bug#50865: 28.0.50; Emoji with emoji modifier in Linux console garbles emacs display

[Aura Kelloniemi <kaura.dev@sange.fi>]

On 2021-09-28 at 21:35 +0300, Eli Zaretskii <eliz@gnu.org> wrote:
 > That should not be that way.  Some characters are double-width, and
 > should take up 2 columns on display.

I noticed, that Linux console does not understand most of the zero-width
characters either. It happily prints most of the code points in the list of
zero-width characters. Of course they are printed just as diamonds, because
Linux cannot store enough glyphs in its 512-glyph font space, but anyway it
prints a diamond for such characters as <COMBINING GRAVE ACCENT>.

The character range \y200B-\u200F seems to be an exception here. When I try to
print one of these characters on a Linxu VT, it really prints nothing.

When I insert zero-width characters in Emacs, the diamonds representing the
characters are printed interspersed by the padding spaces added by emacs. The
cursor is left behind the extending line of characters as a type, because
Emacs thinks, that the zero-width characters really do not print anything,
even though they do.

I believe that the one viable solution is to make char-width-table a terminal
local variable, so that there can be a simplified version for terminals that
don't understand Unicode correctly.

-- 
Aura