Re: Why does dired go through extra efforts to avoid unibyte names

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Date: Fri, 29 Dec 2017 09:34:53 -0500
> Cc: emacs-devel@gnu.org
> 
> I bumped into the following code in dired-get-filename:
> 
> 	  ;; The above `read' will return a unibyte string if FILE
> 	  ;; contains eight-bit-control/graphic characters.
> 	  (if (and enable-multibyte-characters
> 		   (not (multibyte-string-p file)))
> 	      (setq file (string-to-multibyte file)))
> 
> and I'm wondering why we don't want a unibyte string here.
> `vc-region-history` told me this comes from the commit appended below,
> which seems to indicate that we're worried about a subsequent encoding,
> but AFAIK unibyte file names are not (re)encoded, and passing them
> through string-to-multibyte would actually make things worse in this
> respect (since it might cause the kind of (re)encoding this is
> supposedly trying to avoid).
> 
> What am I missing?

Why does it matter whether eight-bit-* characters are encoded one more
or one less time?

As for the reason for using string-to-multibyte: maybe it's because we
use concat further down in the function, which will determine whether
the result will be unibyte or multibyte according to its own ideas of
what's TRT?