bug#56692: 29.0.50; scroll-bar in the minibuffer window disappears

bug#56692: 29.0.50; scroll-bar in the minibuffer window disappears

[Visuwesh]

The exact details of this disappearance varies from my Emacs config
started as a daemon and emacs -Q.  To reproduce,

        1. emacs -Q
        2. C-x 2
        3. Witness the disappearance.
        4. M-:
        5. Scroll-bar shows up again.
        6. C-x 0
        7. Scroll-bar shies away.

In GNU Emacs 29.0.50 (build 24, x86_64-pc-linux-gnu, X toolkit, Xaw scroll bars)
 of 2022-07-22 built on astatine
Repository revision: 83c2c36d35f55d012e5dcb2cc566697b225dcf86
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101003
System Description: Debian GNU/Linux bookworm/sid

Configured using:
 'configure --with-sound=alsa --with-x-toolkit=lucid --with-json
 --without-xaw3d --without-gconf --without-libsystemd --without-cairo'

Configured features:
ACL DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG JSON
LIBOTF LIBSELINUX LIBXML2 MODULES NOTIFY INOTIFY PDUMPER PNG RSVG
SECCOMP SOUND SQLITE3 THREADS TIFF TOOLKIT_SCROLL_BARS WEBP X11 XDBE XFT
XIM XINPUT2 XPM LUCID ZLIB

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

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  show-paren-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
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message mailcap yank-media puny dired
dired-loaddefs rfc822 mml mml-sec password-cache epa derived epg rfc6068
epg-config gnus-util text-property-search time-date subr-x mm-decode
mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader
cl-loaddefs cl-lib sendmail rfc2047 rfc2045 ietf-drums mm-util
mail-prsvr mail-utils rmc iso-transl tooltip eldoc paren electric
uniquify ediff-hook vc-hooks lisp-float-type elisp-mode mwheel
term/x-win x-win term/common-win x-dnd tool-bar dnd fontset image
regexp-opt fringe tabulated-list replace newcomment text-mode lisp-mode
prog-mode register page tab-bar menu-bar rfn-eshadow isearch easymenu
timer select scroll-bar mouse jit-lock font-lock syntax font-core
term/tty-colors frame minibuffer nadvice seq simple cl-generic
indonesian philippine 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
composite emoji-zwj charscript charprop case-table epa-hook
jka-cmpr-hook help abbrev obarray oclosure cl-preloaded button loaddefs
faces cus-face macroexp files window text-properties overlay sha1 md5
base64 format env code-pages mule custom widget keymap
hashtable-print-readable backquote threads dbusbind inotify
dynamic-setting system-font-setting font-render-setting x-toolkit
xinput2 x multi-tty make-network-process emacs)

Memory information:
((conses 16 36120 8870)
 (symbols 48 5070 0)
 (strings 32 13991 1912)
 (string-bytes 1 433533)
 (vectors 16 9173)
 (vector-slots 8 144946 13933)
 (floats 8 25 23)
 (intervals 56 231 0)
 (buffers 992 10))

bug#56692: 29.0.50; scroll-bar in the minibuffer window disappears

[Po Lu via Bug reports for GNU Emacs, the Swiss army knife of text editors]

Visuwesh <visuweshm@gmail.com> writes:

> The exact details of this disappearance varies from my Emacs config
> started as a daemon and emacs -Q.  To reproduce,
>
>         1. emacs -Q
>         2. C-x 2
>         3. Witness the disappearance.
>         4. M-:
>         5. Scroll-bar shows up again.
>         6. C-x 0
>         7. Scroll-bar shies away.

I fixed this on master but to be frank I don't know why it works, and
why this call to move_it_to in set_vertical_scroll_bar makes the scroll
bar not redeemed in inactive mini windows after redisplay_window ends:

--->	  move_it_to (&it, -1, it.last_visible_x, window_box_height (w), -1,
		      MOVE_TO_X | MOVE_TO_Y);

If anyone else can figure it out, I would be very grateful.

TIA.

bug#56692: 29.0.50; scroll-bar in the minibuffer window disappears

[Eli Zaretskii]

> From: Visuwesh <visuweshm@gmail.com>
> Date: Fri, 22 Jul 2022 11:04:29 +0530
> 
> The exact details of this disappearance varies from my Emacs config
> started as a daemon and emacs -Q.  To reproduce,
> 
>         1. emacs -Q
>         2. C-x 2
>         3. Witness the disappearance.
>         4. M-:
>         5. Scroll-bar shows up again.
>         6. C-x 0
>         7. Scroll-bar shies away.

Thanks, should be fixed now.

bug#56692: 29.0.50; scroll-bar in the minibuffer window disappears

[Visuwesh]

[வெள்ளி ஜூலை 22, 2022] Eli Zaretskii wrote:

>> From: Visuwesh <visuweshm@gmail.com>
>> Date: Fri, 22 Jul 2022 11:04:29 +0530
>> 
>> The exact details of this disappearance varies from my Emacs config
>> started as a daemon and emacs -Q.  To reproduce,
>> 
>>         1. emacs -Q
>>         2. C-x 2
>>         3. Witness the disappearance.
>>         4. M-:
>>         5. Scroll-bar shows up again.
>>         6. C-x 0
>>         7. Scroll-bar shies away.
>
> Thanks, should be fixed now.

Can confirm that is fixed, thanks.

bug#56692: 29.0.50; scroll-bar in the minibuffer window disappears

[Eli Zaretskii]

> Cc: 56692@debbugs.gnu.org
> Date: Fri, 22 Jul 2022 19:53:59 +0800
> From:  Po Lu via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> Visuwesh <visuweshm@gmail.com> writes:
> 
> > The exact details of this disappearance varies from my Emacs config
> > started as a daemon and emacs -Q.  To reproduce,
> >
> >         1. emacs -Q
> >         2. C-x 2
> >         3. Witness the disappearance.
> >         4. M-:
> >         5. Scroll-bar shows up again.
> >         6. C-x 0
> >         7. Scroll-bar shies away.
> 
> I fixed this on master but to be frank I don't know why it works, and
> why this call to move_it_to in set_vertical_scroll_bar makes the scroll
> bar not redeemed in inactive mini windows after redisplay_window ends:
> 
> --->	  move_it_to (&it, -1, it.last_visible_x, window_box_height (w), -1,
> 		      MOVE_TO_X | MOVE_TO_Y);

move_it_to was signaling an error in that case, that's why the scroll
bar didn't appear: the set_vertical_scroll_bar_hook method wasn't
called.

I fixed it now properly (I hope).  I guess it's one of those "TIL"
days...

> If anyone else can figure it out, I would be very grateful.

See the comment I added there, and if that's not clear enough, feel
free to ask.

bug#56692: 29.0.50; scroll-bar in the minibuffer window disappears

[Po Lu via Bug reports for GNU Emacs, the Swiss army knife of text editors]

Eli Zaretskii <eliz@gnu.org> writes:

> move_it_to was signaling an error in that case, that's why the scroll
> bar didn't appear: the set_vertical_scroll_bar_hook method wasn't
> called.
>
> I fixed it now properly (I hope).  I guess it's one of those "TIL"
> days...

Thanks.  TIL it is actually possible for move_it_to to signal.

> See the comment I added there, and if that's not clear enough, feel
> free to ask.

It is clear enough now, thanks.

bug#56692: 29.0.50; scroll-bar in the minibuffer window disappears

[Eli Zaretskii]

> From: Po Lu <luangruo@yahoo.com>
> Cc: visuweshm@gmail.com,  56692@debbugs.gnu.org
> Date: Sat, 23 Jul 2022 09:12:48 +0800
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > move_it_to was signaling an error in that case, that's why the scroll
> > bar didn't appear: the set_vertical_scroll_bar_hook method wasn't
> > called.
> >
> > I fixed it now properly (I hope).  I guess it's one of those "TIL"
> > days...
> 
> Thanks.  TIL it is actually possible for move_it_to to signal.

It isn't.  But move_it_to calls the low-level display code, which
examines text properties at buffer positions it's supposed to
traverse, and text-property APIs _can_ signal errors because they must
validate the positions they are asked to examine, see
validate_interval_range.

The lesson is that calling these functions when the window's buffer is
not the current_buffer can cause all kinds of trouble due to our
reliance on ZV and other similar values.  My personal TIL part is that
there could be code in redisplay_window, apart of its very beginning,
where that condition is not necessarily true.