[DRAFT][PATCH] org-encode-time compatibility and convenience helper

[Max Nikulin <manikulin@gmail.com>]

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Hi,

After a recent report of incorrect daylight saving time handling in agenda:

Ignacio Casso [BUG] org-agenda thinks timestamps after 23:00 correspond 
to the next day Tue, 29 Mar 2022 15:09:10 +0200
https://list.orgmode.org/PAXPR06MB7760238F410CBE3203F78EE0C61E9@PAXPR06MB7760.eurprd06.prod.outlook.com

I tried to create a compatibility helper that will use currently 
recommended way to call `encode-time' with single list argument for 
Emacs-27 and newer, but use the only available call style as separated 
arguments for older Emacs versions.

 From my point of view
- it should work at the compile or load time to minimize runtime 
performance impact,
- since both ways to call `encode-time' are necessary (in a half of 
cases a list returned by `decode-time' is available, in other cases 
timestamps are assembled from scratch, none is preferred), it should be 
convenient in both cases,
- it should allow Org to work even if support of multiple `encode-time' 
arguments will be removed from Emacs.

Paul Eggert proposed org-encode-time-1 defsubst/defun
https://debbugs.gnu.org/cgi/bugreport.cgi?bug=54764#10

My patch requires more changes since the macro is just defined but not 
actually used. It does not fix the problem with "no DST" flag returned 
by some function in Org. I can prepare next patches, but I think it 
should be decided at first which approach should be accepted by Org Mode:
- org-encode-time accepting both list or separate arguments
- mix of `encode-time' with multiple arguments and org-encode-time-1 for 
lists.

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From e330999cefe40d6d9a2f25abfd48b1f332b3688d Mon Sep 17 00:00:00 2001
From: Max Nikulin <manikulin@gmail.com>
Date: Fri, 8 Apr 2022 23:10:50 +0700
Subject: [PATCH] org-macs.el: Introduce a helper for `encode-time'

* lisp/org-macs.el (org-encode-time): New compatibility and convenience
helper macro to allow a list for time components or separate arguments
independently of Emacs version.
* testing/lisp/test-org.el (test-org/org-encode-time): Tests for various
ways to call `org-encode-time'.

Ensure recommended way to call `encode-time' for Emacs-27 and newer with
hope to avoid bugs due to attempts to modernize the code similar to
bug#54731.
---
 lisp/org-macs.el         | 20 ++++++++++++++++++
 testing/lisp/test-org.el | 45 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 65 insertions(+)

diff --git a/lisp/org-macs.el b/lisp/org-macs.el
index a09115e7c..7e8c23d09 100644
--- a/lisp/org-macs.el
+++ b/lisp/org-macs.el
@@ -1225,6 +1225,26 @@ nil, just return 0."
 	(b (org-2ft b)))
     (and (> a 0) (> b 0) (\= a b))))
 
+(if (version< emacs-version "27.1")
+    (defmacro org-encode-time (&rest time)
+      (if (cdr time)
+          `(encode-time ,@time)
+        `(apply #'encode-time ,(car time))))
+  (defmacro org-encode-time (&rest time)
+    (pcase (length time)
+      (1 `(encode-time ,(car time)))
+      (6 `(encode-time (list ,@time nil -1 nil)))
+      (9 `(encode-time (list ,@time)))
+      (_ (error "`org-encode-time' may be called with 1, 6, or 9 arguments but %d given"
+                (length time))))))
+(put 'org-encode-time 'function-documentation
+     "Compatibility and convenience helper for `encode-time'.
+May be called with 9 components list (SECONDS ... YEAR IGNORED DST ZONE)
+as the recommended way since Emacs-27 or with 6 or 9 separate arguments
+similar to the only possible variant for Emacs-26 and earlier.
+Warning: use -1 for DST that means guess actual value, nil means no
+daylight saving time and may be wrong at particular time.")
+
 (defun org-parse-time-string (s &optional nodefault)
   "Parse Org time string S.
 
diff --git a/testing/lisp/test-org.el b/testing/lisp/test-org.el
index 6aecc3af8..a0ed36362 100644
--- a/testing/lisp/test-org.el
+++ b/testing/lisp/test-org.el
@@ -179,6 +179,51 @@
 \f
 ;;; Date and time analysis
 
+(ert-deftest test-org/org-encode-time ()
+  "Test various ways to call `org-encode-time'"
+  ;; list as the sole argument
+  (should (string-equal
+           "2022-03-24 23:30:01"
+           (format-time-string
+            "%F %T"
+            (org-encode-time '(01 30 23 24 03 2022 nil -1 nil)))))
+  ;; SECOND...YEAR
+  (should (string-equal
+           "2022-03-24 23:30:02"
+           (format-time-string
+            "%F %T"
+            (org-encode-time 02 30 23 24 03 2022))))
+  ;; SECOND...YEAR IGNORED DST ZONE
+  (should (string-equal
+           "2022-03-24 23:30:03"
+           (format-time-string
+            "%F %T"
+            (org-encode-time 03 30 23 24 03 2022 nil -1 nil))))
+  ;; function call
+  (should (string-equal
+           "2022-03-24 23:30:04"
+           (format-time-string
+            "%F %T"
+            (org-encode-time (apply #'list 04 30 23 '(24 03 2022 nil -1 nil))))))
+  ;; wrong number of arguments
+  (if (not (version< emacs-version "27.1"))
+      (should-error (string-equal
+                     "2022-03-24 23:30:05"
+                     (format-time-string
+                      "%F %T"
+                      (org-encode-time 05 30 23 24 03 2022 nil)))))
+  ;; daylight saving time
+  (let ((tz (getenv "TZ")))
+    (unwind-protect
+        (progn
+          (setenv "TZ" "Europe/Madrid")
+          (should (string-equal
+                   "2022-03-31 23:30:06"
+                   (format-time-string
+                    "%F %T"
+                    (org-encode-time 06 30 23 31 03 2022)))))
+      (setenv "TZ" tz))))
+
 (ert-deftest test-org/org-read-date ()
   "Test `org-read-date' specifications."
   ;; Parse ISO date with abbreviated year and month.
-- 
2.25.1