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

From: Lars Ingebrigtsen <[email-masked]>
Date: Wed, 25 Aug 2021 18:32:15 +0200

Dmitry Kurochkin <[email-masked]> 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