org-agenda.el: Support argument collection for custom bulk functions

* lisp/org-agenda.el (org-agenda-bulk-custom-functions): Add
documentation about argument collection for custom bulk functions.
(org-agenda-bulk-action): Support function to collect arguments for
custom bulk functions.
* etc/ORG-NEWS (Option ~org-agenda-bulk-custom-functions~ now supports
collecting bulk arguments): Add entry to NEWS.

etc/ORG-NEWS

@@ -88,6 +88,12 @@ New variable ~org-html-meta-tags~ makes it possible to customize the
 values, or a function that generates such a list (see
 ~org-html-meta-tags-default~ as an example of the latter).
 
+*** Option ~org-agenda-bulk-custom-functions~ now supports collecting bulk arguments
+
+When specifying a custom agenda bulk option, you can now also specify
+a function which collects the arguments to be used with each call to
+the custom function.
+
 ** New features
 *** =ob-python= improvements to =:return= header argument 
 

lisp/org-agenda.el

@@ -2080,9 +2080,25 @@ For example, this value makes those two functions available:
 
 With selected entries in an agenda buffer, `B R' will call
 the custom function `set-category' on the selected entries.
-Note that functions in this alist don't need to be quoted."
-  :type '(alist :key-type character :value-type (group function))
-  :version "24.1"
+Note that functions in this alist don't need to be quoted.
+
+You can also specify a function which collects arguments to be
+used for each call to your bulk custom function.  The argument
+collecting function will be run once and should return a list of
+arguments to pass to the bulk function.  For example:
+
+  \\='((?R set-category get-category))
+
+Now, `B R' will call the custom `get-category' which would prompt
+the user once for a category.  That category is then passed as an
+argument to `set-category' for each entry it's called against."
+  :type
+  '(alist :key-type character
+	  :value-type
+          (group (function :tag "Bulk Custom Function")
+		 (choice (function :tag "Bulk Custom Argument Function")
+		         (const :tag "No Bulk Custom Argument Function" nil))))
+  :package-version '(Org . "9.5")
   :group 'org-agenda)
 
 (defmacro org-agenda-with-point-at-orig-entry (string &rest body)
@@ -10487,10 +10503,15 @@ The prefix arg is passed through to the command if possible."
 		(completing-read "Function: " obarray #'fboundp t nil nil))))
 
 	(action
-	 (pcase (assoc action org-agenda-bulk-custom-functions)
-	   (`(,_ ,f) (setq cmd f) (setq redo-at-end t))
-	   (_ (user-error "Invalid bulk action: %c" action)))))
-
+         (setq cmd
+               (pcase (assoc action org-agenda-bulk-custom-functions)
+                 (`(,_ ,fn)
+                  fn)
+                 (`(,_ ,fn ,arg-fn)
+                  (apply #'apply-partially fn (funcall arg-fn)))
+                 (_
+                  (user-error "Invalid bulk action: %c" action))))
+         (setq redo-at-end t)))
       ;; Sort the markers, to make sure that parents are handled
       ;; before children.
       (setq entries (sort entries