ox: Better return value for `org-export-get-optional-title'

* lisp/ox.el (org-export-get-optional-title): Return regular title
  when no optional title is found.
* lisp/ox-ascii.el (org-ascii--build-title): Apply change to
  `org-export-get-optional-title'.
* lisp/ox-html.el (org-html--format-toc-headline): Apply change to
  `org-export-get-optional-title'.
* lisp/ox-latex.el (org-latex-headline): Apply change to
  `org-export-get-optional-title'.
* testing/lisp/test-ox.el: Add tests.

lisp/ox-ascii.el

@@ -551,7 +551,7 @@ If optional argument NOTAGS is non-nil, no tags will be added to
 the title.
 
 When optional argument TOC is non-nil, use optional title if
-possible."
+possible.  It doesn't apply to `inlinetask' elements."
   (let* ((headlinep (eq (org-element-type element) 'headline))
 	 (numbers
 	  ;; Numbering is specific to headlines.
@@ -565,8 +565,9 @@ possible."
 	 (text
 	  (org-trim
 	   (org-export-data
-	    (or (and toc headlinep (org-export-get-optional-title element info))
-		(org-element-property :title element)) info)))
+	    (if (and toc headlinep) (org-export-get-optional-title element info)
+	      (org-element-property :title element))
+	    info)))
 	 (todo
 	  (and (plist-get info :with-todo-keywords)
 	       (let ((todo (org-element-property :todo-keyword element)))

lisp/ox-html.el

@@ -1160,9 +1160,7 @@ INFO is a plist used as a communication channel."
 	    ;; Body.
 	    (concat section-number
 		    (org-export-data
-		     (or (org-export-get-optional-title headline info)
-			 (org-element-property :title headline))
-		     info)
+		     (org-export-get-optional-title headline info) info)
 		    (and tags "   ") (org-html--tags tags)))))
 
 (defun org-html-toc (depth info)

lisp/ox-latex.el

@@ -1480,9 +1480,7 @@ holding contextual information."
 	       (funcall org-latex-format-headline-function
 			todo todo-type priority
 			(org-export-data
-			 (or (org-export-get-optional-title headline info)
-			     (org-element-property :title headline))
-			 info)
+			 (org-export-get-optional-title headline info) info)
 			(and (eq (plist-get info :with-tags) t) tags))))
 	  (if (and opt-title (string-match "\\`\\\\\\(.*?\\){" section-fmt))
 	      (format (replace-match "\\1[%s]" nil nil section-fmt 1)

lisp/ox.el

@@ -3550,9 +3550,10 @@ fail, the fall-back value is \"???\"."
 
 (defun org-export-get-optional-title (headline info)
   "Return optional title for HEADLINE, as a secondary string.
-INFO is a plist used as a communication channel.  If no such
-title is defined, return nil."
-  (org-element-property :optional-title headline))
+INFO is a plist used as a communication channel.  If no optional
+title is defined, fall-back to the regular title."
+  (or (org-element-property :optional-title headline)
+      (org-element-property :title headline)))
 
 (defun org-export-first-sibling-p (headline info)
   "Non-nil when HEADLINE is the first sibling in its sub-tree.

testing/lisp/test-ox.el

@@ -1018,6 +1018,24 @@ Paragraph[fn:1]"
   ;; Otherwise, return it as a roman number.
   (should (equal (org-export-number-to-roman 1449) "MCDXLIX")))
 
+(ert-deftest test-org-export/get-optional-title ()
+  "Test `org-export-get-optional-title' specifications."
+  ;; If OPTIONAL_TITLE property is defined, use it.
+  (should
+   (equal '("opt")
+	  (org-test-with-parsed-data
+	      "* Headline\n:PROPERTIES:\n:OPTIONAL_TITLE: opt\n:END:"
+	    (org-export-get-optional-title
+	     (org-element-map tree 'headline 'identity info t)
+	     info))))
+  ;; Otherwise, fall-back to regular title.
+  (should
+   (equal '("Headline")
+	  (org-test-with-parsed-data "* Headline"
+	    (org-export-get-optional-title
+	     (org-element-map tree 'headline 'identity info t)
+	     info)))))
+
 (ert-deftest test-org-export/get-tags ()
   "Test `org-export-get-tags' specifications."
   (let ((org-export-exclude-tags '("noexport"))