bug#35507: Gnus mojibakifies UTF-8 text/x-patch attachments from Thunderbird

[Eli Zaretskii]

> From: "Basil L. Contovounesios" <contovob@tcd.ie>
> Cc: Noam Postavsky <npostavs@gmail.com>,  <35507@debbugs.gnu.org>,  
> <andrewjmoreton@gmail.com>
> Date: Fri, 03 May 2019 15:02:01 +0100
> 
> Question following an initial reading of (info "(elisp) Coding System
> Basics"): would it be better in this case to use prefer-utf-8 instead of
> undecided?  If not, why not?

Because we have no reason to prefer UTF-8 in this case.  No one tells
us that x-patch will be predominantly encoded in UTF-8.

The RFC doesn't say that UTF-8 is the default, either, and
text/x-patch is not defined anywhere with that default.  Which means
there's no default, and in that case 'undecided' is better, because it
heeds to the preferences of the user.