bug#17905: 24.3.50; writing with a giant font triggers RTL text entry

[Joe Corneli]

My eyesight is very bad without my glasses, and I was experimenting with
a giant font on my laptop that I could comfortably read without them.

To replicate my set-up: shift+click and select "Increase Buffer Text
Size" several times, to get letters that are about an inch tall!  The
buffer is in fundamental mode.  Emacs is compiled with Xft support.

I was able to replicate the following weird behavior by following the
above recipe with emacs -q --no-site-file, using the font that is the
default there.

Here's a sample text generated by simply typing with a giant-sized font:

SAMPLE:

Maybe it's when the lines are particularly long, like if I keep writing
after a ?seog rosruc eht erehw fo yltnednepedni ,elihw

(DECRYPTED):

Maybe it's when the lines are particularly long, like if I keep writing
after a while, independently of where the cursor goes?

It seems that quite reliably, with this giant font, the lines will flip
to RTL after writing for a while.  If I write in the same buffer in a
window that doesn't have the giant font set, it doesn't trigger RTL.
Here's a text I wrote, starting in window in which the buffer is
normal-sized, and then switching, back to the giant sized buffer after a
while:

SAMPLE:

Is it true even if the font size is a bit smaller, I wonder, or does it
only happen with my glasses off?  Is there a particular point when it
hits, or does it only happen if I get going with some particular word in
the way?  ...ezis tnof yb dereggirt eb ot yletinifed smees tI

Finally, here's a text written in the giant-sized buffer that can be
used to estimate where it switches:

SAMPLE:

a b c d e f g h i j k l m n o p q r s t u v w x y z a b c d e f g h i j k l m n 
u t s r q p o

... hm, it seems to flip at EXACTLY AT 80 CHARACTERS!  (That matches the
first sample text above, too.)




In GNU Emacs 24.3.50.2 (x86_64-apple-darwin13.1.0, X toolkit, Xaw scroll bars)
 of 2014-04-19 on Joes-MacBook-Pro.local
Repository revision: 116800 lekktu@gmail.com-20140319022451-z8fp3icgftf8zjg6
Windowing system distributor `The X.Org Foundation', version 11.0.11406000
Configured using:
 `configure --with-x-toolkit=lucid CPPFLAGS=-I/opt/local/include
 LDFLAGS=-L/opt/local/lib'

Important settings:
  locale-coding-system: nil

Major mode: Fundamental

Minor modes in effect:
  show-paren-mode: t
  TeX-PDF-mode: t
  shell-dirtrack-mode: t
  global-hl-line-mode: t
  tooltip-mode: t
  mouse-wheel-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: 1

Recent input:
i n g SPC q u i t e SPC l i k e SPC i t SPC b e f o 
r e , SPC c e r t a i n l y . SPC SPC A n d SPC i t 
SPC d o e s n ' t SPC h a p p e n SPC e v e r y SPC 
t i m e C-e C-e C-e C-e <down> M-> <return> <return> 
M a y b e SPC i t ' s SPC w h e n SPC t h e SPC l i 
n e s SPC a r e SPC p a r t i c u l a r l y SPC l o 
n g , SPC l i k e SPC i f SPC t h e SPC <backspace> 
<backspace> <backspace> <backspace> <backspace> SPC 
I S-SPC k e e p SPC w r i t i n g SPC a f t e r SPC 
a SPC w h i l e , SPC i n d e p e n d e n t l y SPC 
o f SPC w h e r e SPC t h e SPC c u r s o r SPC g o 
e s ? C-e <down> <down> <return> <return> <up> <up> 
C-e <down> C-SPC <up> <up> <up> <up> <up> <up> <up> 
<up> M-w M-x C-g C-x C-w <backspace> <backspace> <backspace> 
<backspace> <backspace> <backspace> <backspace> <backspace> 
<backspace> <backspace> <backspace> <backspace> <backspace> 
<backspace> <backspace> <backspace> <backspace> b i 
g <return> M-x s w <tab> - <tab> b u <tab> <tab> - 
<tab> f <tab> <return> s m a l l <return> C-y <up> 
<up> <down> <down> <down> <up> <up> C-SPC M-> M-w M-x 
r e p <tab> o <tab> r <tab> <return>

Recent messages:
Saved text until "osruc eht erehw fo yltnednepedni ,elihw
"
Quit
Saving file /Users/joe/big...
Wrote /Users/joe/big
Making completion list...
Mark set
End of buffer
Mark activated
Making completion list... [2 times]

Load-path shadows:
/Users/joe/.emacs.d/elpa/mediawiki-2.2.3/mediawiki hides 
~/thesis.git/config/elisp/mediawiki
~/diaspora.el/libraries/markdown-mode hides 
~/thesis.git/config/elisp/markdown-mode
~/thesis.git/config/elisp/tex-mode hides 
/usr/local/share/emacs/24.3.50/lisp/textmodes/tex-mode
~/elisp/emms/lisp/tq hides /usr/local/share/emacs/24.3.50/lisp/emacs-lisp/tq

Features:
(shadow emacsbug align rect novice etags tutorial grep scheme js imenu
cc-mode cc-fonts cc-guess cc-menus cc-cmds cc-styles cc-align cc-engine
cc-vars cc-defs plain-tex tex-buf python mmm-cmds eieio-opt texmathp pp
url-queue bibtex shr-color timezone parse-time dabbrev ispell qp
network-stream starttls mailalias mail-extr sort face-remap sh-script
smie executable pcmpl-unix vc-git font-latex latexenc misearch
multi-isearch dired-aux help-mode paren cus-start cus-load w3m-load
w3m-proc w3m-util mule-util dired-x info-look info tex-mode latex
tex-style tex crm compile compare-w org org-macro org-footnote
org-pcomplete org-list org-faces org-entities org-version ob-emacs-lisp
ob ob-tangle org-src ob-ref ob-lob ob-table ob-keys ob-exp ob-comint
ob-core ob-eval org-compat org-macs org-loaddefs cal-menu calendar
cal-loaddefs tramp tramp-compat tramp-loaddefs trampver shell pcomplete
eww google-translate ert find-func ewoc debug diaspora diaspora-bookmark
diaspora-stream-mode diaspora-misc diaspora-main diaspora-messages htmlr
sgml-mode diaspora-contacts diaspora-aspects diaspora-notifications
diaspora-stream diaspora-comments diaspora-post diaspora-http-errors
diaspora-post-edit-mode skeleton diaspora-new diaspora-urls
diaspora-mode markdown-translator json mmm-mode mmm-class mmm-region
mmm-utils mmm-univ mmm-auto mmm-vars mmm-compat gnutls shr mu4e
mu4e-speedbar speedbar sb-image ezimage dframe mu4e-main mu4e-view epa
epg epg-config browse-url comint ansi-color mu4e-headers mu4e-compose
mu4e-draft mu4e-actions ido rfc2368 mu4e-mark mu4e-message html2text
mu4e-proc mu4e-utils doc-view jka-compr image-mode mu4e-lists mu4e-about
mu4e-vars message rfc822 mailabbrev gmm-utils mailheader mu4e-meta
smtpmail-multi smtpmail sendmail load-theme-buffer-local
highlight-indentation poly-markdown markdown-mode derived thingatpt
edmacro kmacro polymode pcase poly-base polymode-weave polymode-export
polymode-methods polymode-classes polymode-common cl-macs gv format-spec
eieio-custom eieio-base color jabber-autoloads package apropos emms-mark
emms-history emms-cache emms-info-ogginfo emms-info-mp3info emms-info
later-do emms-playlist-mode emms-player-vlc advice emms-player-mplayer
emms-player-simple emms-source-playlist emms-source-file dired
emms-setup emms emms-compat emstar cl hl-line mediawiki url-cache ring
mm-url gnus gnus-ems nnheader mail-utils wid-edit cl-loaddefs cl-lib mml
easymenu mml-sec mm-decode mm-bodies mm-encode url-http tls url
url-proxy url-privacy url-expand url-methods url-history mailcap
url-auth mail-parse rfc2231 rfc2047 rfc2045 ietf-drums url-cookie
url-domsuf url-util url-parse auth-source eieio byte-opt bytecomp
byte-compile cconv eieio-core gnus-util mm-util help-fns mail-prsvr
password-cache url-gw url-vars outline-magic noutline outline easy-mmode
tex-site auto-loads time-date 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
x-toolkit x multi-tty emacs)