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

[Andreas Röhler]

On 14.05.19 12:02, Andreas Röhler wrote:
> On 13.05.19 21:25, npostavs@gmail.com wrote:
> > Andreas Röhler <andreas.roehler@easy-emacs.de> 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)))