bug#25279: 26.0.50; Slowdown/crash on certain characters

[Richard Copley]

Two corrections inline below.

On 26 December 2016 at 20:09, Richard Copley <rcopley@gmail.com> wrote:
> From emacs -Q:
> Insert MUSIC FLAT SIGN or RIGHTWARDS DOUBLE ARROW in a buffer.
> Move point around in the buffer or edit the buffer text.
> Emacs gets very slow, consuming a lot of CPU.
> Sometimes it completely grinds to a halt.
>
> MUSIC FLAT SIGN and RIGHTWARDS DOUBLE ARROW are examples
> that cause this problem for me. MUSIC SHARP SIGN and
> RIGHTWARDS ARROW are examples that do not cause a problem.
>
> Below are the contents of the describe-char buffer for these
> characters (with the character itself asterisked out in each
> case so as not to crash my Emacs while I edit this mail).
>
> Note the categories. They seem illogical. Are they supposed
> to be like that? Why?
>
> Note the fonts. Could there be a bug in "Malgun Gothic"?
> As far as I know it's a Korean font installed by default with Windows.
> Could there be a bug in "Consolas"? Why does Emacs find the MUSIC
> SHARP SIGN glyph but not the MUSIC FLAT SIGN glyph from Consolas?

Oops: "Consolas" doesn't have either character. "MS Gothic" has
a glyph for MUSIC SHARP SIGN but not for MUSIC FLAT SIGN.
That goes some way towards explaining why it takes longer to find
a glyph for MUSIC FLAT SIGN. (But I still don't know what to do
about it.)

> I asked about this on IRC and there exist Windows Emacs users who
> don't have the issue, so it may be influenced by environmental
> factors.
>
> Is there anything I can do to avoid it?
> Install better fonts? (Any suggestions?)
> Uninstall bad fonts?
> Configure Emacs to search fonts in a different order?
>

> ** RIGHTWARDS DOUBLE ARROW (bad!):

Oops: I previously gave the describe-char buffer for RIGHTWARDS ARROW.
Here's the text for RIGHTWARDS DOUBLE ARROW:

             position: 148 of 150 (98%), column: 0
            character: * (displayed as *) (codepoint 8658, #o20722, #x21d2)
    preferred charset: unicode (Unicode (ISO10646))
code point in charset: 0x21D2
               script: symbol
               syntax: .     which means: punctuation
             category: .:Base, h:Korean, j:Japanese
             to input: type "C-x 8 RET 21d2" or "C-x 8 RET RIGHTWARDS
DOUBLE ARROW"
          buffer code: #xE2 #x87 #x92
            file code: not encodable by coding system iso-latin-1-dos
              display: by this font (glyph code)
    uniscribe:-outline-Malgun
Gothic-normal-normal-normal-sans-11-*-*-*-p-*-ksc5601.1987-0 (#x22D)

Character code properties: customize what to show
  name: RIGHTWARDS DOUBLE ARROW
  old-name: RIGHT DOUBLE ARROW
  general-category: Sm (Symbol, Math)
  decomposition: (8658) ('*')

> ** MUSIC FLAT SIGN (bad!):
>
>              position: 146 of 148 (98%), column: 0
>             character: * (displayed as *) (codepoint 9837, #o23155, #x266d)
>     preferred charset: unicode (Unicode (ISO10646))
> code point in charset: 0x266D
>                script: symbol
>                syntax: _     which means: symbol
>              category: .:Base, h:Korean, j:Japanese
>              to input: type "C-x 8 RET 266d" or "C-x 8 RET MUSIC FLAT SIGN"
>           buffer code: #xE2 #x99 #xAD
>             file code: not encodable by coding system iso-latin-1-dos
>               display: by this font (glyph code)
>     uniscribe:-outline-Malgun
> Gothic-normal-normal-normal-sans-11-*-*-*-p-*-ksc5601.1987-0 (#xCF2)
>
> Character code properties: customize what to show
>   name: MUSIC FLAT SIGN
>   old-name: FLAT
>   general-category: So (Symbol, Other)
>   decomposition: (9837) ('*')
>
> ** MUSIC SHARP SIGN (ok!):
>
>              position: 148 of 152 (97%), column: 0
>             character: * (displayed as *) (codepoint 9839, #o23157, #x266f)
>     preferred charset: unicode (Unicode (ISO10646))
> code point in charset: 0x266F
>                script: symbol
>                syntax: _     which means: symbol
>              category: .:Base, j:Japanese
>              to input: type "C-x 8 RET 266f" or "C-x 8 RET MUSIC SHARP SIGN"
>           buffer code: #xE2 #x99 #xAF
>             file code: not encodable by coding system iso-latin-1-dos
>               display: by this font (glyph code)
>     uniscribe:-outline-MS
> Gothic-normal-normal-normal-mono-11-*-*-*-c-*-gb2312.1980*-* (#x761)
>
> Character code properties: customize what to show
>   name: MUSIC SHARP SIGN
>   old-name: SHARP
>   general-category: Sm (Symbol, Math)
>   decomposition: (9839) ('*')
>
> RIGHTWARDS ARROW (ok!):
>
>              position: 148 of 150 (98%), column: 0
>             character: * (displayed as *) (codepoint 8594, #o20622, #x2192)
>     preferred charset: unicode (Unicode (ISO10646))
> code point in charset: 0x2192
>                script: symbol
>                syntax: .     which means: punctuation
>              category: .:Base, c:Chinese, h:Korean, j:Japanese
>              to input: type "C-x 8 RET 2192" or "C-x 8 RET RIGHTWARDS ARROW"
>           buffer code: #xE2 #x86 #x92
>             file code: not encodable by coding system iso-latin-1-dos
>               display: by this font (glyph code)
>     
> uniscribe:-outline-Consolas-normal-normal-normal-mono-11-*-*-*-c-*-iso8859-1
> (#x365)
>
> Character code properties: customize what to show
>   name: RIGHTWARDS ARROW
>   old-name: RIGHT ARROW
>   general-category: Sm (Symbol, Math)
>   decomposition: (8594) ('*')
>
> In GNU Emacs 26.0.50.10 (x86_64-w64-mingw32)
>  of 2016-12-26 built on MACHINE
> Repository revision: a8a24b5be7f8cb6741f28000ae34c5b39ad9644e
> Windowing system distributor 'Microsoft Corp.', version 10.0.14393
> Recent messages:
> Making completion list... [3 times]
> Quit [2 times]
> Mark saved where search started [2 times]
> delete-backward-char: Text is read-only
> Making completion list... [6 times]
> uncompressing eintr.info.gz...done
> C-c f is undefined
> Making completion list...
> Quit [7 times]
> nil
> Quit
> Configured using:
>  'configure --prefix=/mingw64 --with-modules --without-imagemagick
>  --enable-locallisppath=/site-lisp
>  PKG_CONFIG_PATH=/mingw64/lib/pkgconfig:/mingw64/share/pkgconfig'
>
> Configured features:
> XPM JPEG TIFF GIF PNG RSVG SOUND DBUS NOTIFY ACL GNUTLS LIBXML2 ZLIB
> TOOLKIT_SCROLL_BARS MODULES
>
> Important settings:
>   value of $LANG: en_GB.UTF-8
>   locale-coding-system: cp1252
>
> Major mode: Lisp Interaction
>
> Minor modes in effect:
>   tooltip-mode: t
>   global-eldoc-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
>   auto-composition-mode: t
>   auto-encryption-mode: t
>   auto-compression-mode: t
>   line-number-mode: t
>   transient-mark-mode: t
>
> Load-path shadows:
> None found.
>
> Features:
> (shadow sort mail-extr emacsbug message subr-x puny seq byte-opt gv
> bytecomp byte-compile cl-extra help-mode cconv cl-loaddefs pcase cl-lib
> dired dired-loaddefs format-spec rfc822 mml mml-sec password-cache epa
> derived epg epg-config gnus-util rmail rmail-loaddefs mm-decode
> mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader
> sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils
> jka-compr misearch multi-isearch info easymenu time-date mule-util
> tooltip eldoc electric uniquify ediff-hook vc-hooks lisp-float-type
> mwheel dos-w32 ls-lisp disp-table term/w32-win w32-win w32-vars
> term/common-win tool-bar dnd fontset image regexp-opt fringe
> tabulated-list replace newcomment text-mode elisp-mode lisp-mode
> prog-mode register page menu-bar rfn-eshadow isearch timer select
> scroll-bar mouse jit-lock font-lock syntax facemenu font-core
> term/tty-colors 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 composite charscript case-table epa-hook jka-cmpr-hook help
> simple abbrev obarray 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 w32notify dbusbind w32 multi-tty make-network-process emacs)
>
> Memory information:
> ((conses 16 105644 8301)
>  (symbols 56 20593 0)
>  (miscs 48 44 180)
>  (strings 32 22316 4034)
>  (string-bytes 1 651472)
>  (vectors 16 14275)
>  (vector-slots 8 449241 5484)
>  (floats 8 184 173)
>  (intervals 56 414 1299)
>  (buffers 976 12))