org-element-org-data-parser: Allow leading blank lines before property drawer

* lisp/org-element.el (org-element--get-global-node-properties):
(org-element-org-data-parser):
(org-element--current-element): Allow blank lines at the beginning of
Org document.  Blank lines where allowed in the past (:contents-begin
started after the blank lines), but it was previously not possible to
have top-level property drawer in an Org document starting from blank
lines.  Now, it is possible.

* testing/lisp/test-org-element.el (test-org-element/org-data-parser):
Add new tests.

Reported-by: Tom Alexander <tom@fizz.buzz>
Link: https://orgmode.org/list/0ec8c4ae-4f5b-4e37-8c5c-f92ef497a461@app.fastmail.com

lisp/org-element.el

@@ -1528,6 +1528,8 @@ Alter DATA by side effect."
   (with-current-buffer (org-element-property :buffer data)
     (org-with-wide-buffer
      (goto-char (point-min))
+     (org-skip-whitespace)
+     (forward-line 0)
      (while (and (org-at-comment-p) (bolp)) (forward-line))
      (let ((props (org-element--get-node-properties t data))
            (has-category? nil))
@@ -1568,6 +1570,8 @@ Return a new syntax node of `org-data' type containing `:begin',
                           (or
                            (org-with-wide-buffer
                             (goto-char (point-min))
+                            (org-skip-whitespace)
+                            (forward-line 0)
                             (while (and (org-at-comment-p) (bolp)) (forward-line))
                             (when (looking-at org-property-drawer-re)
                               (goto-char (match-end 0))
@@ -4592,7 +4596,9 @@ element it has to parse."
                  (save-excursion
                    (forward-line -1)   ; faster than beginning-of-line
                    (skip-chars-forward "[:blank:]") ; faster than looking-at-p
-                   (not (eolp)))) ; very cheap
+                   (or (not (eolp)) ; very cheap
+                       ;; Document-wide property drawer may be preceded by blank lines.
+                       (progn (skip-chars-backward " \t\n\r") (bobp)))))
 	        (_ nil))
 	      (looking-at-p org-property-drawer-re))
 	 (org-element-property-drawer-parser limit))

testing/lisp/test-org-element.el

@@ -2750,7 +2750,7 @@ Outside list"
    (eq 'property-drawer
        (org-test-with-temp-text "# C\n# C\n<point>:PROPERTIES:\n:prop: value\n:END:"
 	 (org-element-type (org-element-at-point)))))
-  (should-not
+  (should
    (eq 'property-drawer
        (org-test-with-temp-text "\n<point>:PROPERTIES:\n:prop: value\n:END:"
 	 (org-element-type (org-element-at-point)))))
@@ -3271,6 +3271,38 @@ Outside list"
    (org-test-with-temp-text "#+BEGIN_VERSE\nC\n#+END_VERSE\n "
      (= (org-element-property :end (org-element-at-point)) (point-max)))))
 
+;;; Org data.
+
+(ert-deftest test-org-element/org-data-parser ()
+  "Test `org-data' parser."
+  ;; Standard test.
+  (org-test-with-temp-text "This is test."
+    (let ((data (org-element-lineage (org-element-at-point) 'org-data)))
+      (should (equal 1 (org-element-begin data)))
+      (should (equal (point-max) (org-element-end data)))))
+  ;; Parse top-level property drawer.
+  (should
+   (equal
+    "bar"
+    (org-test-with-temp-text ":PROPERTIES:
+:FOO: bar
+:END:"
+      (org-element-property-inherited :FOO (org-element-at-point)))))
+  ;; With leading comment line.
+  (org-test-with-temp-text "# comment
+:PROPERTIES:
+:FOO: bar
+:END:"
+    (should (equal "bar" (org-element-property-inherited :FOO (org-element-at-point)))))
+  ;; Blank line on top.
+  (should
+   (equal
+    "bar"
+    (org-test-with-temp-text "
+:PROPERTIES:
+:FOO: bar<point>
+:END:"
+      (org-element-property-inherited :FOO (org-element-at-point))))))
 
 
 ;;; Test Interpreters.