bug#72570: 31.0.50; Regression in date-to-time

[Ulrich Mueller <ulm@gentoo.org>]

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>>>>> On Tue, 13 Aug 2024, Paul Eggert wrote:

> On 2024-08-13 14:11, Ulrich Mueller wrote:
>> (Assuming that the fallback code is still needed today.
>> From commit history in the Gnus repository, it looks like the call to
>> timezone-make-date-arpa-standard was first added on 2000-01-06 in
>> https://github.com/dabrahams/gnus/commit/f1c5b21410f6e574913bbcf97ffd5e98d9ab89ac#diff-c8e4386c2f71d2573b4b5e6549e54c51cdf1fa649c6578ebd377f84e27576c93L32 .
>> The rationale for the change was to make the function "... more robust,
>> e.g. against the crop of year 100 dates in Jan 2000".)

> If that's the only reason it's there, we can simply remove the call to
> timezone-make-date-arpa-standard. That would be better to coating the
> pig with even more lipstick.

IIUC timezone-parse-date is the function that is used for parsing a date
in the fallback code. Its function documentation says:

| Understands the following styles:
|  (1) 14 Apr 89 03:20[:12] [GMT]
|  (2) Fri, 17 Mar 89 4:01[:33] [GMT]
|  (3) Mon Jan 16 16:12[:37] [GMT] 1989
|  (4) 6 May 1992 1641-JST (Wednesday)
|  (5) 22-AUG-1993 10:59:12.82
|  (6) Thu, 11 Apr 16:17:12 91 [MET]
|  (7) Mon, 6  Jul 16:47:20 T 1992 [MET]
|  (8) 1996-06-24 21:13:12 [GMT]
|  (9) 1996-06-24 21:13-ZONE
|  (10) 19960624T211312

I've used these to make some test cases for ERT, see the attached file.
The current date-to-time correctly handles styles 1, 2, 3, 6 (without
timezone), 7 (without timezone), 8, and 10. It returns an incorrect
result for styles 4, 5, 6 (with timezone), 7 (with timezone), and 9.

If I redefine date-to-time with the fallback code removed, the test
results are identical (somewhat surprisingly).

So I'd conclude that we don't gain much from the fallback code.


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(ert-deftest test-date-to-time ()
  ;; Test cases are the formats mentioned in the docstring
  ;; of timezone-parse-date
  (let ((date-list
	 '(("14 Apr 89 03:20"              (00 20 03 14 04 1989 nil -1 nil))
	   ("14 Apr 89 03:20:12"           (12 20 03 14 04 1989 nil -1 nil))
	   ("14 Apr 89 03:20 GMT"          (00 20 03 14 04 1989 nil nil 0))
	   ("14 Apr 89 03:20:12 GMT"       (12 20 03 14 04 1989 nil nil 0))
	   ("Fri, 17 Mar 89 4:01"          (00 01 04 17 03 1989 nil -1 nil))
	   ("Fri, 17 Mar 89 4:01:33"       (33 01 04 17 03 1989 nil -1 nil))
	   ("Fri, 17 Mar 89 4:01 GMT"      (00 01 04 17 03 1989 nil nil 0))
	   ("Fri, 17 Mar 89 4:01:33 GMT"   (33 01 04 17 03 1989 nil nil 0))
	   ("Mon Jan 16 16:12 1989"        (00 12 16 16 01 1989 nil -1 nil))
	   ("Mon Jan 16 16:12:37 1989"     (37 12 16 16 01 1989 nil -1 nil))
	   ("Mon Jan 16 16:12 GMT 1989"    (00 12 16 16 01 1989 nil nil 0))
	   ("Mon Jan 16 16:12:37 GMT 1989" (37 12 16 16 01 1989 nil nil 0))
	   ("Thu, 11 Apr 16:17:12 91"      (12 17 16 11 04 1991 nil -1 nil))
	   ("Mon, 6  Jul 16:47:20 T 1992"  (20 47 16 06 07 1992 nil -1 nil))
	   ("1996-06-24 21:13:12"          (12 13 21 24 06 1996 nil -1 nil))
	   ("1996-06-24 21:13:12 GMT"      (12 13 21 24 06 1996 nil nil 0))
	   ("19960624t211312"              (12 13 21 24 06 1996 nil -1 nil))
	   ;; fails to parse time, returns 00:00:00
	   ;("6 May 1992 1641-JST (Wednesday)"
	   ;                                (00 41 16 06 05 1992 nil nil 32400))
	   ;; parses date incorrectly as 1982-01-01
	   ;("22-AUG-1993 10:59:12.82"      (12 59 10 22 08 1993 nil -1 nil))
	   ;; fails to parse timezone
	   ;("Thu, 11 Apr 16:17:12 91 MET"  (12 17 16 11 04 1991 nil nil 3600))
	   ;("Mon, 6  Jul 16:47:20 T 1992 MET"
	   ;                                (20 47 16 06 07 1992 nil nil 3600))
	   ;; fails to parse time, returns 00:00:00
	   ;("1996-06-24 21:13-JST"         (00 13 21 24 06 1996 nil nil 32400))
	   ))
	(process-environment (copy-sequence process-environment))
	(tz (getenv "TZ")))
    (unwind-protect
	(progn
	  (setenv "TZ" "UTC")
	  (dolist (date date-list)
	    (should (equal
		     (date-to-time (car date))
		     (encode-time (cadr date))))))
      ;; This is needed because setenv handles TZ specially.
      ;; So, restoring the environment is not enough.
      (setenv "TZ" tz))))