bug#36858: 27.0.50; display bugs with display-fill-column-indicator-mode

[Ergus]

On Wed, Aug 07, 2019 at 05:38:30PM +0300, Eli Zaretskii wrote:
> > Date: Mon, 5 Aug 2019 17:27:47 +0200
> > From: Ergus <spacibba@aol.com>
> > Cc: 36858@debbugs.gnu.org, Davor Rotim <rotim.davor@gmail.com>
> >
> > 1) The condition ends_at_zv_p didn't work as expected, I don't know If
> > this is an issue somewhere else, but at least in my tests, the condition
> > was always false. (for all the lines implied before and after ZV, where
> > there was company window or not)
> >
> > So the filter condition I am using now is:
> >
> > IT_CHARPOS (*it) < ZV
> >
> > which seems to work fine.
> >
> > 2) There is a corner case because the indicator is never generated for
> > the latest line in the buffer. So a \n is required always at the end of
> > the buffer if there is text, which for me is fine (unix format), but I
> > don't know if I should correct that, should I?
>
> Unix format has nothing to do with this, as in a buffer we always have
> only \n characters at end of line.  But notr having the indicator show
> in the last line of a buffer that doesn't end in a newline is
> unfortunate.  Which is why I suggested to test the ends_at_zv_p flag.
> What exactly didn't work with it?  Can you show me a test case where
> the glyph rows past ZV don't have this flag set?  Maybe you should
> test the enabled_p flag as well?
Hi Eli:

I just made this test:

in this code (in xdisp.c):

if (it->current_x < indicator_column_x)
 {
   it->face_id = merge_faces (it->w, Qextend_to_end_of_line,
                              0, extend_face_merged_id);

   it->char_to_display = XFIXNAT (Vdisplay_fill_column_indicator_character);
   PRODUCE_GLYPHS (it);

   it->face_id = extend_face_merged_id;
}

I changed char_to_display:

it->char_to_display = (it->glyph_row->ends_at_zv_p) ? '1' : '0';

And then I obtained the attached image.

As you can see the condition returns 0 for lines before zv, for the last
text line and for the company extra lines.

> > In terminal emacs, in the original emacs-26 code, in the function:
> > extend_face_to_end_of_line the code was:
> >
> > ```
> >  face = FACE_FROM_ID (f, (it->face_before_selective_p
> >                            ? it->saved_face_id
> >                            : it->face_id));
> >  (...)
> >
> >  if (it->glyph_row->ends_at_zv_p)
> >      it->face_id = default_face->id;
> >  else
> >      it->face_id = face->id;
> >  PRODUCE_GLYPHS (it);
> >
> >  while (it->current_x <= it->last_visible_x)
> >      PRODUCE_GLYPHS (it);
> > ```
> >
> > So the rest of the line was filled with the last face, (so this issue was
> > already there since then, because the rest of the line is filled with an
> > underlined face)
> >
> > I can change the code to fill the rest of the line with a new merged
> > face (as I do for graphical emacs), but I think that this fix is
> > unrelated with dfci, so maybe someone else must give a look before to
> > prevent me breaking anything.
>
> This is a more general issue, and I will respond to your question on
> emacs-devel.
>
> Thanks.

Screenshot_2019-08-07_18-10-20.png
Description: PNG image