bug#57728: 29.0.50; Emacs writes wrong glyph at the bottom-right corner of text terminals

[Akib Azmain Turja via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

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Eli Zaretskii <eliz@gnu.org> writes:

>> From: Akib Azmain Turja <akib@disroot.org>
>> Cc: 57728@debbugs.gnu.org
>> Date: Sun, 11 Sep 2022 19:38:45 +0600
>> 
>>   1. Run emacs -Q.
>
> "emacs -Q -nw", I guess?  We are talking about TTY display, right?

Oh, yes.  I first tried on Linux console, where just emacs -Q is enough.

>
>>   2. M-: (or any other command that asks for a string).
>>   3. Write some garbage until the minibuffer window scrolls.  (I used
>>      (dotimes (i 10000) (+ (% (random) 26) ?a)) to generate the garbage
>>      in *scratch* buffer and copied to the minibuffer, but you can write
>>      anything you want.)
>
> Will this do:
>
>   M-: ssssssssssssssssssssssssssssssssssssssssssssssssssss
>
> (keep typing 's' until you get past the right edge of the window, and
> the minibuffer resizes to be 2 screen lines instead of just one)?

I don't think so.  Emacs redisplay optimizations will optimize away many
things.  Try to write random character like 'asn,csr,.jwsarcwasr,.cp'
and repeat it (kill and yank yank yank...) until the mini window fills
and scrolls some lines (maybe ten).  Make sure that
(window-max-chars-per-line) is not a multiple of the length of the base
string (which you killed).

>
>>   4. Scroll down a line.
>
> With C-n? or with something else?

C-p, or possibly C-u 1 M-v.

>
>>   5. You should now see that the last character cell (i.e. the character
>>      cell on the bottom-left corner) contains a continuation ('\')
>>      glyph.
>
> Bottom-left corner or bottom-right corner?  If bottom-right, then this
> '\' is the continuation glyph, telling you that the line is continued
> on the next screen line.

Ah, my mistake.  It is the bottom-right corner.

>
>>   6. Scroll up two lines.
>
> With C-p?
>
> Also, I cannot scroll up two lines unless I first make the mini-window
> at least lines high.

C-n, or possibly C-u 2 C-v.

>
>>   7. The continuation glyph on the line before the last one doesn't
>>      appear.  Tested on Linux console, St, Xterm and Kitty.
>
> I don't see this here, but maybe that's because my terminal isn't
> kitty.  It does behave like xterm, though.

What do mean?

>
>>   8. Scroll down more than two lines.
>>   9. Exit minibuffer.  The continuation glyph will still stay there on
>>      some terminals.  Tested on St, Kitty.
>
> Here, it never goes away.
>
>> I hope this is clearer.
>
> Unfortunately, not really.

Is it clear enough now?

>
> Thanks.
>
>
>

-- 
Akib Azmain Turja

Find me on Mastodon at @akib@hostux.social.

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