bug#26396: 25.1; char-displayable-p on a latin1 tty

[Eli Zaretskii <eliz@gnu.org>]

> Cc: user42_kevin@yahoo.com.au, 26396@debbugs.gnu.org
> From: Paul Eggert <eggert@cs.ucla.edu>
> Date: Mon, 17 Apr 2017 11:08:09 -0700
> 
> On 04/17/2017 01:08 AM, Eli Zaretskii wrote:
> 
> > My reading of the code is that at least some of these unsupported
> > characters will NOT be displayed as \uNNNNN, but rather as some
> > fallback glyph produced by the console itself, which is not what we
> > want, I think.
> Yes, that's what happens. It's not ideal, and perhaps it could be 
> improved. (I hope by someone else....)

Lat's hope.

> There are similar display problems even in unibyte mode on the Linux 
> console. Sometimes a character above U+00FF  is displayed as '\uNNNN', 
> sometimes as '?', sometimes the same character is displayed in different 
> forms depending on what else is in the buffer, and I don't know why. 
> (And likewise, I don't want to spend time worrying about this, as the 
> 1990s are long gone....)

Yes, the TTY code that handles such characters has some very weird
logic.

Can you show an example of a character displayed in different forms
depending on buffer contents?  I'd like to look what the code does and
why.

Thanks.