ox-icalendar: Fix export of diary-style timestamps

* lisp/ox-icalendar.el (org-icalendar-entry): Include timestamps of
type diary when `:with-timestamps' is `active'.
* lisp/ox.el (org-export--skip-p): Include timestamps of type diary
when `:with-timestamps' is `active'.
*
testing/lisp/test-ox-icalendar.el (test-ox-icalendar/diary-timestamp):
Unit test for exporting timestamps of type diary.

etc/ORG-NEWS

@@ -57,6 +57,20 @@ remote resources in the =#+include:='s.  Now, an error is thrown to
 avoid seemingly ignored =#+include= statements when publishing via
 batch scripts.
 
+*** Diary-style timestamps are exported together with active timestamps
+
+~org-export-with-timestamps~ and ~org-icalendar-with-timestamps~ now
+treat diary-style timestamps as a type of active timestamp for
+purposes of export.
+
+This mainly affects iCalendar export, where diary timestamps will now
+be included when only active timestamps are exported (the default).
+
+This should have minimal impact on non-iCalendar exporters, since
+~org-export-with-timestamps~ was already ~t~ by default.  However,
+users who manually set ~org-export-with-timestamps~ to ~active~ will
+now have diary timestamps included as well.
+
 ** New features
 
 # We list the most important features, and the features that may

lisp/ox-icalendar.el

@@ -746,7 +746,7 @@ inlinetask within the section."
 	       (lambda (ts)
 		 (when (let ((type (org-element-property :type ts)))
 			 (cl-case (plist-get info :with-timestamps)
-			   (active (memq type '(active active-range)))
+			   (active (memq type '(active active-range diary)))
 			   (inactive (memq type '(inactive inactive-range)))
 			   ((t) t)))
 		   (let ((uid (format "TS%d-%s" (cl-incf counter) uid)))

lisp/ox.el

@@ -1860,7 +1860,7 @@ not exported."
        (cl-case (plist-get options :with-timestamps)
 	 ((nil) t)
 	 (active
-	  (not (memq (org-element-property :type datum) '(active active-range))))
+	  (not (memq (org-element-property :type datum) '(active active-range diary))))
 	 (inactive
 	  (not (memq (org-element-property :type datum)
 		     '(inactive inactive-range)))))))))

testing/lisp/test-ox-icalendar.el

@@ -128,5 +128,20 @@ SCHEDULED: <2023-03-26 Sun .+1m>"
          (when (file-exists-p tmp-ics)
            (delete-file tmp-ics))))))))
 
+(ert-deftest test-ox-icalendar/diary-timestamp ()
+  "Test icalendar export of diary timestamps."
+  (let* ((tmp-ics (org-test-with-temp-text-in-file
+                   "* First Sunday of the month
+<%%(diary-float t 0 1)>"
+                   (expand-file-name (org-icalendar-export-to-ics)))))
+    (unwind-protect
+        (with-temp-buffer
+          (insert-file-contents tmp-ics)
+          (save-excursion
+            (should (search-forward "SUMMARY:First Sunday of the month")))
+          (save-excursion
+            (should (search-forward "RRULE:FREQ=MONTHLY;BYDAY=1SU"))))
+      (when (file-exists-p tmp-ics) (delete-file tmp-ics)))))
+
 (provide 'test-ox-icalendar)
 ;;; test-ox-icalendar.el ends here