bug#2015: 23.0.60; Rmail decodes messages incorrectly

bug#2015: 23.0.60; Rmail decodes messages incorrectly

[Eli Zaretskii]

Please write in English if possible, because the Emacs maintainers
usually do not have translators to read other languages for them.

Your bug report will be posted to the emacs-pretest-bug@gnu.org mailing list.

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

Rmail does not correctly decode quoted-printable messages.  For
example, a message that has these headers:

  Content-Type: text/plain; charset=WINDOWS-1252; delsp=yes; format=flowed
  Content-Transfer-Encoding: quoted-printable

Shows a Windows-1252 character \226 as an octal escape, and says that
the buffer's encoding is undecided-unix.

In addition, Rmail before mbox merge would rewrite
Content-Transfer-Encoding header into "8-bit", when it decoded the
quoted-printable encoding, but the current Rmail does not.

If Emacs crashed, and you have the Emacs process in the gdb debugger,
please include the output from the following gdb commands:
    `bt full' and `xbacktrace'.
If you would like to further debug the crash, please read the file
d:/gnu/emacs/etc/DEBUG for instructions.


In GNU Emacs 23.0.60.1 (i386-mingw-nt5.1.2600)
 of 2009-01-24 on HOME-C4E4A596F7
Windowing system distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-gcc (3.4)'

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: ENU
  value of $XMODIFIERS: nil
  locale-coding-system: cp1255
  default-enable-multibyte-characters: t

Major mode: RMAIL

Minor modes in effect:
  tooltip-mode: t
  tool-bar-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  global-auto-composition-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
<help-echo> C-u M-x r m a i l <return> ~ / d a <tab> 
m a i l . i <tab> <return> <help-echo> <help-echo> 
<help-echo> <help-echo> <help-echo> <help-echo> M-x 
r m a u <backspace> i l - s <tab> u <tab> <return> 
<C-next> C-g C-x o C-u 1 2 C-x ^ p C-x C-s p p n n 
n n p p p p n n n o d a <tab> x x <tab> x <backspace> 
<backspace> <backspace> X X X X . r m a i l <return> 
y e s <return> p o <return> <help-echo> <down-mouse-1> 
<help-echo> <drag-mouse-1> <help-echo> C-x C-s p p 
n n n C-x C-b C-x 4 b <return> <help-echo> <down-mouse-1> 
<help-echo> <drag-mouse-1> C-x o <help-echo> t <next> 
<next> <next> <down> <down> <down> <down> <down> <down> 
<down> <right> <right> <right> <right> <right> <right> 
<right> <right> <right> <right> <right> <right> <right> 
<right> <right> <right> <right> <right> <right> <right> 
<right> <right> <right> <right> <right> <right> <right> 
<right> <right> <right> <right> <left> <prior> <prior> 
<prior> <prior> <next> M-x r e p o <tab> r <tab> <
return>

Recent messages:
Type y, n, ! or SPC (the space bar): 
Quit
Wrote d:/usr/eli/data/mail.in
No following nondeleted message
No previous nondeleted message
Making completion list...
Added to d:/usr/eli/data/XXXX.rmail [2 times]
Wrote d:/usr/eli/data/mail.in
call-interactively: Beginning of buffer
Making completion list...

bug#2015: 23.0.60; Rmail decodes messages incorrectly

[Chong Yidong]

> Rmail does not correctly decode quoted-printable messages.  For
> example, a message that has these headers:
>
>   Content-Type: text/plain; charset=WINDOWS-1252; delsp=yes;
>   format=flowed
>   Content-Transfer-Encoding: quoted-printable
>
> Shows a Windows-1252 character \226 as an octal escape, and says that
> the buffer's encoding is undecided-unix.
>
> In addition, Rmail before mbox merge would rewrite
> Content-Transfer-Encoding header into "8-bit", when it decoded the
> quoted-printable encoding, but the current Rmail does not.

IIUC, the new Rmail decodes quoted-printable messages during message
display, leaving the original message unchanged in the Rmail file.
That's why it does not change Content-Transfer-Encoding to "8bit".

I don't see why Rmail would fail to correctly decode a message with the
headers you provided.  Here's a shot in the dark: if you add the line

  (setq last-coding-system-used nil)

to line 2564 of rmail.el, just before the call to rmail-decode-region,
is there any improvement?