org-footnote: Do not move point if definition is unreachable

* lisp/org-footnote.el (org-footnote-goto-definition): Throw an error
  when definition is outside narrowed part of buffer.  Do not move
  point either.

* testing/lisp/test-org-footnote.el (test-org-footnote/goto-definition):
  New test.

Reported-by: Rasmus <rasmus@gmx.us>
<http://permalink.gmane.org/gmane.emacs.orgmode/97158>

lisp/org-footnote.el

@@ -360,17 +360,20 @@ If no footnote is found, return nil."
   "Move point to the definition of the footnote LABEL.
 Return a non-nil value when a definition has been found."
   (interactive "sLabel: ")
-  (org-mark-ring-push)
   (let ((def (org-footnote-get-definition label)))
-    (if (not def)
-	(error "Cannot find definition of footnote %s" label)
+    (cond
+     ((not def) (user-error "Cannot find definition of footnote %s" label))
+     ((> (nth 1 def) (point-max))
+      (user-error "Footnote definition outside of narrowed part of buffer"))
+     (t
+      (org-mark-ring-push)
       (goto-char (nth 1 def))
-      (looking-at (format "\\[%s\\]\\|\\[%s:" label label))
+      (looking-at (format "\\[%s[]:]" label))
       (goto-char (match-end 0))
       (org-show-context 'link-search)
       (when (derived-mode-p 'org-mode)
 	(message "Edit definition and go back with `C-c &' or, if unique, with `C-c C-c'."))
-      t)))
+      t))))
 
 (defun org-footnote-goto-previous-reference (label)
   "Find the first closest (to point) reference of footnote with label LABEL."

testing/lisp/test-org-footnote.el

@@ -152,6 +152,33 @@
 	    (org-footnote-delete "1")
 	    (org-trim (buffer-string))))))
 
+(ert-deftest test-org-footnote/goto-definition ()
+  "Test `org-footnote-goto-definition' specifications."
+  ;; Error on unknown definitions.
+  (should-error
+   (org-test-with-temp-text "No footnote definition"
+     (org-footnote-goto-definition "fn:1")))
+  ;; Error when trying to reach a definition outside narrowed part of
+  ;; buffer.
+  (should-error
+   (org-test-with-temp-text "Some text<point>\n[fn:1] Definition."
+     (narrow-to-region (point-min) (point))
+     (org-footnote-goto-definition "fn:1")))
+  ;; Otherwise, move at the beginning of the definition, including
+  ;; anonymous footnotes.
+  (should
+   (equal
+    " Definition."
+    (org-test-with-temp-text "Some text\n[fn:1] Definition."
+      (org-footnote-goto-definition "fn:1")
+      (buffer-substring (point) (point-max)))))
+  (should
+   (equal
+    "definition]"
+    (org-test-with-temp-text "Some text[fn:label:definition]"
+      (org-footnote-goto-definition "fn:label")
+      (buffer-substring (point) (point-max))))))
+
 (ert-deftest test-org-footnote/normalize-in-org ()
   "Test specifications for `org-footnote-normalize' in an Org buffer."
   ;; 1. With a non-nil `org-footnote-section'.