bug#22169: 25.0.50; File name compiletion doesn't work with non-ASCII characters on OS X

[Eli Zaretskii]

> Date: Tue, 15 Dec 2015 06:12:47 +0100
> From: Anders Lindgren <andlind@gmail.com>
> Cc: 22169@debbugs.gnu.org
> 
>     > file-name-coding-system
>     > utf-8-nfd
>     
>     Where is that defined?
> 
> In ns-win.el

I think we should remove that, and leave behind an alias that uses
utf-8-hfs, which is provided by Emacs.  There's no reason to maintain
2 identical definitions.

> I tried setting it to nil. This made completion work. However, the letters are
> presented in decomposed form, so that pressing backspace first converts "å" to
> "a", a second backspace deletes the "a" -- this is not how we would like to
> present file names to users.

When you set file-name-coding-system to nil, Emacs uses
default-file-name-system, which is utf-8, so it doesn't
compose/decompose characters, and that's why you see what you see.
IOW, using nil is a step backward.

What does this return:

  M-: (file-name-all-completion "åäö" "/that/empty/directory/") RET

Also, what is your value of completion-ignore-case?