org-pcomplete: Modify completion for buffer keywords

* lisp/org-pcomplete.el (pcomplete/org-mode/file-option): Collect
  valid keywords for completion without requiring the whole export
  framework.
(pcomplete/org-mode/file-option/options): Rewrite using new export
  framework.  Only complete up to the colon.
(pcomplete/org-mode/file-option/x): Removed macro.
(pcomplete/org-mode/file-option/title,
 pcomplete/org-mode/file-option/author,
 pcomplete/org-mode/file-option/email,
 pcomplete/org-mode/file-option/date): Removed functions.
(pcomplete/org-mode/file-option/infojs_opt): New function.

Completion for some keywords was removed because it provided only the
default value, which is the same as not writing the keyword at all.  In
other words, a user would almost always want to modify the completed
value, which makes the completion moot.

lisp/org-pcomplete.el

@@ -35,7 +35,6 @@
 (require 'pcomplete)
 
 (declare-function org-split-string "org" (string &optional separators))
-(declare-function org-get-current-options "org-exp" ())
 (declare-function org-make-org-heading-search-string "org"
 		  (&optional string heading))
 (declare-function org-get-buffer-tags "org" ())
@@ -140,11 +139,12 @@ When completing for #+STARTUP, for example, this function returns
 		 (car (org-thing-at-point)))
 		pcomplete-default-completion-function))))
 
-(defvar org-options-keywords)                ; From org.el
-(defvar org-additional-option-like-keywords) ; From org.el
+(defvar org-options-keywords)		 ; From org.el
+(defvar org-element-block-name-alist)	 ; From org-element.el
+(defvar org-element-affiliated-keywords) ; From org-element.el
+(declare-function org-get-export-keywords "org" ())
 (defun pcomplete/org-mode/file-option ()
   "Complete against all valid file options."
-  (require 'org-exp)
   (pcomplete-here
    (org-pcomplete-case-double
     (mapcar (lambda (x)
@@ -152,7 +152,16 @@ When completing for #+STARTUP, for example, this function returns
 		  (concat x " ")
 		x))
 	    (append org-options-keywords
-		    org-additional-option-like-keywords)))
+		    org-element-affiliated-keywords
+		    (let (block-names)
+		      (mapc (lambda (block-name)
+			      (let ((name (car block-name)))
+				(push (concat "END_" name) block-names)
+				(push (concat "BEGIN_" name) block-names)))
+			    org-element-block-name-alist)
+		      block-names)
+		    (mapcar (lambda (keyword) (concat keyword ":"))
+			    (org-get-export-keywords)))))
    (substring pcomplete-stub 2)))
 
 (defvar org-startup-options)
@@ -169,37 +178,31 @@ When completing for #+STARTUP, for example, this function returns
 		(setq opts (delete "showstars" opts)))))
 	    opts))))
 
-(defmacro pcomplete/org-mode/file-option/x (option)
-  "Complete arguments for OPTION."
-  `(while
-       (pcomplete-here
-	(pcomplete-uniqify-list
-	 (delq nil
-	       (mapcar (lambda(o)
-			 (when (string-match (concat "^[ \t]*#\\+"
-						     ,option ":[ \t]+\\(.*\\)[ \t]*$") o)
-			   (match-string 1 o)))
-		       (split-string (org-get-current-options) "\n")))))))
-
 (defun pcomplete/org-mode/file-option/options ()
   "Complete arguments for the #+OPTIONS file option."
-  (pcomplete/org-mode/file-option/x "OPTIONS"))
+  (while (pcomplete-here
+	  (pcomplete-uniqify-list
+	   (append
+	    ;; Hard-coded OPTION items always available.
+	    '("H:" "\\n:" "num:" "timestamp:" "arch:" "author:" "c:"
+	      "creator:" "date:" "d:" "email:" "*:" "e:" "::" "f:"
+	      "inline:" "tex:" "p:" "pri:" "':" "-:" "stat:" "^:" "toc:"
+	      "|:" "tags:" "tasks:" "<:" "todo:")
+	    ;; OPTION items from registered back-ends.
+	    (let (items)
+	      (dolist (back-end (org-bound-and-true-p
+				 org-export-registered-backends))
+		(dolist (option (plist-get (cdr back-end) :options-alist))
+		  (let ((item (nth 2 option)))
+		    (when item (push (concat item ":") items)))))
+	      items))))))
 
-(defun pcomplete/org-mode/file-option/title ()
-  "Complete arguments for the #+TITLE file option."
-  (pcomplete/org-mode/file-option/x "TITLE"))
-
-(defun pcomplete/org-mode/file-option/author ()
-  "Complete arguments for the #+AUTHOR file option."
-  (pcomplete/org-mode/file-option/x "AUTHOR"))
-
-(defun pcomplete/org-mode/file-option/email ()
-  "Complete arguments for the #+EMAIL file option."
-  (pcomplete/org-mode/file-option/x "EMAIL"))
-
-(defun pcomplete/org-mode/file-option/date ()
-  "Complete arguments for the #+DATE file option."
-  (pcomplete/org-mode/file-option/x "DATE"))
+(defun pcomplete/org-mode/file-option/infojs_opt ()
+  "Complete arguments for the #+INFOJS_OPT file option."
+  (while (pcomplete-here
+	  (pcomplete-uniqify-list
+	   (mapcar (lambda (item) (format "%s:" (car item)))
+		   (org-bound-and-true-p org-infojs-opts-table))))))
 
 (defun pcomplete/org-mode/file-option/bind ()
   "Complete arguments for the #+BIND file option, which are variable names."