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

[Joseph Turner <joseph@ushin.org>]

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 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.

Fantastic!  Yes, it appears that select-safe-coding-system does account
for buffer-file-coding-system.  So, hyperdrive.el can just encode with

(select-safe-coding-system (point-min) (point-max) nil nil FILENAME)

Simple.

Thank you!!

Joseph