bug#23377: 25.0.93; Completion is extremely slow for insert-char

[N. Jackson]

emacs -Q
C-x 8 RET TAB

This takes over a minute on my Emacs before the completions buffer is
displayed listing the characters. (On subsequent invocations, it's more
like eight seconds.) On Emacs 24 it is effectively instantaneous.

There seems to have been a change whereby the character is shown besides
it's name. This might be a very nice feature, except that it's too slow,
and it seems a bit of a waste because a large proportion of the
characters are unavailable and are shown as little boxes with tiny
numbers inside.

Perhaps there should be a way to turn this feature off? (I don't see
anything about insert-char in NEWS.)

By the way, yes, this is the way I usually use this command. I hit TAB
immediately to get a full list of characters and then `C-x o C-x 1'
because I don't use special characters often enough to remember their
names and I need to get thoroughly immersed in the whole list to see the
naming patterns again and jog my memory.


In GNU Emacs 25.0.93.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.18.9)
 of 2016-04-23 built on moondust
Repository revision: 5c587fdff164e8b90beb47f6da64b4884290e40a
Windowing system distributor 'Fedora Project', version 11.0.11803000
System Description:     Fedora release 23 (Twenty Three)

Configured using:
 'configure --enable-checking=yes,glyphs --enable-check-lisp-object-type
 'CFLAGS=-O0 -g3 -gdwarf-4''

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND DBUS GCONF GSETTINGS NOTIFY
ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11

Important settings:
  value of $LC_MONETARY: en_DK.utf8
  value of $LC_NUMERIC: en_DK.utf8
  value of $LC_TIME: en_DK.utf8
  value of $LANG: en_CA.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Group

Minor modes in effect:
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  shell-dirtrack-mode: t
  gnus-undo-mode: t
  recentf-mode: t
  display-battery-mode: t
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  desktop-save-mode: t
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  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
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  auto-composition-mode: t
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  auto-compression-mode: t
  temp-buffer-resize-mode: t
  buffer-read-only: t
  size-indication-mode: t
  column-number-mode: t
  line-number-mode: t
  global-visual-line-mode: t
  visual-line-mode: t
  transient-mark-mode: t

Recent messages:
Reading incoming mail from file...
nnfolder: Reading incoming mail (no new mail)...done
Reading active file via nnfolder...done
Checking new news...done
Auto-saving...
Updating buffer list...
Formats have changed, recompiling...done
Updating buffer list...done
Commands: m, u, t, RET, g, k, S, D, Q; q to quit; h for help
Making completion list...
Quit

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