bug#4240: 23.1.50; C-u doesn't work with Swedish characters

[Eli Zaretskii <eliz@gnu.org>]

> From: Juri Linkov <juri@jurta.org>
> Date: Sun, 23 Aug 2009 21:54:04 +0300
> Cc: 4240@emacsbugs.donarmstrong.com
> 
> > I hit "C-u ä" expecting it to come out as "ääää".  Instead it comes out
> > as "ä\344\344ä".  I try "C-u C-u ä" and it comes out as "ä" followed by
> > fourteen "\344" and then a trailing "ä".  This happens no matter which
> > kind of repetition I'm doing, be it using C-u or using e.g. M-3.  It's
> > always the leading and the trailing character that come out right, all
> > of the other ones are "broken".
> 
> Please see bug#4037:
> http://emacsbugs.donarmstrong.com/cgi-bin/bugreport.cgi?bug=4037
> 
> I received no confirmation that my proposed fix is correct.

I think those two lines are not necessary anymore and should be
removed (together with the comments which explain their need).  I
think they belong to the old pre-unicode days when raw eight-bit
characters needed such special treatment.

Handa-san, can you please comment on that?

> Maybe the right fix is to reverse negation?

Why, do you see that the code without these two lines don't DTRT when
the characters are inserted into a unibyte buffer?  If it works in
both cases, it's the evidence that I'm right and this code is not
needed anymore.

> It seems logical to check if a buffer is unibyte before converting
> from unibyte to multibyte, but I don't understand what this code was
> supposed to do.

It was supposed to produce a multibyte character from a unibyte one,
by using a special locale-dependent table that mapped, e.g., 8859-1
encoded Latin-1 characters in the range [128..255] to the
corresponding multibyte codepoints of Latin-1 characters in the
internal representation of characters Emacs 22 used.  See the Emacs 22
definition of unibyte_char_to_multibyte in src/charset.c.

Nowadays we don't need that, since we have a special range of
multibyte codepoints for representing unibyte characters in multibyte
buffers and strings, and insert-char and the primitives it calls
already DTRT with them.  So there should be no need to do anything
special outside insert-char.