Optionally avoid that switching to previous or next buffer shows that buffer twice.

* window.el (switch-to-visible-buffer): New option.
(switch-to-prev-buffer, switch-to-next-buffer): Observe
switch-to-visible-buffer.  Make sure that checking for a window
showing a buffer already is done on the same frame.

* windows.texi (Window History): Describe new option
switch-to-visible-buffer.

doc/lispref/ChangeLog

+2012-03-27  Martin Rudalics  <rudalics@gmx.at>
+
+	* windows.texi (Window History): Describe new option
+	switch-to-visible-buffer.
+
 2012-03-27  Glenn Morris  <rgm@gnu.org>
 
 	* searching.texi (String Search): Add xref to Emacs manual.

doc/lispref/windows.texi

@@ -2073,7 +2073,8 @@ or killed or has been already shown by a recent invocation of
 If repeated invocations of this command have already shown all buffers
 previously shown in @var{window}, further invocations will show buffers
 from the buffer list of the frame @var{window} appears on (@pxref{The
-Buffer List}).
+Buffer List}) trying to skip buffers that are already shown in another
+window on that frame.
 @end deffn
 
 @deffn Command switch-to-next-buffer &optional window
@@ -2087,6 +2088,19 @@ can be undone, this function tries to show a buffer from the buffer list
 of the frame @var{window} appears on (@pxref{The Buffer List}).
 @end deffn
 
+By default @code{switch-to-prev-buffer} and @code{switch-to-next-buffer}
+can switch to a buffer that is already shown in another window on the
+same frame.  The following option can be used to override that behavior.
+
+@defopt switch-to-visible-buffer
+If this variable is non-@code{nil}, @code{switch-to-prev-buffer} and
+@code{switch-to-next-buffer} may switch to a buffer that is already
+visible on the same frame, provided the buffer was shown in the argument
+window before.  If it's @code{nil}, @code{switch-to-prev-buffer} and
+@code{switch-to-next-buffer} always try to avoid switching to a buffer
+that is already visible in another window on the same frame.
+@end defopt
+
 
 @node Dedicated Windows
 @section Dedicated Windows

lisp/ChangeLog

+2012-03-27  Martin Rudalics  <rudalics@gmx.at>
+
+	* window.el (switch-to-visible-buffer): New option.
+	(switch-to-prev-buffer, switch-to-next-buffer): Observe
+	switch-to-visible-buffer.  Make sure that checking for a window
+	showing a buffer already is done on the same frame.
+
 2012-03-27  Glenn Morris  <rgm@gnu.org>
 
 	* startup.el (mail-host-address): Doc fix.

lisp/window.el

@@ -2575,6 +2575,18 @@ before was current this also makes BUFFER the current buffer."
     (when point
       (set-window-point-1 window point))))
 
+(defcustom switch-to-visible-buffer t
+  "If non-nil, allow switching to an already visible buffer.
+If this variable is non-nil, `switch-to-prev-buffer' and
+`switch-to-next-buffer' may switch to an already visible buffer
+provided the buffer was shown in the argument window before.  If
+this variable is nil, `switch-to-prev-buffer' and
+`switch-to-next-buffer' always try to avoid switching to a buffer
+that is already visible in another window on the same frame."
+  :type 'boolean
+  :version "24.1"
+  :group 'windows)
+
 (defun switch-to-prev-buffer (&optional window bury-or-kill)
   "In WINDOW switch to previous buffer.
 WINDOW must be a live window and defaults to the selected one.
@@ -2584,6 +2596,7 @@ shown in WINDOW is about to be buried or killed and consequently
 shall not be switched to in future invocations of this command."
   (interactive)
   (let* ((window (window-normalize-window window t))
+	 (frame (window-frame window))
 	 (old-buffer (window-buffer window))
 	 ;; Save this since it's destroyed by `set-window-buffer'.
 	 (next-buffers (window-next-buffers window))
@@ -2602,14 +2615,13 @@ shall not be switched to in future invocations of this command."
 		   (not (eq new-buffer old-buffer))
                    (or bury-or-kill
 		       (not (memq new-buffer next-buffers))))
-          ;; _DO_ show visible buffers as advertized in Elisp manual 28.14
-          ;;  on `switch-to-prev-buffer' & `switch-to-next-buffer'
-          ;;(if (get-buffer-window new-buffer)
-	  ;;    ;; Try to avoid showing a buffer visible in some other window.
-	  ;;    (setq visible new-buffer)
+	  (if (and (not switch-to-visible-buffer)
+		   (get-buffer-window new-buffer frame))
+	      ;; Try to avoid showing a buffer visible in some other window.
+	      (setq visible new-buffer)
           (set-window-buffer-start-and-point
            window new-buffer (nth 1 entry) (nth 2 entry))
-          (throw 'found t)))
+          (throw 'found t))))
       ;; Scan reverted buffer list of WINDOW's frame next, skipping
       ;; entries of next buffers.  Note that when we bury or kill a
       ;; buffer we don't reverse the global buffer list to avoid showing
@@ -2617,15 +2629,16 @@ shall not be switched to in future invocations of this command."
       ;; buffer list in order to make sure that switching to the
       ;; previous/next buffer traverse it in opposite directions.
       (dolist (buffer (if bury-or-kill
-			  (buffer-list (window-frame window))
-			(nreverse (buffer-list (window-frame window)))))
+			  (buffer-list frame)
+			(nreverse (buffer-list frame))))
 	(when (and (buffer-live-p buffer)
 		   (not (eq buffer old-buffer))
 		   (not (eq (aref (buffer-name buffer) 0) ?\s))
 		   (or bury-or-kill (not (memq buffer next-buffers))))
-	  (if (get-buffer-window buffer)
+	  (if (get-buffer-window buffer frame)
 	      ;; Try to avoid showing a buffer visible in some other window.
-	      (setq visible buffer)
+	      (unless visible
+		(setq visible buffer))
 	    (setq new-buffer buffer)
 	    (set-window-buffer-start-and-point window new-buffer)
 	    (throw 'found t))))
@@ -2678,6 +2691,7 @@ shall not be switched to in future invocations of this command."
 WINDOW must be a live window and defaults to the selected one."
   (interactive)
   (let* ((window (window-normalize-window window t))
+	 (frame (window-frame window))
 	 (old-buffer (window-buffer window))
 	 (next-buffers (window-next-buffers window))
 	 new-buffer entry killed-buffers visible)
@@ -2698,11 +2712,11 @@ WINDOW must be a live window and defaults to the selected one."
 	  (throw 'found t)))
       ;; Scan the buffer list of WINDOW's frame next, skipping previous
       ;; buffers entries.
-      (dolist (buffer (buffer-list (window-frame window)))
+      (dolist (buffer (buffer-list frame))
 	(when (and (buffer-live-p buffer) (not (eq buffer old-buffer))
 		   (not (eq (aref (buffer-name buffer) 0) ?\s))
 		   (not (assq buffer (window-prev-buffers window))))
-	  (if (get-buffer-window buffer)
+	  (if (get-buffer-window buffer frame)
 	      ;; Try to avoid showing a buffer visible in some other window.
 	      (setq visible buffer)
 	    (setq new-buffer buffer)
@@ -2716,9 +2730,14 @@ WINDOW must be a live window and defaults to the selected one."
 		       (not (setq killed-buffers
 				  (cons new-buffer killed-buffers))))
 		   (not (eq new-buffer old-buffer)))
-	  (set-window-buffer-start-and-point
-	   window new-buffer (nth 1 entry) (nth 2 entry))
-	  (throw 'found t)))
+	  (if (and (not switch-to-visible-buffer)
+		   (get-buffer-window new-buffer frame))
+	      ;; Try to avoid showing a buffer visible in some other window.
+	      (unless visible
+		(setq visible new-buffer))
+	    (set-window-buffer-start-and-point
+	     window new-buffer (nth 1 entry) (nth 2 entry))
+	    (throw 'found t))))
 
       ;; Show a buffer visible in another window.
       (when visible