Add desktop-registry-current-desktop

* desktop-registry.el (desktop-registry--canonicalize-dir):
  (desktop-registry-current-desktop): New functions.
  (desktop-registry-add-directory): Use
  `desktop-registry--canonicalize-dir' to get the "clean" directory
  name.

NEWS

@@ -5,3 +5,6 @@
 
   - Add =desktop-registry-remove-desktop= command to remove desktops you
     no longer (want to) use.
+
+  - Add =desktop-registry-current-desktop= function to get the name of
+    the currently loaded desktop.

README.org

@@ -27,3 +27,14 @@ to fix that.
 
   When you're done with a desktop or want to get rid of a desktop for
   another reason you can use =desktop-registry-remove-desktop=.
+
+** With org-capture-templates
+
+   The =desktop-registry-current-desktop= can be used to insert the
+   currently loaded desktop into an org capture template.
+
+   #+BEGIN_SRC emacs-lisp
+     (add-to-list 'org-capture-templates
+                  '("t" "Task" entry nil
+                    "* TODO %?  :%(desktop-registry-current-desktop):"))
+   #+END_SRC

desktop-registry.el

@@ -44,11 +44,27 @@
 (defvar desktop-registry--history nil
   "History variable for `desktop-registry'.")
 
+(defun desktop-registry--canonicalize-dir (dir)
+  "Canonicalize DIR for use."
+  (directory-file-name (expand-file-name dir)))
+
+;;;###autoload
+(defun desktop-registry-current-desktop ()
+  "Get the name of the currently loaded desktop.
+
+Returns an empty string when `desktop-dirname' is nil."
+  (if desktop-dirname
+      (let ((canonical
+             (desktop-registry--canonicalize-dir desktop-dirname)))
+        (car (cl-find-if (lambda (d) (equal (cdr d) canonical))
+                         desktop-registry-registry)))
+    ""))
+
 ;;;###autoload
 (defun desktop-registry-add-directory (dir)
   "Add DIR to the desktop registry."
   (interactive "DDirectory: ")
-  (let* ((clean-dir (directory-file-name (expand-file-name dir)))
+  (let* ((clean-dir (desktop-registry--canonicalize-dir dir))
          (label (file-name-base clean-dir)))
     (unless (assoc label desktop-registry-registry)
       (customize-save-variable