bug#23098: 25.0.92; (recenter -1) can leave point in the middle of the window

[Jorgen Schaefer <jorgen.schaefer@gmail.com>]

Hello!

Evaluating the following code in "emacs -Q" leaves point in the middle
of the window, instead of at the end of the window as expected. Certain
modes (IRC) want to keep the buffer flushed at the end of the window,
this problem interferes with that behavior and causes very weird jumpy
scrolling.


(require 'cl)
(let* ((b (get-buffer-create "*Bug Repro*"))
       (w (selected-window))
       (l (window-height w))
       o)
  (set-window-buffer w b)
  (select-window w)
  (set-buffer b)
  (erase-buffer)
  (cl-dotimes (i (* l 2))
              (insert "foo\n"))
  (goto-char (point-min))
  (forward-line (+ l 2))
  (setq o (make-overlay (point) (point)))
  (overlay-put o 'after-string "\n")
  (goto-char (point-max))
  (recenter -1))


That is, if there is a multi-line overlay that would be shown only
halfway.

I have seen similar behavior with some forms of invisible text, but have
not been able to create reproduction steps for that.

Regards,
Jorgen


In GNU Emacs 25.0.92.1 (x86_64-unknown-linux-gnu)
 of 2016-03-14 built on loki.jorgenschaefer.de
Repository revision: 1b9d6163b023aaefd15d38ea28e968a113202402
System Description:	Debian GNU/Linux 8.3 (jessie)

Configured using:
 'configure --enable-checking --without-x 'CFLAGS=-ggdb3 -O0'
 LDFLAGS=-ggdb3'