Subject: select-active-regions only half-working

From: David De La Harpe Golden <[email-masked]>
Date: Sat, 06 Sep 2008 06:53:28 +0100

Package: emacs
Version: 23.0.60
Severity: normal
Tags: patch

The select-active-regions in-tree does not work in all cases - it works
when the region is changed by moving the mark but not when it is changed
by certain other means e.g. moving the point with the keyboard.
(Workaround:  C-x C-x C-x C-x ...).

There were a couple of approaches tried a while back (see emacs-devel
"Improved X Selections" thread).  The idle timer seemed to work best in
practice, despite (or because of) "coarse graining" i.e. a bunch of
small region changes in a row don't reupdate the selection for each
change, only kicks in when emacs has idled.

Attached patch is a simple idle-timer based implementation.

Concerns here may also apply to the activate-mark-hook (which states
in its documentation that it is rerun when region changes). Having that
work similarly with the same method would probably mean that
active region timer would have to be enabled whenever the mark is
active, not just when select-active-regions is on.

Index: lisp/simple.el
===================================================================
RCS file: /sources/emacs/emacs/lisp/simple.el,v
retrieving revision 1.945
diff -U 8 -r1.945 simple.el
--- lisp/simple.el	15 Aug 2008 00:30:44 -0000	1.945
+++ lisp/simple.el	6 Sep 2008 05:41:14 -0000
@@ -3439,18 +3439,46 @@
 
 (defun activate-mark ()
   "Activate the mark."
   (when (mark t)
     (setq mark-active t)
     (unless transient-mark-mode
       (setq transient-mark-mode 'lambda))))
 
+(defvar select-active-regions-timer nil)
+
+(defvar select-active-regions-last-region-hash nil)
+
+(defun select-active-regions-maybe-set-selection ()
+  "Implements `select-active-regions', called from idle timer
+`select-active-regions-timer'"
+  (and select-active-regions
+       (region-active-p)
+       (> (region-end) (region-beginning))
+       (if (or (not select-active-regions-last-region-hash)
+	       (x-selection-owner-p nil))
+	   (let ((region-hash
+		  (md5 (current-buffer) (region-beginning)
+		       (region-end) nil t)))
+	     (unless (string-equal region-hash
+				   select-active-regions-last-region-hash)
+	       (x-set-selection
+		nil (buffer-substring (region-beginning) (region-end)))
+	       (setq select-active-regions-last-region-hash
+		     region-hash)))
+	 (setq select-active-regions-last-region-hash nil))))
+
 (defcustom select-active-regions nil
-  "If non-nil, an active region automatically becomes the window selection."
+  "If non-nil, an active region automatically becomes the window selection.
+
+In conjunction with this, you might want to:
+rebind mouse-2 to `mouse-yank-primary', set `x-select-enable-primary' to nil,
+set `x-select-enable-clipboard' to non-nil, set `mouse-drag-copy-region'
+to nil, and turn on `transient-mark-mode'."
   :type 'boolean
   :group 'killing
   :version "23.1")
 
 (defun set-mark (pos)
   "Set this buffer's mark to POS.  Don't use this function!
 That is to say, don't use this function unless you want
 the user to see that the mark has moved, and you want the previous
@@ -3466,19 +3494,26 @@
 store it in a Lisp variable.  Example:
 
    (let ((beg (point))) (forward-line 1) (delete-region beg (point)))."
 
   (if pos
       (progn
 	(setq mark-active t)
 	(run-hooks 'activate-mark-hook)
-	(and select-active-regions
-	     (x-set-selection
-	      nil (buffer-substring (region-beginning) (region-end))))
+	(if select-active-regions
+	    (progn
+	      (unless select-active-regions-timer
+		(setq select-active-regions-timer
+		      (run-with-idle-timer
+		       0.1 t 'select-active-regions-maybe-set-selection)))
+	      (select-active-regions-maybe-set-selection))
+	  (when select-active-regions-timer
+	    (cancel-timer select-active-regions-timer)
+	    (setq select-active-regions-timer nil)))
 	(set-marker (mark-marker) pos (current-buffer)))
     ;; Normally we never clear mark-active except in Transient Mark mode.
     ;; But when we actually clear out the mark value too,
     ;; we must clear mark-active in any mode.
     (setq mark-active nil)
     (run-hooks 'deactivate-mark-hook)
     (set-marker (mark-marker) nil)))
 
2008-09-06 David De La Harpe Golden <[email-masked]>

	* simple.el: idle-timer implementation of select-active-regions