Re: "... the window start at a meaningless point within a line."

[Alan Mackenzie <acm@muc.de>]

Hello, Eli.

On Sun, Nov 01, 2015 at 05:40:15AM +0200, Eli Zaretskii wrote:
> > Date: Sat, 31 Oct 2015 21:17:40 +0000
> > Cc: emacs-devel@gnu.org
> > From: Alan Mackenzie <acm@muc.de>
> > 
> > pixel-wise resizing isn't a good idea on ttys.

> It isn't supposed to be needed there.

> > > +	  eassert (WINDOW_LIVE_P (prev_window));
> > > +	  reseat_at_window_start (&it);
> > > +	  it.current_x = it.hpos = it.vpos = 0;
> > > +	  move_it_to (&it, goal_pt, -1, -1, -1, MOVE_TO_POS);
> > > +	  nlines_prev_window = nlines + it.vpos + 1;
> > > +	  pw = XWINDOW (prev_window);
> > > +	  SET_TEXT_POS_FROM_MARKER (pw_top, pw->start);   <=================================
> > > +	  start_display (&it, pw, pw_top);
> > > +	  move_it_to (&it, -1, -1, it.last_visible_y - 1, -1, MOVE_TO_Y);
> > > +	  move_it_by_lines (&it, nlines_prev_window);
> > > +	  /* Pretend the original move worked as intended.  */
> > > +	  it.vpos = vpos;
> > > +	}
> > > +
> > >        /* Move to the goal column, if one was specified.  If the window
> > >  	 was originally hscrolled, the goal column is interpreted as
> > >  	 an addition to the hscroll amount.  */
> > 
> > , and it happened because prev_window is 0.  Presumably the left hand
> > window on the first frame has no previous.  I can't see how the
> > WINDOW_LIVE_P check failed to catch this.

> It is imperative to understand why that test missed, maybe you didn't
> compile with --enable-checking?

I hadn't compiled with --enable-checking.

> Anyway, if this can legitimately happen, i.e. if the exact_start flag
> can be set in the left-side window of the two windows under Follow
> mode, then the WINDOW_LIVE_P test should be in an 'if' test, and the
> following code should be skipped if the test fails.

DONE.  This version now doesn't segfault.  So I'll go back to your
previous mail to make some more comments.

-- 
Alan Mackenzie (Nuremberg, Germany).