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

[martin rudalics]

> 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