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

[Ergus]

On Wed, Aug 07, 2019 at 08:29:13PM +0300, Eli Zaretskii wrote:
> > This issue is already fixed with the other condition I mentioned:
> >
> > IT_CHARPOS (*it) < ZV
> >
> > But ends_at_zv_p this also need to be fixed because there are some tests
> > inside extend_face_to_end_of_line that compare with ends_at_zv_p. In the
> > worst case we need to remove these comparisons.
>
> Not sure I understand why the comparisons need to be removed.  Can you
> elaborate?

> > But ideally the flag must be set before right?
>
> In a buffer showing only buffer text (no after-strings at EOB), all
> the glyph rows starting from the one showing EOB have their
> ends_at_zv_p flag set.

Hi:

In my tests inside extend_face_to_end_of_line the flag ends_at_zv_p is
always false. And for the last line (where it is supposed to be true)
the function extend_face_to_end_of_line is not called at all. So
actually all the code like:

              if (it->glyph_row->ends_at_zv_p)
                it->face_id = default_face->id;
              else
                it->face_id = face->id;

does nothing now.

We should fix this in order to create an indicator also for the last
line.

I think that the problem is in the condition:

if (!get_next_display_element (it)) inside display_line that filters the
call to  extend_face_to_end_of_line with:

if (row->reversed_p
   || lookup_basic_face (it->w, it->f, DEFAULT_FACE_ID) !=
   DEFAULT_FACE_ID)
     extend_face_to_end_of_line (it);

And needs to be extended probably with with:

|| (!row_text_area_empty (row))