Number `Table' captions in pandoc export

Works around a bug in pandoc (present in at least up to and including
pandoc 1.18), where captions for Tables/Figures/Equations/etc. are not
numbered, unlike in other org-mode exporters.

This adds a function `org-pandoc-set-caption-title' to add a numbered
label (`Table %d', `Figure %d' etc.) to the caption.

Additionally, pandoc doesn't seem to pick up on #+LABEL: specifiers for
link targets to Tables/Figures/etc., so this function additionally adds
a manual target for any hyperlinks.

Overrides the table export function to add this caption processing
before sending the table to pandoc.

ox-pandoc.el

@@ -214,6 +214,7 @@
 (org-export-define-derived-backend 'pandoc 'org
  :translate-alist '((latex-environment . org-pandoc-latex-environ)
  (link . org-pandoc-link)
+ (table . org-pandoc-table)
  (template . org-pandoc-template)
  (paragraph . org-pandoc-identity))
  ;; :export-block "PANDOC"
@@ -1249,6 +1250,42 @@ t means output to buffer."
  (concat (make-temp-name ".tmp") ".org") s)
  a s v b e (lambda (f) (org-pandoc-run-to-buffer-or-file f format s buf-or-open))))
 
+(defun org-pandoc--has-caption-p (element _info)
+ "Non-nil when ELEMENT has a caption affiliated keyword.
+INFO is a plist used as a communication channel. This function
+is meant to be used as a predicate for `org-export-get-ordinal'."
+ (org-element-property :caption element))
+
+(defun org-pandoc-set-caption-title (element info fmt pred)
+ "Manually sets a numbered leader for the caption.
+Works around a bug in pandoc (present in at least up-to and
+including pandoc 1.18) which doesn't number things like Tables
+and Figures. ELEMENT is the org-mode element. INFO is a plist
+holding contextual information. FMT is the format of the caption
+label, e.g., \"Table %d:\", or \"Figure %d:\". PRED is a
+predicate function used by org-mode to keep track of
+table/figure/etc. numbers."
+ (let* ((caption (org-element-property :caption element))
+ (name (org-element-property :name element))
+ (name-target (when name (concat "<<" name ">>"))))
+ ;; caption is, e.g. "(((#("Testing table" 0 13 (:parent #8)))))"
+ ;; name is a link target, e.g., tab:test-table
+ ;; (cl-caaar caption) is then, e.g., "Testing table"
+ ;; name-target would be, e.g., "<<tab:test-table>>"
+ (when caption
+ (if (member org-pandoc-format '(beamer beamer-pdf latex latex-pdf))
+ (setf (cl-caaar caption) (concat name-target (cl-caaar caption)))
+ ;; Get sequence number of current src-block among every
+ ;; src-block with a caption. Additionally translate the caption
+ ;; label into the local language.
+ (let ((reference (org-export-get-ordinal element info nil pred))
+ (title-fmt (org-export-translate fmt :utf-8 info)))
+ ;; Set the text of the caption to have, e.g., 'Table <num>:
+ ;; ' prepended. Also add a target for any hyperlinks to this
+ ;; table. Pandoc doesn't pick up #+LABEL: elements.
+ (setf (cl-caaar caption) (concat (format title-fmt reference)
+ " " name-target (cl-caaar caption))))))))
+
 (defun org-pandoc-latex-environ (blob contents _info)
  "Transcode a latex environment for export with pandoc.
 Works around a bug in
@@ -1301,6 +1338,15 @@ description of the link, as a string, or nil. INFO is ignored."
  (org-export-custom-protocol-maybe link contents 'org)
  (org-element-link-interpreter link contents)))
 
+(defun org-pandoc-table (table contents info)
+ "Transcode a TABLE element from Org to Pandoc.
+CONTENTS is the contents of the table. INFO is a plist holding
+contextual information."
+ (org-pandoc-set-caption-title table info "Table %d:"
+ #'org-pandoc--has-caption-p)
+ ;; Export the table with it's modified caption
+ (org-export-expand table contents t))
+
 (defun org-pandoc-template (contents info)
  "Template processor for CONTENTS and INFO.
 Option table is created in this stage."