ob-tangle: only create links for blocks that will actually tangle

this commit includes a unit test

* lisp/ob-tangle.el (org-babel-tangle-collect-blocks): only create
  links for blocks that will actually tangle

lisp/ob-tangle.el

@@ -276,11 +276,12 @@ code blocks by language."
       (let* ((start-line (save-restriction (widen)
 					   (+ 1 (line-number-at-pos (point)))))
 	     (file (buffer-file-name))
-	     (link (progn (call-interactively 'org-store-link)
-                          (org-babel-clean-text-properties
-			   (car (pop org-stored-links)))))
              (info (org-babel-get-src-block-info))
 	     (params (nth 2 info))
+	     (link (unless (string= (cdr (assoc :tangle params)) "no")
+		     (progn (call-interactively 'org-store-link)
+			    (org-babel-clean-text-properties
+			     (car (pop org-stored-links))))))
              (source-name (intern (or (nth 4 info)
                                       (format "%s:%d"
 					      current-heading block-counter))))

testing/examples/babel.org

@@ -41,3 +41,21 @@
 #+results:
 : 4
 
+
+* excessive id links on tangling
+  :PROPERTIES:
+  :ID:       ef06fd7f-012b-4fde-87a2-2ae91504ea7e
+  :END:
+
+** no, don't give me an ID
+#+begin_src emacs-lisp :tangle no
+  (message "not to be tangled")
+#+end_src
+
+** yes, I'd love an ID
+   :PROPERTIES:
+   :ID:       ae7b55ca-9ef2-4d30-bd48-da30e35fd0f3
+   :END:
+#+begin_src emacs-lisp :tangle no
+  (message "for tangling")
+#+end_src

testing/lisp/test-ob-tangle.el

@@ -43,6 +43,14 @@
 	(should-not (exp-p "no"))
 	(should (exp-p "tangle"))))))
 
+(ert-deftest ob-tangle/no-excessive-id-insertion-on-tangle ()
+  "Don't add IDs to headings without tangling code blocks."
+  (org-test-at-id "ae7b55ca-9ef2-4d30-bd48-da30e35fd0f3"
+    (org-babel-next-src-block)
+    (org-babel-tangle)
+    (org-babel-previous-src-block)
+    (should (null (org-id-get)))))
+
 (provide 'test-ob-tangle)
 
 ;;; test-ob-tangle.el ends here