FIXME: Support subseconds.
             (if (match-beginning 11)
                 (setq seconds (read (substring isodurationstring
                                                (match-beginning 12)
@@ -719,9 +721,12 @@ FIXME: multiple comma-separated values should be allowed!"
   "Add TIME1 to TIME2.
 Both times must be given in decoded form.  One of these times must be
 valid (year > 1900 or something)."
-  ;; FIXME: does this function exist already?
+  ;; FIXME: does this function exist already?  Can we use decoded-time-add?
   (decode-time (encode-time
-                (+ (decoded-time-second time1) (decoded-time-second time2))
+		;; FIXME: Support subseconds.
+		(time-convert (time-add (decoded-time-second time1)
+					(decoded-time-second time2))
+			      'integer)
                 (+ (decoded-time-minute time1) (decoded-time-minute time2))
                 (+ (decoded-time-hour time1) (decoded-time-hour time2))
                 (+ (decoded-time-day time1) (decoded-time-day time2))
diff --git a/lisp/calendar/iso8601.el b/lisp/calendar/iso8601.el
index 30352c7e75f..0f42c824e32 100644
--- a/lisp/calendar/iso8601.el
+++ b/lisp/calendar/iso8601.el
@@ -322,9 +322,10 @@ Return the number of minutes."
                                             duration))))
     (list start end
           (or duration
+	      ;; FIXME: Support subseconds.
               (decode-time (time-subtract (iso8601--encode-time end)
                                           (iso8601--encode-time start))
-                           (or (decoded-time-zone end) 0))))))
+			   (or (decoded-time-zone end) 0) 'integer)))))
 
 (defun iso8601--match (regexp string)
   (string-match (concat "\\`" regexp "\\'") string))
diff --git a/lisp/gnus/gnus-delay.el b/lisp/gnus/gnus-delay.el
index aabf23924a0..512011fa73b 100644
--- a/lisp/gnus/gnus-delay.el
+++ b/lisp/gnus/gnus-delay.el
@@ -98,7 +98,7 @@ DELAY is a string, giving the length of the time.  Possible values are:
 	   (setq hour   (string-to-number (match-string 1 delay))
 		 minute (string-to-number (match-string 2 delay)))
 	   ;; Use current time, except...
-	   (setq deadline (decode-time))
+	   (setq deadline (decode-time nil nil t))
 	   ;; ... for minute and hour.
 	   (setq deadline (apply #'encode-time (car deadline) minute hour
 				 (nthcdr 3 deadline)))
diff --git a/lisp/gnus/gnus-util.el b/lisp/gnus/gnus-util.el
index c6be59fd19f..f73af8e261c 100644
--- a/lisp/gnus/gnus-util.el
+++ b/lisp/gnus/gnus-util.el
@@ -357,24 +357,24 @@ Symbols are also allowed; their print names are used instead."
 ;; the full date if it's older)
 
 (defun gnus-seconds-today ()
-  "Return the number of seconds passed today."
-  (let ((now (decode-time)))
+  "Return the integer number of seconds passed today."
+  (let ((now (decode-time nil nil 'integer)))
     (+ (decoded-time-second now)
        (* (decoded-time-minute now) 60)
        (* (decoded-time-hour now) 3600))))
 
 (defun gnus-seconds-month ()
-  "Return the number of seconds passed this month."
-  (let ((now (decode-time)))
+  "Return the integer number of seconds passed this month."
+  (let ((now (decode-time nil nil 'integer)))
     (+ (decoded-time-second now)
        (* (decoded-time-minute now) 60)
        (* (decoded-time-hour now) 3600)
        (* (- (decoded-time-day now) 1) 3600 24))))
 
 (defun gnus-seconds-year ()
-  "Return the number of seconds passed this year."
+  "Return the integer number of seconds passed this year."
   (let* ((current (current-time))
-	 (now (decode-time current))
+	 (now (decode-time current nil 'integer))
 	 (days (format-time-string "%j" current)))
     (+ (decoded-time-second now)
        (* (decoded-time-minute now) 60)
diff --git a/lisp/gnus/message.el b/lisp/gnus/message.el
index 0a540a62214..48d79107ea8 100644
--- a/lisp/gnus/message.el
+++ b/lisp/gnus/message.el
@@ -5508,7 +5508,7 @@ If NOW, use that time instead."
   "Make date string for the Expires header.  Expiry in DAYS days.
 
 In posting styles use `(\"Expires\" (make-expires-date 30))'."
-  (let* ((cur (decode-time))
+  (let* ((cur (decode-time nil nil 'integer))
 	 (nday (+ days (decoded-time-day cur))))
     (setf (decoded-time-day cur) nday)
     (message-make-date (encode-time cur))))
diff --git a/lisp/midnight.el b/lisp/midnight.el
index fa41d80a69e..aad5236819d 100644
--- a/lisp/midnight.el
+++ b/lisp/midnight.el
@@ -193,8 +193,8 @@ The default value is `clean-buffer-list'."
   :type 'hook)
 
 (defun midnight-next ()
-  "Return the number of seconds till the next midnight."
-  (pcase-let ((`(,sec ,min ,hrs) (decode-time)))
+  "Return the number of whole or partial seconds till the next midnight."
+  (pcase-let ((`(,sec ,min ,hrs) (decode-time nil nil 'integer)))
     (- (* 24 60 60) (* 60 60 hrs) (* 60 min) sec)))
 
 ;;;###autoload
diff --git a/lisp/org/org-timer.el b/lisp/org/org-timer.el
index 6529a8b0ddf..20b33a1ef5f 100644
--- a/lisp/org/org-timer.el
+++ b/lisp/org/org-timer.el
@@ -385,7 +385,8 @@ VALUE can be `on', `off', or `paused'."
       (message "No timer set")
     (let* ((rtime (decode-time
 		   (time-subtract (timer--time org-timer-countdown-timer)
-				  nil)))
+				  nil)
+		   'integer))
 	   (rsecs (nth 0 rtime))
 	   (rmins (nth 1 rtime)))
       (message "%d minute(s) %d seconds left before next time out"
diff --git a/lisp/vc/ediff-mult.el b/lisp/vc/ediff-mult.el
index 1bdaca268e5..66d14e6b06d 100644
--- a/lisp/vc/ediff-mult.el
+++ b/lisp/vc/ediff-mult.el
@@ -1210,7 +1210,8 @@ behavior."
 	  (decoded-time-year time)
 	  (ediff-fill-leading-zero (decoded-time-hour time))
 	  (ediff-fill-leading-zero (decoded-time-minute time))
-	  (ediff-fill-leading-zero (decoded-time-second time))))
+	  (ediff-fill-leading-zero (time-convert (decoded-time-second time)
+						 'integer))))
 
 ;; Draw the directories
 (defun ediff-insert-dirs-in-meta-buffer (meta-list)