contrib/lisp/org-export: Fix headline numbering

* contrib/lisp/org-export.el (org-export-persistent-properties-list):
  Remove unused persistent properties.
(org-export-initialize-persistent-properties): Delegate headline
  numbering alist to `org-export-collect-headline-numbering'.
(org-export-collect-headline-numbering): New function.
(org-export-update-info): Remove part relative to headline numbering.
(org-export-get-headline-number): Use new `:headline-numbering' to get
  current headline number.

Headline numbering is not done on demand anymore, but built once and
for all at the beginning of the export process, and stored in an
alist, accessible through the `:headline-numbering' property in the
communication channel.

contrib/lisp/org-export.el

@@ -610,6 +610,12 @@ while every other back-end will ignore it."
 ;;   - category :: persistent
 ;;   - type :: integer
 
+;; + `headline-numbering' :: Alist between headlines' beginning
+;;      position and their numbering, as a list of numbers
+;;      (cf. `org-export-get-headline-number').
+;;   - category :: persistent
+;;   - type :: alist (INTEGER . LIST)
+
 ;; + `included-files' :: List of files, with full path, included in
 ;;      the current buffer, through the "#+include:" keyword.  It is
 ;;      mainly used to verify that no infinite recursive inclusion
@@ -1096,14 +1102,14 @@ retrieved."
 ;; `org-export-use-select-tag-p' determines if an headline makes use
 ;; of an export tag enforcing inclusion. `org-export-get-min-level'
 ;; gets the minimal exportable level, used as a basis to compute
-;; relative level for headlines. Eventually,
-;; `org-export-get-point-max' returns the maximum exportable ending
-;; position in the parse tree.
+;; relative level for headlines. `org-export-get-point-max' returns
+;; the maximum exportable ending position in the parse tree.
+;; Eventually `org-export-collect-headline-numbering' builds an alist
+;; between headlines' beginning position and their numbering.
 
 (defconst org-export-persistent-properties-list
-  '(:babel-data-alist :babel-info-alist :babel-results-alist :code-refs
-                      :headline-offset :parse-tree :point-max
-                      :seen-footnote-labels :total-loc :use-select-tags)
+  '(:code-refs :headline-alist :headline-offset :headline-offset :parse-tree
+               :point-max :seen-footnote-labels :total-loc :use-select-tags)
   "List of persistent properties.")
 
 (defconst org-export-persistent-properties nil
@@ -1132,6 +1138,9 @@ Following initial persistent properties are set:
                    of level 2 should be considered as a level
                    1 headline in the context.
 
+`:headline-numbering' Alist of all headlines' beginning position
+                   as key an the associated numbering as value.
+
 `:parse-tree'      Whole parse tree.
 
 `:point-max'       Last position in the parse tree
@@ -1178,7 +1187,11 @@ Following initial persistent properties are set:
                     (list (org-element-get-property :raw-value headline)
                           (org-element-get-property :begin headline)
                           (org-element-get-property :end headline))))))
-  ;; 6. `:back-end'
+  ;; 6. `:headline-numbering'
+  (setq options (org-export-set-property
+                 options :headline-numbering
+                 (org-export-collect-headline-numbering data options)))
+  ;; 7. `:back-end'
   (setq options (org-export-set-property options :back-end backend)))
 
 (defun org-export-use-select-tags-p (data options)
@@ -1224,6 +1237,30 @@ OPTIONS is a plist holding export options."
           (org-element-get-contents data))
     pos-max))
 
+(defun org-export-collect-headline-numbering (data options)
+  "Return numbering of all exportable headlines in a parse tree.
+
+DATA is the parse tree.  OPTIONS is the plist holding export
+options.
+
+Return an alist whose key is headline's beginning position and
+value is its associated numbering (in the shape of a list of
+numbers)."
+  (let ((numbering (make-vector org-export-max-depth 0)))
+    (org-element-map
+     data
+     'headline
+     (lambda (headline info)
+       (let ((relative-level (1- (org-export-get-relative-level blob info))))
+         (cons
+          (org-element-get-property :begin headline)
+          (loop for n across numbering
+                for idx from 0 to org-export-max-depth
+                when (< idx relative-level) collect n
+                when (= idx relative-level) collect (aset numbering idx (1+ n))
+                when (> idx relative-level) do (aset numbering idx 0)))))
+     options)))
+
 
 ;;;; Properties Management
 
@@ -1255,18 +1292,11 @@ The following properties are updated:
                          (plist).
 `previous-element'        Previous element's type (symbol).
 `previous-object'         Previous object's type (symbol).
-`previous-section-number' Numbering of the previous headline
-                          (vector).
 `seen-footnote-labels'    List of already parsed footnote
                           labels (string list)
 
 Return the property list."
-  (let* ((type (and (not (stringp blob)) (car blob)))
-         (relative-level (and (eq type 'headline)
-                              (org-export-get-relative-level blob info)))
-         (current-num (and (eq type 'headline)
-                           (or (plist-get info :previous-section-number)
-                               (make-vector org-export-max-depth 0)))))
+  (let* ((type (and (not (stringp blob)) (car blob))))
     (cond
      ;; Case 1: We're moving into a recursive blob.
      (recursep
@@ -1275,20 +1305,15 @@ Return the property list."
        `(:genealogy ,(cons type (plist-get info :genealogy))
                     :previous-element nil
                     :previous-object nil
-                    :parent-properties ,(if (memq type org-element-all-elements)
-                                            (nth 1 blob)
-                                          (plist-get info :parent-properties))
+                    :parent-properties
+                    ,(if (memq type org-element-all-elements)
+                         (nth 1 blob)
+                       (plist-get info :parent-properties))
                     :inherited-properties
                     ,(if (eq type 'headline)
                          (org-combine-plists
                           (plist-get info :inherited-properties) (nth 1 blob))
-                       (plist-get info :inherited-properties))
-                    :previous-section-number
-                    ,(let ((current-num (copy-sequence current-num)))
-                       (if (not (eq type 'headline))
-                           current-num
-                         (progn (incf (aref current-num (1- relative-level)))
-                                current-num))))
+                       (plist-get info :inherited-properties)))
        ;; Add persistent properties.
        org-export-persistent-properties))
      ;; Case 2: No recursion.
@@ -1304,12 +1329,6 @@ Return the property list."
           (unless (and label (member label seen-labels))
             (setq info (org-export-set-property
                         info :seen-footnote-labels (push label seen-labels))))))
-      ;; At an headline: update section number.
-      (when (eq type 'headline)
-        (setq info (org-export-set-property
-                    info :previous-section-number
-                    (progn (incf (aref current-num (1- relative-level)))
-                           current-num))))
       ;; Set `:previous-element' or `:previous-object' according to
       ;; BLOB.
       (setq info (cond ((not type)
@@ -2055,12 +2074,8 @@ INFO is a plist holding contextual information."
 (defun org-export-get-headline-number (headline info)
   "Return HEADLINE numbering as a list of numbers.
 INFO is a plist holding contextual information."
-  (let ((relative-level (org-export-get-relative-level headline info))
-        (previous-numbering (or (plist-get info :previous-section-number)
-                                (make-vector org-export-max-depth 0))))
-    (loop for n across previous-numbering
-          for i from 1 to relative-level
-          collect (if (= i relative-level) (1+ n) n))))
+  (cdr (assq (org-element-get-property :begin headline)
+             (plist-get info :headline-numbering))))
 
 (defun org-export-number-to-roman (n)
   "Convert integer N into a roman numeral."