Subject: Re: bug#10971: Problem with `split-window-keep-point' set to `nil'

From: martin rudalics <[email-masked]>
Date: Fri, 09 Mar 2012 16:21:02 +0100

> 0. emacs -Q
 > 1. M-: (setq split-window-keep-point nil) RET
 > 2. Visit the attached file.

Vist any file large enough to extend beyond the end of the selected
window.

 > 3. C-x 2
 >
 > The point in the original (top) window has moved (unnecessarily) from
 > the first line to the last visible one.
 >
 > The docstring of the variable `split-window-keep-point' says:
 >
 >  If non-nil, C-x 2 preserves point in the new window.
 >  If nil, adjust point in the two windows to minimize redisplay.
 >  [...]
 >
 > But in this case there was no need to adjust point, because it was in
 > a position which would remain visible after the splitting.
 >
 > This behavior is specially annoying if you are in a Dired buffer and
 > do `C-o' on a file (the point jumps to the last visible line).

Does the attached patch give better results?

martin
=== modified file 'lisp/window.el'
--- lisp/window.el	2012-02-12 05:10:30 +0000
+++ lisp/window.el	2012-03-09 15:12:05 +0000
@@ -3282,22 +3282,23 @@
     (setq new-window (split-window nil size))
     (unless split-window-keep-point
       (with-current-buffer (window-buffer)
-	(goto-char (window-start))
-	(setq moved (vertical-motion (window-height)))
-	(set-window-start new-window (point))
-	(when (> (point) (window-point new-window))
-	  (set-window-point new-window (point)))
-	(when (= moved (window-height))
-	  (setq moved-by-window-height t)
-	  (vertical-motion -1))
-	(setq bottom (point)))
-      (and moved-by-window-height
-	   (<= bottom (point))
-	   (set-window-point old-window (1- bottom)))
-      (and moved-by-window-height
-	   (<= (window-start new-window) old-point)
-	   (set-window-point new-window old-point)
-	   (select-window new-window)))
+	(save-excursion
+	  (goto-char (window-start))
+	  (setq moved (vertical-motion (window-height)))
+	  (set-window-start new-window (point))
+	  (when (> (point) (window-point new-window))
+	    (set-window-point new-window (point)))
+	  (when (= moved (window-height))
+	    (setq moved-by-window-height t)
+	    (vertical-motion -1))
+	  (setq bottom (point)))
+	(and moved-by-window-height
+	     (<= bottom (point))
+	     (set-window-point old-window (1- bottom)))
+	(and moved-by-window-height
+	     (<= (window-start new-window) old-point)
+	     (set-window-point new-window old-point)
+	     (select-window new-window))))
     ;; Always copy quit-restore parameter in interactive use.
     (let ((quit-restore (window-parameter old-window 'quit-restore)))
       (when quit-restore