bug#1174: 23.0.60; Some UTF-8 mails displaying wrongly in Emacs 23

[Stefan Monnier <monnier@iro.umontreal.ca>]

> I never saw this problem myself.  I cannot see any difference with a
> few UTF-8 articles (C-T-E: 8bit, [1]), neither with Emacs 22 (with
> current Gnus trunk) or Emacs trunk (Gnus 5.13 from there).  Stefan,
> what are the "accidental emacs-mule-valid byte sequences" that trigger
> this problem?  It would be good if someone could send me a problematic
> article. [2]

In Emacs-22, the problem was more difficult to trigger: you had to
receive an email whose undecoded text contained emacs-mule escape
sequences, which is rather uncommon.  With Emacs-23, it's a lot more
common since the internal encoding has changed to a variant of utf-8:
an 8bit body using utf-8 will see its content unwillingly decoded during
nnimap-demule which leads to the bugs we've seen recently.

I'm pretty sure that string-as-multibyte is wrong here in general.
Maybe the problem is that nnimap-demule is used blindly in different
contexts where some need string-to-multibyte and some need
string-as-multibyte.  E.g. maybe Simon's problem was linked to imap
groups with non-ASCII chars in their names, rather than in the
message bodies.


        Stefan