GNU bug report logs -
#23594
25.0.94; Display errors on Linux tty
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Message #23 received at 23594 <at> debbugs.gnu.org (full text, mbox):
> Date: Sun, 22 May 2016 09:38:13 +0000
> Cc: 23594 <at> debbugs.gnu.org
> From: Alan Mackenzie <acm <at> muc.de>
>
> On Sat, May 21, 2016 at 10:09:38PM +0300, Eli Zaretskii wrote:
> > > > This bug exists since we started showing the 'decomposition' of
> > > > characters in Emacs 24.1. With LF, we send a literal LF character
> > > > to the screen.
>
> That's only half the story. The literal LF doesn't seem to be the
> problem.
What do you mean by "literal LF"? A newline ends a line, and is never
displayed at all, the display engine "swallows" it so it disappears
without a trace, and instead instructs the terminal to move to the
next line.
> Rather, it's got a 'composition text-property attached to it.
> The string we're trying to display is
>
> #(" decomposition: (10) ('\n')\n" 24 25 (composition (0 1 [9 10 9])))
> ^
> |
> 24
>
> What is this composition trying to do? The [9 10 9] is [\t \n \t].
It tries to prevent the character from being composed with surrounding
ones, so that we could display there combining marks and other similar
stuff.
> Under X-Windows, the same string is displayed, this time successfully.
> The call
> (inseert #(" decomposition: .... [9 10 9])))
> works on X-Windows, the "\n" with the composition property being
> displayed as a square box.
Why is that a "success", exactly? Is the user supposed to guess that
the box represents a LF?
> > > OK. The next question is is it easy to fix?
>
> > Yes. We should not send control characters to that buffer.
>
> It seems to me there is a bug in the display engine here: the same
> string which is displayed successfully in X-Windows goes badly wrong on
> a Linux tty.
>
> Comments?
IMO, there's no such thing as a successful display of an unadorned LF
(or any other control character), on any kind of terminal. What would
be the graphics for that?
This bug report was last modified 3 years and 291 days ago.
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