bug#9034: point adjustment (with invisible text) moves to the next line

[Lars Ingebrigtsen]

Dmitry Kurochkin <dmitry.kurochkin@gmail.com> writes:

>   (progn (switch-to-buffer "test")
>          (insert "aline1\nbline2\ncline3\n")
>          (put-text-property 7 14 'invisible t) ; region [\nbline2]
>          (goto-char (point-min)))
>
> After that in the test buffer do M-: (progn (end-of-visual-line)
> (point)).  `end-of-visual-line' moves point to position 14 as expected.
> But after that the point is adjusted to position 15, as can be checked
> by C-x =.

(I'm going through old bug reports that unfortunately got weren't
resolved at the time.)

This problem is still present in Emacs 28, and as previously noted, any
command you do (with `M-:') makes point advance to the next line.  (It's
not 100% reproducible -- sometimes nothing happens, and sometimes it
advances.)

So `C-e' and then, for instance `M-: 4 RET' will advance point here.

Also as previously noted, if Vglobal_disable_point_adjustment is on,
then this doesn't happen, so the problem almost has to be here:

command_loop_1
...
      if (current_buffer == prev_buffer
          && XBUFFER (XWINDOW (selected_window)->contents) == current_buffer
          && last_point_position != PT
          && NILP (Vdisable_point_adjustment)
          && NILP (Vglobal_disable_point_adjustment))
        {
          if (last_point_position > BEGV
              && last_point_position < ZV
              && (composition_adjust_point (last_point_position,
                                            last_point_position)
                  != last_point_position))
            /* The last point was temporarily set within a grapheme
               cluster to prevent automatic composition.  To recover
               the automatic composition, we must update the
               display.  */
            windows_or_buffers_changed = 21;
          if (!already_adjusted)
            adjust_point_for_property (last_point_position,
                                       MODIFF != prev_modiff);
        }

I haven't tried to debug any further -- is it obvious to anybody what's
failing here, by any chance?  :-)

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no