Fix iso8601-parse so unknown DST is -1, not nil

The convention in a decoded time’s dst flag is that t means DST,
nil means standard time, and -1 means unknown.  This differs from
the convention for other components of a decoded time, where nil
means unknown.  Fix some places where iso8601-parse mistakenly
treated nil as meaning that the dst flag was unknown.
* doc/lispref/os.texi (Time Parsing):
Adjust to match parse-time-string’s doc string.
* lisp/calendar/iso8601.el (iso8601-parse):
Set dst flag to nil if a numeric time zone or "Z" is given.
(iso8601--decoded-time): Default dst flag to -1 if no dst
flag or zone is given.
* lisp/calendar/time-date.el (decoded-time-set-defaults):
When we don’t have a time zone, set the dst flag consistently
with DEFAULT-ZONE.
* test/lisp/calendar/iso8601-tests.el (test-iso8601-date-years)
(test-iso8601-date-dates, test-iso8601-date-obsolete)
(test-iso8601-date-weeks, test-iso8601-date-ordinals)
(test-iso8601-time, test-iso8601-combined)
(test-iso8601-duration, test-iso8601-intervals)
(standard-test-dates, standard-test-time-of-day-local-time)
(standard-test-time-of-day-fractions)
(nonstandard-test-time-of-day-decimals)
(standard-test-time-of-day-beginning-of-day)
(standard-test-date-and-time-of-day, standard-test-interval):
Adjust tests to match fixed behavior.

4 files changed, 87 insertions, 83 deletions

diff --git a/doc/lispref/os.texi b/doc/lispref/os.texi
index 201ca18c1e4..a034ccdcd5c 100644
--- a/doc/lispref/os.texi
+++ b/doc/lispref/os.texi
@@ -1689,7 +1689,8 @@ following form:
 @noindent
 The format of this list is the same as what @code{decode-time} accepts
 (@pxref{Time Conversion}), and is described in more detail there.  Any
-element that cannot be determined from the input will be set to
+@code{dst} element that cannot be determined from the input is set to
+@minus{}1, and any other unknown element is set to
 @code{nil}.  The argument @var{string} should resemble an RFC 822 (or later) or
 ISO 8601 string, like ``Fri, 25 Mar 2016 16:24:56 +0100'' or
 ``1998-09-12T12:21:54-0200'', but this function will attempt to parse
diff --git a/lisp/calendar/iso8601.el b/lisp/calendar/iso8601.el
index ae1dab17252..e42fe0fa21f 100644
--- a/lisp/calendar/iso8601.el
+++ b/lisp/calendar/iso8601.el
@@ -136,7 +136,8 @@ See `decode-time' for the meaning of FORM."
       (when zone-string
         (setf (decoded-time-zone date)
               ;; The time zone in decoded times are in seconds.
-              (* (iso8601-parse-zone zone-string) 60)))
+              (* (iso8601-parse-zone zone-string) 60))
+        (setf (decoded-time-dst date) nil))
       date)))
 
 (defun iso8601-parse-date (string)
@@ -332,6 +333,9 @@ Return the number of minutes."
     (list start end
           (or duration
               ;; FIXME: Support subseconds.
+              ;; FIXME: It makes no sense to decode a time difference
+              ;; according to (decoded-time-zone end), or according to
+              ;; any other time zone for that matter.
               (decode-time (time-subtract (iso8601--encode-time end)
                                           (iso8601--encode-time start))
                            (or (decoded-time-zone end) 0) 'integer)))))
@@ -354,7 +358,7 @@ Return the number of minutes."
         (iso8601--value month)
         (iso8601--value year)
         nil
-        dst
+        (if (or dst zone) dst -1)
         zone))
 
 (defun iso8601--encode-time (time)
diff --git a/lisp/calendar/time-date.el b/lisp/calendar/time-date.el
index 1e589ece29d..e2402de8010 100644
--- a/lisp/calendar/time-date.el
+++ b/lisp/calendar/time-date.el
@@ -515,15 +515,14 @@ TIME is modified and returned."
   (unless (decoded-time-year time)
     (setf (decoded-time-year time) 0))
 
-  ;; When we don't have a time zone and we don't have a DST, then mark
-  ;; it as unknown.
-  (when (and (not (decoded-time-zone time))
-             (not (decoded-time-dst time)))
-    (setf (decoded-time-dst time) -1))
-
-  (when (and (not (decoded-time-zone time))
-             default-zone)
-    (setf (decoded-time-zone time) 0))
+  ;; When we don't have a time zone, default to DEFAULT-ZONE without
+  ;; DST if DEFAULT-ZONE if given, and to unknown DST otherwise.
+  (unless (decoded-time-zone time)
+    (if default-zone
+        (progn (setf (decoded-time-zone time) default-zone)
+               (setf (decoded-time-dst time) nil))
+      (setf (decoded-time-dst time) -1)))
+
   time)
 
 (provide 'time-date)
diff --git a/test/lisp/calendar/iso8601-tests.el b/test/lisp/calendar/iso8601-tests.el
index 430680c5077..6e7a4724a6b 100644
--- a/test/lisp/calendar/iso8601-tests.el
+++ b/test/lisp/calendar/iso8601-tests.el
@@ -24,49 +24,49 @@
 
 (ert-deftest test-iso8601-date-years ()
   (should (equal (iso8601-parse-date "1985")
-                 '(nil nil nil nil nil 1985 nil nil nil)))
+                  '(nil nil nil nil nil 1985 nil -1 nil)))
   (should (equal (iso8601-parse-date "-0003")
-                 '(nil nil nil nil nil -3 nil nil nil)))
+                  '(nil nil nil nil nil -3 nil -1 nil)))
   (should (equal (iso8601-parse-date "+1985")
-                 '(nil nil nil nil nil 1985 nil nil nil))))
+                  '(nil nil nil nil nil 1985 nil -1 nil))))
 
 (ert-deftest test-iso8601-date-dates ()
   (should (equal (iso8601-parse-date "1985-03-14")
-                 '(nil nil nil 14 3 1985 nil nil nil)))
+                  '(nil nil nil 14 3 1985 nil -1 nil)))
   (should (equal (iso8601-parse-date "19850314")
-                 '(nil nil nil 14 3 1985 nil nil nil)))
+                  '(nil nil nil 14 3 1985 nil -1 nil)))
   (should (equal (iso8601-parse-date "1985-02")
-                 '(nil nil nil nil 2 1985 nil nil nil))))
+                  '(nil nil nil nil 2 1985 nil -1 nil))))
 
 (ert-deftest test-iso8601-date-obsolete ()
   (should (equal (iso8601-parse-date "--02-01")
-                 '(nil nil nil 1 2 nil nil nil nil)))
+                  '(nil nil nil 1 2 nil nil -1 nil)))
   (should (equal (iso8601-parse-date "--0201")
-                 '(nil nil nil 1 2 nil nil nil nil))))
+                  '(nil nil nil 1 2 nil nil -1 nil))))
 
 (ert-deftest test-iso8601-date-weeks ()
   (should (equal (iso8601-parse-date "2008W39-6")
-                 '(nil nil nil 27 9 2008 nil nil nil)))
+                  '(nil nil nil 27 9 2008 nil -1 nil)))
   (should (equal (iso8601-parse-date "2009W01-1")
-                 '(nil nil nil 29 12 2008 nil nil nil)))
+                  '(nil nil nil 29 12 2008 nil -1 nil)))
   (should (equal (iso8601-parse-date "2009W53-7")
-                 '(nil nil nil 3 1 2010 nil nil nil))))
+                  '(nil nil nil 3 1 2010 nil -1 nil))))
 
 (ert-deftest test-iso8601-date-ordinals ()
   (should (equal (iso8601-parse-date "1981-095")
-                 '(nil nil nil 5 4 1981 nil nil nil))))
+                  '(nil nil nil 5 4 1981 nil -1 nil))))
 
 (ert-deftest test-iso8601-time ()
   (should (equal (iso8601-parse-time "13:47:30")
-                 '(30 47 13 nil nil nil nil nil nil)))
+                  '(30 47 13 nil nil nil nil -1 nil)))
   (should (equal (iso8601-parse-time "134730")
-                 '(30 47 13 nil nil nil nil nil nil)))
+                  '(30 47 13 nil nil nil nil -1 nil)))
   (should (equal (iso8601-parse-time "1347")
-                 '(0 47 13 nil nil nil nil nil nil))))
+                  '(0 47 13 nil nil nil nil -1 nil))))
 
 (ert-deftest test-iso8601-combined ()
   (should (equal (iso8601-parse "2008-03-02T13:47:30")
-                 '(30 47 13 2 3 2008 nil nil nil)))
+                  '(30 47 13 2 3 2008 nil -1 nil)))
   (should (equal (iso8601-parse "2008-03-02T13:47:30Z")
                  '(30 47 13 2 3 2008 nil nil 0)))
   (should (equal (iso8601-parse "2008-03-02T13:47:30+01:00")
@@ -76,13 +76,13 @@
 
 (ert-deftest test-iso8601-duration ()
   (should (equal (iso8601-parse-duration "P3Y6M4DT12H30M5S")
-                 '(5 30 12 4 6 3 nil nil nil)))
+                  '(5 30 12 4 6 3 nil -1 nil)))
   (should (equal (iso8601-parse-duration "P1M")
-                 '(0 0 0 0 1 0 nil nil nil)))
+                  '(0 0 0 0 1 0 nil -1 nil)))
   (should (equal (iso8601-parse-duration "PT1M")
-                 '(0 1 0 0 0 0 nil nil nil)))
+                  '(0 1 0 0 0 0 nil -1 nil)))
   (should (equal (iso8601-parse-duration "P0003-06-04T12:30:05")
-                 '(5 30 12 4 6 3 nil nil nil))))
+                  '(5 30 12 4 6 3 nil -1 nil))))
 
 (ert-deftest test-iso8601-invalid ()
   (should-not (iso8601-valid-p " 2008-03-02T13:47:30-01"))
@@ -101,88 +101,88 @@
   (should (equal (iso8601-parse-interval "2007-03-01T13:00:00Z/P1Y2M10DT2H30M")
                  '((0 0 13 1 3 2007 nil nil 0)
                    (0 30 15 11 5 2008 nil nil 0)
-                   (0 30 2 10 2 1 nil nil nil))))
+                    (0 30 2 10 2 1 nil -1 nil))))
   (should (equal (iso8601-parse-interval "P1Y2M10DT2H30M/2008-05-11T15:30:00Z")
                  '((0 0 13 1 3 2007 nil nil 0)
                    (0 30 15 11 5 2008 nil nil 0)
-                   (0 30 2 10 2 1 nil nil nil)))))
+                    (0 30 2 10 2 1 nil -1 nil)))))
 
 (ert-deftest standard-test-dates ()
   (should (equal (iso8601-parse-date "19850412")
-                 '(nil nil nil 12 4 1985 nil nil nil)))
+                  '(nil nil nil 12 4 1985 nil -1 nil)))
   (should (equal (iso8601-parse-date "1985-04-12")
-                 '(nil nil nil 12 4 1985 nil nil nil)))
+                  '(nil nil nil 12 4 1985 nil -1 nil)))
 
   (should (equal (iso8601-parse-date "1985102")
-                 '(nil nil nil 12 4 1985 nil nil nil)))
+                  '(nil nil nil 12 4 1985 nil -1 nil)))
   (should (equal (iso8601-parse-date "1985-102")
-                 '(nil nil nil 12 4 1985 nil nil nil)))
+                  '(nil nil nil 12 4 1985 nil -1 nil)))
 
   (should (equal (iso8601-parse-date "1985W155")
-                 '(nil nil nil 12 4 1985 nil nil nil)))
+                  '(nil nil nil 12 4 1985 nil -1 nil)))
   (should (equal (iso8601-parse-date "1985-W15-5")
-                 '(nil nil nil 12 4 1985 nil nil nil)))
+                  '(nil nil nil 12 4 1985 nil -1 nil)))
 
   (should (equal (iso8601-parse-date "1985W15")
-                 '(nil nil nil 7 4 1985 nil nil nil)))
+                  '(nil nil nil 7 4 1985 nil -1 nil)))
   (should (equal (iso8601-parse-date "1985-W15")
-                 '(nil nil nil 7 4 1985 nil nil nil)))
+                  '(nil nil nil 7 4 1985 nil -1 nil)))
 
   (should (equal (iso8601-parse-date "1985-04")
-                 '(nil nil nil nil 4 1985 nil nil nil)))
+                  '(nil nil nil nil 4 1985 nil -1 nil)))
 
   (should (equal (iso8601-parse-date "1985")
-                 '(nil nil nil nil nil 1985 nil nil nil)))
+                  '(nil nil nil nil nil 1985 nil -1 nil)))
 
   (should (equal (iso8601-parse-date "+1985-04-12")
-                 '(nil nil nil 12 4 1985 nil nil nil)))
+                  '(nil nil nil 12 4 1985 nil -1 nil)))
   (should (equal (iso8601-parse-date "+19850412")
-                 '(nil nil nil 12 4 1985 nil nil nil))))
+                  '(nil nil nil 12 4 1985 nil -1 nil))))
 
 (ert-deftest standard-test-time-of-day-local-time ()
   (should (equal (iso8601-parse-time "152746")
-                 '(46 27 15 nil nil nil nil nil nil)))
+                  '(46 27 15 nil nil nil nil -1 nil)))
   (should (equal (iso8601-parse-time "15:27:46")
-                 '(46 27 15 nil nil nil nil nil nil)))
+                  '(46 27 15 nil nil nil nil -1 nil)))
 
   (should (equal (iso8601-parse-time "1528")
-                 '(0 28 15 nil nil nil nil nil nil)))
+                  '(0 28 15 nil nil nil nil -1 nil)))
   (should (equal (iso8601-parse-time "15:28")
-                 '(0 28 15 nil nil nil nil nil nil)))
+                  '(0 28 15 nil nil nil nil -1 nil)))
 
   (should (equal (iso8601-parse-time "15")
-                 '(0 0 15 nil nil nil nil nil nil))))
+                  '(0 0 15 nil nil nil nil -1 nil))))
 
 (ert-deftest standard-test-time-of-day-fractions ()
   (should (equal (iso8601-parse-time "152735,5" t)
-                 '((355 . 10) 27 15 nil nil nil nil nil nil)))
+                  '((355 . 10) 27 15 nil nil nil nil -1 nil)))
   (should (equal (iso8601-parse-time "15:27:35,5" t)
-                 '((355 . 10) 27 15 nil nil nil nil nil nil)))
+                  '((355 . 10) 27 15 nil nil nil nil -1 nil)))
 
   (should (equal (iso8601-parse-time "2320,5" t)
-                 '(30 20 23 nil nil nil nil nil nil)))
+                  '(30 20 23 nil nil nil nil -1 nil)))
   (should (equal (iso8601-parse-time "23:20,8" t)
-                 '(48 20 23 nil nil nil nil nil nil)))
+                  '(48 20 23 nil nil nil nil -1 nil)))
 
   (should (equal (iso8601-parse-time "23,3" t)
-                 '(0 18 23 nil nil nil nil nil nil))))
+                  '(0 18 23 nil nil nil nil -1 nil))))
 
 (ert-deftest nonstandard-test-time-of-day-decimals ()
   (should (equal (iso8601-parse-time "15:27:35.123" t)
-                 '((35123 . 1000) 27 15 nil nil nil nil nil nil)))
+                  '((35123 . 1000) 27 15 nil nil nil nil -1 nil)))
   (should (equal (iso8601-parse-time "15:27:35.123456789" t)
-                 '((35123456789 . 1000000000) 27 15 nil nil nil nil nil nil))))
+                  '((35123456789 . 1000000000) 27 15 nil nil nil nil -1 nil))))
 
 (ert-deftest standard-test-time-of-day-beginning-of-day ()
   (should (equal (iso8601-parse-time "000000")
-                 '(0 0 0 nil nil nil nil nil nil)))
+                  '(0 0 0 nil nil nil nil -1 nil)))
   (should (equal (iso8601-parse-time "00:00:00")
-                 '(0 0 0 nil nil nil nil nil nil)))
+                  '(0 0 0 nil nil nil nil -1 nil)))
 
   (should (equal (iso8601-parse-time "0000")
-                 '(0 0 0 nil nil nil nil nil nil)))
+                  '(0 0 0 nil nil nil nil -1 nil)))
   (should (equal (iso8601-parse-time "00:00")
-                 '(0 0 0 nil nil nil nil nil nil))))
+                  '(0 0 0 nil nil nil nil -1 nil))))
 
 (ert-deftest standard-test-time-of-day-utc ()
   (should (equal (iso8601-parse-time "232030Z")
@@ -222,9 +222,9 @@
 
 (ert-deftest standard-test-date-and-time-of-day ()
   (should (equal (iso8601-parse "19850412T101530")
-                 '(30 15 10 12 4 1985 nil nil nil)))
+                  '(30 15 10 12 4 1985 nil -1 nil)))
   (should (equal (iso8601-parse "1985-04-12T10:15:30")
-                 '(30 15 10 12 4 1985 nil nil nil)))
+                  '(30 15 10 12 4 1985 nil -1 nil)))
 
   (should (equal (iso8601-parse "1985102T235030Z")
                  '(30 50 23 12 4 1985 nil nil 0)))
@@ -232,9 +232,9 @@
                  '(30 50 23 12 4 1985 nil nil 0)))
 
   (should (equal (iso8601-parse "1985W155T235030")
-                 '(30 50 23 12 4 1985 nil nil nil)))
+                  '(30 50 23 12 4 1985 nil -1 nil)))
   (should (equal (iso8601-parse "1985-W155T23:50:30")
-                 '(30 50 23 12 4 1985 nil nil nil))))
+                  '(30 50 23 12 4 1985 nil -1 nil))))
 
 (ert-deftest standard-test-interval ()
   ;; A time interval starting at 20 minutes and 50 seconds past 23
@@ -256,48 +256,48 @@
   ;; This example doesn't seem valid according to the standard.
   ;; "0625" is unambiguous, and means "the year 625".  Weird.
   ;; (should (equal (iso8601-parse-interval "19850412/0625")
-  ;;                '((nil nil nil 12 4 1985 nil nil nil)
-  ;;                  (nil nil nil nil nil 625 nil nil nil)
+  ;;                 '((nil nil nil 12 4 1985 nil -1 nil)
+  ;;                   (nil nil nil nil nil 625 nil -1 nil)
   ;;                  (0 17 0 22 9 609 5 nil 0))))
 
   ;; A time interval of 2 years, 10 months, 15 days, 10 hours, 20
   ;; minutes and 30 seconds.
   (should (equal (iso8601-parse-duration "P2Y10M15DT10H20M30S")
-                 '(30 20 10 15 10 2 nil nil nil)))
+                  '(30 20 10 15 10 2 nil -1 nil)))
 
   (should (equal (iso8601-parse-duration "P00021015T102030")
-                 '(30 20 10 15 10 2 nil nil nil)))
+                  '(30 20 10 15 10 2 nil -1 nil)))
   (should (equal (iso8601-parse-duration "P0002-10-15T10:20:30")
-                 '(30 20 10 15 10 2 nil nil nil)))
+                  '(30 20 10 15 10 2 nil -1 nil)))
 
   ;; A time interval of 1 year and 6 months.
   (should (equal (iso8601-parse-duration "P1Y6M")
-                 '(0 0 0 0 6 1 nil nil nil)))
+                  '(0 0 0 0 6 1 nil -1 nil)))
   (should (equal (iso8601-parse-duration "P0001-06")
-                 '(nil nil nil nil 6 1 nil nil nil)))
+                  '(nil nil nil nil 6 1 nil -1 nil)))
 
   ;; A time interval of seventy-two hours.
   (should (equal (iso8601-parse-duration "PT72H")
-                 '(0 0 72 0 0 0 nil nil nil)))
+                  '(0 0 72 0 0 0 nil -1 nil)))
 
   ;; Defined by start and duration
   ;; A time interval of 1 year, 2 months, 15 days and 12 hours,
   ;; beginning on 12 April 1985 at 20 minutes past 23 hours.
   (should (equal (iso8601-parse-interval "19850412T232000/P1Y2M15DT12H")
-                 '((0 20 23 12 4 1985 nil nil nil)
-                   (0 20 11 28 6 1986 nil nil nil)
-                   (0 0 12 15 2 1 nil nil nil))))
+                  '((0 20 23 12 4 1985 nil -1 nil)
+                    (0 20 11 28 6 1986 nil -1 nil)
+                    (0 0 12 15 2 1 nil -1 nil))))
   (should (equal (iso8601-parse-interval "1985-04-12T23:20:00/P1Y2M15DT12H")
-                 '((0 20 23 12 4 1985 nil nil nil)
-                   (0 20 11 28 6 1986 nil nil nil)
-                   (0 0 12 15 2 1 nil nil nil))))
+                  '((0 20 23 12 4 1985 nil -1 nil)
+                    (0 20 11 28 6 1986 nil -1 nil)
+                    (0 0 12 15 2 1 nil -1 nil))))
 
   ;; Defined by duration and end
   ;; A time interval of 1 year, 2 months, 15 days and 12 hours, ending
   ;; on 12 April 1985 at 20 minutes past 23 hour.
   (should (equal (iso8601-parse-interval "P1Y2M15DT12H/19850412T232000")
-                 '((0 20 11 28 1 1984 nil nil nil)
-                   (0 20 23 12 4 1985 nil nil nil)
-                   (0 0 12 15 2 1 nil nil nil)))))
+                  '((0 20 11 28 1 1984 nil -1 nil)
+                    (0 20 23 12 4 1985 nil -1 nil)
+                    (0 0 12 15 2 1 nil -1 nil)))))
 
 ;;; iso8601-tests.el ends here