ox: Do not build TOC for headlines below H value

* lisp/ox.el (org-export-collect-headlines): Do not build TOC for
  headlines below H value.
* testing/lisp/test-ox.el: Add test.

Reported-by: Jambunathan K <kjambunathan@gmail.com>

lisp/ox.el

@@ -4829,14 +4829,14 @@ information.
 
 Return a list of all exportable headlines as parsed elements.
 Footnote sections, if any, will be ignored."
-  (unless (wholenump n) (setq n (plist-get info :headline-levels)))
-  (org-element-map (plist-get info :parse-tree) 'headline
-    (lambda (headline)
-      (unless (org-element-property :footnote-section-p headline)
-	;; Strip contents from HEADLINE.
-	(let ((relative-level (org-export-get-relative-level headline info)))
-	  (unless (> relative-level n) headline))))
-    info))
+  (let ((limit (plist-get info :headline-levels)))
+    (setq n (if (wholenump n) (min n limit) limit))
+    (org-element-map (plist-get info :parse-tree) 'headline
+      #'(lambda (headline)
+	  (unless (org-element-property :footnote-section-p headline)
+	    (let ((level (org-export-get-relative-level headline info)))
+	      (and (<= level n) headline))))
+      info)))
 
 (defun org-export-collect-elements (type info &optional predicate)
   "Collect referenceable elements of a determined type.

testing/lisp/test-ox.el

@@ -2485,6 +2485,36 @@ Another text. (ref:text)
       info))))
 
 
+
+;;; Tables of Contents
+
+(ert-deftest test-org-export/collect-headlines ()
+  "Test `org-export-collect-headlines' specifications."
+  ;; Standard test.
+  (should
+   (= 2
+      (length
+       (org-test-with-parsed-data "* H1\n** H2"
+	 (org-export-collect-headlines info)))))
+  ;; Do not collect headlines below optional argument.
+  (should
+   (= 1
+      (length
+       (org-test-with-parsed-data "* H1\n** H2"
+	 (org-export-collect-headlines info 1)))))
+  ;; Never collect headlines below maximum headline level.
+  (should
+   (= 1
+      (length
+       (org-test-with-parsed-data "#+OPTIONS: H:1\n* H1\n** H2"
+	 (org-export-collect-headlines info)))))
+  (should
+   (= 1
+      (length
+       (org-test-with-parsed-data "#+OPTIONS: H:1\n* H1\n** H2"
+	 (org-export-collect-headlines info 2))))))
+
+
 
 ;;; Templates