Changes to message-mode and encoding in Emacs26

[Alex Bennée]

Hi,

I've just recently updated to the Emacs 26 branch and I've run into an
odd problem with message encoding. Despite (I think) having utf-8 set
throughout when sending email I get a warning complaining that utf-8
can't encode my name.

While composing everything works fine, the character is described as:

            character: é (displayed as é) (codepoint 233, #o351, #xe9)
    preferred charset: unicode-bmp (Unicode Basic Multilingual Plane 
(U+0000..U+FFFF))
code point in charset: 0xE9
               script: latin
               syntax: w        which means: word
             category: .:Base, L:Left-to-right (strong), c:Chinese, j:Japanese, 
l:Latin, v:Viet
             to input: type "C-x 8 RET e9" or "C-x 8 RET LATIN SMALL LETTER E 
WITH ACUTE"
          buffer code: #xC3 #xA9
            file code: #xC3 #xA9 (encoded by coding system utf-8-unix)
              display: terminal code #xC3 #xA9

But when I send it ends up:

            character:  (displayed as ) (codepoint 4194243, #o17777703, 
#x3fffc3)
    preferred charset: eight-bit (Raw bytes 128-255)
code point in charset: 0xC3
               syntax: w        which means: word
             category: L:Left-to-right (strong)
             to input: type "C-x 8 RET 3fffc3"
          buffer code: #xC3
            file code: not encodable by coding system utf-8-unix
              display: not encodable for terminal

And a prompt:

  These default coding systems were tried to encode text
  in the buffer ‘1506440244.6bae7e76af4f300b.zen:2,S’:
    (utf-8-unix (347 . 4194243) (348 . 4194217))
  However, each of them encountered characters it couldn’t encode:
    utf-8-unix cannot encode these:

  Click on a character (or switch to this window by ‘M-x other-window’
  and select the characters by RET) to jump to the place it appears,
  where ‘C-u C-x =’ will give information about it.

  Select one of the safe coding systems listed below,
  or cancel the writing with C-g and edit the buffer
     to remove or modify the problematic characters,
  or specify any other coding system (and risk losing
     the problematic characters).

    raw-text no-conversion

If I force raw-text it seems to look fine. Any idea what's going on?

There is a bug raised with mu4e (the mail client using message-mode):

  https://github.com/djcb/mu/issues/1081

--
Alex Bennée