bug#16800: 24.3; flyspell works slow on very short words at the end of big file

[Aleksey Cherepanov <aleksey.4erepanov@gmail.com>]

Package: emacs
Version: 24.3
Severity: normal

Dear Maintainers,

It is a copy of bug #739412 in Debian. Debian uses bug tracker
similar to this one. The bug on web:
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=739412
Address to continue thread there:
739412@bugs.debian.org

   * What led up to the situation?

I faced a problem editing my big .org file (2mb+) with flyspell-mode
enabled. I edit it every day, regularly mistype and get words of one
or two letters that are wrong in Russian and cause flyspell work slow.

This one-liner produces "good" file to reproduce the bug.
perl -e 'print(((join " ", ("met and") x 10) . "\n") x 30000)' > t.txt

Typing "nd" at the end of file gives a huge pause even on a fast
computer. But "mw" or "md" does not give pauses because they are not
substrings in this file. It is repeatable with emacs -Q.

   * What exactly did you do (or not do) that was effective (or
     ineffective)?

 So exact sequence is
$ emacs --version
GNU Emacs 24.3.1
$ emacs23 --version
GNU Emacs 23.4.1
$ perl -e 'print(((join " ", ("met and") x 10) . "\n") x 30000)' > t.txt
$ LANG=C emacs -Q t.txt
 Then in emacs:
M-x flyspell-mode RET
M->
nd SPC

'emacs23 -Q t.txt' works the same way. LANG=C affects regular words
because default dictionary is Russian on my system so without LANG=C
all words ("met" and "and") are considered misspelled. But it does not
affect huge pause at the end.

   * What was the outcome of this action?

Huge pause when emacs does not react on keys except C-g. Word "nd" is
colored as misspelled after the pause. C-g stops emacs internal
thinking and I could work without waiting but word "nd" is not colored
as misspelled word.

   * What outcome did you expect instead?

I expect it to work as fast as with other words like "md" or "mw" that
does not produce a pause and are colored immediately.


I tried to patch flyspell-word-search-backward and
flyspell-word-search-forward functions from flyspell.el replacing
search-backward with word-search-backward and search-forward with
word-search-forward (perl -pe 's/\(search-/(word-search-/' ). It
solved the problem but I do not know what it broke.

I expect problems with this solution because I do not know if
flyspell's meaning of word is the same as emacs' one. I think it is
described in flyspell-get-word function that is called after search-*
in the patched functions.

flyspell-duplicate-distance variable on its own could mitigate the
problem but it changes the behaviour so I do not want to use this
variable.

Thanks!

-- 
Regards,
Aleksey Cherepanov


In GNU Emacs 24.3.1 (x86_64-pc-linux-gnu, GTK+ Version 3.8.6)
 of 2013-12-23 on brahms, modified by Debian
Windowing system distributor `The X.Org Foundation', version 11.0.11405000
System Description:	Debian GNU/Linux testing (jessie)

Configured using:
 `configure '--build' 'x86_64-linux-gnu' '--build' 'x86_64-linux-gnu'
 '--prefix=/usr' '--sharedstatedir=/var/lib' '--libexecdir=/usr/lib'
 '--localstatedir=/var/lib' '--infodir=/usr/share/info'
 '--mandir=/usr/share/man' '--with-pop=yes'
 '--enable-locallisppath=/etc/emacs24:/etc/emacs:/usr/local/share/emacs/24.3/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/24.3/site-lisp:/usr/share/emacs/site-lisp'
 '--with-crt-dir=/usr/lib/x86_64-linux-gnu' '--with-x=yes'
 '--with-x-toolkit=gtk3' '--with-toolkit-scroll-bars'
 'build_alias=x86_64-linux-gnu' 'CFLAGS=-g -O2 -fstack-protector
 --param=ssp-buffer-size=4 -Wformat -Werror=format-security -Wall'
 'LDFLAGS=-Wl,-z,relro' 'CPPFLAGS=-D_FORTIFY_SOURCE=2''

Important settings:
  value of $LANG: ru_RU.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t