bug#6920: 23.2; ESC passed out of order to post-read-conversion

[Ryan Johnson]

 This problem shows up running in terminal mode on a cygwin xterm,
apparently because it sends terminal escape sequences one character at a
time (where linux usually sends the whole thing at once). To reproduce,
run the following three elisp commands:

(define-coding-system 'utf-8-echo
  "Echoes all input to the message area"
  :coding-type 'utf-8
  :mnemonic ?U
  :ascii-compatible-p t
  :charset-list '(unicode)
  :post-read-conversion 'echo-conversion)
(defun echo-conversion (len)
  (let* ((p (point))
     (e (+ p len))
     (str (buffer-substring p e)))
    (message "%s" str)
    len))
(set-keyboard-coding-system 'utf-8-echo)

Then start using the left arrow key to navigate. The escape sequence is
'^[OD' and every few arrow presses garbled bits of the "OD" portion will
appear in the buffer and the point doesn't move properly. A
representative sample of the message buffer looks like this:

^[
O
D
^[
O
D
O
D
^[ [2 times]
O
D

The lossage buffer (below) shows how emacs becomes very confused as a
result, reporting 'ESC O D O D D O D D ESC' at one point. Defining a
similar coding system based on iso-8859-1 instead of utf-8 causes emacs
to crash. Unfortunately, cygwin-gdb doesn't trap the signal so I can't
produce a stack trace, but sometimes it gets stuck in an endless loop
inside malloc, which suggests some sort of memory corruption is the
culprit. As far as I know, 'ESC O D' is valid in both coding systems
so that shouldn't be the problem.

System info follows...

In GNU Emacs 23.2.1 (i686-pc-cygwin)
 of 2010-08-12 on host
configured using `configure  '--prefix=/home/Ryan/apps/emacs-23.2' 
'--without-xpm' '--without-png' '--without-gif''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: C.UTF-8
  value of $XMODIFIERS: nil
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

Major mode: Emacs-Lisp

Minor modes in effect:
  tooltip-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
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
ESC [ > 0 ; 2 6 2 ; 0 c ESC ] 1 1 ; r g b : 0 0 0 0
/ 0 0 0 0 / 0 0 0 0 ESC \ ESC O B ESC O B ESC O B ESC
O B ESC O B ESC O B ESC O B ESC O B ESC O B ESC O B
ESC O B ESC O B ESC O B ESC O B ESC C-x ESC [ 1 ; 5
B ESC C-x ESC x s e t - k e y TAB RET u t f - 8 - e
c h o RET O D D ESC O D ESC O D ESC O D ESC O D O D
D ESC O D ESC O D ESC O D ESC O D ESC O D O D D O D
D ESC O D ESC O D ESC x r e p o r t - e m TAB RET

Recent messages:
t
-
e
m

^M
E
S
C
^M

Load-path shadows:
None found.

Features:
(shadow sort mail-extr message sendmail regexp-opt ecomplete rfc822 mml
easymenu mml-sec password-cache mm-decode mm-bodies mm-encode mailcap
mail-parse rfc2231 rfc2047 rfc2045 qp ietf-drums mailabbrev nnheader
gnus-util netrc time-date mm-util mail-prsvr gmm-utils wid-edit
mailheader canlock sha1 hex-util hashcash mail-utils emacsbug tooltip
ediff-hook vc-hooks lisp-float-type mwheel x-win x-dnd tool-bar dnd
fontset image fringe lisp-mode register page menu-bar rfn-eshadow timer
select scroll-bar mldrag 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 loaddefs button minibuffer faces
cus-face files text-properties overlay md5 base64 format env code-pages
mule custom widget hashtable-print-readable backquote
make-network-process x multi-tty emacs)