bug#27141: 26.0.50; mml-generate-mime-1 broken

[Katsumi Yamaoka]

On Thu, 01 Jun 2017 07:20:13 +0200, Lars Ingebrigtsen wrote:
> Katsumi Yamaoka <yamaoka@jpl.org> writes:

>> On Tue, 30 May 2017 15:09:28 +0900, Katsumi Yamaoka wrote:
>>> So, as for at least mail forwarding, `mml-generate-mime-1' is
>>> seriously broken.

>> I've reverted it to the emacs-25 version (with some modifications)
>> for a emergency fix.

> Well, the function was reworked because it destroys files when
> forwarding them, I seem to recall?  So this seems like it's just
> changing one bug for another...

OK, could you please re-revert and fix it?  I did have no idea
to fix the bug in this construction...

(with-temp-buffer
  (set-buffer-multibyte nil)
  (insert
   (with-temp-buffer ;; <- unibyte
     (insert something) ;; <- multibyte
     (encode-coding ...)
     (buffer-string))))

Thanks.