Re: move-beginning-of-line misbehaves on wrapped-line invisible text - recent cvs checkout

[Ken Manheimer <ken.manheimer@gmail.com>]

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On 1/22/06, Ken Manheimer <ken.manheimer@gmail.com> wrote:
> this works for me!

... but i've discovered what i think is a bug in rms' new
move-beginning-of-line code.

i'm attaching another bit of elisp to construct a demonstration.  it
appears that move-beginning-of-line will _sometimes_ go to the wrong
place - the beginning of the buffer, in this case - if hidden text
it's traversing begins with a newline.

my best guess at a fix for the recent move-beginning-of-lines would be
to remove the first

  (skip-chars-backward "^\n")

- the one before the loop.  that resolves both this current problem
and the previous one i demonstrated.  unfortunately, i can't be
confident about any fix i invent, because i'm hazy about some of the
contingencies move-beginning-of-line is supposed to handle - i don't
know enough about fields, and am still a bit unclear about some
wording in the function's docstring and rms explanation.

(gmail may be preventing sending of application/octet-stream
attachments, which is how it recognizes .el files, so the attachment
may be omitted.  if so, i'll resend with the attachment as a text
file.)

> On 1/19/06, Richard M. Stallman <rms@gnu.org> wrote:
> >     move-beginning-of-line is supposed to move to the beginning of the
> >     current _display_ line.  emphasis on "display" is because i'm not
> >     quite clear what it means.
> >
> > I believe the idea is that newlines that don't really appear as such
> > do not count.
> >
> > I don't see the problems you reported with the medium-size lines,
> > but I do see the problem with the longest line.  This seems to fix it.
> > Does this give good results in general?
>
> i see none of the problems that had been showing without the patch.  i
> haven't exercised emacs very much with the change, but see that it's
> already in CVS.  i'll report if i encounter any problems with it.
> thanks!
>
> ken
>
> > *** simple.el   05 Jan 2006 10:48:16 -0500      1.783
> > --- simple.el   19 Jan 2006 12:11:57 -0500
> > ***************
> > *** 3734,3740 ****
> >     (or arg (setq arg 1))
> >     (if (/= arg 1)
> >         (line-move (1- arg) t))
> > !   (beginning-of-line 1)
> >     (let ((orig (point)))
> >       (vertical-motion 0)
> >       (if (/= orig (point))
> > --- 3735,3747 ----
> >     (or arg (setq arg 1))
> >     (if (/= arg 1)
> >         (line-move (1- arg) t))
> > !
> > !   ;; Move to beginning-of-line, ignoring fields and invisibles.
> > !   (skip-chars-backward "^\n")
> > !   (while (and (not (bobp)) (line-move-invisible-p (1- (point))))
> > !     (goto-char (previous-char-property-change (1- (point))))
> > !     (skip-chars-backward "^\n"))
> > !
> >     (let ((orig (point)))
> >       (vertical-motion 0)
> >       (if (/= orig (point))
> >
>

[-- Attachment #2: overlay-prob2.el --]
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(defvar overlay-prob-category nil
  "Variable for demonstrating overlay problem w/categories")
(setplist 'overlay-prob-category nil)
(put 'overlay-prob-category 'invisible 'outline)
(defun construct-overlay-problem ()
  (interactive)
  (let* ((buffer (get-buffer-create "overlay-problem"))
         beg
         offset
         ol)
    (pop-to-buffer buffer)
    (erase-buffer)
    (outline-mode)
    (insert "This may demonstrate a bug in move-beginning-of-line\n")
    (insert "(actually, previous-char-property-change).  In my emacs 20.0.50\n")
    (insert "build (CVS as of 22Jan2006), a property change is skipped.\n")
    (insert "Follow these instructions for a demonstration.\n")
    (insert "\n")
    (insert "At the end of the last line, after the hidden text, do a\n")
    (insert "move-beginning-of-line")
    (insert (substitute-command-keys "(\\[move-beginning-of-line])\n\n"))
    (insert "In my build, the cursor goes to the beginning of the buffer.\n")
    (insert "\n")
    (insert (substitute-command-keys "Do \\[move-beginning-of-line]"))
    (insert " at the end of this line ")
    (setq beg (point))
    (insert "\n some characters *including leading newline* to hide")
    (setq ol (make-overlay beg (point)))
    (overlay-put ol 'category 'overlay-prob-category)))












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