Subject: bug#35708: [27.0.50]: thingatpt.el, thing-at-point-looking-at redundant

From: Andreas Röhler <[email-masked]>
Date: Tue, 14 May 2019 12:02:15 +0200

On 13.05.19 21:25, [email-masked] wrote:
> Andreas Röhler <[email-masked]> writes:
>
>> Thought at something like below, which should pass the test:
>>
>> (defun ar-thing-at-point-looking-at (regexp)
>>    "Return t if regexp matches at or before point, nil otherwise."
>>    (save-excursion
>>        (while (not (or (looking-at regexp)(bolp)))
>>        (forward-char -1))
>>        (looking-at regexp)))
> I think it's an optimization to use re-search-backward instead of moving
> on character at a time and calling looking-at in lisp.
>
>

Hmm, current thing-at-point-looking-at might be slow with large buffers. 
The slightly modified test should reveal it:

(ert-deftest thing-at-point-looking-at-2 ()
   (with-temp-buffer
     (insert "1abcd 222abcd")
     (dotimes (_ 99999) (insert " asdf "))
     (goto-char (point-min))
     (let ((m2 (progn (search-forward "2abcd")
                      (match-data))))
       (goto-char (point-min))
       (search-forward "2ab")
       (should (thing-at-point-looking-at "2abcd"))
       (should (equal (match-data) m2)))))

But let me correct the alternative delivered, as it didn't match before 
point:

(defun ar-regexp-atpt (regexp)

"Return t if REGEXP matches at or before point, nil otherwise.

Changes match-data"
   (save-excursion
     (if (looking-at regexp)
     (while
         (save-excursion
           (and (not (bobp))
            (progn (backward-char) (looking-at regexp)))))
       (while (not (or (bobp) (backward-char) (looking-at regexp))))
       (ar-regexp-atpt regexp))
     (looking-at regexp)))