GNU bug report logs - #8667
24.0.50; `bounds-of-thing-at-point' returns (N . N) for `comment'

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#8667: closed (24.0.50; `bounds-of-thing-at-point' returns (N
 . N) for `comment')
Date: Fri, 13 May 2011 17:06:02 +0000

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Your message dated Fri, 13 May 2011 14:05:06 -0300
with message-id <jwvsjsi4jp7.fsf-monnier+emacs <at> gnu.org>
and subject line Re: bug#8667: 24.0.50; `bounds-of-thing-at-point' returns (N . N) for `comment'
has caused the GNU bug report #8667,
regarding 24.0.50; `bounds-of-thing-at-point' returns (N . N) for `comment'
to be marked as done.

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From: "Drew Adams" <drew.adams <at> oracle.com>
To: <bug-gnu-emacs <at> gnu.org>
Subject: 24.0.50; `bounds-of-thing-at-point' returns (N . N) for `comment'
Date: Thu, 12 May 2011 17:46:33 -0700

emacs -Q
 
Put point at position 3061 in file thingatpt.el (i.e., just before the
`a' of `condition-case').
 
M-: (bounds-of-thing-at-point 'comment)
returns (3061 . 3061), which represents an empty thing, "".
 
This happens at most positions, probably all positions outside a comment.
 
The code should handle this kind of case correctly (in other respects it
seems to work OK for comments).
 
The problem is that there is no `beginning-op' or `end-op' and all of
the calls to `forward-thing' (with 1 and -1) do not move point at all,
and return nil.  So the code falls through to the end:
 
(let ((end (point))
      (real-beg
       (progn
        (funcall
         (or (get thing 'beginning-op)
             (lambda () (forward-thing thing -1))))
        (point))))
  ;; real-beg = end = (point).  Result is (cons 3061 . 3061).
  (if (and real-beg end (<= real-beg orig) (<= orig end))
      (cons real-beg end)))

`bounds-of-thing-at-point' should foresee such a case (that `forward-THING' does
nothing).  IOW, it should of course be fixed for this problem.

But it sounds like `forward-comment' should also be fixed so that it acts like
other `forward-THING' functions, and not just be a no-op when outside a comment.
 
In GNU Emacs 24.0.50.1 (i386-mingw-nt5.1.2600)
 of 2011-05-10 on 3249CTO
Windowing system distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-gcc (4.5) --no-opt --cflags
-Ic:/build/include'
 

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From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: "Drew Adams" <drew.adams <at> oracle.com>
Cc: 8667-close <at> debbugs.gnu.org
Subject: Re: bug#8667: 24.0.50;
	`bounds-of-thing-at-point' returns (N . N) for `comment'
Date: Fri, 13 May 2011 14:05:06 -0300

Installed a patch along the lines of what you suggested.

>> I think `forward-whitespace' is incorrect: \n should be \n+, like this:
>> 
>> (defun forward-whitespace (arg)
>> (interactive "p")
>> (if (natnump arg)
>> (re-search-forward "[ \t]+\\|\n+" nil 'move arg)
>> (while (< arg 0)
>> (if (re-search-backward "[ \t]+\\|\n+" nil 'move)
>> (or (eq (char-after (match-beginning 0)) 10)
>> (skip-chars-backward " \t")))
>> (setq arg (1+ arg)))))

The current behavior is clearly intentional (the (skip-chars-backward "
\t") shows that the function wants to treat newlines as
not-just-whitespace).  So I'd rather not change it.


        Stefan

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