bug#28343: 24.5; isearch highlighting slow - suppress for single space character

[Ed Avis]

Run Emacs in a fairly large terminal, say 200x200 characters.  Go to the
end of a buffer with some text in it (long enough to fill the screen)
and do C-r SPACE.  This is an isearch backwards for the space character.
If you have highlighting turned on, Emacs then starts highlighting
backwards all the space characters in the buffer.  But this can be slow,
a noticeable few seconds even on a fast machine.  (I think it depends on
the vagaries of memory management and possibly Lisp compiling, since
it's not always quite that bad; a second attempt takes only about half a
second.  But still it seems a long time.)

A small tweak to isearch would suppress the highlighting when what has
been typed so far is just a space character.  If the user types space
and then C-s or C-r again, to indicate that he or she really does want
to search for single spaces, then you can highlight at that point of
course.




In GNU Emacs 24.5.1 (x86_64-redhat-linux-gnu, GTK+ Version 3.18.9)
 of 2016-04-11 on buildvm-25.phx2.fedoraproject.org
Configured using:
 `configure --build=x86_64-redhat-linux-gnu
 --host=x86_64-redhat-linux-gnu --program-prefix=
 --disable-dependency-tracking --prefix=/usr --exec-prefix=/usr
 --bindir=/usr/bin --sbindir=/usr/sbin --sysconfdir=/etc
 --datadir=/usr/share --includedir=/usr/include --libdir=/usr/lib64
 --libexecdir=/usr/libexec --localstatedir=/var
 --sharedstatedir=/var/lib --mandir=/usr/share/man
 --infodir=/usr/share/info --with-dbus --with-gif --with-jpeg --with-png
 --with-rsvg --with-tiff --with-xft --with-xpm --with-x-toolkit=gtk3
 --with-gpm=no build_alias=x86_64-redhat-linux-gnu
 host_alias=x86_64-redhat-linux-gnu 'CFLAGS=-DMAIL_USE_LOCKF -O2 -g
 -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2
 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4
 -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1
 -m64 -mtune=generic' LDFLAGS=-Wl,-z,relro'

Important settings:
  value of $LC_COLLATE: C
  value of $LC_CTYPE: en_GB.UTF-8
  value of $LC_MESSAGES: en_GB.UTF-8
  value of $LC_MONETARY: en_GB.UTF-8
  value of $LC_NUMERIC: en_GB.UTF-8
  value of $LC_TIME: en_GB.UTF-8
  value of $LANG: en_GB.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Shell

Minor modes in effect:
  diff-auto-refine-mode: t
  show-paren-mode: t
  shell-dirtrack-mode: t
  tooltip-mode: t
  mouse-wheel-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent messages:
Wrote /home/eda/git_working/repos/linux/crontab.tradingsystems.wcl-linux-live
Finding changes in 
/home/eda/git_working/repos/linux/crontab.tradingsystems.wcl-linux-live...done
Mark set
Press C-c C-c when you are done editing.
Enter a change comment.  Type C-c C-c when done
Checking in 
/home/eda/git_working/repos/linux/crontab.tradingsystems.wcl-linux-live...done
To git@wcl-git01.wcl.local:dev/repos.git
   1c5ba2f..fe19716  master -> master
Mark set [5 times]
Quit

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug sendmail smerge-mode pcmpl-x sh-script
smie executable dired-aux dired hideshow etags tabify imenu man warnings
rect ediff-ptch ediff-merg ediff-wind ediff-diff ediff-mult ediff-help
ediff-init ediff-util ediff ispell edmacro kmacro vc-bzr vc-sccs vc-svn
vc-cvs vc-rcs python json mule-util log-view nxml-uchnm rng-xsd
xsd-regexp rng-cmpct rng-nxml rng-valid rng-loc rng-uri rng-parse
nxml-parse rng-match rng-dt rng-util rng-pttrn nxml-ns nxml-mode
nxml-outln nxml-rap nxml-util nxml-glyph nxml-enc xmltok log-edit
message idna format-spec rfc822 mml mml-sec mm-decode mm-bodies
mm-encode mail-parse rfc2231 rfc2047 rfc2045 ietf-drums mailabbrev
mail-utils gmm-utils mailheader pcvs-util add-log diff-mode easy-mmode
vc vc-dispatcher cus-edit wid-edit perl-mode dabbrev help-mode cus-start
cus-load misearch multi-isearch vc-git sql easymenu view ffap thingatpt
url-parse auth-source eieio byte-opt bytecomp byte-compile cl-extra
cl-loaddefs cl-lib cconv eieio-core gnus-util mm-util help-fns
mail-prsvr password-cache url-vars pcmpl-unix xterm time-date paren
server compile shell pcomplete comint ring ansi-color tooltip electric
uniquify ediff-hook vc-hooks lisp-float-type mwheel x-win x-dnd 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
dbusbind gfilenotify dynamic-setting system-font-setting
font-render-setting move-toolbar gtk x-toolkit x multi-tty emacs)

Memory information:
((conses 16 3566802 246952)
 (symbols 48 28992 0)
 (miscs 40 1061 7737)
 (strings 32 83808 42796)
 (string-bytes 1 3341365)
 (vectors 16 31594)
 (vector-slots 8 1520686 341468)
 (floats 8 437 1264)
 (intervals 56 500006 936)
 (buffers 960 186)
 (heap 1024 138763 8917))