scroll-top-bottom (was: delete-selection-mode)

[Juri Linkov]

>> The pc-select-override-scroll-error feature is something more.
>
> I think it should be moved to simple.el since it is not directly related
> to pc-select and is useful globally outside of pc-select.

This feature is implemented by CUA mode, but it would be very useful
for users who don't use CUA.  To support it in the core, I've implemented
a new user option `scroll-top-bottom' (that defines the scrolling behavior
at the top/bottom of the buffer).

If this is better to implement in Lisp, then `scroll-up' and
`scroll-down' should be moved from window.c to window.el.

=== modified file 'lisp/emulation/pc-select.el'
--- lisp/emulation/pc-select.el 2010-03-12 17:47:22 +0000
+++ lisp/emulation/pc-select.el 2010-03-19 23:59:44 +0000
@@ -93,6 +93,9 @@ (defcustom pc-select-override-scroll-err
 errors are suppressed."
   :type 'boolean
   :group 'pc-select)
+(define-obsolete-variable-alias 'pc-select-override-scroll-error
+                                'scroll-top-bottom
+                                "24.1")
 
 (defcustom pc-select-selection-keys-only nil
   "*Non-nil means only bind the basic selection keys when started.

=== modified file 'lisp/cus-start.el'
--- lisp/cus-start.el   2010-01-13 08:35:10 +0000
+++ lisp/cus-start.el   2010-03-19 23:55:19 +0000
@@ -306,6 +306,12 @@ (let ((all '(;; alloc.c
                       (const :tag "Off (nil)" :value nil)
                       (const :tag "Full screen (t)" :value t)
                       (other :tag "Always" 1)) "22.1")
+            (scroll-top-bottom
+             windows (choice
+                      (const :tag "Off (nil)" :value nil)
+                      (other :tag "Move to top/bottom (t)" :value t))
+             "24.1")
             (recenter-redisplay windows
                                 (choice
                                  (const :tag "Never (nil)" :value nil)

=== modified file 'src/window.c'
--- src/window.c        2010-01-13 08:35:10 +0000
+++ src/window.c        2010-03-19 23:57:16 +0000
@@ -168,6 +168,11 @@ (at your option) any later version.
 
 Lisp_Object Vscroll_preserve_screen_position;
 
+/* Non-nil means scroll commands move point to top/bottom of buffer
+   before signalling an error.  */
+
+Lisp_Object Vscroll_top_bottom;
+
 /* Non-nil means that text is inserted before window's markers.  */
 
 Lisp_Object Vwindow_point_insertion_type;
@@ -5014,7 +5019,12 @@
                            - it.current_y + it.max_ascent + it.max_descent);
              adjust_glyphs (it.f);
            }
-         else if (noerror)
+         else if (!NILP (Vscroll_top_bottom) && PT < ZV)
+           {
+             SET_PT (ZV);
+             return;
+           }
+         else if (noerror)
            return;
          else if (n < 0)       /* could happen with empty buffers */
            xsignal0 (Qbeginning_of_buffer);
@@ -5027,7 +5037,12 @@
            /* The first line was only partially visible, make it fully
               visible. */
            w->vscroll = 0;
-         else if (noerror)
+         else if (!NILP (Vscroll_top_bottom) && PT > BEGV)
+           {
+             SET_PT (BEGV);
+             return;
+           }
+         else if (noerror)
            return;
          else
            xsignal0 (Qbeginning_of_buffer);
@@ -5242,7 +5257,12 @@
 
   if (lose)
     {
-      if (noerror)
+      if (!NILP (Vscroll_top_bottom) && PT > BEGV)
+       {
+         SET_PT (BEGV);
+         return;
+       }
+      else if (noerror)
        return;
       else
        xsignal0 (Qbeginning_of_buffer);
@@ -5328,7 +5348,12 @@
     }
   else
     {
-      if (noerror)
+      if (!NILP (Vscroll_top_bottom) && PT < ZV)
+       {
+         SET_PT (ZV);
+         return;
+       }
+      else if (noerror)
        return;
       else
        xsignal0 (Qend_of_buffer);
@@ -7268,6 +7293,15 @@
 Any other value means point always keeps its screen position.  */);
   Vscroll_preserve_screen_position = Qnil;
 
+  DEFVAR_LISP ("scroll-top-bottom",
+              &Vscroll_top_bottom,
+              doc: /* Controls if scroll commands move point to the top/bottom 
of the buffer.
+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.  */);
+  Vscroll_top_bottom = Qnil;
+
   DEFVAR_LISP ("window-point-insertion-type", &Vwindow_point_insertion_type,
               doc: /* Type of marker to use for `window-point'.  */);
   Vwindow_point_insertion_type = Qnil;

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