org-capture: Expand keywords within %(sexp) placeholder in template

* lisp/org-capture.el: (org-capture--expand-keyword-in-embedded-elisp): New function.
(org-capture-expand-embedded-elisp): Use new function.

doc/org.texi

@@ -6853,7 +6853,9 @@ dynamic insertion of content.  The templates are expanded in the order given her
 @smallexample
 %[@var{file}]     @r{Insert the contents of the file given by @var{file}.}
 %(@var{sexp})     @r{Evaluate Elisp @var{sexp} and replace with the result.}
-            @r{The sexp must return a string.}
+                  @r{For convenience, %:keyword (see below) placeholders}
+                  @r{within the expression will be expanded prior to this.}
+                  @r{The sexp must return a string.}
 %<...>      @r{The result of format-time-string on the ... format specification.}
 %t          @r{Timestamp, date only.}
 %T          @r{Timestamp, with date and time.}

lisp/org-capture.el

@@ -223,7 +223,9 @@ freely formatted text.  Furthermore, the following %-escapes will
 be replaced with content and expanded in this order:
 
   %[pathname] Insert the contents of the file given by `pathname'.
-  %(sexp)     Evaluate elisp `(sexp)' and replace with the result.
+  %(sexp)     Evaluate elisp `(sexp)' and replace it with the results.
+              For convenience, %:keyword (see below) placeholders within
+              the expression will be expanded prior to this.
   %<...>      The result of format-time-string on the ... format specification.
   %t          Time stamp, date only.
   %T          Time stamp with date and time.
@@ -1621,10 +1623,26 @@ The template may still contain \"%?\" for cursor positioning."
       (goto-char (match-beginning 0))
       (let ((template-start (point)))
 	(forward-char 1)
-	(let ((result (org-eval (read (current-buffer)))))
+	(let ((result (org-eval
+		       (org-capture--expand-keyword-in-embedded-elisp
+			(read (current-buffer))))))
 	  (delete-region template-start (point))
 	  (insert result))))))
 
+(defun org-capture--expand-keyword-in-embedded-elisp (attr)
+  "Recursively replace capture link keywords in ATTR sexp.
+Such keywords are prefixed with "%:".  See `org-capture-template'
+for more information."
+  (cond ((consp attr)
+	 (mapcar 'org-capture--expand-keyword-in-embedded-elisp attr))
+	((symbolp attr)
+	 (let* ((attr-symbol (symbol-name attr))
+		(key (and (string-match "%\\(:.*\\)" attr-symbol)
+			  (intern (match-string 1 attr-symbol)))))
+	   (or (plist-get org-store-link-plist key)
+	       attr)))
+	(t attr)))
+
 (defun org-capture-inside-embedded-elisp-p ()
   "Return non-nil if point is inside of embedded elisp %(sexp)."
   (let (beg end)