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

From: Andreas Röhler <[email-masked]>
Date: Tue, 14 May 2019 12:49:07 +0200

On 14.05.19 12:02, Andreas Röhler wrote:
>
> 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)))
>
>
>
>

Another fix, as a bug showed up when testing (ar-regexp-atpt "[a-z]+"):

(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
         (and (not (bobp))
          (or (progn (backward-char) (looking-at regexp))
              (forward-char 1))))
       (while (not (or (bobp) (backward-char) (looking-at regexp))))
       (ar-regexp-atpt regexp))
     (looking-at regexp)))