Re: Using overlay in register

[Masatake YAMATO]

> This is a very good idea.  Thanks for working on it.
> 
> I see a possible bug here:
> 
>     +(defun register-put-overlay-at-point (register)
>     +  "Put a overlay associated with REGISTER at the point."
>     +  (let ((overlay (make-overlay (point) 
>     +                        (1+ (point))
>     +                        (current-buffer)
> 
> This will get an error at the end of the buffer.
> 
> What should it do at the end?  Make an empty overlay?
> It could have a before-string, perhaps.

Thank you for reviwing and suggestion. I have used after-string.
If the point is at the end of line, set a space to an overlay's
'after-string property. 

I have added an function: With mouse-3 on an overlay(or 
after-string " "), you can clear the overlay.

> What should it do at the end?  Make an empty overlay?
> It could have a before-string, perhaps.
> 
>     +(defun register-get-overlay-position (overlay)
>     +  "Get the position for OVERLAY."
>     +  (min (overlay-start overlay) (overlay-end overlay)))
> 
> What's the purpose of using min here?
> Why not just use overlay-start?
> (In some places you did so.)

I have seen emacs's strange behaviors twice; Emacs returned an overlay whose 
start is
greater than its end. I cannot find the way to reproduce it.
(overlay-start overlay) < (overlay-end overlay) is guaranteed?

Masatake YAMATO

Index: lisp/register.el
===================================================================
RCS file: /cvsroot/emacs/emacs/lisp/register.el,v
retrieving revision 1.48
diff -u -r1.48 register.el
--- lisp/register.el    16 Mar 2004 09:52:36 -0000      1.48
+++ lisp/register.el    21 Mar 2004 13:44:58 -0000
@@ -31,9 +31,20 @@
 
 ;;; Code:
 
+(defgroup register ()
+  "register commands for Emacs."
+  :group 'editing
+  :prefix "register-")
+
+(defface register-point
+  '((((class color)) (:box "blue"))
+    (t (:underline t)))
+  "Face for the overlay associated with register."
+  :group 'register)
+
 (defvar register-alist nil
   "Alist of elements (NAME . CONTENTS), one for each Emacs register.
-NAME is a character (a number).  CONTENTS is a string, number, marker or list.
+NAME is a character (a number).  CONTENTS is a string, number, overlay or list.
 A list of strings represents a rectangle.
 A list of the form (file . NAME) represents the file named NAME.
 A list of the form (file-query NAME POSITION) represents position POSITION
@@ -50,23 +61,80 @@
 (defun set-register (register value)
   "Set contents of Emacs register named REGISTER to VALUE.  Returns VALUE.
 See the documentation of the variable `register-alist' for possible VALUE."
+  ;; If the old value is overlay, delete it first.
+  (let ((overlay (get-register register)))
+    (if (overlayp overlay)
+       (delete-overlay overlay)))
   (let ((aelt (assq register register-alist)))
     (if aelt
        (setcdr aelt value)
       (push (cons register value) register-alist))
     value))
 
+(defun register-clear-register (register)
+  (interactive "cClear register: ")
+  (set-register register nil))
+
+(defun register-clear-overlay-at-point (event)
+  "Clear the register associated with an overlay pointed by EVENT."
+  (interactive "e")
+  (save-excursion
+    (mouse-set-point event)
+    (let ((overlays (overlays-in (point) 
+                                (+ (point) (if (eolp) 0 1))))
+         o
+         r)
+      ;; Search 'register property from the all overlays.
+      (while (and overlays (null r))
+       (setq o (car overlays)
+             r (overlay-get o 'register)
+             overlays (cdr overlays))
+       (when r
+         (register-clear-register r)))
+      (unless r
+       (error "No overlay for register at this point.")))))
+
+(defun register-put-overlay-at-point (register)
+  "Put a overlay associated with REGISTER at the point."
+  (let* ((help (format "Register: %s\nType \"%s %s\" to jump here.\nMouse-3 to 
clear this register."
+                      (single-key-description register)
+                      (substitute-command-keys "\\[jump-to-register]")
+                      (single-key-description register)))
+        (overlay (make-overlay (point)
+                               (+ (point) (if (eolp) 0 1))
+                               (current-buffer)
+                               t))
+        (keymap '(keymap (mouse-3 . register-clear-overlay-at-point))))
+    (overlay-put overlay 'register register)
+    (if (eolp)
+       ;; Zero length overlay with " ".
+       (overlay-put overlay 'after-string
+                    (propertize " "
+                                'face 'register-point
+                                'help-echo help
+                                'mouse-face 'highlight
+                                'keymap keymap))
+      (overlay-put overlay 'face 'register-point)
+      (overlay-put overlay 'help-echo help)
+      (overlay-put overlay 'mouse-face 'highlight)
+      (overlay-put overlay 'keymap keymap))
+    overlay))
+
+(defun register-get-overlay-position (overlay)
+  "Get the position for OVERLAY."
+  (min (overlay-start overlay) (overlay-end overlay)))
+ 
 (defun point-to-register (register &optional arg)
   "Store current location of point in register REGISTER.
 With prefix argument, store current frame configuration.
 Use \\[jump-to-register] to go to that location or restore that configuration.
 Argument is a character, naming the register."
   (interactive "cPoint to register: \nP")
-  ;; Turn the marker into a file-ref if the buffer is killed.
+  ;; Turn the overlay into a file-ref if the buffer is killed.
   (add-hook 'kill-buffer-hook 'register-swap-out nil t)
   (set-register register
                (if arg (list (current-frame-configuration) (point-marker))
-                 (point-marker))))
+                 (register-put-overlay-at-point register))))
 
 (defun window-configuration-to-register (register &optional arg)
   "Store the window configuration of the selected frame in register REGISTER.
@@ -106,11 +174,11 @@
      ((and (consp val) (window-configuration-p (car val)))
       (set-window-configuration (car val))
       (goto-char (cadr val)))
-     ((markerp val)
-      (or (marker-buffer val)
+     ((overlayp val)
+      (or (overlay-buffer val)
          (error "That register's buffer no longer exists"))
-      (switch-to-buffer (marker-buffer val))
-      (goto-char val))
+      (switch-to-buffer (overlay-buffer val))
+      (goto-char (register-get-overlay-position val)))
      ((and (consp val) (eq (car val) 'file))
       (find-file (cdr val)))
      ((and (consp val) (eq (car val) 'file-query))
@@ -123,15 +191,15 @@
       (error "Register doesn't contain a buffer position or configuration")))))
 
 (defun register-swap-out ()
-  "Turn markers into file-query references when a buffer is killed."
+  "Turn overlays into file-query references when a buffer is killed."
   (and buffer-file-name
        (dolist (elem register-alist)
-        (and (markerp (cdr elem))
-             (eq (marker-buffer (cdr elem)) (current-buffer))
+        (and (overlayp (cdr elem))
+             (eq (overlay-buffer (cdr elem)) (current-buffer))
              (setcdr elem
                      (list 'file-query
                            buffer-file-name
-                           (marker-position (cdr elem))))))))
+                           (overlay-start (cdr elem))))))))
 
 (defun number-to-register (number register)
   "Store a number in a register.
@@ -187,14 +255,14 @@
      ((numberp val)
       (princ val))
 
-     ((markerp val)
-      (let ((buf (marker-buffer val)))
+     ((overlayp val)
+      (let ((buf (overlay-buffer val)))
        (if (null buf)
-           (princ "a marker in no buffer")
+           (princ "a overlay in no buffer")
          (princ "a buffer position:\n    buffer ")
          (princ (buffer-name buf))
          (princ ", position ")
-         (princ (marker-position val)))))
+         (princ (register-get-overlay-position val)))))
 
      ((and (consp val) (window-configuration-p (car val)))
       (princ "a window configuration."))
@@ -264,8 +332,8 @@
       (insert-for-yank val))
      ((numberp val)
       (princ val (current-buffer)))
-     ((and (markerp val) (marker-position val))
-      (princ (marker-position val) (current-buffer)))
+     ((and (overlayp val) (overlay-start val))
+      (princ (register-get-overlay-position val) (current-buffer)))
      (t
       (error "Register does not contain text"))))
   (if (not arg) (exchange-point-and-mark)))