Fix `org-display-inline-images' with "clickable images"

* lisp/org.el (org-display-inline-images): Even though Org syntax
  doesn't support nested links, display an image when the function is
  called on a link that contains a single file name in its
  description.

Reported-by: "Dietrich Foethke" <foethke@web.de>
<http://lists.gnu.org/r/emacs-orgmode/2019-02/msg00280.html>

lisp/org.el

@@ -18752,7 +18752,8 @@ conventions:
      from `image-file-name-regexp' and it has no contents.
 
   2. Its description consists in a single link of the previous
-     type.
+     type.  In this case, that link must be a well-formed plain
+     or angle link, i.e., it must have an explicit \"file\" type.
 
 When optional argument INCLUDE-LINKED is non-nil, also links with
 a text description part will be inlined.  This can be nice for
@@ -18768,8 +18769,7 @@ boundaries."
     (unless refresh
       (org-remove-inline-images)
       (when (fboundp 'clear-image-cache) (clear-image-cache)))
-    (org-with-wide-buffer
-     (goto-char (or beg (point-min)))
+    (org-with-point-at (or beg 1)
       (let* ((case-fold-search t)
 	     (file-extension-re (image-file-name-regexp))
 	     (link-abbrevs (mapcar #'car
@@ -18778,23 +18778,47 @@ boundaries."
 	     ;; Check absolute, relative file names and explicit
 	     ;; "file:" links.  Also check link abbreviations since
 	     ;; some might expand to "file" links.
-	    (file-types-re (format "[][]\\[\\(?:file\\|[./~]%s\\)"
+	     (file-types-re
+	      (format "\\[\\[\\(?:file%s:\\|[./~]\\)\\|\\]\\[\\(<?file:\\)"
 		      (if (not link-abbrevs) ""
-				     (format "\\|\\(?:%s:\\)"
-					     (regexp-opt link-abbrevs))))))
+			(concat "\\|" (regexp-opt link-abbrevs))))))
 	(while (re-search-forward file-types-re end t)
-	 (let ((link (save-match-data (org-element-context))))
-	   ;; Check if we're at an inline image, i.e., an image file
-	   ;; link without a description (unless INCLUDE-LINKED is
-	   ;; non-nil).
-	   (when (and (equal "file" (org-element-property :type link))
-		      (or include-linked
-			  (null (org-element-contents link)))
-		      (string-match-p file-extension-re
+	  (let* ((link (org-element-lineage
+			(save-match-data (org-element-context))
+			'(link) t))
+		 (inner-start (match-beginning 1))
+		 (path
+		  (cond
+		   ;; No link at point; no inline image.
+		   ((not link) nil)
+		   ;; File link without a description.  Also handle
+		   ;; INCLUDE-LINKED here since it should have
+		   ;; precedence over the next case.  I.e., if link
+		   ;; contains filenames in both the path and the
+		   ;; description, prioritize the path only when
+		   ;; INCLUDE-LINKED is non-nil.
+		   ((or (not (org-element-property :contents-begin link))
+			include-linked)
+		    (and (equal "file" (org-element-property :type link))
 			 (org-element-property :path link)))
-	     (let ((file (expand-file-name
-			  (org-link-unescape
-			   (org-element-property :path link)))))
+		   ;; Link with a description.  Check if description
+		   ;; is a filename.  Even if Org doesn't have syntax
+		   ;; for those -- clickable image -- constructs, fake
+		   ;; them, as in `org-export-insert-image-links'.
+		   ((not inner-start) nil)
+		   (t
+		    (org-with-point-at inner-start
+		      (and (looking-at
+			    (if (char-equal ?< (char-after inner-start))
+				org-angle-link-re
+			      org-plain-link-re))
+			   ;; File name must fill the whole
+			   ;; description.
+			   (= (org-element-property :contents-end link)
+			      (match-end 0))
+			   (match-string 2)))))))
+	    (when (and path (string-match-p file-extension-re path))
+	      (let ((file (expand-file-name (org-link-unescape path))))
 		(when (file-exists-p file)
 		  (let ((width
 			 ;; Apply `org-image-actual-width' specifications.