Re: Display of undisplayable characters: \U01F3A8 instead of diamond

[Eli Zaretskii <eliz@gnu.org>]

> From: Richard Stallman <rms@gnu.org>
> Date: Thu, 25 Aug 2022 23:33:57 -0400
> 
> The text-based Linux console is unable to display many Unicode
> characters.  In Emacs 29, display of undisplayable characters has
> changed.  It used to show them with a diamond.  Now it shows the
> unicode character code as hex, preceded by \U.
> 
> I find that change quite inconvenient.  It makes the text harder to
> read.  Showing the codes does no good, since I don't know these codes,
> not even for characters I am familiar with.  To find out what
> character a code represents, I have to use C-u C-x =, just as I did
> before.

This is a standard Emacs way of displaying unsupported characters on
TTY frames.  I fail to see how this is worse than displaying the same
diamond glyph for any unsupported character, because with the
character codes you at least know when the characters are different,
even without "C-u C-x =".

You can have some (many) of the characters show in a more readable
form by invoking "M-x latin1-display-ucs-per-lynx RET".  The
particular character you mentioned is not affected by that, though.

Is this specifically about that U+1F3A8 character?  Or is this more
general?

> I last built the sources in May.  Has this changed in a significant
> way since then?

I don't think so, but I don't have access to the Linux console to
check.

> I could not find, in NEWS, anything about this change -- it ought to
> be in NEWS .

From my POV, it's a bugfix, and we don't call out those in NEWS.  What
you saw before was a bug in the way Emacs detected which characters
the Linux console is capable of displaying.

> Nor a way to go back to the old
> behavior.  Is there a way?  If not, would people please create a way?

What would you want Emacs to do instead?  Writing a code of an
unsupported character to a text-mode terminal is out of the question:
it can easily mess up the entire display.  What else is possible that
would satisfy you?

> As a separate question, do users generally like this change?
> Would it be better to return to the old diamond method as the default?

I don't use the Linux console, so I cannot answer that.