bug#29772: 25.1; Display artefacts caused by scroll-bar-mode 'left with tool-bar-mode nil

[Christopher Allen <cpcallen@gmail.com>]

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Run the following command to open a long file with toolbar disabled and
left-hand-side scrollbars:

$ emacs -Q -eval "(custom-set-variables '(scroll-bar-mode (quote
left)) '(tool-bar-mode nil))" ~/.bash_history

(Substitute any long file in place of .bash_history; ideally it should
be >10 windows tall.)

Then scroll up and down by any means (cursor keys, dragging scrollbar
handle, or using scrollwheel / trackpad gestures).

Observe that the scrollbar leaves behind artefacts (see attached
example).  Such artifacts do not seem to appear when the toolbar is
present; I note in that case the scrollbar appears a few pixels to the
left.


In GNU Emacs 25.1.1 (x86_64-apple-darwin13.4.0, NS appkit-1265.21
Version 10.9.5 (Build 13F1911))
 of 2016-09-21 built on builder10-9.porkrind.org
Windowing system distributor 'Apple', version 10.3.1404
Configured using:
 'configure --with-ns '--enable-locallisppath=/Library/Application
 Support/Emacs/${version}/site-lisp:/Library/Application
 Support/Emacs/site-lisp' --with-modules'

Configured features:
NOTIFY ACL GNUTLS LIBXML2 ZLIB TOOLKIT_SCROLL_BARS NS MODULES

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

Major mode: Shell-script

Minor modes in effect:
  sh-electric-here-document-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-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 messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Setting up indent for shell type bash
Indentation variables are now local.
Indentation setup for shell type bash
<wheel-left> is undefined
mwheel-scroll: Beginning of buffer [10 times]
mwheel-scroll: End of buffer [5 times]
mwheel-scroll: Beginning of buffer [24 times]

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message dired format-spec rfc822 mml
mml-sec password-cache epg epg-config gnus-util mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail
rfc2047 rfc2045 ietf-drums mm-util help-fns help-mode easymenu
cl-loaddefs pcase cl-lib mail-prsvr mail-utils sh-script smie executable
time-date mule-util tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel ns-win ucs-normalize term/common-win tool-bar dnd
fontset image regexp-opt fringe tabulated-list newcomment elisp-mode
lisp-mode prog-mode register page menu-bar rfn-eshadow timer select
scroll-bar mouse jit-lock font-lock syntax facemenu font-core frame
cl-generic cham georgian utf-8-lang misc-lang vietnamese tibetan thai
tai-viet lao korean japanese eucjp-ms cp51932 hebrew greek romanian
slovak czech european ethiopic indian cyrillic chinese charscript
case-table epa-hook jka-cmpr-hook help simple abbrev minibuffer
cl-preloaded 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 kqueue cocoa ns
multi-tty make-network-process emacs)

Memory information:
((conses 16 203508 5208)
 (symbols 48 19903 0)
 (miscs 40 54 128)
 (strings 32 17071 5621)
 (string-bytes 1 477841)
 (vectors 16 33562)
 (vector-slots 8 667242 3657)
 (floats 8 160 41)
 (intervals 56 330 0)
 (buffers 976 19))

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