bug#28936: enhancement request: remove vertical scroll bar automatically when not needed

[Keith David Bershatsky <esq@lawlist.com>]

Here is a first draft with a simple test (modifying xdisp.c), which probably nukes more than just the selected window's scroll bars when removing them, but it may be sufficient to revive this enhancement request in the event anyone is interested.

 finish_scroll_bars:

   if ((WINDOW_HAS_VERTICAL_SCROLL_BAR (w) || WINDOW_HAS_HORIZONTAL_SCROLL_BAR (w))
        && ZV - BEGV > BUF_Z (XBUFFER (w->contents)) - w->window_end_pos - marker_position (w->start))
    {
      if (WINDOW_HAS_VERTICAL_SCROLL_BAR (w))
	/* Set the thumb's position and size.  */
	set_vertical_scroll_bar (w);

      if (WINDOW_HAS_HORIZONTAL_SCROLL_BAR (w))
	/* Set the thumb's position and size.  */
	set_horizontal_scroll_bar (w);

      /* Note that we actually used the scroll bar attached to this
	 window, so it shouldn't be deleted at the end of redisplay.  */
      if (FRAME_TERMINAL (f)->redeem_scroll_bar_hook)
        (*FRAME_TERMINAL (f)->redeem_scroll_bar_hook) (w);
    }
    else
      {
        (*FRAME_TERMINAL (f)->condemn_scroll_bars_hook) (f);
        (*FRAME_TERMINAL (f)->judge_scroll_bars_hook) (f);
      }


Keith