Re: How to get buffer byte length (not number of characters)?

[Eli Zaretskii <eliz@gnu.org>]

> From: Joseph Turner <joseph@ushin.org>
> Cc: emacs-devel@gnu.org,  schwab@suse.de,  adam@alphapapa.net
> Date: Fri, 23 Aug 2024 09:59:22 -0700
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> From: Joseph Turner <joseph@ushin.org>
> >> Cc: emacs-devel@gnu.org,  schwab@suse.de,  adam@alphapapa.net
> >> Date: Fri, 23 Aug 2024 00:43:52 -0700
> >> 
> >> I'm surprised that
> >> 
> >> (with-temp-buffer
> >>   (insert "你好")
> >>   (set-buffer-file-coding-system 'chinese-big5)
> >>   (car (find-coding-systems-region (point-min) (point-max))))
> >> 
> >> returns 'utf-8 and not 'chinese-big5.
> >
> > What does coding-system-priority-list returns in your case?
> 
> 'utf-8

That explains what you see, then.

> >> Are the codings intended to be
> >> ordered by priority?
> >
> > Yes.
> >
> >> If so, should buffer-file-coding-system be at the front of the list
> >> if it's safe?
> >
> > How do you know it's safe?
> >
> > If your application needs to prefer buffer-file-coding-system, then
> > you should see if buffer-file-coding-system is a member of the list
> > returned by find-coding-systems-region, and if so, use that.
> 
> I'd have thought that most applications would want to prefer
> buffer-file-coding-system if it's a member of the list returned by
> find-coding-systems-region, but perhaps not.

Most applications use select-safe-coding-system, which AFAIR already
does all that.