Problem opening a MIME attachment

Hello,

I encounter a problem opening a MIME attachment with an external
viewer with emacs 29.1 (Gnus v5.13) on Windows (I had the same problem
with version 28.1). Problem occurs when the filename has characters
other than 7-bit ASCII. I have not found any trace of this problem,
which surprises me.

Content-Type is defined as follows:

Content-Type: message/external-body;
 name="c:/somedirs/XXX =?iso-8859-1?Q?R=E9<snipped>";
 access-type=LOCAL-FILE

The viewer is launched in mm-display-external by start-process with
following args:

  - path to cmdproxy.exe
  - -c
  - path to the viewer exe and the attachment filename encoded in
    iso-8859-1

The viewer fails to open the file. The parameter received by the
viewer is not encoded in iso-8859-1: 0x160 for è, 0x201A for é, ... It
appears the problem disappear when I set coding-system-for-write to
buffer-file-coding-system before calling start-process but I am not
sure this is the correct fix.


-- 
Pascal Quesseveur
[email protected]