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

[Gerd Möllmann]

Eli Zaretskii <eliz@gnu.org> writes:

>> My theory is that no-one but tty_write_glyphs knows that it didn't write
>> to the bottom-right corner.
>
> You are saying that update_frame_line tells tty_write_glyphs to write
> the '\', but tty_write_glyphs doesn't in this case?
>
> But why would we need to write that character if we know it's already
> there (because all lines end with it)?  That should only happen if we
> scroll the region instead of rewriting lines one by one.  Is that what
> happens in this case?

I'm sorry, I don't know what exactly happens here.

Perhaps insert_glyphs, say in the middle of the line, shifts something
to the bottom-right corner, and write_glyphs is expected to overwrite
it, which it doesn't?  Or something like that.