Re: [Emacs-diffs] /srv/bzr/emacs/trunk r99831: Scrolling commands which does not signal errors at top/bottom.

[Juri Linkov]

> This fixes one problem, but not the other: scroll-(up|down)-command do
> not preserve the column.

I see now what do you mean.  This patch takes care of that:

=== modified file 'lisp/simple.el'
--- lisp/simple.el      2010-04-05 19:08:58 +0000
+++ lisp/simple.el      2010-04-06 20:18:23 +0000
@@ -4877,6 +4877,16 @@ (define-globalized-minor-mode global-vis
 ;;; of buffer at first key-press (instead moves to top/bottom
 ;;; of buffer).
 
+(defcustom scroll-error-top-bottom nil
+  "Move point to top/bottom of buffer before signalling a scrolling error.
+A value of nil means just signal an error if no more scrolling possible.
+A value of t means point moves to the beginning or the end of the buffer
+\(depending on scrolling direction) when no more scrolling possible.
+When point is already on that position, then signal an error."
+  :type 'boolean
+  :group 'scrolling
+  :version "24.1")
+
 (defun scroll-up-command (&optional arg)
   "Scroll text of selected window upward ARG lines; or near full screen if no 
ARG.
 If `scroll-up' cannot scroll window further, move cursor to the bottom line.
@@ -4886,6 +4896,8 @@ (defun scroll-up-command (&optional arg)
 If ARG is the atom `-', scroll downward by nearly full screen."
   (interactive "^P")
   (cond
+   ((null scroll-error-top-bottom)
+    (scroll-up arg))
    ((eq arg '-) (scroll-down-command nil))
    ((< (prefix-numeric-value arg) 0)
     (scroll-down-command (- (prefix-numeric-value arg))))
@@ -4893,7 +4905,14 @@ (defun scroll-up-command (&optional arg)
     (scroll-up arg))  ; signal error
    (t
     (condition-case nil
-       (scroll-up arg)
+       (progn
+         (when (and scroll-preserve-screen-position
+                    (not (eq scroll-preserve-screen-position t)))
+           (setq temporary-goal-column
+                 (if (and track-eol (eolp) (not (bolp)))
+                     most-positive-fixnum
+                   (current-column))))
+         (scroll-up arg))
       (end-of-buffer
        (if arg
           ;; When scrolling by ARG lines can't be done,
@@ -4901,7 +4920,10 @@ (defun scroll-up-command (&optional arg)
           (forward-line arg)
         ;; When ARG is nil for full-screen scrolling,
         ;; move to the bottom of the buffer.
-        (goto-char (point-max))))))))
+        (goto-char (point-max))
+        (when (and scroll-preserve-screen-position
+                   (not (eq scroll-preserve-screen-position t)))
+          (line-move-to-column (truncate temporary-goal-column)))))))))
 
 (put 'scroll-up-command 'isearch-scroll t)
 
@@ -4914,6 +4936,8 @@ (defun scroll-down-command (&optional ar
 If ARG is the atom `-', scroll upward by nearly full screen."
   (interactive "^P")
   (cond
+   ((null scroll-error-top-bottom)
+    (scroll-down arg))
    ((eq arg '-) (scroll-up-command nil))
    ((< (prefix-numeric-value arg) 0)
     (scroll-up-command (- (prefix-numeric-value arg))))
@@ -4921,7 +4945,14 @@ (defun scroll-down-command (&optional ar
     (scroll-down arg))  ; signal error
    (t
     (condition-case nil
-       (scroll-down arg)
+       (progn
+         (when (and scroll-preserve-screen-position
+                    (not (eq scroll-preserve-screen-position t)))
+           (setq temporary-goal-column
+                 (if (and track-eol (eolp) (not (bolp)))
+                     most-positive-fixnum
+                   (current-column))))
+         (scroll-down arg))
       (beginning-of-buffer
        (if arg
           ;; When scrolling by ARG lines can't be done,
@@ -4929,7 +4960,10 @@ (defun scroll-down-command (&optional ar
           (forward-line (- arg))
         ;; When ARG is nil for full-screen scrolling,
         ;; move to the top of the buffer.
-        (goto-char (point-min))))))))
+        (goto-char (point-min))
+        (when (and scroll-preserve-screen-position
+                   (not (eq scroll-preserve-screen-position t)))
+          (line-move-to-column (truncate temporary-goal-column)))))))))
 
 (put 'scroll-down-command 'isearch-scroll t)
 

-- 
Juri Linkov
http://www.jurta.org/emacs/