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

[Kévin Le Gouguec]

Richard Stallman <rms@gnu.org> writes:

> 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.
>
> I last built the sources in May.  Has this changed in a significant
> way since then?
>
> I could not find, in NEWS, anything about this change -- it ought to
> be in NEWS .  Nor a way to go back to the old
> behavior.  Is there a way?  If not, would people please create a way?
>
> As a separate question, do users generally like this change?
> Would it be better to return to the old diamond method as the default?

That brings to mind a discussion in January, where (IIRC; apologies for
any inaccuracies) you reported that Emacs degraded to displaying
diamonds when it had no glyphs for precomposed Unicode codepoints:

<E1nCZ9R-0005I0-5n@fencepost.gnu.org>

While one subthread went into displaying those codepoints with sequences
of ASCII characters, another subthread dealt with
glyphless-char-display-control; the default value for characters which
fall in the 'no-font group were supposed to be handled with the hex-code
method, but weren't.  Eli fixed that inconsistency:

<837dalfp4t.fsf@gnu.org>

IIUC this was considered a bugfix, which might explain why NEWS does not
mention it?

I can't find a way to tweak glyphless-char-display-control to let TTY
frames show diamonds again…  maybe a new value display method would be
needed for that purpose?

The 'acronym method could display something useful IIUC, though I don't
know what would be the smartest way to fill in char-acronym-table.

(Hope I'm not confused and that thread was indeed the source of the
change you mention; apologies for the noise if not)