Re: [PATCH] Improve error reporting when serializing non-Unicode strings to JSON

[Eli Zaretskii <eliz@gnu.org>]

> From: Philipp Stephani <p.stephani2@gmail.com>
> Date: Sat, 23 Dec 2017 14:29:56 +0000
> Cc: emacs-devel@gnu.org, phst@google.com
> 
>  OK, but why do we need external functions for doing that?  What is
>  missing in our own code to detect such a situation?
> 
> Not much I think, it's just easiest to use Gnulib functions because they are well-documented, have a clean
> interface, and are probably bug-free.
> coding.c has check_utf_8, which is quite similar, but has an incompatible interface (it takes struct
> coding_system objects) and also checks for embedded newlines, which isn't necessary here. 

So let's use check_utf_8, as its downsides don't sound serious to me,
and OTOH using unistring functions will bloat Emacs for the benefit of
a single use case, not to mention create two different methods for
doing the same job, which IMO is even more confusing to any newcomer
to the Emacs internals.

Btw, doesn't find_charsets_in_text do the same job cleaner and
quicker?  AFAIU, all you need is make sure there are no characters
from the 2 eight-bit-* charsets in the text, or did I miss something?