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

From: Andreas Röhler <[email-masked]>
Date: Wed, 15 May 2019 08:59:19 +0200

Am 14.05.19 um 16:34 schrieb [email-masked]:
> Andreas Röhler <[email-masked]> writes:
>
>>> 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))
>>>        (search-forward "2ab")
>>>        (should (thing-at-point-looking-at "2abcd"))
> Yes, in this case, since the loop over looking-at only needs to iterate
> twice, so it will be faster.  But what about when there is no match?
> E.g.,
>
> (with-temp-buffer
>    (dotimes (_ 99999) (insert " asdf "))
>    (goto-char (point-max))
>    (list :ar-regexp-atpt (benchmark-run (ar-regexp-atpt "foo"))
>          :thing-at-point-looking-at (benchmark-run (thing-at-point-looking-at "foo"))))
>
>> 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))
> What's this recursive call for?  It triggers (error "Lisp nesting
> exceeds ‘max-lisp-eval-depth’") in the benchmark above.
>
>>      (looking-at regexp)))

The recursive call needed a guard:     (unless (bobp)

It is called after function went backward while not looking-at matches,

Now the result for the 99999 is

(:ar-regexp-atpt (0.774574453 0 0.0) :thing-at-point-looking-at 
(0.000798669 0 0.0))

The fixed form:

(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))))
       (unless (bobp) (ar-regexp-atpt regexp)))
     (looking-at regexp)))