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[debbugs-tracker] bug#17244: closed (24.3.90; `line-move-visual' errors


From: GNU bug Tracking System
Subject: [debbugs-tracker] bug#17244: closed (24.3.90; `line-move-visual' errors when moving across wrapped lines with an overlay property of 'display)
Date: Sat, 12 Apr 2014 11:32:01 +0000

Your message dated Sat, 12 Apr 2014 14:31:20 +0300
with message-id <address@hidden>
and subject line Re: bug#17244: 24.3.90; `line-move-visual' errors when moving 
across wrapped lines with an     overlay property of 'display
has caused the debbugs.gnu.org bug report #17244,
regarding 24.3.90; `line-move-visual' errors when moving across wrapped lines 
with an overlay property of 'display
to be marked as done.

(If you believe you have received this mail in error, please contact
address@hidden)


-- 
17244: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=17244
GNU Bug Tracking System
Contact address@hidden with problems
--- Begin Message --- Subject: 24.3.90; `line-move-visual' errors when moving across wrapped lines with an overlay property of 'display Date: Fri, 11 Apr 2014 15:28:55 -0600
Starting from Emacs -Q, create a buffer with the following contents.
Notice that the first two (2) lines are blank, and the next is one long
line (in case it gets broken by email)

#### buffer start:


;; I think this needs to be really long here.  Why?  I don't really know, but a guess.  I think this needs to be really long here.  Why?  I don't really know, but a guess.  I think this needs to be really long here.  Why?  I don't really know, but a guess.  I think this needs to be really long here.  Why?  I don't really know, but a guess.  I think this needs to be really long here.  Why?  I don't really know, but a guess.  I think this needs to be really long here.  Why?  I don't really know, but a guess.
(let ((ov (make-overlay 3 515)))
 (overlay-put ov 'display "hi\n"))
(line-move-visual -5)

1. Make sure the window is skinny enough that the comment line wraps.
2. Evaluate the first form, creating an overlay.
3. Evaluate the second form.  It is important that point be at the end
   of the "line-move-visual" line.
4. You get a warning about beginning-of-buffer, when it clearly did not
   reach the beginning-of-buffer.

As near as I can tell, the incorrect error message is because it doesn’t 
move as far at it thinks it should (the real bug), and it assumes the 
reason it didn't is because it made it to the beginning (or end) of the 
buffer.

-Ivan

In GNU Emacs 24.3.90.1 (x86_64-apple-darwin13.1.0, NS apple-appkit-1265.19)
of 2014-04-11 on iandrus-osx
Windowing system distributor `Apple', version 10.3.1265
Configured using:
`configure --with-ns'

Important settings:
 value of $LANG: en_US.UTF-8
 locale-coding-system: utf-8-unix

Major mode: Emacs-Lisp

Minor modes in effect:
 tooltip-mode: t
 electric-indent-mode: t
 mouse-wheel-mode: t
 tool-bar-mode: t
 menu-bar-mode: t
 file-name-shadow-mode: t
 global-font-lock-mode: t
 font-lock-mode: t
 blink-cursor-mode: t
 auto-composition-mode: t
 auto-encryption-mode: t
 auto-compression-mode: t
 line-number-mode: t
 transient-mark-mode: t

Recent input:
<down-mouse-1> <mouse-1> C-x C-e <down> C-x C-e <down-mouse-1>
<mouse-1> <up> <up> <up> <up> <up> <down> <down> <up>
<up> <down> <down> <up> <up> <down> <down> <down> <down>
<down> <up> <up> <up> <up> <up> <down> <down> <down>
<down> <down> <up> <up> <up> <up> <up> <down> <down>
<down> <down> <down> <down> C-x C-e <down> <down> <down>
<down> C-e C-x C-e <down-mouse-1> <mouse-1> <return>
SPC SPC SPC SPC SPC C-x C-e C-/ C-/ <help-echo> C-c
C-c s-x C-/ M-x m a i <tab> <C-backspace> r e p o <tab>
r t <tab> <return>

Recent messages:
line-move-visual: Beginning of buffer
Beginning of buffer [5 times]
t
line-move-visual: Beginning of buffer
t
Undo! [2 times]
C-c C-c is undefined
Undo!
Making completion list...
C-c C-c is undefined

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr emacsbug message format-spec rfc822 mml
mml-sec mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev
gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util
help-fns mail-prsvr mail-utils help-mode easymenu vc-hg time-date
tooltip electric uniquify ediff-hook vc-hooks lisp-float-type mwheel
ns-win tool-bar dnd fontset image regexp-opt fringe tabulated-list
newcomment lisp-mode prog-mode register page menu-bar rfn-eshadow timer
select scroll-bar mouse jit-lock font-lock syntax facemenu font-core
frame cham georgian utf-8-lang misc-lang vietnamese tibetan thai
tai-viet lao korean japanese hebrew greek romanian slovak czech european
ethiopic indian cyrillic chinese case-table epa-hook jka-cmpr-hook help
simple abbrev minibuffer nadvice loaddefs button faces cus-face macroexp
files text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote make-network-process
cocoa ns multi-tty emacs)

Memory information:
((conses 16 74077 4946)
(symbols 48 17641 0)
(miscs 40 49 163)
(strings 32 10552 3708)
(string-bytes 1 281155)
(vectors 16 9174)
(vector-slots 8 367902 7774)
(floats 8 54 455)
(intervals 56 212 7)
(buffers 960 13))


--- End Message ---
--- Begin Message --- Subject: Re: bug#17244: 24.3.90; `line-move-visual' errors when moving across wrapped lines with an overlay property of 'display Date: Sat, 12 Apr 2014 14:31:20 +0300
> Date: Fri, 11 Apr 2014 15:28:55 -0600
> From: Ivan Andrus <address@hidden>
> 
> Starting from Emacs -Q, create a buffer with the following contents.
> Notice that the first two (2) lines are blank, and the next is one long
> line (in case it gets broken by email)
> 
> #### buffer start:
> 
> 
> ;; I think this needs to be really long here.  Why?  I don't really know,
> but a guess.  I think this needs to be really long here.  Why?  I don't
> really know, but a guess.  I think this needs to be really long here.  Why?
>  I don't really know, but a guess.  I think this needs to be really long
> here.  Why?  I don't really know, but a guess.  I think this needs to be
> really long here.  Why?  I don't really know, but a guess.  I think this
> needs to be really long here.  Why?  I don't really know, but a guess.
> (let ((ov (make-overlay 3 515)))
>  (overlay-put ov 'display "hi\n"))
> (line-move-visual -5)
> 
> 1. Make sure the window is skinny enough that the comment line wraps.
> 2. Evaluate the first form, creating an overlay.
> 3. Evaluate the second form.  It is important that point be at the end
>    of the "line-move-visual" line.
> 4. You get a warning about beginning-of-buffer, when it clearly did not
>    reach the beginning-of-buffer.
> 
> As near as I can tell, the incorrect error message is because it doesn't
> move as far at it thinks it should (the real bug), and it assumes the
> reason it didn't is because it made it to the beginning (or end) of the
> buffer.

Thanks for the report.  I fixed this in revision 116947 on the
emacs-24 branch.

<rant>
To tell the truth, Lisp code which covers large portions of buffer
text with much shorter display strings that include newlines deserves
to be broken.  The current Emacs display engine was never designed to
handle situations where the displayed text is so starkly different
from buffer text, so the result of trying to fix "bugs" such as this
one is a never-ending series of band-aids, one upon the other, which
make the code utterly incomprehensible and unmaintainable.

So I'm this close to refusing to fix such "bugs", and instead asking
the authors of such Lisp to either find more benign ways of expressing
what they need, or work around the limitations of the display engine
in their own Lisp.
</rant>


--- End Message ---

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