bug#12925: 24.1; string-make-unibyte instead of string-as-unibyte

[Eli Zaretskii <eliz@gnu.org>]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Date: Tue, 01 Jun 2021 09:02:13 +0200
> Cc: 12925@debbugs.gnu.org, Ethan Glasser-Camp <ethan.glasser.camp@gmail.com>
> 
> Stefan Monnier <monnier@iro.umontreal.ca> writes:
> 
> >> Why does inserting multibyte text into a unibyte buffer corrupt it
> >> like this?
> >
> > Because the right thing (i.e. signaling an error) was not backward
> > compatible with broken code that assumed that chars can be presented
> > with 8bit (i.e. code written in the glory days of latin-N, koi-8, ...).
> >
> > We could/should probably try to do the right thing now, since such
> > broken code is probably much less common.
> 
> (Now eight years later.)
> 
> So the suggestion is to make inserting multibyte strings into a unibyte
> buffer signal an error (instead of inserting the lower byte of
> characters).
> 
> Has anybody experimented with doing this and seeing whether this signals
> a lot of errors in daily usage?

Why not make both methods do the same: insert the bytes of the
multibyte text into the unibyte buffer?

Making the buffer unibyte after insertion is a PITA, because it could
be very slow if the text in the buffer is long.  That's why people may
wish to do it the other way around: making an empty buffer unibyte is
a snap.