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

[Drew Adams]

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'