bug#27270: display-raw-bytes-as-hex generates ambiguous output for Emacs strings

[Eli Zaretskii]

> Cc: Eli Zaretskii <eliz@gnu.org>, 27270@debbugs.gnu.org,
>  v.schneidermann@gmail.com
> From: Paul Eggert <eggert@cs.ucla.edu>
> Date: Thu, 8 Jun 2017 08:56:31 -0700
> 
> (setq display-raw-bytes-as-hex t) C-j
> (format "%c%c" ?\u0090 ?5) C-j
> 
> Emacs displays this:
> 
> "\x905"
> 
> which is the wrong string visually.

How is that different from "\2205" you get under the default settings?

> The string should be 
> displayed unambiguously, either like this:
> 
> "\x80\ 5"
> 
> or via some other means.

We do use "some other means": the raw byte has a different face.  But
if you evaluate the above in *scratch*, you won't see that because of
font-lock.  Turn off font-lock-mode, and you will clearly see where
the raw byte ends and "normal" text begins.