org-element: Fix search failed error in `org-element-context'

* lisp/org-element.el (org-element-context): Make sure point is on tag
  line before searching for it.

* testing/lisp/test-org-element.el (test-org-element/context): Add test.
  Small refactoring.

Reported-by: Kaushal Modi <kaushal.modi@gmail.com>
<http://permalink.gmane.org/gmane.emacs.orgmode/105018>

lisp/org-element.el

@@ -5735,15 +5735,15 @@ Providing it allows for quicker computation."
     (org-with-wide-buffer
      (let* ((pos (point))
 	    (element (or element (org-element-at-point)))
-	    (type (org-element-type element)))
+	    (type (org-element-type element))
+	    (post (org-element-property :post-affiliated element)))
        ;; If point is inside an element containing objects or
        ;; a secondary string, narrow buffer to the container and
        ;; proceed with parsing.  Otherwise, return ELEMENT.
        (cond
 	;; At a parsed affiliated keyword, check if we're inside main
 	;; or dual value.
-	((let ((post (org-element-property :post-affiliated element)))
-	   (and post (< pos post)))
+	((and post (< pos post))
 	 (beginning-of-line)
 	 (let ((case-fold-search t)) (looking-at org-element--affiliated-re))
 	 (cond
@@ -5762,7 +5762,8 @@ Providing it allows for quicker computation."
 	;; At an item, objects can only be located within tag, if any.
 	((eq type 'item)
 	 (let ((tag (org-element-property :tag element)))
-	   (if (not tag) (throw 'objects-forbidden element)
+	   (if (or (not tag) (/= (line-beginning-position) post))
+	       (throw 'objects-forbidden element)
 	     (beginning-of-line)
 	     (search-forward tag (line-end-position))
 	     (goto-char (match-beginning 0))

testing/lisp/test-org-element.el

@@ -3332,36 +3332,43 @@ Text
   ;; Return closest object containing point.
   (should
    (eq 'underline
-       (org-test-with-temp-text "Some *text with _underline_ text*"
-	 (progn (search-forward "under")
-		(org-element-type (org-element-context))))))
+       (org-test-with-temp-text "Some *text with _under<point>line_ text*"
+	 (org-element-type (org-element-context)))))
   ;; Find objects in secondary strings.
   (should
    (eq 'underline
-       (org-test-with-temp-text "* Headline _with_ underlining"
-	 (progn (search-forward "w")
-		(org-element-type (org-element-context))))))
+       (org-test-with-temp-text "* Headline _<point>with_ underlining"
+	 (org-element-type (org-element-context)))))
   ;; Find objects in objects.
   (should
    (eq 'macro
-       (org-test-with-temp-text "| a | {{{macro}}} |"
-	 (progn (search-forward "{")
-		(org-element-type (org-element-context))))))
+       (org-test-with-temp-text "| a | {<point>{{macro}}} |"
+	 (org-element-type (org-element-context)))))
   (should
    (eq 'table-cell
-       (org-test-with-temp-text "| a | b {{{macro}}} |"
-	 (progn (search-forward "b")
-		(org-element-type (org-element-context))))))
+       (org-test-with-temp-text "| a | b<point> {{{macro}}} |"
+	 (org-element-type (org-element-context)))))
   ;; Find objects in planning lines.
   (should
    (eq 'timestamp
-       (org-test-with-temp-text "* H\n  SCHEDULED: <2012-03-29 thu.>"
-	 (search-forward "2012")
+       (org-test-with-temp-text "* H\n  SCHEDULED: <2012<point>-03-29 thu.>"
 	 (org-element-type (org-element-context)))))
   (should-not
    (eq 'timestamp
-       (org-test-with-temp-text "* H\n  SCHEDULED: <2012-03-29 thu.>"
-	 (search-forward "SCHEDULED")
+       (org-test-with-temp-text "* H\n  SCHEDULED<point>: <2012-03-29 thu.>"
+	 (org-element-type (org-element-context)))))
+  ;; Find objects in item tags.
+  (should
+   (eq 'bold
+       (org-test-with-temp-text "- *bo<point>ld* ::"
+	 (org-element-type (org-element-context)))))
+  (should-not
+   (eq 'bold
+       (org-test-with-temp-text "- *bold* ::<point>"
+	 (org-element-type (org-element-context)))))
+  (should-not
+   (eq 'bold
+       (org-test-with-temp-text "- *bold* ::\n<point>"
 	 (org-element-type (org-element-context)))))
   ;; Do not find objects in table rules.
   (should
@@ -3371,14 +3378,12 @@ Text
   ;; Find objects in parsed affiliated keywords.
   (should
    (eq 'macro
-       (org-test-with-temp-text "#+CAPTION: {{{macro}}}\n| a | b |."
-	 (progn (search-forward "{")
-		(org-element-type (org-element-context))))))
+       (org-test-with-temp-text "#+CAPTION: {<point>{{macro}}}\n| a | b |"
+	 (org-element-type (org-element-context)))))
   (should
    (eq 'bold
-       (org-test-with-temp-text "#+caption: *bold*\nParagraph"
-	 (progn (search-forward "*")
-		(org-element-type (org-element-context))))))
+       (org-test-with-temp-text "#+caption: *<point>bold*\nParagraph"
+	 (org-element-type (org-element-context)))))
   ;; Find objects at the end of buffer.
   (should
    (eq 'bold
@@ -3388,35 +3393,28 @@ Text
   ;; Correctly set `:parent' property.
   (should
    (eq 'paragraph
-       (org-test-with-temp-text "Some *bold* text"
-	 (progn (search-forward "bold")
-		(org-element-type
-		 (org-element-property :parent (org-element-context)))))))
+       (org-test-with-temp-text "Some *bold<point>* text"
+	 (org-element-type
+	  (org-element-property :parent (org-element-context))))))
   ;; Between two objects, return the second one.
   (should
    (eq 'macro
-       (org-test-with-temp-text "<<target>>{{{test}}}"
-	 (progn (search-forward "{")
-		(backward-char)
-		(org-element-type (org-element-context))))))
+       (org-test-with-temp-text "<<target>><point>{{{test}}}"
+	 (org-element-type (org-element-context)))))
   ;; Test optional argument.
   (should
    (eq 'underline
-       (org-test-with-temp-text "Some *text with _underline_ text*"
-	 (progn
-	   (search-forward "under")
-	   (org-element-type (org-element-context (org-element-at-point)))))))
+       (org-test-with-temp-text "Some *text with _under<point>line_ text*"
+	 (org-element-type (org-element-context (org-element-at-point))))))
   ;; Special case: bold object at the beginning of a headline.
   (should
    (eq 'bold
-       (org-test-with-temp-text "* *bold*"
-	 (search-forward "bo")
+       (org-test-with-temp-text "* *bo<point>ld*"
 	 (org-element-type (org-element-context)))))
   ;; Special case: incomplete cell at the end of a table row.
   (should
    (eq 'table-cell
-       (org-test-with-temp-text "|a|b|c"
-	 (goto-char (point-max))
+       (org-test-with-temp-text "|a|b|c<point>"
 	 (org-element-type (org-element-context)))))
   ;; Special case: objects in inline footnotes.
   (should