bug#20847: [display engine] 25.0.50; company-mode popup makes point jump to an entirely different location

[Eli Zaretskii <eliz@gnu.org>]

> Cc: 20847@debbugs.gnu.org
> From: Dmitry Gutov <dgutov@yandex.ru>
> Date: Mon, 22 Jun 2015 13:57:48 +0300
> 
> On 06/22/2015 05:43 AM, Eli Zaretskii wrote:
> 
> > Something like that, but perhaps using end-of-visual-line as well.
> 
> Ok, so there's a function for that. Would (eq (point) (save-excursion 
> (end-of-visual-line) (point))) not suffice?

To determine whether point is at the last position on that line?  Yes.

> >> Does that constitute at least three different cases we'd need to handle?
> >>
> >> - Not near the window edge
> >> - near the edge and newline
> >> - near the edge and no newline?
> >
> > I'm not sure I understand the meaning of "near" here.
> 
> Sorry for being unclear. Let's replace that word with "at".

I see.  Is this something you need to determine in addition to knowing
whether point is at the last position of a screen line?  If so, you
should keep in mind that the last position of a line could in some
rare cases be somewhat farther from the edge -- if the next "thing" to
display is wider than the space left till the edge.

> >> I'm not sure what you mean by "losing some of the text".
> >
> > The rightmost characters in each continued line are removed from
> > display because you put a newline there.
> 
> Do you have an example? Unless there's a misunderstanding, this would 
> seem like a bug to me.

The example I have is the exact recipe with which you started this bug
report.  As soon as you type "el" in step 6, and the "tooltip" with
completions pops up, look at the next paragraph of text below the
"tooltip" -- you will see the rightmost character on every line of
that paragraph disappear.  (For this to show, you need to have both
fringes, but "emacs -Q" should make sure you do.)