Subject: Re: [PATCH] bug#13248: 24.2.50; select-window moves point (in comint-postoutput-scroll-to-bottom)

From: Vitalie Spinu <[email-masked]>
Date: Tue, 25 Dec 2012 01:18:56 +0100

>> martin rudalics <[email-masked]>
  >> on Fri, 21 Dec 2012 15:25:07 +0100 wrote:

[...]

  >> So the point is clearly moved in select-window. Moreover the (point)
  >> equals (window-end) just before select-window is called, so it is
  >> visible. Consequently, the following (comint-adjust-point selected) is
  >> completely screwed because it relies on point *not* being moved!

[...]

  >> 
  >> The variable `comint-scroll-show-maximum-output' is the default t, this
  >> is why comint runs `comint-postoutput-scroll-to-bottom' in its
  >> `comint-output-filter-functions'.
  >> 
  >> I can propose a patch for commit to reset the point, 

[...]

Here is a patch of the comint-postoutput-scroll-to-bottom to circumvent
resetting the point on select-window. 

    Thanks, 
    Vitalie

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 6d5e77d..dc5a4be 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,8 @@
+2012-12-24  Vitalie Spinu  <[email-masked]>
+
+	* comint.el (comint-postoutput-scroll-to-bottom): Don't reset
+	buffer point on select-window (Bug#13248).
+
 2012-12-24  Dmitry Gutov  <[email-masked]>
 
 	* progmodes/ruby-mode.el: Bump the version to 1.2 (Bug#13200).
diff --git a/lisp/comint.el b/lisp/comint.el
index cff9afe..fa3764d 100644
--- a/lisp/comint.el
+++ b/lisp/comint.el
@@ -2120,12 +2120,14 @@ This function should be in the list `comint-output-filter-functions'."
 	 ((bound-and-true-p follow-mode)
 	  (follow-comint-scroll-to-bottom))
 	 (t
-	  (let ((selected (selected-window)))
+	  (let ((selected (selected-window))
+                ;; select-window resets point; thus, save
+                (old-point (point)))
 	    (dolist (w (get-buffer-window-list current nil t))
 	      (select-window w)
 	      (unwind-protect
 		  (progn
-		    (comint-adjust-point selected)
+		    (comint-adjust-point selected old-point)
 		    ;; Optionally scroll to the bottom of the window.
 		    (and comint-scroll-show-maximum-output
 			 (eobp)
@@ -2133,9 +2135,12 @@ This function should be in the list `comint-output-filter-functions'."
 		(select-window selected))))))
       (set-buffer current))))
 
-(defun comint-adjust-point (selected)
+(defun comint-adjust-point (selected &optional saved-point)
   "Move point in the selected window based on Comint settings.
-SELECTED is the window that was originally selected."
+SELECTED is the window that was originally selected.
+
+If SAVED-POINT is given, use it as reference instead of the
+current point."
   (let ((process (get-buffer-process (current-buffer))))
     (and (< (point) (process-mark process))
 	 (or (memq comint-move-point-for-output '(t all))
@@ -2144,7 +2149,8 @@ SELECTED is the window that was originally selected."
 		 (if (eq (selected-window) selected) 'this 'others))
 	     ;; If point was at the end, keep it at end.
 	     (and (marker-position comint-last-output-start)
-		  (>= (point) comint-last-output-start)))
+		  (>= (or saved-point (point))
+                      comint-last-output-start)))
 	 (goto-char (process-mark process)))))
 
 (defun comint-truncate-buffer (&optional _string)