bug#52209: 28.0.60; [PATCH] date-to-time fails on pure dates

[Bob Rogers]

   From: Bob Rogers <rogers-emacs@rgrjr.homedns.org>
   Date: Sun, 20 Feb 2022 17:14:36 -0500

      From: Lars Ingebrigtsen <larsi@gnus.org>
      Date: Sun, 20 Feb 2022 13:21:54 +0100

      Bob Rogers <rogers-emacs@rgrjr.homedns.org> writes:

      > Here's what I have for this phase of the plan; let me know what you
      > think.  It took longer than expected because it became a project unto
      > itself, and so my procrastinator kicked in, making it longer still.  :-/

      :-)

      Have you benchmarked your new implementation versus the current one?
      It's important that the parsing is performant, otherwise it'd slow down
      many things that parse a large number of date strings.

   No benchmarking; I will do that presently.

Benchmarking code and results attached.  I extracted a handful of
non-error cases from the tests as being more representative than any of
the error cases; the resulting numbers make it seem like any difference
between the two implementations is in the noise.

   But this is my first foray into elisp benchmarking, so I may have
overlooked something.  Fortunately, email dates are not that diverse, so
I am hoping this sampling may be broad enough.

                                        -- Bob

;;; ietf-drums-date-timings.el --- timing ietf-drums-date.el -*- 
lexical-binding: t -*-

;; Copyright (C) 2022 Free Software Foundation, Inc.

;; Author: Bob Rogers <rogers@rgrjr.com>

(defun run-timings (parse-fn)
  (dolist (case '(("Mon, 22 Feb 2016 19:35:42 +0100"
                   (42 35 19 22 2 2016 1 -1 3600)
                   (22219 21758))
                  ("22 Feb 2016 19:35:42 +0100"
                   (42 35 19 22 2 2016 nil -1 3600)
                   (22219 21758))
                  ("Mon, 22 February 2016 19:35:42 +0100"
                   (42 35 19 22 2 2016 1 -1 3600)
                   (22219 21758))
                  ("Mon, 22 feb 2016 19:35:42 +0100"
                   (42 35 19 22 2 2016 1 -1 3600)
                   (22219 21758))
                  ("Monday, 22 february 2016 19:35:42 +0100"
                   (42 35 19 22 2 2016 1 -1 3600)
                   (22219 21758))
                  ("Monday, 22 february 2016 19:35:42 PST"
                   (42 35 19 22 2 2016 1 nil -28800)
                   (22219 54158))
                  ("Friday, 21 Sep 2018 13:47:58 PDT"
                   (58 47 13 21 9 2018 5 t -25200)
                   (23461 22782))
                  ("Friday, 21 Sep 2018 13:47:58"
                   (58 47 13 21 9 2018 5 -1 nil)
                   (23461 11982))))
    (funcall parse-fn (car case))))

(benchmark-run-compiled 10000 (run-timings #'ietf-drums-parse-date))
;; (7.220905228 83 3.3420971879999968)
;; (7.24936647 83 3.3321491059999993)
;; (7.3240701370000005 84 3.371737411)
;; (/ (+ 7.249 7.324 7.324) 3) 7.299

(defun ietf-drums-old-parse-date (string)
  "Return an Emacs time spec from STRING."
  (encode-time (parse-time-string string)))

(benchmark-run 10000 (run-timings #'ietf-drums-old-parse-date))
;; (7.249068317 83 3.3251401939999994)
;; (7.317397244 84 3.3750772899999983)
;; (7.268244294 84 3.3820036280000005)
;; (/ (+ 7.249 7.317 7.268) 3) 7.278